12 - Building Pathology Flashcards
Q. What are the typical building defects?
A. Penetrating damp. Rising damp. Condensation. Fungal and insect attack. Movement and cracking due to subsidence, settlement or heave. Cold bridging. Cavity wall tie failure. Failure to flat roof covering such as puncture damage to single ply roofing.
Q. Explain the different types of cracking you might see on a two-residential building?
A. Subsidence, settlement and heave.
Q. When investigating structural cracking to brickwork in residential/low rise property what recognised standards would you refer to assist in classifying the cracking?
A. BRE Digest 251. It provides classification of visible damage to walls and category of damage 0-5, 0 = hairline cracks and 5 = structural damage which requires major repairs.
Q. What are the limitations of using a borescope to inspect the cavity of a 1960/1970s domestic dwelling?
Their grave disadvantage is that their viewing is effectively limited to a straight line (rigid borescope).
Also the viewing is subject to the width of the cavity, the space in the cavity needs to allow for the borescope to enter enough to get a proper viewing.
Q. Are there any limitations with the use of a damp meter?
A. Need to be aware of the material its being used on i.e. behind the plaster if there is black ash mortar contains carbon which is highly conductive and triggers elevated moisture readings on the meter.
Can you expand on BRE 251 ? What are the crack categories ? What are common causes of cracking ?
I have read bre digest 251 assessment of damage in low rise buildings. This defines cracks and assessment of cracking from level 0 a hairline cracking less than 0.1mm up to structural damage cracks greater than 25mm.
Level 0-5 from bRE digest 251. 0 - Hairline crack less than 0.1mm 1 - fine crack - up to 1mm 2 - up to 5mm 3 - 5-15mm 4 - extensive damage - 15-25mm 5 - 25mm+ structural damage
Can you expand don what your local building stock is ?
Predominantly Victorian redisnetial buildings
What is wall tie failure and how would you identify it ?
IDENTIFICATION — Horizontal cracking in every 5 or so brick course or in render. It’s the corrosion of old steel ties such as large fishtail. The corrosion increases the steel up to 4 times leading to the cracking.
REMEDY — use borescope to determine the defect is wall tie failure. Locate wall ties and isolate or removed to ensure no further damage. Install replacement stainless steel mechanical fixed ties secured with an epoxy resin if required
What is rot and how would you identify it ?
Dry Rot – Wood shrinks and splits into cuboidal cracks. Wood is light in weight and crumbles under fingers. Usually mycelium on the surface which is grey when wet and yellow/purple when dry. Fruiting body usually brown/red in colour. Indoors only.
Wet Rot – Wood shrinks and splits. Wood darkens. Mycelium grows on surface which can be white, brown, green or amber in colour. Fruiting bodies can be different colours and occurs internally or externally.
What did you learn from your PCA Wood destroying insects CPD ?
The investigation, types of insects and remedial actions
Can you expand on what trada tables are please ?
TRADA’s Span tables have been in existence for decades now, helping designer and builders quickly look up the right sized softwood members for domestic projects.
In 1991 the Span tables were paid for by government and were included within the Building Regulations.
Pethfoot- why did you advise the client that further opening up works would be required regarding the dry rot ? What is dry rot ? What remedial measures did you introduce ?
o A fungal infestation that can have degradation effect on timber. Active at between 20-35% humidity and 0-26oC, fruiting body a rust colour with cotton wool like strands, reactive to light and can travel / grow up to 1m per year, can move through masonry.
What are the stages of dry rot ?
Spore
Hyphae
Mycelium
Fruiting Body
What are the ideal temp and humid for dry rot ?
20-35 % humidity and 0-26oc
Pethfoot - What were the remedial actions for the dry rot ?
Remove compete timber, treat with fungicide (probor 10) rapid drying out of area, introduced of ventilation and reinstall new floor structure
Pethoof t- How did you identify the woodworm was active ?
Fresh dusting or frassing under or next to the holes;
You can see light coloured wood in the holes, which have sharp edges;
Edges of wooden beams and joists are breaking away to reveal fresh, light wood underneath.
Pethfoot - How did you ensure the remaining /affected woodworm timbers were suitable to remain ?
They were allr replaced in this scenario
Pethfoot - what implications did the listing have on the remedial works ?
Limited the available options, concrete replacement floor was not suitable. We liaised with the conservation officer to this regard
What are the different types of common damp in buildings ?
condensation, rising damp and penetrating damp
How would you identity between dry and wet rot. ?
Dry rot is the most serious form of fungus decay in a building, spreads onto and destroys much of the timber. On the other hand, the wet rot fungus occurs more frequently but is less serious, the decay is usually detained to where the timber becomes and stays wet.
The Wet rot fungus tends to grow on porous surfaces, for example, timber with a high moisture content of around 50% while for dry rot to grow moisture of around 20% needs to be present. If left untreated wet rot can cause major structural problems as it can lead to weakened timbers.
For moisture content to be suitable for wet rot growth there has to be a source of constant moisture – this could be as a result of defective plumbing or damaged guttering. Wet rot cannot spread through masonry and will cease to grow when the source of moisture is taken away. Due to the parts of the building that tend to have the correct moisture levels, for example, underfloor areas, dry rot can often cause significant damage before the homeowner is aware that there is even a problem with dry rot in the property.
What are wood boring insects >
A wood boring insect is a common term that covers many species of beetles that as larvae eat and destroy timbers.
Wood boring insects are usually found in areas within a property that are poorly ventilated with a high humidity such as for example a sub floor crawl space. This is usually because these conditions become perfect for the larvae to hibernate and transform into a woodworm beetle.
What are the treatment options ?
Treatment and removal of affected timbers
How do you use a protimeter and what are the limitations ?
Calibrated for timber, used to verify visual inspection cannot be relied upon.
What is a borescope and how do you use it ?
Camera to inspect, normally required to make hole to view iot a cavity as ane example
What is limecrete ?
Limecrete is a mix of natural hydraulic lime (NHL5) and sharp sand. Sometimes glass fibres are mixed in to give a more durable surface.
267 Jesmond road, at what intervals did you inspect ?
Every 3 months
What is concrete carbonation ?
Concrete carbonation is the result of an electrochemical reaction between carbon dioxide, moisture and calcium hydroxide that is present in cement, producing calcium carbonate. Calcium carbonate lowers the alkalinity of concrete from pH12 – 13 to around pH9. This hardens the concrete and increases its compressive strength, but at this reduced pH level the protective passivation layer surrounding the reinforcing steel begins breaks down, leaving the steel vulnerable to corrosion.
Rust (Iron oxide) has up to 6 times larger volume than the original steel, so as the steel reinforcements rust, the expansion causes the concrete to crack and spall.
What is ASR ?
Most common alkali-aggregate reaction. Concrete is highly alkaline. Water within the pores will also be alkaline. The water can react with silica in the aggregate which produces a gel which expands and causes the concrete to crack.
Identified by cracking that is bordered by a colourless gel which leads to spalling. Further testing can be carried out in labs to confirm.
For it to occur, it needs silica in the aggregate, moisture and high alkalinity. Remedies include removing the cause of moisture, remove damaged concrete. Introduce secondary reinforcement if needed.
Can you give me four examples of wood boring insects ?
COMMON FURNITURE BEETLE (WOODWORM)
3-5m long, dull brown
Lines of pits on wings
Found on or around damaged timber LATE MARCH – EARLY AUGUST (particularly warm weather.
Softwood, European hardwoods
1-2mm dia. Circular flight holes
Flight holes random orientation, mainly in direction of grain.
Bore dust, cream coloured, lemon shaped pellets.
Life cycle 2-5 years
LONG HORN BEETLE
Adult 10-12mm, black or dull brown.
Sapwood or softwoods particularly roof timbers.
South-west of London mainly surrey.
Flight holes, few large oval, 6-10mm largest dimension.
JULY to OCTOBER
Cream coloured, sausage shaped.
DEATHWATCH 6-9mm long, chocolate brown MARCH to JUNE Bore dust, disc shaped cream pellets Flight holes circular 3mm diameter Mostly oak and elm (hardwoods)
WEEVIL
3-5mm long, brownish black. Distinctive long snout.
All year around.
Flight holes, small ragged, 1mm diameter.
Decayed softwood and hardwoods in damp conditions.
Mostly found in below ground conditions.
Can you give me a examples of deleterious materials ?
Asbestos Calcium chlorides Calcium silicate bricks CFC’s Formaldehyde Hair plaster HAC (High Alumina Cement) Hollow clay pot floors Lead Nickel sulphides
What isa deleterious material ?
The term ‘deleterious materials’ is a broad one, encompassing not only materials that are dangerous to health or which are the causes of failures in buildings, but increasingly, materials which are environmentally damaging
Why did you carry out concrete testing? What is sulphate attack?
Carbonation occurs when the alkaline elements of the concrete react with carbon dioxide creating calcium carbonate which lowers the PH level of the concrete which reduces the passivity. If there is inadequate coverage, the carbon dioxide can react with the protective coating on the steel and corrode it. Levels of carbonation impacted by compaction, temperature, humidity, carbon dioxide levels.
Identify by carrying out an onsite test that will change colour when it comes into contact with high alkaline concrete.
It is remedied by removing the delaminated concrete, cleaning the re-bar and patching the concrete.
Did you refer to any standards for your design?
Approved Doc M, BS 8300 - design of an accessible and inclusive built environment
What roof covering did you recommend with option C, was it felt? How would you monitor the construction or the works on site?
Single ply membrane
Were any beams used for support where you removed the walls?
yes, designed by structural engineer, steel.
Which other parts of the building regs did you refer to for your designs?
Part M, L, A, F
Did you check the condition of the timber joists of the garage?
Yes, and reviewed the sizes based on current trada tables.
How did you inspect the roof covering to the garage?
Ladders and camera pole
What materials can wall ties be made of ?
Iron, steel, stainless steel
Difference between wet and dry rot ?
Dry rot can penetrate masonry, different humidity, One of the main differences between wet rot and dry rot is that wet rot needs a higher moisture content to grow. Wet rot fungus likes to grow on timber with a high moisture content of around 50% and above while for dry rot to grow it will germinate at a lower timber moisture content of around 20% to 30%.
Why is dry rot seen to be more problematic than wet rot ?
Can penetrate masonry
Where would you seek guidance regarding wall tie failure ?
Approved Document A for modern buildings
BRE 401
What are the spacings for wall ties ?
Vertical 450mm or every 6-8 courses and horizontal 900mm. See Approved doc A Table 5 for for information. It shows tie length and cavity width.
What indicators would you look out for if you suspect dry rot?
Dry Rot – Wood shrinks and splits into cuboidal cracks. Wood is light in weight and crumbles under fingers. Usually mycelium on the surface which is grey when wet and yellow/purple when dry. Fruiting body usually brown/red in colour. Indoors only.
