Structural Components Flashcards
INSPECTION SCOPE
Wind applies force that tries to push the house sideways, a phenomenon called racking.
The structural components must reliably resist all forces over time, the fourth dimension.
A home inspector is not required to, and should not, evaluate the adequacy of the structural components of the house.
Defer to contractors and engineers to determine the nature and extent of structural defects.
Structural components that are in scope of a home inspection include the visible and accessible parts of the foundation, floor structure, wall structure, ceiling structure, and roof structure.
Attic:
a usually uninhabitable space above the ceiling of the highest habitable area and below the roof framing. Also called a crawl space in some markets.
Axial force (load):
the vertical force acting on a structural member, such as a column or a beam, that places the member under compression at the loading point.
Basement (cellar):
an area that is partially or completely below grade; often has a ceiling height of 7 feet or more, but sometimes less in older houses.
Basement (daylight, walk out):
a basement that has a door to the exterior.
Beam (girder):
a structural member that carries loads from other members such as joists, rafters, and other beams.
Bow (bowed):
a condition where a structural member is curved along its long axis. Braced wall: see shear wall.
Ceiling joist:
a horizontal structural member that forms the ceiling of a room below an attic.
Ceiling, vaulted:
a ceiling that extends at an angle above the top of a full-height wall; the ceiling finish (drywall) is usually attached directly to the rafters.
Ceiling, tray (or trey):
a horizontal ceiling raised above the top of a full-height wall; the ceiling is often raised in one or two risers and decorated with crown molding.
Cinder block:
a concrete masonry unit made using coal ash or other residue of combustion. Cinder blocks are less common in modern residential construction. Cinder blocks may contain corrosive materials. See Concrete masonry unit (CMU).
Collar tie:
a horizontal member (usually a 1x4 or a 2x4) installed in the upper third of the attic between two rafters to help tie rafters together at the ridge.
Column:
a generic term describing a structural member designed to support a concentrated vertical load. A column is usually a tall and relatively narrow component. Also called a post, especially when used with decks. See Pier and Pile.
Compression:
The force that crushes or shortens a structural member. A beam under a vertical load is under compression on the top. See Tension force (load).
Concrete masonry unit (CMU):
a usually rectangular block made from concrete, aggregate, and water and intended for installation with other blocks to form walls and other structures. See Cinder block.
Condominium:
a form of real property ownership in which the owner holds 100% ownership of a dwelling unit and shares ownership of the common elements. Condominium does not describe a type of building.
Crawl space:
an accessible area within the foundation walls below the first habitable story usually having a soil floor, and a small distance between the soil and the floor joists. Also used to describe an attic in some markets.
Creep:
see Deformed.
Crown (camber):
a condition where a board or beam is curved along the long axis. See Bow (bowed). Most dimensional lumber joists have a natural crown which should be installed with the high side vertical. Manufactured beams have a camber built into the beam. The crown or camber installed with the high side vertical usually becomes straight when a load is applied.
Cup (cupped):
a condition where a board is curved along the face of the board.
Deflect (deflection):
a condition where a structural member bends from its normal shape, such as when a joist bends under a load. Deflect implies a temporary condition wherein the member will return to its normal shape when the load is removed.
Deformed (deformation):
a condition where a structural member changes shape or dimension from its normal shape or dimension. Permanent deformation occurs when the member will not return to its normal shape or dimension when the load is removed. Permanent deformation is called creep.
Dormer:
a projection above a sloped roof that usually contains a window. A dormer usually has two sidewalls and a gable roof, but it may have any style roof.
Eaves:
the extension of the rafters beyond the exterior wall of the building.
Footing (footer):
the part of a foundation that transmits loads directly to the soil, usually made from concrete in modern houses.
Girder:
see Beam (girder).
Ground snow load:
the estimated weight of accumulated snow on a surface; used when determining rafter span distance and fastening requirements for ceiling joists to rafters and ceiling joists to each other. Also used when determining cantilevered floor joist and deck floor joist span distance.
grout (masonry):
mortar with a high water content and a fluid-like consistency; used to fill cores of masonry such as concrete masonry units (CMUs).
Header:
a beam above an opening in a wall such as a door or window.
Joist:
a horizontal structural member that supports a floor or ceiling.
Keyway:
a slot or groove used to secure concrete or masonry walls that are built at different times. A keyway is cut into the footing during finishing to help keep concrete or masonry walls from sliding off the footing.
Kicker:
a piece of lumber, usually a 2x4, that is connected to a rafter and to a ceiling joist to reduce rafter thrust that could move the wall on which the rafter bears. A kicker serves the same function as a rafter tie. See Rafter tie.
Load (dead):
the downward force on a structure imposed by the building materials and by permanently attached fixtures such as HVAC equipment.
Load (live):
the downward force on a structure imposed by occupants and their belongings. Live load does not include environmental loads such as wind and earthquakes.
Pier:
a column designed to support a concentrated vertical load, often installed above ground, but may be installed below ground.
Pilaster:
a column that supports a concentrated vertical load. A pilaster may be on the interior or the exterior of a building, and may be taller and more decorative than a pier.
Pile:
a column installed in the ground that is designed to support a concentrated vertical load. A pile is part of the foundation of a house, and is usually found where the soil has poor load-bearing capacity or is unstable.
Pitch (of a roof):
the ratio of the total height of a roof to the total horizontal distance that the roof covers. For example, if the total height of the roof from the top plate to the ridge is 12 feet and the total horizontal distance between the exterior walls under the roof is 24 feet, the roof has a ½ pitch. See slope (of a roof).
Plumb:
Vertical.
Plumb cut:
a vertical cut of a rafter at the ridge or at a hip and valley rafter; also the vertical cut of a stair stringer at its support.
Purlin:
a brace installed near the midpoint of a rafter that transmits the rafter load to a load-bearing wall and allows the rafter to span a greater distance. A purlin consists of a purlin that is at least as wide as the rafter, and a purlin brace that is at least a 2x4 and bears on a load-bearing wall. Purlin braces should be installed at least every 4 feet.
Rack (racking):
the distortion or movement of a structure or its components; usually caused by wind or seismic loads.
Rafter:
an inclined roof structural member that supports the roof sheathing and roof covering.
Rafter (common):
an inclined roof structural member that runs between the ridge and the top plate.
Rafter (fill-in):
a dimensional lumber rafter used with trusses and I-joist rafters to construct parts of the roof system where trusses and I-joists are not practical.
Rafter (hip):
an ascending rafter formed at the intersection of two hip roof sections. Hip rafters may need to be supported at a ridge board by a brace to a load-bearing wall.
Rafter (jack):
a rafter that runs between a hip or valley rafter and the ridge, or between two rafters. Rafters that run between a hip rafter and the ridge are hip jack rafters, and rafters that run between a valley rafter and the ridge are valley jack rafters. Rafters that run between valley and hip rafters are cripple jack rafters.
rafter (valley):
a descending rafter formed by the intersection of two roofs. Valley rafters are load-bearing members. Valley rafters may need to be supported at a ridge board by a brace to a load-bearing wall.
rafter tail:
the part of a rafter that extends past the exterior wall top and forms part of the eaves.
rafter tie:
a horizontal member running between rafters on opposite sides of the roof when ceiling joists run perpendicular to the rafters. Rafter ties act like ceiling joists to keep the rafters from pushing the walls out.
ridge:
the top horizontal board or beam of a roof. Most roofs use a ridge board, which is a place to fasten rafters, and does not provide structural support. Roofs supporting vaulted ceilings should usually have a ridge beam designed to provide structural support. Ridge boards and ridge beams should be deep enough so that the entire plumb cut of the rafter bears on the ridge.
rotate (rotation):
a condition where a structural member moves laterally from its normal position relative to vertical, such as when a foundation wall moves inward due to pressure from soil.
seat cut:
the horizontal rafter cut at a wall top or a valley. Also the horizontal cut at the end of a stairway stringer.
shear:
the deformation of a structural member (such as a beam) in which parallel planes slide relative to each other.
shear wall:
a wall designed not to change shape (rack) under loads such as wind and earthquake; also called a braced wall. See rack (racking).
sheathing:
(1) the material covering the top of the rafters; (2) the material covering the top of the floor joists, also called the subfloor; (3) the material covering the exterior wall structural components.
slope (of a roof):
the number of inches that a roof increases in height (rise) for every 12 inches of horizontal distance (run). The slope is usually expressed as 4/12 or 4:12 where the first number is the rise and the second number is always 12, the run. The terms pitch and slope are sometimes used as synonyms. This is not technically correct. See Pitch (of a roof).
span:
the horizontal distance between structural supports. Overspan is an informal term that refers to a joist or a rafter that is longer than allowed between structural supports. Rafter span is measured horizontally, not along the length of the rafter.
square (squared):
a condition that occurs when intersecting walls form a 90° angle. Squared walls can be determined by measuring and applying the formula A2 + B2 = C2 to the right triangle formed by the walls.
stud:
(1) a grade of lumber used in wall construction rated below #2 grade and approximately equal to #3 grade; (2) a vertical structural member in a wall.
stud (cripple):
a less than full height vertical structural member usually found under windows and in partial height walls.
Stud (jack):
a less than full height vertical structural member placed under a header to provide bearing support for the header.
stud (king):
a full height vertical structural member placed on the sides of a header.
Tension force (load):
The force that pulls or stretches a structural member. A beam under a vertical load is under tension on the bottom. Contrast Compression.
townhouse:
a single family attached dwelling with all of the following: (1) three or more dwellings in one building, (2) dwelling extends from the foundation to the roof, (3) a yard or public way on at least two sides. A townhouse is a type of building, not a form of real property ownership.
FOUNDATIONS
A house can move in any direction.
Gravity is always trying to move the house down. Footings, or similar components such as piles or piers, must be designed not to deform or break under the load imposed by gravity and to transmit the load to the soil or to bedrock.
The load imposed by occupants, furnishings, snow, and any other variable loads are called the live load.
Soils are classified according to the Unified Soil Classification System.
A geotechnical engineer specializes in foundation problems caused by poor soil.
Water can exert tremendous pressure on a house
Hydrostatic pressure can exert lateral (horizontal) force on foundation walls causing them to rotate, bow, and crack.
This upward force is often called frost heave.
Securing the framing to the foundation is the purpose of bolts and straps attached to the bottom plate.
Wind can move the house horizontally by exerting lateral force against the walls and roof.
The house walls must be adequately braced against the lateral force to prevent wall movement called racking.
Securing a house against wind forces begins at the foundation and extends in an unbroken path to the rafters.
A common footing for houses built during the last 100 years is the continuous spread footing, also called a ribbon footing.
The bottom of footings should be at least 12 inches below undisturbed ground and below the local frost line.
The minimum thickness of a modern spread footing is between 6 inches and 19 inches.
The minimum width ranges between 12 inches to 49 inches.
Piles and Piers
Piles are used to support foundations that must be placed on soil with poor load-bearing capacity and to raise houses above the local flood level.
Piles used in residential foundations are usually wood that has a diameter between 8 inches and 14 inches or square sizes between 6x6 to 12x12 inches.
Piles support loads by bearing on rock or good load-bearing soil or by friction of soil surrounding the pile.
A pier is a component that supports a point (concentrated) load. A pier can be below grade and support a footing or grade beam, or it can be above grade and support a house structural beam. Piers should bear on a footing (called a pier pad or pad footing) of appropriate size. Piers may be constructed using concrete masonry units (CMUs), bricks, or poured concrete, and reinforced with steel as necessary.
The difference between a pile, a pier, and a column is semantic. If it is constructed using CMUs or concrete, it is often called a pier regardless of whether it is above or below grade. If it is constructed using steel or wood and installed above grade, it is often called a column. If it is constructed using steel or wood and installed below grade, it is often called a pile. All perform the same function.
Wood and steel columns should be secured against lateral movement at the bottom, except that columns 48 inches tall or less in a crawl space need not be secured at the bottom unless the house is in a D seismic zone.
Masonry piers should be built using mortar; dry stacking is not acceptable.
Masonry piers should have a solid cap at least 4 inches thick. The cap may be a solid cap block, solid bricks, or the top CMU may be filled with grout. Masonry piers should have a minimum dimension of 8 inches. The maximum height of an 8x16 inch hollow CMU pier is 32 inches and the maximum height of a an 8x16 inch solid CMU pier is 80 inches.
Columns
Wood columns should be at least 4x4 inch preservative treated or decay resistant wood
Steel columns should be at least 3 inch diameter Schedule 40 pipe that is painted inside and outside with rust-inhibiting paint.
Columns in basements should be secured at the bottom.
Columns 48 inches tall or less located in crawl spaces are allowed to be unsecured at the bottom
One-piece steel screw jack columns are usually acceptable as permanent columns if they are properly secured at the bottom, and if they are made from the proper materials.
Telescoping columns (where one section fits into another section) are usually considered temporary supports and are not considered appropriate to provide permanent support.
Columns retrofitted in basements and supported by the basement floor are likely not on an appropriately thick footing.
Typical Defects in Columns that home inspectors should report include:
- absent, deteriorated footings,
- footings inadequate size and thickness (e. g., patio slab converted to finished space),
- cracked, uplifted, settled footings (these defects can sometimes be inferred by the condition of the foundation wall),
- masonry piers dry stacked, too tall for material, absent solid cap, absent or deteriorated mortar,
- rotated masonry piers,
- CMU hollow (core) side installed horizontally,
- wood and steel columns not secured at bottom, bowed, rotated, wrong type or material, size too small, deteriorated especially at the bottom,
- wood columns damaged by wood destroying organisms and fungi.
Reportable Cracks or Bowing of a Column
There is no agreed upon standard for what constitutes a reportable crack in a footing. A common guideline is that cracks exceeding ¼ inch in width or ¼ inch vertical displacement should be considered for evaluation and repair.
There is no agreed upon standard for what constitutes reportable rotation or bowing of a column or pier. A common guideline is that rotation exceeding ¾ inch in 8 feet should be considered for evaluation and action.
Basement Foundation
A basement is an area that is entirely or partially below grade.
A basement that is entirely below grade is sometimes called a cellar. A basement that has a full-height door to the exterior (not a bulkhead door) is sometimes called a walk-out or daylight basement.
Concrete Basement Walls
Modern basement walls are often concrete, either cast-in-place walls or precast walls (panels)
Vertical dowels of reinforcing steel should be placed in the footings and a U-shaped groove (called a keyway) should be cut into the top of the wet footing concrete to help the foundation walls resist sliding off the footings.
Horizontal reinforcing steel should be installed in the walls to help the walls resist lateral load from the soil
Precast concrete panels come in standard heights between 8 and 10 feet.
Precast concrete panels come in standard heights between 8 and 10 feet.
Note that CMUs are sometimes called cinder blocks.
Permanent Wood Foundations
Permanent wood foundations are used in some areas.
Footings for these foundations consist of crushed stone or gravel that is at least 8 inches deep and at least 16 inches wide.
A preservative treated footing plate that is at least 2 x 8 is required, along with a preservative treated bottom plate. The basement floor should also be set on gravel with a vapor retarder installed above the gravel.
The entire foundation system should be drained with an active sump pump system.
Permanent wood foundation walls are built using preservative treated plywood.
The walls should be (at least) dampproofed, and a moisture barrier (at least 6 mil polyethylene) should be installed on walls below grade. Joints between panels should be sealed with caulk or other appropriate sealant. Stone or gravel fill should be placed against the wood foundation walls.
Stone Foundations
Stone foundation walls are frequently encountered in older houses (usually at least one hundred years old), although they are allowed to be built in modern construction.
Current requirements for stone foundation walls include a minimum thickness of 16 inches, a maximum height of soil against the wall of 8 feet, and a maximum soil pressure against the wall of 30 pounds per square foot.
Basements with stone foundations frequently have water issues.
Water can enter the basement by leaking between or through the stones, or by migrating between or through the stones as water vapor.
The mortar used with old stone foundations is usually a soft lime-based mortar that is prone to deterioration when exposed to moisture.
Repairing lime-based mortar with modern mortar or other cement-based can make matters worse by holding water against the lime-based mortar causing further mortar deterioration.
Brick Foundations
Brick foundations share most of the water issues that plague stone foundations, and can have more serious issues because brick is hygroscopic (absorbs water).
GRADE AND DRAINAGE AROUND BRICK FOUNDATIONS IS EXTREMELY IMPORTANT.
Waterproofing, Dampproofing, Foundation Drains
All basements should be either waterproofed or dampproofed.
Waterproofing is intended to stop the flow of liquid water under hydrostatic pressure.
One method of waterproofing concrete and masonry walls involves applying a tar-like substance (A BITUMINUOS COATING) to the wall, and covering it with 6-mil polyethylene from the top of the footing to finish grade.
Dampproofing is intended to stop the flow of water vapor and small amounts of liquid water not under hydrostatic pressure.
Masonry walls should first be parged with at least ⅜ inch of Portland cement on the exterior side.
Modern foundation drains are installed using perforated plastic pipe covered with a fabric “sock” that is similar in texture to cheesecloth.
Clay drain tiles are also allowed and are common in older houses if they have foundation drains.
Typical Potentially Significant Basement Defects
A thorough discussion of foundation defects is out of scope for this book.
There is no agreed upon standard for what constitutes reportable foundation defects.
1. wall rotating (usually leaning in from top)
2. wall bulging (part of wall protrudes in from the exterior side), and long horizontal cracks in walls
3. Vertical, diagonal, or stair step cracks wider at one end
4. out of plane cracking (part of wall moved horizontally relative to rest of wall)
5.out of plane cracking (part of wall moved vertically relative to rest of wall)
6. wall sliding (entire wall moves relative to footing, wall may not be cracked)
7. Foundation settlement or rotation (entire foundation settles or rotates, can be uniform, or one side or corner can settle or rotate)
8. Building movement off of the foundation
9. water stains on wall, dampness, liquid water, also owner belongings raised above floor
Typical Less Significant Basement Defects
- Uniform width cracks less than ⅛ inch wide.
- Voids, aggregate pockets, honeycombing in concrete walls
- spalling (material disintegrating; could be structural if large amounts of material are unsound)
- Efflorescence (white powder on walls)
- Cold joint
Typical Repairs of Non-structural Cracks and Water Infiltration
Home inspectors should not recommend specific repairs.
- Hydraulic cement
- Polyurethane foam
- Epoxy
- Waterproofing liquid coatings (applied to interior)
Typical Repairs of Structural Defects
Home inspectors should report evidence of foundation repairs
- Buttress
- Sister Walls
- Steel I-Beams
- Carbon Fiber Mats
- Tieback anchors
- Plate anchors
- Push piers and helical piers
- Slab jacking/foam jacking
Crawl Space foundation
A crawl space is an unfinished area under the first story of a house and has a lower height than a basement.
Wood floor joists that are not preservative treated should be at least 18 inches above a crawl space soil floor (whether or not covered).
Wood beams that are not preservative treated should be at least 12 inches above a crawl space soil floor
Current minimum crawl space access opening requirements are 18x24 inches if access is through the floor, and 16x24 inches if access is through a side wall. The opening should be 22x30 inches if equipment requiring service and replacement is in the crawl space. Crawl space access openings in some older houses may not comply with comply with current requirements.
The crawl space floor should be cleared of wood, cardboard, and similar materials including tree and plant debris and construction lumber.
Safety Issues Crawl spaces can present numerous dangerous and toxic animals, plants, and substances such as spiders, snakes, mold, raw sewage, and energized electrical wires.
Safety Issues Crawl spaces
Crawl spaces can present numerous dangerous and toxic animals, plants, and substances such as spiders, snakes, mold, raw sewage, and energized electrical wires.
Slab-on-Grade foundation
slab-on-grade foundations are, as the name states, slabs of concrete installed on level ground.
There are two types of slab-on-grade foundations. A mat or floating slab foundation is a slab of concrete that has a uniform thickness. The entire slab is essentially a footing.
A monolithic or turned-down edge slab foundation is a slab of concrete with footings at the perimeter and at interior load-bearing walls.
The remainder of the slab should be at least 3½ inches thick. The concrete for these slabs should be laid during a single pour.
Slab-on-grade foundations, and basement floors that serve usable or habitable space, should be built on at least 4 inches of sand or gravel and at least a 6-mil polyethylene vapor retarder. This is primarily to reduce moisture entering the house from below, and it can also help reduce entry of radon and other soil gasses.
Slab-on-Stem Wall foundation
Slab-on-stem wall foundations are similar to slab-on-grade foundations except that a spread footing is poured and a short wall made from CMUs or poured concrete is constructed first.
There are two types of slab-on-stem wall foundations. The concrete may float on the soil (a floating slab), or it may bear on the stem wall around the perimeter. Bearing on the stem wall is the better option, but is not required. The garage floor slab frequently floats.
Insulation around the slab perimeter is required for both slab-on-grade and slab-on-stem wall foundations in newer houses located in cooler climate zones
Post-Tensioned Slabs
Slab foundations in areas with unstable soil may be reinforced with cables that are placed under tension after the concrete is poured.
Slab Foundation Defects and Standards
Typical Defects that home inspectors should report include:
- cracks (often concealed by floor coverings but may be visible around the perimeter),
- uplift and settlement,
- uneven or not level,
- cracking, crazing, spalling, dusting, popouts,
- damaged perimeter insulation (newer houses),
- efflorescence (caused by poor water management).
Concrete Slab Surface Defects
A concrete slab surface defect (e. g., crazing, dusting, spalling) is one that is non-structural and affects the appearance of the concrete.
Almost all concrete slab surface defects occur because of one or more of the following errors:
(1) improperly preparing and compacting the soil or material under the concrete,
(2) using an improper concrete mix, such as too much water or inadequately air-entrained,
(3) improperly placing, finishing, and curing the concrete.
Concrete cracks for many reasons, and most concrete is cracked.
Random shrinkage cracks can also be the result of not installing control joints or improper control joint spacing.
Shrinkage cracks are usually cosmetic.
Larger cracks (more than ¼ inch wide), especially cracks with vertical displacement, are often the result of the soil under the concrete settling or uplifting
CRAZING appears as many small surface cracks that may look like an _________ ___________.
Irregular honeycomb.
SPALLING (SCALING) is when the finished surface (about ⅛ inch deep) of the concrete ______ over several square inches or more
Separates
DUSTING is when a fine ______ regularly appears on concrete finished surface
Powder
A ______ is when a small, usually conical shaped, part of the concrete surface breaks away. ______s are usually about 1 to 2 inches across and 1/2 to 1 inch deep.
POPOUT
FLOOR SYSTEM
The most common residential framing system is platform framing.
The less common residential framing system is BALLOON framing.
Floor systems are designed to support a specified uniformly distributed live load without deflecting more than a specific amount.
The uniform live load is 30 psf for sleeping rooms (bedrooms) and 40 psf for all other rooms
The maximum allowed deflection under the uniform load is L/360 where L is the joist, truss, or beam span in inches.
A uniformly distributed load can be different from a point load.
These loads can cause a floor system to deflect more than L/360 yet still be within the design parameters.
Dimensional Lumber Floor Systems
Dimensional lumber is wood that is cut into standard sizes.
The actual size of dimensional lumber is usually about ½ inch smaller than the nominal size.
The actual depth of larger depth dimensional lumber is now about ¾ inches smaller than the nominal size.
Common species used for framing lumber include Douglas fir, hem fir, spruce, pine, fir (SPF), and Southern pine.
Number 2 grade lumber is currently the most commonly used dimensional lumber in residential floor systems.
The two most important properties are the stiffness of the lumber, and its resistance to permanent deformation (bending) under load.
Delamination, swelling, and deterioration are common reasons for squeaky, soft, and uneven floors.
Home inspectors are not required to determine the allowed span of these components regardless of when the house was built.
Home inspectors are not required to determine the allowed span of these components regardless of when the house was built.
A floor joist or beam should have at least 1½ inches bearing on wood and at least 3 inches bearing on concrete or masonry.
Bolts at least ½ inch in diameter or straps designed for the purpose should be spaced at least every 6 feet. Bolts should have a washer and a fully tightened nut. A bolt or strap should be located not more than 1 foot from the edge of each plate section and ½ inch bolts should not be closer than 3½ inches to a plate joint.
Bolts should be installed in the middle third of the plate.
Floor joists should be restrained against twisting by being attached to a full-depth rim joist where the joists bear on the foundation. This is called lateral restraint or blocking.
Joists from opposite sides that meet at an interior wall or beam should lap each other at least 3 inches and should be fastened to each other. Blocking is also required at interior walls or beams if there is a load-bearing wall above.
Bridging is often installed near the center of a floor joist span to help prevent twisting.
Bridging is not required for floor joists 2x12 and smaller.
The extension of a floor beyond a supporting wall is called a cantilever.
The cantilevered part of the floor places an additional uplift load on the part of the floor system inside the supporting wall (the backspan)
The joist length inside the supporting wall (the backspan distance) should be at least 3 feet for every 1 foot of cantilever distance when the cantilevered floor supports an exterior bearing wall and a roof
The backspan distance should be at least 2 feet for every 1 foot of cantilever distance when the floor supports an exterior balcony.
Two (trimmer) joists are connected together on each side of the opening to make a beam that distributes the load imposed by the joists that are interrupted by the opening. Two (header) joists are installed between the trimmer joists if the opening is wider than 4 feet.
Most dimensional lumber floor joists, especially longer joists, have a slight curve along the length dimension. This is called the CROWN.
Joists and beams installed with the crown side down can cause floor squeaks because of the gap between the floor sheathing and the joist.
Plywood and OSB floor sheathing should be installed with the long dimension perpendicular to the floor joists and extending across at least 3 joists.
No piece should be less than 24 inches wide.
Typical plywood thickness used for floor sheathing is 15/32 (½) inch or 23/32 (¾) inch; the former is limited to floor joist spacing of 16 inches on center while the later may span up to 24 inches on center.
Typical Defects Floor system defects fall into two categories (per se and evidence-based). Examples of evidence based defects are:
Improperly notched joist and beam Improperly bored joist and beam Inadequate joist and beam bearing on support Inadequate beam support Improper joist hanger installation Excessively long joist or beam cantilever Damaged joist and beam. Deformed (sagging) joist and beam Excessively deflecting (springy) floor Squeaky floor
Typical Repairs Structural repairs usually require a building permit
Sister joist
Blocking
Mending joists or plates
Columns and piers
Wood I-Joists and Engineered Wood (floors and roofs)
Wood I-joists are engineered wood joists that are usually used as floor joists, but can be used as ceiling joists and rafters
The vertical piece is called the web and the wood strips are called the flanges
structural composite lumber (SCL)
laminated veneer lumber (LVL),
parallel strand lumber (PSL),
laminated strand lumber (LSL),
oriented strand lumber (OSL).
This class of engineered wood is made from strands (thin veneers for LVLs) of wood
Glue laminated lumber (GLL): These products are often called Gluelams. GLL is made with a CAMBER (like a crown in dimensional lumber)
Typical Defects I-Joists
Often difficult to know with certainty if these materials are improperly installed
Improperly notched I-joist and beam
Improperly bored I-joist
Improperly bored engineered lumber beam
Absent/improperly installed filler blocks and backer blocks
Absent/improperly installed web stiffeners or squash blocks under load-bearing walls
Inadequate I-joist and beam bearing on support
Absent/improperly installed support under non-load-bearing walls
Dimensional lumber used in I-joist system
Floor Trusses
Wood floor trusses are engineered components that are usually made from 2x4 dimensional lumber laid out in a rectangle with members in the center to distribute the load along the truss.
The top and bottom horizontal members are called chords and the members in the center are called webs.
Trusses using metal plates are called metal plate connected trusses.
Draftstopping
Draftstopping is intended to slow the horizontal spread of fire in a house. Draftstopping consists of a membrane that divides the area into approximately equal parts that are each less than 1,000 square feet.
Typical draftstopping membranes include ½ inch thick drywall and ⅜ inch thick plywood or OSB.
Typical Defects for Trusses
Improperly modified and damaged truss
Absent and damaged gusset plates
Cut and damaged truss braces
WALL SYSTEM
Walls must support vertical loads from above. Walls must resist horizontal loads imposed by wind. These wind loads can simultaneously push the walls on the windward side and pull the walls on the leeward side.
Concrete masonry unit (CMU) walls are common in some markets and are especially common where resistance to wind loads is required.
These proprietary systems use forms that look like Legos and are made from materials such as polystyrene.
Structural insulated panels (SIPs) are another newer construction material that uses insulated panels built in a factory and shipped to the construction site
FIREBLOCKING AND FIRE SEPARATION
The purpose of fireblocking is to slow the spread of fire in concealed vertical spaces between stories, between the top story and the attic, and in long horizontal spaces.
Horizontal fireblocking should be installed when the concealed horizontal space exceeds 10 feet long.
Typical Fireblocking Materials
Fireblocking materials include: nominal 2 inch lumber, 2 pieces of nominal 1 inch thick lumber, 23/32(¾) inch thick OSB and plywood, ½ inch thick drywall, batts of mineral wool or fiberglass insulation firmly secured in place, approved fire-resistant caulk and foam.
Fire Separation Between an Attached Garage and the House
A garage should be separated from habitable space above by at least ⅝ inch thick Type X drywall applied to the garage ceiling, and the structural walls supporting the habitable space above should be covered by at least ½ inch thick drywall installed on the garage side.
Bedrooms should not have a door that opens into the garage.
Doors between the garage and the house should be at least 1¾ inch thick solid or steel.
Fire separation Between Buildings
Buildings closer than 5 feet to the lot line should have a 1-hour rated firewall on the side near the lot line.
Buildings closer than 3 feet to the lot line should have no windows or doors on the side near the lot line.
Fire Separation Between Units
Two 1-hour rated firewalls (or one 2-hour rated firewall) running from the foundation to the roof sheathing should separate units in a townhouse building.
The firewalls should either extend as a parapet wall at least 30 inches above the roof, or the roof covering should be non-combustible (e. g., fiberglass shingles) and ⅝ inch thick Type X drywall should be installed at the underside of the roof sheathing for at least 4 feet on both sides of the firewall.
Typical Defects of Fireblocking and Fire Separation that home inspectors should report include:
- chases visible in the attic not fireblocked, especially chases around metal chimneys serving factory-built fireplaces,
- pull-down attic stairs in the garage not fire rated (a thin plywood cover),
- attic access openings in the garage made from wood,
- pet doors installed in walls and doors into the garage,
- flexible HVAC ducts penetrate the wall or ceiling,
- bedroom opens directly into garage,
- HVAC supply and return openings located in the garage,
- damaged firewall in attic between townhouses and between two-family dwellings,
- glazing in the door between the garage and the living space.
Foam Plastic Materials
Foam plastic insulation comes in two broad categories: sheet insulation and spray foam insulation.
Both categories of foam plastic insulation ignite easily and create toxic fumes when they burn. Because of the fire safety issues, foam plastic insulation is usually required to be covered by a thermal barrier or by an ignition barrier.
Thermal barriers include at least ½ inch thick drywall or one of several other another approved materials.
Ignition barriers include ¼ inch thick OSB and plywood, ⅜ inch thick drywall.
Wood-Framed Wall Systems
The most common residential wall system in North America is the platform-framed wall made from dimensional lumber components including a single sill plate or sole plate, studs, and a double top plate.
Headers provide support for spaces above openings for doors and windows. Headers are supported by king studs (at the sides of headers) and jack (trimmer) studs under the header.
The horizontal wood under a window is the sill.
Short studs under (and sometimes above) the windows are called cripples.
Wood-framed wall construction techniques and requirements depend on several factors
1. Wind Speed Risk
2. Wind Exposure Risk
3. Houses in Seismic Rick Zones need more wall bracing, more robust foundations, and more robust wall attachment to the foundation to keep the house on the foundation and to reduce racking.
Wood-framed walls in newer houses are usually built using stud grade 2x4 lumber.
Stud grade and #3 grade lumber may be used for walls up to 10 feet tall.
Taller walls should be built using #2 grade or better lumber.
Studs may be solid, or they may be a form of structural composite lumber made from smaller pieces of lumber that have their ends cut in a tongue-and-groove like manner called finger joints.
For load-bearing exterior walls less than 10 feet tall supporting 1 story and a roof, 2x4s may be spaced up to 24 inches on center
For load-bearing exterior walls less than 10 feet tall supporting 2 stories and a roof, 2x6s should be spaced not more than 16 inches on center.
Walls more than 10 feet tall should usually be built using at least 2x6s.
Exterior walls should bear on at least one preservative treated sill plate made from nominal 2 inch thick material that is as wide as the stud.
When top plates are notched more than 50%, one 16 gauge metal plate should be installed to bind the plates together.
Headers should be installed above openings in load-bearing exterior walls and above openings in interior load-bearing walls to distribute the load above around the opening.
Deformed (sagging) ceilings and walls above windows and doors are frequently the result of headers that are undersized or that have been removed.
Headers should be built using #2 grade lumber.
All nails are not the same.
Many wood-framed house walls are covered with a material called sheathing that provides structural stability for the wall and some resistance to air flow.
Wall Bracing
Exterior walls and some interior walls need to be braced to reduce racking.
Evaluating the adequacy of visible wall bracing is out of scope for a home inspection.
Identifying the presence of visible wall bracing in exposed walls is within the scope of a home inspection.
Every braced wall should have at least two wall braces and longer walls may need more. Common wall bracing methods include let-in braces and wood structural panel braces
A let-in brace is usually a 1x4 that is installed in a notch cut into the studs and plates
The brace should be installed at about a 45° angle from the bottom plate to the top plate and should be attached at each stud and the plates.
Wood structural panel braces are usually at least ⅜ inch thick OSB or plywood, but some types of panel siding can serve as bracing.
Each wall brace should begin within 12½ feet from each wall end (10 feet for new houses).
There should be a wall brace at least every 25 feet.
Typical Defects of Wall Systems
Improperly notched studs Improperly bored studs Water damage Wood destroying organism damage Improper stud size, spacing, material Inadequate number of studs under point loads Excessively notched top plate Inadequate attachment of walls to each other: walls should be attached to each other Improperly braced walls
Typical Repairs of Wall Systems
Sister studs
Stud shoes
Blocking
Concrete Masonry Unit (CMU) and Structural Brick Wall Systems
CMUs are often called cinder blocks.
Concrete masonry unit (CMU) above-grade walls for houses are usually constructed using hollow core CMUs with nominal 8x8x16 inch dimensions.
Six inch nominal dimension CMUs may be used for single story houses with a wall height of 9 feet or less.
The CMU cores may be left unfilled in areas with low wind and seismic risks; however, a minimum 4 inch thick solid cap block or a fully grouted top CMU course is necessary when wood will bear on the CMUs.
Reinforcing with steel rods and filling cores with grout is usually required in wind and seismic risk areas.
Support is required over doors and windows
Single wythe structural brick construction is the same as for CMUs.
A wythe is a wall of bricks, so a 1-wythe wall is one wall of bricks and a 2-wythe wall is two walls of bricks separated by no more than a few inches.
The wythes of a multiple wythe structural brick wall must be bonded together by some means.
Masonry headers may be used, in which case the short side of the brick will be visible at 24 to 34 inch intervals vertically. Metal wall ties may also be used, in which case there may be no visible evidence of bonding between wythes.
Both CMUs and structural bricks are hygroscopic, meaning they usually absorb water.
Typical CMU Potentially Significant Defects
wall rotating (usually leaning out) wall bulging (part of wall protrudes out or caves in), and long horizontal cracks in walls Vertical, diagonal, or stair step cracks wider at one end
Typical CMU Less Significant Defects
Home inspectors should look for brown stains, which usually indicate possible water infiltration, inside, at, and below the defect. Note that poor water management such as blocked gutters, improper flashing, and absent or blocked weep holes can cause most of the following defects:
- Uniform width cracks in mortar less than ⅛ inch wide
- Absent and deteriorating mortar
- Loose masonry
- Spalling
- Algae
- Plants growing on or near masonry
- Efflorescence
Typical CMU Repairs
Tuck pointing (repointing)
Anchors
Surface Sealants
Typical CMU Modifications/Repairs
Attachment of structures such as porches and decks to insulating concrete form houses should use approved connectors installed according to manufacturer’s instructions
Structural Insulated Panel Wall Systems (SIPS)
Structural insulated panels (SIPs) are constructed by gluing insulation (usually polyisocyanurate or polystyrene) between sheets of 7/16 inch thick OSB.
SIPs can be used as a wall system and as a roof system.
Panels are manufactured in a factory in lengths up to 24 feet, and in several thicknesses between 4 and 12 inches depending on the desired insulating R-value.
Advantages of SIPs include high R-value, low air infiltration rates, and faster construction schedules.
SIPs are also known as stressed-skin panels.
Panels may be erected on slab foundations and on crawl space and basement foundation walls.
These joints should be sealed with a caulk-like sealant made for SIPs. A double top plate is installed above the panels. All wall framing lumber should be #2 grade spruce pine fir or better.
SIPs may not be designed to provide structural support for structures such as porch roofs and decks. Modifications and additions that rely on SIPS for structural support should be designed by a qualified engineer and installed by a qualified contractor with appropriate permits.
Typical SIP Modifications/Repairs
SIPs may not be designed to provide structural support for structures such as porch roofs and decks. Modifications and additions that rely on SIPS for structural support should be designed by a qualified engineer and installed by a qualified contractor with appropriate permits.
Uncommon Wall Materials and Systems
Uncommon wall materials include:
•adobe brick,
•cold-formed steel,
•logs,
•rammed earth,
•straw bales,
•structural stone.
Uncommon wall framing systems include post-and-beam and timber framing
Home inspectors who are unfamiliar with these systems should report their unfamiliarity and recommend evaluation by a specialist.
Cold Formed Steel: One defect that is more pronounced in steel compared to wood is thermal bridging because steel is a much more efficient conductor of heat compared to wood
Log Houses
The log walls of modern log houses are usually fastened together using long spikes or machine bolts, usually spaced at intervals of 18 to 36 inches. The corners of log houses are made using one of several systems including butt-and-pass, saddle-notch, and butting into corner posts. The spaces between logs are filled with caulk or by using a process called chinking.
Modern chinking material is elastomeric.
Common log house problems include deteriorated caulking or chinking, unsealed cracks (checks) in the logs (especially on the top side), deteriorated stain or other protective coating, logs that move out of position in the log stack, and damage by wood destroying organisms.
Log houses should have eaves of sufficient depth to provide some protection to the logs from the weather.
Timber and Post-and-Beam Framing
Post-and- beam framing uses mechanical fasteners (e. g., bolts) and steel plates to connect members together, while timber framing uses mortise-and-tenon joints. A mortise is a hole chiseled into a member and a tenon is a projection in a member designed to fit in the mortise. A wood peg secures the joint.
ROOF AND CEILING SYSTEM
The rafters and ceiling joists are partners.
They must resist vertical live loads and dead loads pushing down from above.
More fasteners are required in snow country the roof system must resist lateral movement in seismic areas, so more fasteners and connections are required, especially for heavy roofs such as concrete tiles.
The maximum allowed deflection under the uniform load for rafters with a slope greater than 3/12 is L/180 where L is the rafter length in inches between supports measured horizontally, not along the length of the rafter.
The maximum allowed deflection under the uniform load for ceiling joists finished with drywall and for low slope rafters is L/240
Roof Styles
There are four roof styles:
1. The gable roof is triangle shaped with the rafters forming the legs, and the ceiling joists forming the base.
2. The hip roof is one containing four roof sections that meet at the top (ridge).
3. The shed roof is a usually rectangular shaped roof that usually terminates at a sidewall or a roof. Shed roofs are common on porches and on room additions. 4. The low slope (flat) roof is a horizontal, usually rectangular, roof. Any roof with a slope less than 3/12 is usually considered a low slope roof, although most have a slope less than 1/12. A low slope roof should have a slope of at least ¼/12 toward the drainage points.
Other less common roof styles include the Gambrel roof and the Mansard roof. These roof styles, especially the Gambrel, are often associated with barns.
Each rafter forms an isosceles right triangle. Common rafter length may be estimated using the formula A2 + B2 = C2 where C is the approximate rafter length, A is the height from the top wall plate to the ridge, and B runs from the ridge to the top wall plate.
Jack rafter length may be estimated using the same formula.
Dimensional Lumber roof Systems
The most common residential roof structural system in North America is the dimensional lumber (stick-framed) roof made from wood components including
ceiling joists
rafters
collar ties
rafter ties
purlins
sheathing
An attic is assumed to be usable for storage if there is more than 42 inches vertical distance between the top of the ceiling joists and the bottom of the rafters.
Attics that are usable for storage have a higher assumed live load compared to attics that are not usable for storage
Rafter maximum allowed span distances are based on three additional factors: ground snow load, dead load, and whether the ceiling is attached to the rafters.
Dead load depends on the roof covering. The 10 psf dead load is assumed for light roof coverings such as fiberglass shingles and wood. The 20 psf dead load is assumed for heavy roof coverings such as tile and slate.
It is important to be aware of the situation where a heavy roof covering may be installed on rafters designed for a light roof covering. These roofs can become deformed, sometimes significantly.
Typical Construction Techniques
Ceiling joists are usually installed on the top of the highest story wall.
The two ceiling joists should lap each other at least 3 inches.
The quantity of fasteners is three or four in many houses, but can be much greater for lower slope roofs in high ground snow load areas.
When ceiling joists are installed perpendicular to the rafters, rafter ties should be installed between the rafters.
Rafter ties should be installed using the same methods as ceiling joists because rafter ties perform the same function. Kickers may be installed instead of rafter ties.
Ceiling joists and rafters may have lateral support or bridging installed every 8 feet.
This usually consists of a 2x4 fastened across the top of the ceiling joist or rafter, and may also consist of lumber fastened vertically to the horizontal member (a strongback).
Rafters should be installed directly opposite each other at the ridge board or a ridge beam, if a ridge board or a ridge beam is installed.
A ridge board is not required, but if used it should be at least nominal 1 inch thick and as deep as the deepest rafter plumb cut
At least 1½ inches of the rafter seat cut should bear on a wood wall plate or other wood structural support, or at least 3 inches on masonry or concrete. The seat cut should not bear only on roof sheathing.
A strap or a collar tie should be installed at 4 feet on center, if this option is used.
A gusset plate should be installed on every rafter pair, if this option is used. Collar ties are no longer required if rafters bear on a ridge board or a ridge beam.
Where a rafter tail extends past the wall, this notch is sometimes called a bird’s-mouth cut. At least 3½ inches of the rafter should be intact above the bird’s-mouth cut. Where the ceiling joist is notched, not more than ¼ of the actual rafter depth may be notched.
A purlin may be used to support rafters that span too great a distance horizontally.
The purlin is the horizontal member on which the rafter bears.
It should be at least as deep as the rafter (e.g. a 2x6 purlin should support a 2x6 rafter)
The purlin brace, also called a strut, should be at least a 2x4 and should be doubled if the brace length is greater than 8 feet.
The purlin and brace should be installed at an angle that is at least 45° to horizontal.
The braces should bear on a load-bearing wall and should not be spaced more than 4 feet apart.
The rafters should be covered with some type of sheathing.
Lumber may be installed as spaced (skip) sheathing when wood roof coverings are used.
Plywood and OSB roof sheathing should be installed with the long dimension perpendicular to the rafters and extending across at least 3 rafters. No piece should be less than 24 inches wide; it will be too weak to withstand the design load. The span rating for plywood and OSB is stamped on each sheet as two numbers separated by a slash, such as 24/16, 32/16, and 24-0. The first number is the maximum span between rafters when edge support is provided and the second number is the maximum span between floor joists. Edge support for roof sheathing is usually provided by metal clips often called H-clips.
Typical Defects Roof system defects
Typical Defects Roof system defects fall into two categories. Some defects are defective per se, meaning that the condition is defective regardless of whether there is current visible evidence of an adverse impact caused by the defect. An improperly notched rafter is defective per se. The adverse impact may not have occurred, yet. Other defects are evidence-based, meaning that there is current visible evidence of an adverse impact, whether or not there is an identified reason for the defect. An excessively bowed ceiling joist is an example of an adverse impact that may have no identified reason, yet.
- Water staining and damage around roof penetrations such as plumbing vents, appliance vents, skylights, chimneys
- Water staining and damage in valleys
- Water staining and damage near eaves
- Water staining, damage, and mold on rafters and sheathing (localized)
- Water staining, damage and mold on rafters and sheathing and rust on roofing nails that penetrate the sheathing (widespread)
- Fire damage
- Improperly bored and notched ceiling joists and rafters
- Defective purlins
- Deformed rafters
- Deformed ceiling joists
- Damaged joists and rafters
- Wood destroying organism damage
- Inadequate support of hip and valley rafters
- Inadequate bearing of rafters at ridge, hip, or valley
- Sheathing less than 24 inches wide (plywood and OSB)
- Inadequate attic access
- Inadequate attic ventilation
Typical Repairs and Modifications
Typical Repairs and Modifications to Roofs include:
- Sister rafters and joists
- Spliced (scabbed) rafters and joists
- Blocking
- Purlins
- Roof for addition supported by existing rafters
Truss roof Systems
The top and bottom horizontal members are called chords and the members in the center are called webs
The webs may be attached to the chords using metal plates called gusset plates, or by inserting the webs into a groove cut into the chords
Typical Truss Roof System Defects
Typical Truss Roof System Defects include:
- Damaged, absent, cut, modified truss chord or web
- Damaged, absent, loose gusset plates
- Damaged, absent, cut truss brace (including gable-end bracing)
- Truss uplift
- Truss not plumb
- Truss chord not straight
- Piggyback truss not attached to main truss
- Piggyback truss not bearing on purlins
- Owner belongings stored on trusses or in racks hung from trusses
Typical Repairs and Modifications on Truss Roof Systems
Typical Repairs and Modifications on Truss Roof Systems include:
- Scabs on truss members
- Gusset plate reattached using fasteners
- Roof for addition, porch, etc. supported by existing trusses
Wood I-Joists and Engineered Wood Roof Systems
Wood I-joists are engineered wood joists that are usually used as floor joists, but can be used as ceiling joists and rafters
Attic Access
Attic access is required for three reasons. Access is required for
1. inspection and maintenance,
2. allow firefighters to quickly access the attic
3. allow access to appliances that require maintenance and replacement.
Entering is usually easier than exiting.
Access should be provided to all attic spaces in which the attic floor area exceeds 30 square feet and the vertical height at some point in the attic is 30 inches or more. The opening should be located in a hallway or another equally accessible area.
The rough opening size (before finish materials are installed) should be at least 22 by 30 inches. There should be at least 30 inches of vertical clearance at some point above the opening.
The current requirement for access opening covers and doors is that they be insulated and weather stripped like any other opening to the exterior if the cover or door is in conditioned space.
Access opening covers in an attached garage should comply with fire separation requirements.
Safe access should be provided to appliances located in the attic.
The finished access opening size should be at least 20 inches by 30 inches or large enough to remove the largest appliance, whichever is larger.
The passage should be at least 24 inches wide, 30 inches high, and not more than 20 feet from the access opening.
A level service space at least 30 inches wide and 30 inches deep should be provided in front of all parts of the appliance that could require service.
A light, with a switch near the attic access opening, and a 120 volt receptacle should be provided near the appliance.
A pull-down stair is a folding ladder that is attached to a (usually) plywood cover.
The instructions often specify either 16d nails or ¼ inch diameter lag screws for attaching the stair frame to the ceiling framing.
Pull-down stairs are frequently improperly installed and poorly maintained.
Typical Defects to Attic Access that home inspectors should report include:
- no attic access,
- attic access too small or vertical clearance above access too low,
- attic access located where appliance removal would require damaging permanent construction including closet shelving,
- damaged access cover,
- access cover type breaches fire separation in the garage,
- access path to attic appliances too long, too narrow, or too low,
- service area in front of appliance too narrow or not deep enough,
- pull-down stairs do not completely close (usually weak springs),
- stair frame improperly attached to ceiling framing,
- truss chords cut to install pull-down stairs,
- pull-down ladder not properly trimmed,
- loose or absent pull-down ladder stair hardware.
