Building Pathology L1-3

Question 1

WHAT IS A VISUAL INDICATOR OF CARBONATION IN REINFORCED CONCRETE?

Answer 1

Carbonation causes complete dissolution of the brick protective layer, caused by carbon dioxide in the atmosphere.

The expansion of corroded / rusting steel will result in cracking and spalling of the surface concrete.

This can take several years to take effect on concrete, causing durability issues.

Site test - Solution used to indicate the alkaline level of the concrete, if pink, the concrete is not yet carbonated.

Question 2

WHAT ARE THE CAUSES FOR FLAT ROOF DEFECTS?

Answer 2

Cracking - Lack of protection from the sun / chemical attack

Ponding - Lack of sufficient gradient

Thermal movement - Movement between substrate and membrane

Blistering - Water vapour pressure below roof covering

Flashing / Falls / Detail deterioration or movement

Poor workmanship - Lack of quality in base build or repair

People - By personnel or loose debris

Question 3

WHAT ARE THE REMEDIES FOR FLAT ROOF DEFECTS?

Answer 3

Crazing - Localised repair or full replacement with specialist protection

Ponding - Inc. in gradient and re-covering

Thermal movement - Replace with high performance felt

Blistering - Remove trapped moisture, trace, repair

Flashing / falls - Replace flashing around falls / junctions

People - Avoid footfall / debris building on roof

Question 4

NAME METHODS OF ASSESSING FLAT ROOF DEFECTS?

Answer 4

Electronic leak detection - Weak electrical field on dampened surface to find ‘earths’ into the building, pinpointing penetration point or show water ingress is not caused by a roof leak.

Thermographic examination - Thermographic image highlights areas of moisture retained within the roof to pinpoint location of leak.

Question 5

WHAT ARE THE COMMON DEFECTS ASSOCIATED WITH FLAT ROOFS?

Answer 5

Blistering

Splitting of coverings

Sagging due to failure of the decking between joists

Ponding due to insufficient falls

Damage to flashings

Thermal movement

Crazing

Question 6

WHAT SHOULD BE TAKEN INTO ACCOUNT WHEN CONSIDERING REPAIR / REPLACEMENT OF A FLAT ROOF?

Answer 6

Current age, life expectancy and overall condition

Surveyor should consider the current condition, number / spread of defective areas i.e. localised or widespread, and whether the defect is effecting the surface layer roof structure

Clients intention for the building, the available budget, the building use, disruption caused by repair and possible phasing requirements

Question 7

HOW WOULD YOU APPROACH A FLAT ROOF INSPECTION?

Answer 7

Desktop survey - Gather site info i.e. age, construction, current or previous works to the building

Arrange access and prepare RAMS

Attend site to assess the roof:
- Age
- Previous repairs undertaken
- When and where the roof leaks
- Ponding issues
- Room use beneath
- Footfall frequency

Question 8

WHAT IS DAMP?

Answer 8

A building is considered to be damp when moisture becomes visible through discolouration and staining of finishes, or causes mould growth, sulphate attack, frost damage or drips / puddles

Building regulations for DPCs were developed in early 1900’s but were not always adhered to

Types of damp:
- Condensation
- Rising damp
- Penetrating damp
- Services caused

Question 9

SIGNS OF RISING DAMP?

Answer 9

Internal:
- Unsightly efflorescence
- Wallpaper peeling / visibly damp walls up to 1m
- Blistering
- Decaying skirting boards
- Black, white and green mould growth on walls

External:
- Render degradation
- Efflorescence
- Discolouration
- Cracks in masonry
- Bricks and mortar deterioration

Question 10

CAUSES OF RISING DAMP?

Answer 10

Internally rising groundwater saturates walls with Saltpetre (contained in water)

Damaged or lack of DPC

Via capillary action in masonry

Ground level higher than existing DPC

Cold bridging

Question 11

WHAT IS A COLD BRIDGE?

Answer 11

Weak points in the building envelope allowing heat to pass through more easily, e.g. the roof / wall junction or wall / floor junction. Colder areas not insulated will cause condensation in warmer living areas

Sign - Formation of black mould around skirtings / window openings

Cause - Warm surface or structure meets cold one

Remedy - Eliminate thermal bridge, reducing cross-section with better insulation materials or with a thermal break

Question 12

REMEDIES OF RISING DAMP?

Answer 12

Retrospective / replacement of the DPC

Exterior moisture barrier, inc. excavation down to foundations if the rising damp is permanent

Improve ventilation

Control excess water

Sealing up cracks and moisture barriers

Replace rotting joists / internals affected by damp

Question 13

SIGNS OF PENETRATING DAMP?

Answer 13

Blistering / damaged plaster and wall finishes

Localised dampness

Mould growth

Wet rot affecting floor & wall timbers / skirting boards

Commonly found in roofs, window openings, door openings, brick / stone elevations

Question 14

CAUSE OF PENETRATING DAMP?

Answer 14

Defective porous external envelope:

• Roof, brick / stone elevations (insufficient thickness i.e. one brick thick)
• Cavity the mortar snot bridge external to internal wall
• Cavity tray defective
• Window / door opening
• Missing pointing or render
• Faulty rainwater goods (often cast iron)

External envelope can deteriorate with age, frost or physical damage, promoting penetrating damp

Question 15

REMEDIES OF PENETRATING DAMP?

Answer 15

Re-pointing affected areas, lime mortar preferred for old buildings (highly breathable to allow evaporation of existing moisture)

Fixing cracks / gaps in external envelope

(Consider roof, chimney, parapet, junctions, windows, doors, brick / stonework)

Repair / replace rainwater goods

Inspect and repair / replace cavity trays & cavity ties (blockages)

Question 16

HOW IS A DAMP SURVEY UNDERTAKEN?

Answer 16

Consider building materials, age, locality

Note timescale of damp presence, when it occurs, ay changes since the damp appeared

Methodically check localised areas, i.e. substructure, superstructure, roof void, openings etc from internal & external

Use of devices to monitor moisture levels of materials i.e. Protimeter

Question 17

WHAT IS MOULD GROWTH?

Answer 17

Fungal growth developed on wet material in interior spaces

The primary reason within a building is uncontrolled moisture incursion in the form of liquid flow, condensation, high humidity or capillary action (moisture travelling through building elements via surface tension, against gravity)

Gaps in external envelope

Defective rainwater goods

Occupier use i.e. cooking / drying clothes

Question 18

WHAT ARE THE BENEFITS OF USING LIME MORTAR?

Answer 18

Highly breathable for older, moist buildings

Adhesion properties

Flexible to allow thermal and building movement

Regulates building humidity due to porous properties

Protective layer against frost and water movement due to high quality bonding, reducing water ingress risk

Highly workable during applications

Highly versatile and durable

Question 19

WHAT IS FROST DAMAGE / ATTACK?

Answer 19

Physical process causing deleterious effect on porous brick / stone / concrete due to cyclical freezing & thawing

Course-grained materials sock moisture, undergoes volumetric expansion causing deterioration of the surface (spalling)

Common areas are those exposed to elements, often saturated i.e. parapets and below the DPC and ground level

Question 20

HOW TO REMEDIATE FROST DAMAGE / ATTACK?

Answer 20

Proactive - Ensure constant drainage, no pooling or continuous damp patches to external envelope

Developed attack - Remove and replace affected bricks, re-point with breathable mortar i.e. lime

New attack - Re-point with breathable mortar to allow moisture to evaporate

Question 21

WHAT ARE THE STAGES OF DAMP?

Answer 21

Stage 1 - Visual inspection

Stage 2 - Investigation using moisture meters

Stage 3 - Detailed investigation

Stage 4 - Locating the source

Question 22

HOW CAN YOU TEST FOR DAMP?

Answer 22

Protimeter works by measuring electrical resistance between two electrodes

Protimeters are only accurate measuring moisture content in timber

Other materials gain misleading readings, however, can be used to gain a sense of moisture content

Less accurate than a speedy carbide meter

Question 23

WHAT IS A SPEEDY CARBIDE METER?

Answer 23

Measures moisture content in aggregates, ceramics, abrasives (masonry)

Drill masonry to place dust in a sealed container with a measurement of calcium carbide to confirm moisture content

Dust and calcium carbide releases gas in proportion to the moisture amount present

Question 24

DESCRIBE 3 ISSUES AND REMEDIES FOR RISING DAMP

Answer 24

Issues:
- Lack of DPC
- Defective DPC
- External features bridging the DPC

Remedy:
- Remove external feature causing bridging, injection of water repellent chemicals into brickwork or installing a new DPC layer

DPC not suitable?
- Lime plaster and wash applied externally to minimise damage

Question 25

WHAT IS CONDENSATION AND HOW IS IT CAUSED?

Answer 25

Hot air carries moisture, condenses on cold surface and leaves water droplets on surface

Source - breathing, domestic activities, cooking, eating

Leads to staining at cold bridges, peeling wallpaper & mould growth

Causes:
- Lack of insulation, lack of ventilation and unheated areas of a building

Common areas - Bedrooms, kitchens, bathrooms

Question 26

HOW TO REMEDIATE CONDENSATION?

Answer 26

Reduce moisture generation

Provide adequate ventilation & heating

Improve building insulation

Question 27

HOW LONG WOULD YOU LEAVE BRICK & MORTAR TO DRY OUT PRIOR TO COMMENCING WORKS?

Answer 27

De-humidifier can speed up the process, however 3-4 months minimum recommended

Question 28

TALK ME THROUGH YOUR THOUGHT PROCESS… NUMBER OF CRACKS IN AN EXTERNAL WALL

Answer 28

Note wall material, building form and approx. age

Local factors:
- Trees
- Stumps
- Drainage in the vicinity of the crack inc. rainwater
- Previous alterations to the building

Question 29

WHAT CAUSES CRACKS IN BUILDINGS?

Answer 29

Subsidence

Heave

Settlement

Differential settlement

Lintel failure

Corroded steel lintel

Question 30

WHAT IS SUBSIDENCE?

Answer 30

Downward movement of foundations due to changes in the supporting strata, usually occur in these scenarios:

1. Buildings constructed on shrinkable soils, such as clay, when long dry spells occur and/or water is sucked out by adjacent trees/bushes. Different types of clay shrink/swell at different rates.
2. Water leaks into soil, i.e. burst water mains, softening and washing away the strata. This occurs to soil with high sand or gravel content, sometimes chalk.
3. Previous mining activity, particularly historic mining. Tunnels may collapse causing soil movement near ground level.

Tell tale signs:

Internal - Cracks in walls 3mm or above wider at the top than the bottom, cracks where an extension joins the house, sinking floors, sticking doors / windows.

External - Vertical cracking at centre, diagonal cracks at corners, larger at the top / thinner at bottom, dry soil, trees within vicinity, leaning building, extension separated.

Question 31

WHAT IS HEAVE?

Answer 31

Upward movement in floor slab due to soil movement beneath, inc. in moisture content i.e. removal of a tree in clay soil, or freezing forces

More common in floor slabs than foundations as slabs have less weight to resist heaving forces

Tell tale signs:

Vertical cracking at centre of building, diagonal cracking at corners, larger cracks at base of building / thinner at top

Question 32

WHAT IS SETTLEMENT?

Answer 32

Downward movement of a new build property consolidating or displacing the soil. This can occur a few years after completion of the build, dependant on:

• Existing soil conditions
• Methods of construction
• Size and depth of construction
• Type of structure, its condition and foundations

Opposite to heave, different to subsidence which is unstable soil.

Tell tale signs:
- Step cracks in brick/concrete foundation walls
- Leaning/tilting chimney
- Doors & windows sticking

Question 33

WHAT IS DIFFERENTIAL SETTLEMENT?

Answer 33

If two sections of a building are built from different foundations, or the ground is made up of different soil / strata types, one may settle more than the other causing cracking between two sections of a building.

If one edge moves more than another, the structure tilts, most common with extensions

Question 34

SYMPTOMS OF DIFFERENTIAL SETTLEMENT?

Answer 34

Improper fit & function of doors and windows

Cracks and deterioration of foundations and slabs

Damage to walls and flooring

Structural instability, may be deemed unfit for occupation

Question 35

WHAT SIZE CRACKS ARE OF CONCERN?

Answer 35

Up to 2mm - very slight concern

2mm-5mm - slight / aesthetic concern

5mm-15m - moderate concern

15-25mm - severe

Over 25mm - very severe with stability concerns

Question 36

IF THERE WAS A STEPPED CRACK ON THE CORNER OF A BUILDING, WHAT MIGHT HAVE CAUSED IT?

Answer 36

Settlement

Subsidence

Heave

Question 37

WHAT IF THE CRACKS WERE PRESENT ON CONCRETE?

Answer 37

Consideration of common concrete defects:

• Carbonation
• Chloride attack
• Silica reaction
• Issues relating to structural movement
• Poor design
• Poor construction

Question 38

WHAT IS CARBONATION IN CONCRETE?

Answer 38

CO2 absorbed from outer concrete inwards, can increase tensile and compressive strength, although causes embedded re-bar corrosion (expansive cracking) and degradation of concrete surface.

Commences as soon as concrete is exposed to atmosphere, 1-5mm per year dependant on concrete porosity and permeability.

Concrete has high pH level (13), carbonation reduces this.

Carbonation test - Solution applied, if pink the pH is still high. If clear, the concrete is carbonated. Test is undertaken by spraying solution on freshly exposed concrete surface, or core holes drilled.

Prevention - Apply protective coating once in a fully hardened state or introduce additives during production.

Question 39

WHAT IS CHLORIDE ATTACK?

Answer 39

Chloride penetrates concrete surface increasing the risk of steel reinforcement corrosion

Spalling is caused by expansive corrosion, noted by rust colouring

Causes:
- Calcium chloride as an additive to inc. setting time
- Inadequately washed aggregates with chlorides from the sea

Enter from external environment:
- Seawater exposure
- Use of salt to melt ice
- Presence of chlorides in storage substances

Prevention:
- Inc. reinforcement bar cover
- Coat re-bar in epoxy, cathodic protection or stainless steel clad bar

Question 40

WHAT IS SILICA REACTION?

Answer 40

Deleterious chemical reaction of aggregate and cement

Produces expansive gel, causing pressure leading to expansion and cracking.

Typically ASR will not damage concrete excessively, however, allows corrosion, freeze thaw, sulphate attack, etc due to openings.

Causes:
- High pH levels
- Reactive aggregates
- Presence of water

To spot:
- Looks like crazing to a flat roof
- Can take 10 years after construction to appear, however, highly reactive aggregate as soon as 2 years

To prevent:
- Reduce alkali content of the chosen concrete or use less cement
- Use of supplementary cementing materials i.e. fly ash / slag
- Lower water to cement ratio
- Good curing

To remedy:
- Vapour-permeable membrane applied to concrete, creating a hydrophobic surface (sealed).

Question 41

YOU INSPECT A BUILDING AND IDENTIFY A NUMBER OF CRACKS IN THE EXTERNAL WALL, TAKE ME THROUGH YOUR THOUGHT PROCESS?

Answer 41

Note the material the wall is constructed from and the what form the construction of the building is.

Consider local factors which may be causing cracking:

• Trees
• Stumps
• Alterations to the building, including extensions, converted lofts or internal layout alterations
• Drains in the vicinity of the crack

Question 42

WHAT IS LINTEL FAILURE?

Answer 42

Allows a triangular section of brickwork above the window to drop down, creating a triangular crack from the corner of the window to the centre.

The cracking may be vertical, general movement from above the window junction.

Question 43

WHAT IS A CORRODED STEEL LINTEL?

Answer 43

Where an unprotected structural steel lintel is installed above an opening and an edge is exposed or close to the surface, corrosion can occur over time and cause cracking through expansion.

The increase in volume cracks surrounding brick/blockwork and pointing, causing structural issues.

Remedy - Prevention, avoid the steel being exposed unprotected, or replace the steel lintel if already defective.

Question 44

WHEN WERE DPC’S FIRST IMPLEMENTED?

Answer 44

1875 - DPC became compulsory in London, generally a single layer of slate built into structural walls.

Between 1920’s and 1980’s, the most common DPC’s were bitumen and felt based, with polypropylene introduced in the 1960’s.

Question 45

WHEN WERE CAVITY WALLS FIRST IMPLEMENTED?

Answer 45

1920’s, outer layer protection, inner layer as a dry inner wall.

DPC built into the outer and often ‘bridged’ across the cavity.

Air in the cavity prevented moisture transmitting from the outside to property within.

Cold bridge could occur from fallen mortar, for example, transmitting across to the inner wall.

Question 46

WHEN WERE AIR BRICKS IMPLEMENTED?

Answer 46

Victorian properties - 1837-1901 featured cast iron grilles to promote air flow.

Clay bricks included to help ventilate properties, providing passive ventilation, first implemented around 1920’s onwards.

Question 47

DESCRIBE THE DIFFERENT TYPES OF ROT AND HOW YOU WOULD RECOGNISE THEM

Answer 47

Dry Rot - Wood shrinks and splits into large cuboidal cracking. The wood is light in weight, crumbles under touch and has a dull brown colour with a cotton wool type texture. Mycelium is often visible, greyish in colour and yellow/purple when dry.

Wet Rot - Wood shrinks and splits on a smaller scale with the wood becoming darkened. Mycelium can be white, brown, amber, green or black with flexible strands when dry. The fruiting bodies can be a number of different colours and can occur inside and outside.

Question 48

WHAT IS DRY ROT?

Answer 48

Dry rot is wood decay caused by fungi that digest parts of wood which give it strength and stiffness.

Wood shrinks and splits into large cuboidal cracking. The wood is light in weight, crumbles under touch and has a dull brown colour with a cotton wool type texture. Mycelium is often visible, greyish in colour and yellow/purple when dry.

Question 49

WHAT IS WET ROT?

Answer 49

Wet rot is wood decay caused by fungal species, obtains their food by breaking down the cell walls of wood, resulting in a loss of its structural strength.

Wood shrinks and splits on a smaller scale with the wood becoming darkened. Mycelium can be white, brown, amber, green or black with flexible strands when dry. The fruiting bodies can be a number of different colours and can occur inside and outside. The wet rot has a damp,, musty smell.

Wet rot requires more moisture and is less destructive than dry rot.

Question 50

WHAT ARE THE REMEDIAL MEASURES FOR DRY AND WET ROT?

Answer 50

Locate the source of moisture and promote rapid drying whilst removing the rotten wood.

Surface application of fungicidal fluid and introduction of temporary support measures if necessary.

Question 51

WHAT ARE THE 3 TYPES OF WET ROT?

Answer 51

Brown Rot - Fungus digests cellulose and sugar in timber, giving a brown hue colour. Cellulose is responsible for the woods structural strength, therefore weakening the structure.

White Rot - Lignin is the polymer responsible for wood’s brown colour, this is what white rot feeds on. Without lignin, wet rotted timber can be soft to touch.

Soft Rot - Also digestion of cellulose.

Question 52

THE ENDS OF JOISTS IN AN EXTERNAL WALL HAVE BEEN SERIOUSLY AFFECTED BY DRY ROT, HOW WILL YOU RECOGNISE THIS TYPE OF ROT AND WHAT ACTION WOULD YOU TAKE TO RESOLVE THE PROBLEM?

Answer 52

Dry rot results in a moisture content of 30-40%, occurring in less-ventilated spaces, i.e. floor void/behind timber panelling.

Typical indicators of dry rot:
- Wood shrinkage, dark cracks in a cuboidal manner.
- A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow which often develops under less humid conditions.
- The ‘skin’ can be peeled like a mushroom.
- White fluffy ‘cottonwool’ mycelium develops under humid conditions.

Any affected timbers should be removed and replaced with pre-treated timber. Any remaining timbers at risk of being affected should be treated with fungicide.

Where dry rot has passed through masonry, it should be isolated using containment and/ or masonry sterilisation.

Question 53

THE ENDS OF JOISTS IN AN EXTERNAL WALL HAVE BEEN SERIOUSLY AFFECTED BY WET ROT, HOW WILL YOU RECOGNISE THIS TYPE OF ROT AND WHAT ACTION WOULD YOU TAKE TO RESOLVE THE PROBLEM?

Answer 53

Wet rot results in a high moisture content of 50-60% to propagate and spread.

Usually found where there is a water leak or building failure, such as along window sills or in roof voids.

Typical indicators of wet rot:
- Surface cracking where cracks follow the grain.
- Hyphae strands which are light brown and yellow (key difference from dry rot).
- Infected timber turns dark brown.

Remedy:
First step - Locate and remediate the water ingress location to prevent further damp affecting the timbers.

All infected / damaged timber is removed, as these are structurally impaired due to the decaying action of the wet rot, and the remaining timber treated with a suitable preservative.

If the wet rot is in a confined space, i.e. cupboard/loft space, it may be necessary to improve ventilation.

Question 54

WHAT ARE THE REMEDIAL MEASURES FOR DRY ROT?

Answer 54

Remedials are intrusive.

Establish the full extent of outbreak, parts of which may be concealed beneath floorboards, behind furniture and panels.

Affected timber, similar to wet rot, is to be removed and replaced, including those within 450mm of the affected timber to allow for further contamination.

Surrounding timbers should be treated with chemical biocide to ensure all strands and spores are killed.

Affected plaster in contact with the dry rot is to be removed and replaced, with wall surfaces treated with steriliser or biocide.

Finally, keep the area dry and heated, ensuring timbers are fully dried out to prevent recurrence.

Question 55

EXPLAIN THE LIFE CYCLE OF DRY ROT

Answer 55

4 main dry rot life cycle stages:

1. Spores - Spores are omnipresent (widespread) and in very large numbers, appearing as a fine orange brown dust. The spores are activated when combined with timber and moisture.
2. Hyphae - Where timber and moisture is present, the spores will produce very fine white strands called Hyphae, which allows the dry rot to grow by feeding on the timber. Breaking down the structure of the timber while it grows to form into Mycelium.
3. Mycelium - The resulting Hyphae mass is known as Mycelium, having the ability to grow great distance over various materials, allowing the Mycelium to progressively destroy the structural integrity of a full building if left undetected.
4. Fruiting Body - To perpetuate itself, the fungus creates a fruiting body, a mushroom-like form with a function of pumping out spores to transfer via air currents to other susceptible areas within the building, germinating to create a new attack of dry rot.

At this point, the dry rot life cycle starts over on a separate section of the building’s susceptible timber.

Question 55

NAME COMMON INSECTS KNOWN TO ATTACK TIMBER

Answer 55

Common Furniture Beetle - Most common insect infestation in UK, a wood boring beetle, brown, 2.5mm length, with grooves running down their back lengthways. Either soft or hard wood in damp conditions.

Death Watch Beetle -

House Longhorn Beetle -

Wood Boring Weevils -

The type of rot (Wet/Dry) does not affect the type of wood boring beetle causing decay, the common furniture beetle, deathwatch beetle are usually found in Central and Southern England, and Longhorn Beetle found closer to London.

Question 55

WHAT ARE THE REMEDIAL MEASURES FOR INSECT ATTACK?

Answer 55

3No. categories based on the necessary remedials:

Category A - Insecticidal treatment required for the common furniture beetle, death watch beetle and house longhorn beetle.

Category B - Treatment is only necessary for associated dry rot due to wood boring weevils.

Category C - Where no treatment is required for bark borers.

Remedial measures for these insects:

• First, study flight holes to determine the type of insect attack and whether the infestation is active or dormant.
• Apply two coats of boron based treatment to all affected areas, overlapping at least 300mm onto the sound timber.
• Insecticidal spray, or if worse, gel for penetrating into the timber.
• In a severe attack, replacement timber with pre-treated wood.

Note - applying any treatment without remediating the source of moisture is pointless.

Question 55

WHAT ARE SIGNS OF INSECT ATTACK?

Answer 55

Uneven floors

Skirting board with cuboidal surface

Timber with ‘dart holes’ in it

If moisture content of timber is 20-22% or higher, outbreak of wood boring insect infestation can be expected.

Question 56

EXPLAIN THE LIFE CYCLE OF WOOD BORING INSECTS

Answer 56

Burrow into timber to lay eggs.

Females lay eggs in cracks/crevices which can remain dormant for long periods until reactivated by raised humidity or direct moisture in the timber.

Incubation period of 2 weeks.

Larvae begin their 2-5 year journey inside the wood before seeing daylight, but start eating through timber immediately. Frass can be seen (dust like substance on surface), which is the waste product as they bore through wood.

After the 2-5 years, move towards the surface and develop into adult beetles and leave a hole to indicate their presence.

This is the first point you may realise the insect infestation is there.

Once exited the wood, it’s sole purpose is to mate and lay more eggs, with lifespan outside the timber at 10-14 days for females.

Then, cycle starts again.

The insects in the UK are mostly active between April-August, and can lay dormant for the rest of the year.

Question 57

WHAT REMEDIAL ACTIONS ARE VIABLE FOR SUBSIDENCE?

Answer 57

First, does the building insurance cover subsidence? As it can be rectified…

Timescale - May be up to 2 years or move to properly investigate and recitfy

Question 58

HOW TO TELL IF A BUILDING IS SUBSIDING?

Answer 58

Visible cracks in particular areas of the house - top corners, from junction points of doors/windows.

May need to be measured for as long as 12 months.

Rarely a concern unless cracks appear suddenly and are over 3mm wide.

Could be movement if you find:
- New or expanding cracks in plasterwork or outside brickwork
- Doors / windows sticking for no reason
- Ripping wallpaper
- Sloping or dipping of solid ground floors

Question 59

HOW DO WOODWORMS AFFECT TIMBER IN BUILDINGS?

Answer 59

Typically adult beetles lay eggs on, or just under the surface of the wood members.

The resulting grubs feed on the timber, causing structural and cosmetic damage before hatching as beetles, then breed, lay eggs, and repeat the process causing further damage

Question 60

WHAT IS A WOODWORM INFESTATION LIKELY TO INDICATE?

Answer 60

Woodworm and other insect infestation species require the wooden element to contain a higher moisture content than found in a typical home.

Likely the building also has an issue with excess damp.

Question 60

HOW IS A WOODWORM INFESTATION TREATED?

Answer 60

Generally controlled with chemical insecticides.

Advisable to investigate and locate the source of the damp issue, dry wood is not usually affected so other areas may become affected at a later date.

Question 61

YOU ARE SURVEYING A DEFLECTED TIMBER FLOOR IN AN EARLY 19TH CENTURY BUILDING. WHAT ARE THE CAUSES AND METHODS AVAILABLE TO DEAL WITH THIS IF THE CLIENT REQUIRES A LEVEL FLOOR?

Answer 61

Confirm the cause of deflection:
- Notching
- Rot
- Insufficiently sized joists
- Insufficient centres
- Overloading
- Deterioration of sleeper walls

Confirm if the issue can be remedied and whether the timber floor can be retained.

Potential remedial measures may be to:
- Supplement the timber joists
- Overboard
- Remove and replace with suspended timber floor
- Install an alternative solid floor

Question 62

WHAT ARE THE CAUSES OF DEFLECTION AND THEIR MEANING?

Answer 62

Notching - Holes cut in ceiling / floor joists to run services. If notches are too big, at the end where they bear on a wall/sill, or in the wrong location, the joist can be drastically weakened to support the load it was designed for.

Rot - Wood decaying fungi, causes severe damage to structural elements, floorboards, skirting.

Insufficiently sized joists - Inadequately designed / installed structural joists, not fixed to load bearing construction i.e. elevations / sleeper walls.

Insufficient centres - Joists should be positioned with a maximum centre spacing of 600mm, with initial joist to wall gap of 25-75mm (installing services). Less joists than this can cause structural instability, or deflection.

Overloading - Increased weight / point load to a timber joist may cause deflection.

Deterioration of sleeper walls - Lack of structural stability in ground floor joists can cause deflection.

Question 63

WHAT IS DISTORTION IN TIMBER?

Answer 63

When exposed to fluctuating humidity/moisture levels, different sections of timber expand and contract at varying rates, leading to distortion.

Question 64

WHAT IS DEFLECTION IN TIMBER?

Answer 64

The deformation or bending that occurs in a structural element when it is exposed to an external load (overloading(, rot, insufficiently sized joists or centres, or deterioration of sleeper walls.

Deflection is designed into buildings, dependent on materials used.

I.e., timber frame buildings can move, structural calculation may provide 1/360th at the centre point of a structural beam.

A steel beam with structural glazing cannot deflect, otherwise the glazing will become damaged/shatter.

Golden gate bridge - deflects 4m laterally in strong winds.

Question 65

WHAT IS WARPING IN TIMBER?

Answer 65

Deformity in wood when moisture content changes unevenly, i.e. one wooden board dries faster than another, causing stress that changes the shape of the wood.

Question 66

HOW DO YOU IDENTIFY THE PRESENCE OF WOODWORM?

Answer 66

Holes in the wood with live infestation show powder (faeces) around the holes.

Varied hole sizes, however, typically 1-1.5mm for most common household species.

Adult beetles which emerge from the wood may be found in the summer months.

Question 67

A NEWLY CAST REINFORCED CONCRETE SLAB IS EXHIBITING CRAZING AND CRACKING ON ITS SURFACE, WHAT ARE THE POSSIBLE CAUSES?

Answer 67

Poor or inadequate curing due to environmental conditions being conducive to high evaporation rates and a lack of adequate protection.

Too wet of a mix, excessive floating or use of a jitterbug which depresses the coarse aggregate, resulting in excessive concentration of cement paste and fines at the surface.

Finishing operations performed while bleed water remains at the surface, retaining water within the structure.

Sprinkling cement on the surface to dry up the bleed water.

Question 68

WHAT IS CONCRETE BLEED WATER?

Answer 68

Segregation of excess water in the concrete mix, rising to the surface of the freshly placed concrete.

This appears on the surface as a clear/green water once compacted, but before it has set. When the cement paste has stiffened and set, the bleeding stops.

This causes a weak surface layer as it is too wet when curing, and the solid aggregate sinks under gravity, leading to settlement cracking/crazing.

Avoided by - reducing concrete water content, removing laitance (fine surface particles) by brushing, recompacting concrete, delay power trowelling until the surface water evaporates or is otherwise removed.

Question 69

WHAT ARE NICKEL SULFIDE INCLUSONS?

Answer 69

Microscopic imperfections in glass, known as inclusions, which are inherent in the glass production process.

Most are harmless, but can be disastrous failure of tempered glass(UOL BUILDING).

When glass is rapidly cooled to create tempered (toughened) glass, nickel sulfide inclusions remain in high temperature forms.

Over several years, nickel sulfide reduces to its natural low temperature, and increase in volume.

This causes cracking and additional tensile stresses which, in tempered glass, can lead to failure.

AKA Spontaneous glass failure.

Question 70

WHAT ELSE MAY CAUSE GLAZING TO CRACK IF IT WASN’T NICKEL SULPHIDE?

Answer 70

Structural movement around the window opening putting pressure on the glazing to cause the crack.

Question 71

YOU FIND A LEAK AT HIGH LEVEL ON THE FIRST STOREY OF A 2-STOREY BUILDING WITH TRADITIONAL CAVITY WALL CONSTRUCTION, OUTLINE THE PROCESS YOU WOULD GO THROUGH IN ASSESSING THE POTENTIAL CAUSES OF THE DEFECT?

Answer 71

Review any existing building information prior to inspecting the property.

Look at the whole building to understand the construction, materials used, and assess where alterations have been made.

Prudent to speak to the building owner, asking the leak location and when it is most prevelant.

I would suspect a roof leak and would inspect externally and internally for signs of missing roof coverings and defective or missing flashings around roof penetrations.

When in the roof space, I would also look for evidence of leaking pipes.

Question 72

HOW DOES CAVITY WALL TIE FAILURE PRESENT ITSELF AND HOW WOULD YOU FIX IT?