Building Pathology Flashcards
You mention in your case study project that you inspected the flat roof as part of your initial investigations, what are some causes and remedies of defects associated with flat roofs?
- Crazing – Deterioration of roof surface caused by over-exposure to the elements.
- Ponding – Caused by existing issues/poor falls with the structural deck, minimum gradient of 1:40 is required.
- Thermal Movement – Can cause cracks and splits, often requires re-roofing with a high-performance felt.
- Blistering – Caused by water vapour pressure below roof covering. Blisters can be cut to allow moisture to escape then re-bonded.
- Flashings and Falls around openings – Poor workmanship or deterioration of flashing can lead to water ingress. Detailing must be addressed in line with roof manufacturer approved methods.
- People – Often cause punctures and rips by stepping on debris, often addressed by localised patch repairs.
Can you take us through the inspection process of a flat roof?
- Firstly I would gather historical building information.
- I would then make arrangements for access and prepare necessary RAMS to establish:
o The roofs age
o Previous repairs undertaken
o When and where the roof leaks
o Ponding issues
o Use of rooms below
What is damp?
A building is considered to be damp if the moisture becomes visible through discoloration and staining of finishes causing mould growth, sulphate attack, or frost damage.
Are you aware of different forms of damp?
Yes, the different forms of damp include:
- Rising Damp
This is typically above 1.5m above floor level
Caused by capillary action drawing moisture up through a porous material.
Often caused by a breach or lack of DPC - Penetrating Damp
This is damp entering the building externally
Often caused by driving rain, blocked gutters, leaking roofs, or cracks.
How can you test for damp?
- A protimeter can be used to test the moisture content within the surface.
- The material can also be sampled and sent off for testing.
- Hygrometer can measure the moisture within the air.
*It should be noted however that moisture levels can be affected by natural salts within walls and some materials have safe natural levels of moisture in them.
What types of timber defects are there?
Dry Rot
* Moisture content 20-22%
* Timber is dry and crumbly
* Cuboidal cracking very evident
* Mycelium fungal growth white and strandy with orange fruiting bodies
Wet Rot
* Moisture content above 40%
* Often has damp and musty smell
* Timber is spongy
* Fungus growth
Insect Attack
* Deathwatch, furniture, longhorn beetles
* Leaves holes in timber with evidence of ‘frass’
What remedial measures are available to wet rot?
- Locate and eliminate the source of the damp and promote rapid drying and ventilation.
- Remove and replace the rotten timber.
What remedial measures are available to dry rot?
- Cut out and remove affected timber, as well as 400mm beyond to prevent further contamination
- Treat surrounding timbers with a chemical biocide
- Remove affected plaster
- Area should be kept dry and heated.
You mention a survey you undertook at Bury Records office whereby you identified some defects, could you give some examples of other common defects you have come across?
- Where pitched roofs have undergone a replacement of coverings, say slate being replaced with concrete tiles, it often results in incorrectly installed roof strengthening measures following deflection being experienced. This causes undue loading of the ceiling structure resulting bowing and cracking.
- Cement repointing to older brickwork, which results in spalling of the brickwork faces.
- External ground levels being raised resulting in a breach of DPC causing damp penetration and subsequent mould growth.
What is Condensation?
- When warm, moist air comes into contact with a cold surface.
- Common in bathrooms and causes mould growth and decay of fabric.
- There is also Interstitial Condensation, which occurs between layers of components where a dew point exists.
How can condensation be remedied?
By providing a room with good ventilation, heating the room, and avoiding cold bridges.
You previously encountered a damp issue at 59 Lake Street which you advised was due to high ground levels – what initial repairs did you recommend?
- The first step was to have all the existing internal plaster and client installed tanking removed.
- The wall was then left for a drying out period with the assistance of a dehumidifier.
- After this period the wall was then replastered with a lime based plaster to allow the wall to breathe.
- I then recommended the installation of a land drain externally to alleviate future damp issues.
During your decarbonisation survey at Solebay Primary School, you mention you inspected within the cavity of the external wall – talk us through how you went about doing this?
- With the assistance of contractor, I had a hole drilled in the external leaf of the wall at the mortar joint.
- I then used a probe camera to see inside the cavity.
And following on from this cavity wall survey (at Solebay), what remedial works did you consider possible to remedy the cavity wall tie issue?
I considered that the best solution would be to retrofit helical cavity wall ties to the required spacings.
On this survey you advised that you didn’t see any cracking or bulging – if you had noticed cracking to the brickwork what else would consider a potential cause?
I would investigate the potential for;
* Ground movement (heave or subsidence)
* Lintel failure
* Roof spread
* Thermal expansion/contraction
