Air/ Moisture Flashcards
Stack effect
when hot air rises and escapes through upper level openings of a building, cold air is drawn into the basement and lower floors. the taller the building the greater stack effect.
Flue effect
NAtural aspiring duel fired venting appliance (stove, fireplace, furnace, hotwater tank) burn furl and used air from inside building for combustion. this is vented outside
ex burning fireplace can remove 400-600 cubic feet per minute. always close unused vents and fireplace.
Wind effect
winds cause pressure differential to occur across building envelope. wind hitting building creates high pressure on that side and negative pressure on leeward side.
Neutral pressure plane
NPP explanes how air flows in and out of a building. is NPP is zero, in areas where pressure is lower then NPP air enters the building. in areas where pressure is Higher then NPP (zero) air leaks out of building.
Infiltration
aproxamat heat loss of building heat loss 25-30% air infiltration 25-30% basement 20-25%doors and windows 15-20%walls 7-10%ceilings
Air barrier
maintaining air barrier will reduce pressure differentials and eliminate air infiltration caused by stack, flue and wind effect.
three types of ventilation systems
exhaust systems
supply systems
balances systems
Exhaust systems
draw air out of the buildings. this places building under negative pressure.
Supply systesm
blow air into the building. this places building under positive pressure.
Balanced systems
systems have fans that both supply and exhaust air at equal rates so that no pressure differential is set up across the envelope.
principal exhaust fan
all building must have mechanical ventilation to remove moisture from building. used to move moisture out of building
Makeup air
is air provided intentionally or unintentionally that replaces air being exhausted by ventilation systems.
is there is soil gas present makeup ventilation air is required for dwelling
combustion air
combustion air supply must be located near a NAFFVA to prevent backdrafting of harmful gasses (CO2) and to balance pressure
Co2 detectors
carbon monoxide detectors must be in same rooms as NAFFVA and at leave 5m from bedrooms
Direct venting
direct vented gas appliances are sealed, closed looped units that intake air and exhaust combusted gasses outside. other then providing heat they don’t change pressure.
Soil gas
soil gas is air between soil particles. it can contain radon that is a natural gas that causes cancer. negative pressure can cause radon to be drawn into dwelling through cracks in foundation walls or basement slabs.
Airtightness
air barriers are installed to prevent movement of air through the building envelope. it prevents warm moist air from entering and condensing in envelope.
true or false, airtightness has greater effect on thermal efficiency then the amount of insulation?
TRUE
Air Barrier Leakage rating
air barrier materials are rated by the amount of air in liters that will pass through 1m(square) of material in 1 second at a pressure of 75 Pa.
typical air barrier leakage rating are between 0.024 and 0.1L/(sxm(square)
two types of air barriers
membrane or ridged
types membrane air barriers
either 6mill poly, self adhering membrane (SAM) or house wraps sucha s tyveck and typar.
SAM’s and Poly vapour barrier true or false?
true
house wraps vapour barrier true or false
False
why does poly not perform as well as ridged air barriers in windy climates
because negative pressure on leeward side of building caused poly to get sucked into the stud or ceiling compressing insulation and ripping at staples.
Panel type air barrier
panel type air barrier include drywall, plywood, OSB and ridgid foam insulation. edges must be sealed with tape or caulking.
concrete foundation and walls are good air barriers true or false
true
Gasket materials
gasket materials are used to seal cracks and joints against air leakage. must remain flexible to maintain airtight seal.
examples, foam sill gasket, weather strip and neoprene tape
caulking
used to seal air barrier and further reduce the movement of air through building envelope.
caulking is used to seal …
- around doors and windows
- under sole plates of walls
- around electrical outlet boxes
- around plumbing pipes and vents
- any ceiling penetrations
- at sill plates
- perimeter joist connections
- at cracks in foundations
installation of caulking
should be installed to form a filet or curved bead at right angle joints.
hourglass shape at level joint.
*use backer rod for joints that are bigger then 1/8th
joint tape
used to seal joints in air barriers as well as holes
Electrical boxes and air barriers
plastic “boots” (boxes) are made to surround and connect electrical boxes. these boxes must be sealed to air barrier
- when used with drywall air barrier boxes around electrical units have foam that seals them
weather stripping
weather stripping is used to maintain airtightness around windows and doors.
in sliding units friction strip is used
what happens to weather stripping in hinged units
it is compressed between door or sash and frame
Spray foam
urethane spray foam makes excellent sealant around windows, door and pipes and other penetrations.
expanding and non expanding. expanding can cause deflection in doors and window frames
Testing for airtightness
federal government established the “super energy efficient home program. builders were provided with training and incentives to construct energy efficient homes.
Blower door test
blower door test tests your houses air tightness. a fan, pressure gauge, and computer are put in door frame. all other windows doors and vents are shut. the fan starts pulling all air out of building and instrumentation in blower calculates how much air leaks back into house through building envelope.
ELA equivalent leakage area
Equivalent leakage area is the total area of all the leaks in the building envelope at a depressurization of 10Pa
NLA Normalized leakage
Normalized leakage are is calculated by dividing the ELA by the exterior surface area of the house. gives the size f leakage area in cm square, m scuare OR in square of feet square
R-2000 technical standard calls for 0.7 cm (square)/m(Square)
Or 1 “(square)/ 100 ft (square)
ACH50
is a blower door machine that measures the air leaving the building at an envelope depressurization of 50 Pa. in meters cubed/ hour or feet cubed/hr. when divided by the buildings volume, the number of air changes within 1 hour is calculated.
Older homes have ACH50’s of 10-15 while newer homes have ACH50’s of 4-10.
Sweden requires housed to have ACH50 or 3 while r-2000 requires ACH50 of 1.5
Three phases of moisture
Solid, Liquid, vapour
solid
water is solid state is ice, water expands when it freezes. it expands approximately 10% when freezes. ace force can break concrete.
Liquid
force of gravity caused water to travel to ground. water can be lifted against force of gravity by capillary action. water of any depth will cause hydrostatic pressure. hydrostatic pressure on foundation walls can cause water to be forced into tiny cracks.
Vapour
water vapour is created when liquid water evaporates. it if the temperature is high and the air is dry water will evaporate quickly. heating water to its boiling point will create water vapour regardless of humidity of surrounding air. water vapour molecules are very small and can pass through any permial barrier.
relativity humidity
is the amount of water vapour in the air relative to the total amount it could hold at a given temperature.
there is more water vapour in air at 30% humidity at 35°C
then at 30% humidity at 5°C
what hold more moisture, warm or cold air?
warm air.
Condensation
as air containing water vapour cools, the relative humidity increases. the total volume of water vapour hasn’t changed but the cooler air cannot hold as much. as the temperature decreases the air cannot hold onto the water and it is transformed into water droplets or dew bells.
dewpoint
the dewpoint is the temperature at which water vapour condenses into liquid water.
vapour diffusion.
is the movement of water vapour through substances.
vapour will move from areas of high vapour concentration to low vapour concentration. and will also move from high temperature areas to low temperature areas. (vapour drive)
Airflow
moisture carried into envelope is still in the form of vapour, but traveling around objects not through them. eliminating airflow will shrink flow of moisture in building.
Gravity flow
weight of water causes it to flow to ground. it will take the most direct pathway. flashing and drip edges direct flow away from building.
wind pressure
wind driving rain can find its way into building through the best cladding. wind creates a pressure differential across cladding. front end of cladding will be under high pressure while the back end will be under low pressure.
Capillary action
surface tension of water causes it to be drawn into narrow pores. the force of capillary action is strong enough to cause water to travel significant distances against gravity.
vapour barrier and moisture barriers describe
must be placed on the warm side of the insulation and is intended to reduce water vapour diffusion through the interior finish into the building envelope.
impermeable
less then 60 ng/Pa.s.msquare
semipermeable
60-570 ng/Pa.s.msquare
permeable
greater then 570 ng/ Pa.s.msquare
flexible sheet products (Poly)
most common vapour barrier 6 mill poly. applied over the insulation and is sealed at all penetrations. must withstand UV rays. has vapour permeance os 1.6-5.8 ng/Ps.s.msquare
Kraft paper
is an intelligent vapour barrier. the permeability of kraft paper increases of decreases in direct correlation to the vapour pressure. as vapour pressure increases, the kraft paper becomes more vapour permial, allowing more vapour to pass through it.
Foil membranes
reflective foil membranes can also be used as vapour barriers.they are applied the same as poly.
Self adhearing membranes
SAM’s are often called peel and stick. usually made of rubberized ash vault with plastic surface area.
vapour retarding paint.
when using airtight drywall system for air/vapour barrier the vapour resistance is provided by the painted surface of the drywall. has rating of 34 mg/Ps.s.msquare
Vinyl wall paper
vinyl covering on pre finished drywall is a vapour barrier. in heating climates vinyl is on the warm side of the wall so it causes no problems. in cooling climates it is on cold side because heating is replaced inside by ac and heating. this will cause condensation and mold growth. vinyl wall finishes causes envelope problems in building in southern us
exterior grade plywood an OSB
these act as vapour barrier.the seams must be tongue and groove or sealed with tape. has vapour permeance of 40-57 ng/Pa.s.msquare will osb has 44
foil faced panels
rigid insulation materials faced with aluminum surface are used to insulate against radiant heat loss. aluminum surface is excellent vapour barrier. applied under drywall on inside of building. the joints are sealed to continue barrier. 4.3 ng/Pa.s.msquare
foam panels
extruded polystyrene or polyisocyanurate insulation panels forms good vapour barrier if joints are sealed
Moisture barrier materials
moisture barrier is on the outside of a envelope under the exterior finish. it must repel moisture and leaked rainwater but allow water vapour to pass through it.
sheathing asphalt building paper.
asphalt impregnated kraft paper. used as a moisture barrier. rated at 30minute or 60 minute resistance to water penetration. this finish wi;; deflect any rainwater that penetrates the exterior finish. is self sealing when punctured. comes in 3’ or 1m wide rolls. often two layers of 30 min are applied overlapping joints.
House wrap
hpuse wrap materials are made from spun bonded polyolfin or woven polypropylene (plastic) and comes in wide rolls. large sheets reduce the number of joints and create a continuous barrier. house wraps also make good air barriers if joints are sealed well.
the boat test
boat test is when sheathing material is made into a tiny boat and placed in water. the amount of time it takes for the water to affect the boat is the minute rating of the material. house wraps do not preform well under this test but hold up better to wind.
Horizontal or low-slope surfaces
sheathing paper and house wrap are intended for vertical surfaces and should not be used to protect horizontal or low slope surfaces.
panel products
ridgd insulating foam panels for an air barrier as well as providing thermal insulation. they also can be the moisture barrier is joints are taped.
PVC
polyvinyl chloride membranes are commonly used to surface waterproof decks. PVC membranes are east to form and seal. heat-welded seams make construction of water tight shapes possible.
EPDM
ethylene propylene deinen monomer resembles sheets of inner tube material. used to manufacture built in gutters and as a roofing material. is UV resistant and is sealed at joints using a sealing compound.
Flashing materals
used to prevent rain water entry at
- joints between exterior finishes
- windows and doors
- joints between wall and roof surfaces
- top of parapet
flashings and expansion and contraction
where flashings are continuous over lengths greater then 12’ they must be joined to create expansion joint. horizontal joints on flat surface must mechanically resist the penetration of water and allow for expansion and contraction.
Aluminim flashing
wflexable and comes in lots of colours
will corrode if in contact with mortar or concrete
will react with zinc coated fasteners and treated lumber.
stainless, aluminum ir epoxy coated fasteners should be used.
copper
copper is more durable then aluminum and makes excellent flashing but is very expensive. copper will turn green and can tarnish other surface finishes
effected by concrete and mortar.
Zinc
is durable and is not effected by concrete but not suitable in salty climates.
galvanized or painted steel
easy to work with, economical, durable and stain resistant. has low expansion and does not get effected by concrete or mortar. should not be used with copper or aluminum. scratches will rust
Battens
rainscreen systems either use battens or drainage matts to create a capillary break behind cladding. 2x8 pressure treated plywood strips 3/8 - 3/4” inch thick are used as rain screen battens. BCBC does not require battens to be pressure treated. battens will only cover 20% of surface and 80% will be for drainage.
Drainage mats
constructed of entangled filaments of plastic. mats come in thickness of 1/4 to 3/4. mats can be ordered faced with a breathable filter fabric or as house wrap. they were made for under stucco but work well under shingles or vertical siding.
Bug screen
bottom of capillary break must be open so it can drain freely. it must also keep out insects and rodent. perforated aluminum channels or strips of the same plastic mesh used for screen doors and windows can be used as bug screen.
Controlling moisture penetration from outside then envelope. 4 major ways
four major ways are
- deflection
- drainage
- drying
- durable materials.
deflection
first line of defence, roof projections protect walls of building from exposure to wind driven rain.
slope surfaces
designing the top surfaces of flashings to slope toward the outside of the building to deflect rainwater.
BCBC requires flashing to have minimum slope of 6%.
Flashings
flashings are used to deflect rainwater away from window or door openings. must be installed underneath sheathing paper. must have en dams to prevent wind from blowing water behind cladding
Drip flashing
must be provided at horizontal joints between different materials of exterior finish and under windows. this allows rainwater to drip clear of siding materials
minimum projection of drip flashing
1” beyond the face of exterior finish
Flashing over openings
flashing over window and doors should extend 2” up under the moisture barrier (sheathing paper) n the outside of the building
Drainage (face sealing)
face sealing is used to prevent water penetration into envelope by sealing all the cracks, penetration and joints in cladding.
simple rainscreen
rain water that penetrates the exterior finish must be able to drain out and away from the building. this can b accomplished by installing a capillary break or rain screen between moisture barrier and cladding. moisture can run down moisture barrier and out through bottom of capillary break . then bug screen
- brick veneer over wood frame must be rain screened must be 25mm air space between brick and moisture barrier on wood wall.
Pressure- equalized rainscreen
pressure equalized rain screen system neutralizes the effect of the wind on the face of the cladding.
blowing wind causes pressure drop
blowing wind on cladding lowers pressure and pushed any water through joints holes or cracks.
compartmentalized rain screen cavity behind the cladding m combined with air barrier can withstand this wind. vents in rain screen allow air to be drained.
key steps in pressure equalized rain screen
- air barriers must be continuous and structurally supported.
- rain screen cavities behind each wall face cannot connect, corners must be air tight
- the smaller size the cavity the quicker the pressure-equalization occurs. cavity can be continuous from foundation to roof.
moist climates and rain screen
although not required in all locations in BC it greatly improves the drying and drainage performance of the building envelope. BCBC requires rain screen in wet climates. rain screen systems are required when degree days is less then 3400 and MI (moisture index) is .90 or more. or number of degree days is 3400 and MI is more then 1.
Moisture index
is an indicator of the moisture load imposed on a building by the climate. moisture index for most cities in BC are included in table C-2 in part B appendix c of BCBC
Door and window diapers
if window fails and begins to leak water will enter the wall cavity. this is prevented by window being set into a SAM tray that will catch the leaked water and direct it outside.
door pans
exterior doors should be set into sheet metal flashing pan that will catch any water that leaks through door frame and drain it to the exterior. pans are shingled into moisture barrier with SAM back wall of pan is caulked to the doorsill to maintain air barrier
2-ply sheathing paper
BCBC requires that at least one layer of sheathing paper be applied to the sheathing and that the upper sheet should lap the bottom sheet. all lats should be at least 100 mm.
Roof drainage
should be directed away from building. splash blocks will prevent soil erosion but they main cause exterior finish to remain damp for long periods of time. connecting rainwater leader to storm sewer or to dry well will help keel the siding dry
Fundation drainage
good foundation drainage system starts with perimeter drainage system. code requires below grade foundation walls be damp proofed. asphalt emulsion seals the pours in the concrete to reduce capillary action. in order to waterproof a foundation wall it must be covered in a water proofed membrane. SAM. or dimple board drainage matts are applied to the foundation wall and drains wall to the perimeter drain
Drying
drying is caused by the movement of water vapour, either by airflow (ventilation) or diffusion. drying is primarily done by ventilation.
Spacing sheathing
both plywood and OSB are classified as vapour barriers. sheathing is outside thermal barrier (meaning it will be cold) if sheathing is butted tight together there will be no escape for moisture. sheathing should be spaced on horizontal joints 1” holes can be drilled into blind stud cavities, under windows eetc to promote drying
airtight buildings
energy efficient buildings are air tight buildings. moisture can build up from condensation on any cold surface in these buildings (usually window and doors). to help this a balanced ventilation system with heat recovery ability is needed. super insulated air tight buildings without good ventilation system will not work.
attic ventilation
during heating seasons. attic and vapour barriers receive pressure dude to stack effect. attic must be well ventilated to allow warm moist air that leaks into attic to dry the outside before it can condense. this can be done through vented soffits
crawl spaces
unheated crawl spaces must be ventilated to promote drying. heated crawlspaces must have mechanical ventilation. sealed heated crawlspace reduces stack effect by eliminating air infiltration into a building
Rainscreen cavities
rain screen cavities make space between back of cladding and moisture barrier. code requires bottom of rainscreen to be vented. if the top is vented it will dry better.
landscaping
affects the drying of a building. to promote drying, the ground neer the building should slope away from the building. this ill prevent water from accumulating near the building. BCBC requires minimum 200mm between claddings that are effected by moisture and grade.
durable materials
materials that can go through wet and dry cycles and be exposed to UV without breaking down or deteriorating. .
Material compatibility
materials used in building envelope must be compatible with one another. manufactures will list compatibility issues.
plywood v OSB
plywood gets wet faster but dries faster
both products swell when wet but plywood will return to its original thickness and OSB will not.
pressure treated lumber
used to be cca-a (chromate copper arsenate) but now it is ACQ (alkaline copper quaternary) and CA (copper azole. these have much higher copper content then cca-a. when it gets wet a reaction will happen with metal fasteners so they must be hot galvanized or stainless steel
Attic and crawl space acsess
must be treated and sealed off like and exterior door or window
duct sealing
all ductwork must be sealed at the joints against air leakage. this is critical when ducts pass through unheated spaces like crawlspaces and attics. must be installed s condensation does not build up in duct
sealed polyethylene system
- system is used to improve thermal performance of traditional wood frame buildings.
- poly membrane
advantages of Poly membrane system
- has been used n trades for a long time
- easy for subtrades to work around
- inexpensive
- if building wrap is used as moisture barrier, walls have double air barrier
- used for entire envelope
disadvantages of poly membrane system
- cannot be apart of pressurized rain screen system
- prone to windwashing
- fastening with staples can cause tares
- ## can be damaged easily throughout construction process
procedure of poly membrane system
- plate poly on all walls meeting exterior walls and on bottom of all walls on concrete or interior walls that touch exterior ceiling.
- structural sheathing plywood or OSB should be spaces 1/2” at horizontal joints and 1” holes drilled into sealed stud cavities to allow passage of vapour.
- electrical stuff should be installed with poly pan and sealed to envelope
- all wires and popes must be sealed with acoustaseal
- stapled and sealed with sealant lapped 12”
- poly should be tucked into door and window frames.
- attic ceilings are covered with interior finish before insulation is put in attic so it can support insulation
Attic barrier system
uses different envelope system for walls but used traditional poly membrane system for attic with blow in insulation.
Housewrap air barrier system
tyveck, typar is used as the air barrier and/or moisture barrier.
house wrap air barrier system advantages
- interior plumbing and electrical penetrations do not need to be sealed
- sub trades can be conveniently scheduled.
- is attached to sheathing correctly house wrap can withstand wind pressure and be used in pressurized rainscreen
- having air barrier on outside of the building it prevents wind washing of batt insulation used in stud cavities or mineral wool panels installed on exterior
- high vapour permeability of housewrap allows for drying of the envelope cavity to the exterior
- framing connectors do not have to be caulked.
House wrap air barrier system disadvantages
- less familiar system that requires some details when installing during framing and may require close supervision of subtrades
- primarily used for walls only
- hard to maintain or repair after construction is complete.
- a vapour barrier must be specified. usually sheet poly, foil or vapour retarding paint
- if poly is choses , plate poly must be installed duing framing
- foil membrane should be installed like poly
House wrap air barrier procedure
- house wrap must be carried over exterior topplate during framing so it can be sealed to ceiling air barrier.
- house wrap must be carried under sill late and over the foundation wall so air space is continuous
- ceiling air barriers can be house wrap or poly. if poly is used it can be both air and vapour barrier. if house wrap is used pain or foil will be the vapour barrier.
- all wires and popes that pass through wall plates into attic or crawlspace must be sealed.
- staples should be taped.
rigid panel air barrier systems
airtight drywall air barrier system (ADA) is gasket sealed drywall installed as the air barrier with vapour- retarding paint as a vapour barrier
Advantages of rigid panel air barrier systems
- provides an air barrier using standard finishing materials
- allows for conventional scheduling for sub trades
- provides ridgid air barrier that resists wind washing and can be used in pressurized rain screen application
- easy to maintain after construction process
- can be used over entire envelope
Disadvantages of rigid panel air barrier systems
- not all trades will be familiar with this procedure.
- not allowed in some jurisdictions
- sealing details must be well executed for the system to work efficiently.
- care must be taken if insulation with low vapour permeability is included in the envelope on the cold side of the vapour barrier
Procedure of ridged panel air barrier system
- during framing caulking should be placed between exterior wall plates and floors. rim joints should be caulked to the tops of walls or house wrap around the rim joist to prevent air infiltration.
- during electrical rough in, airtight self sealing boxes should be used.
- plumbing and venting penetrations should occur through solid backing that can be sealed tot he back of drywall with foam tape or caulking.
- foam tape must be applied to all exterior wall perimeters, intercepting wall end studs and lower top plate of wall beneath attic ceiling. gasket material is 3/8” x 1/4” self adhesive PVC foam strips.
- drywall sheets fastened 8” OC
Exterior insulation air barrier system
foam panels insulation used as an air barrier is usually extruded polystyrene or polyisocyanurate
Advantages of exterior insulation air barrier systems
- interior plumbing and electrical penetrations do not need to be air sealed
- easy to schedule sub trades
- rigid roam panels can withstand wind pressure and can be used in a pressurized rainscreen system
- having air barrier on outside of building prevents wind washing.
- framing connections do not have to be caulked, as the external air barriers covers all the gaps between framing members
- panels are both air barrier and insulation. framing is kept warm, reducing the chance of condensation forming in the envelope cavity
Disadvantages of exterior insulation air barrier systems
- used for walls only
- not all trades familiar with this system
- not aloud in all places
- care must be taken if insulation with low permeability is included in the envelope on the cold side of vapour barrier
Procedure of exterior insulation air barrier systems
- foam panels are fastened to sheathing or to structural sheathing with cap head fasteners.
- panels are sealed at joints by stapeling sill gasket to the sheathing behind joints or sealing with tape on surfaces.
- windows and doors must be boxed out to plane with cladding or return details must be created if doors and windows are flush with sheathing
- foam insulation must run up under eaves to keep air barrier continuous. make sure attic ventilation is not blocked
- alternate air barrier is used for the ceiling. this could be drywall or poly.
exterior envelope barrier “the perfect wall”
SAM applied to sheathing becomes a rigid air barrier as well as the vapour barrier and moisture barrier. panel insulation, usually foam is applied over the SAM
Advantages of exterior envelope barrier
- moisture problems in envelope cavity are eliminated. vapour leaking out of building goes directly outside and any water leaking into building can dry into building.
- the entire building structure is thermally protected.
- interior plumbing and electrical penetrations do not need to be air sealed
- sub trades scheduled easy
- rigid air barriers can withstand wind pressure and can be used in a pressurized rainscreen system
- having air barrier on outside of the building prevents wind washing of batt insulation if used in stud cavities
- framing connectors do not need to be caulked
- system can be used on walls floor slabs and roofs
disadvantages of exterior envelope barrier
- expensive
- window, door and other penetrations details must be designed for a thicker exterior finish.
- eaves and decks must be joined to building at top of foam insulation
- not all trades familier
- not allowed everywhere
- needs good HVAC system
Procedure for exterior envelope barrier
- windows and doors boxed out to match cladding or special details
- details such as roof overhangs have to be added on top of air, vapour and thermal barriers in order to keep barriers continuous in wall roof interception.
- sheathing is wrapped with SAM and all windows and door must be sealed with SAM
- screws at least 12” long are used to fasten rainscreen batten and layers of exterior insulation panels to sheathing.
- offset foam insulation panel seams between layers
