Building Pathology

Question 1

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?

Answer 1

• 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.

Question 2

Can you take us through the inspection process of a flat roof?

Answer 2

• 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

Question 3

What is damp?

Answer 3

A building is considered to be damp is the moisture becomes visible through discoloration and staining of finishes causing mould growth, sulphate attack, or frost damage.

Question 4

Are you aware of different forms of damp?

Answer 4

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.

Question 5

How can you test for damp?

Answer 5

• A protimeter can be used to test the prevalence of damp in a building.
• A moisture meter can be used to test the moisture content within the surface.

*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.

Question 6

What types of timber defects are there?

Answer 6

Dry Rot
o Moisture content 20-22%
o Timber is dry and crumbly
o Timber is shrinking and warped due to removal of moisture

Wet Rot
o Moisture content above 40%
o Often has damp and musty smell
o Timber is spongy
o Fungus growth

Insect Attack

Question 7

What remedial measures are available to wet rot?

Answer 7

• Locate and eliminate the source of the damp and promote rapid drying and ventilation.
• Remove and replace the rotten timber.

Question 8

What remedial measures are available to dry rot?

Answer 8

• 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.

Question 9

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?

Answer 9

• 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.

Question 10

What is Condensation?

Answer 10

• 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.

Question 11

How can condensation be remedied?

Answer 11

By providing a room with good ventilation, heating the room, and avoiding cold bridges.

Question 12

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?

Answer 12

• 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.

Question 13

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?

Answer 13

• 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.

Question 14

And following on from this cavity wall survey (at Solebay), what remedial works did you consider possible to remedy the cavity wall tie issue?

Answer 14

I considered that the best solution would be to retrofit helical cavity wall ties to the required spacings.

Question 15

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?

Answer 15

I would investigate the potential for;
o Subsidence
o Heave
o Settlement
o Differential Settlement
o Lintel failure
o Corroded steel lintel

Question 16

Are you able to talk us through your understanding of the difference between subsidence, heave, and settlement?

Answer 16

• Subsidence is movement at ground level, caused by the ground losing moisture due to large trees causing it to shrink. Cracks are often vertical or diagonal and will be larger at the top.
• Heave is the upward movement of the ground, caused by the removal of a tree resulting in increased moisture content. Cracks are often vertical or diagonal and will be larger at the bottom.
• Settlement is movement down due to an increased load. Buildings will settle when first constructed as the new load settles to the bearing capacity of the soil.

Question 17

What size of cracks are of concern?

Answer 17

• Up to 2mm – of slight concern
• 2mm-5mm – slight or aesthetic
• 5mm-15mm – moderate concern
• 15mm-25mm – severe concern
• Over 25mm – Very severe with stability concern

Question 18

What would you consider a probable cause for cracking to concrete?

Answer 18

Common defects such;
o Carbonation
o Chloride attack
o Silica reaction

Question 19

What is RAAC?

Answer 19

• Reinforced Autoclaved Aerated Concrete
• It is a form of pre-cast concrete panels is predominantly found in roofs, walls, and floors.

Question 20

How would you identify RAAC?

Answer 20

• Commonly 400-600mm in width
• Often has bevelled edges
• Soft to touch and can be easily dented with a screwdriver
• Light grey or white in appearance with a smooth surface

Question 21

Why is RAAC a safety risk?

Answer 21

• RAAC is lightweight bubbly concrete
• When exposed to water is susceptible to failure to corrosion of the reinforcement, excessive thermal degradation, or poor original manufacturing.
• Often the reinforcement is incorrectly placed meaning the panels are at risk of shearing off of their support.

Question 22

What would your advice be to your client if they had concerns of RAAC being present in their building?

Answer 22

I would firstly recommend implementing the guidance issued by the DofE which is to follow stages 1 to 5 –
o Stage 1 – Review existing building information for detail on construction
o Stage 2 – Appoint a suitably qualified surveyor to visually assess the building
o Stage 3 – If identified that RAAC is present then a qualified engineer should be appointed to confirm presence
o Stage 4 – A detailed survey should then be carried out to provide a full picture of the condition and quantity of RAAC
o Stage 5 – Management and remediate.

Question 23

Are you aware of possible remediation measures?

Answer 23

• The first option would be to remove the RAAC entirely involving replacement of roof/wall/floor coverings. This however is very costly and disruptive to the building.
• A slightly less disruptive solution is to form a new timber deck beneath the RAAC planks making them redundant in nature. The new timber deck is supported by the existing steel frame of the building.