Where was the dry rot?
Affected the timber floor joists initially and had spread through floor boards, skirtings and the wall plaster to affect timber window lintels, all on the west elevation
What was the cause of the dry rot?
A defective downpipe on the west elevation was causing the timber joists embedded into the solid masonry wall to become damp, and the lack of ventilation within the building created the right enviornment for dry rot to spread
Other than dry rot, what other types of timber decay are you familiar with?
Wet rot and wood-boring insect infestation
What is the difference between wet and dry rot?
- Location:
- Dry rot - rare outside
- Wet rot - stays localised to moisture source
- Type:
- Dry rot - a brown rot
- Wet rot - can either be a white or brown rot
- Hyphae:
- Dry rot - 2-8mm in and brittle when dry
- Wet rot - thinner and flexible when dry
- Mycelium:
- Dry rot - silky white cotton wool-like sheets
- Wet rot - brown branching strands
- Decaying wood:
- Dry rot - deep cuboidal cracking with no skin of sound wood
- Wet rot - smaller cuboidal cracking and a thin veneer of sound wood remains
- Fruiting body:
- Dry rot - reddish brown with grey/white edges
- Wet rot - not very common but usually greenish-brown centre with yellow margins
- Conditions for growth:
- Dry rot - 20-35% timber moisture content, 0-26°C
- Wet rot - 45-60% timber moisture content, -30 to +40°C
How can you tell the difference between wet and dry rot?
- Location - if outside, likely to be wet rot
- Conditions - if space is unventilated, could be dry rot
- Appearance - deep cuboidal cracking, no skin of sound wood, rusty red spores, fruiting body and mycelium would indicate dry rot
- Smell - mushroom smell would indicate dry rot
- Moisture content - dry rot would be between 20-35%, wet rot would be 45-60%
You refer to a specialist undertaking the dry rot survey initially, however ultimately you chose to undertake your own inspection to establish the current state of infestation. Does this mean you are a specialist in dry rot?
Not a specialist but competent in identifying the extent of dry rot
Would you complete a survey and remedial works specification for dry rot?
Yes, however I would seek further input from other parties if necessary (e.g. structural engineer if replacing structural timbers, or a conservation officer in historic buildings)
What remedial works would you recommend for dry rot?
Set out in BRE 299 (Dry Rot: Recognition and Control):
- Establish the size and significance of the attack, particularly if structural timbers are affected as measures may be needed to secure structural integrity
- Locate and eliminate sources of moisture
- Promote rapid drying of the structure through heating and ventilation
- Introduce support measures (e.g. ventilation pathways between sound timber and wet brickwork, barriers such as DPMs or joist hangers etc.)
- Remove all rotted wood and cut away timber 300-450mm beyond last evidence of rot
- Do not retain timber infected by dry rot without seeking expert advice
- Strip back affected plaster and contain fungus within wall by applying surface biocides or fungicidal paints/renders
- Apply localised superficial preservative treatment only to timbers that are likely to remain damp
- Replace any timbers necessary only with preservative pre-treated timbers
What made you think the extent of the rot could have worsened since the report was completed?
From previous research and BRE guidance, I learnt that dry rot can rapidly spread in the correct conditions and as the building had been left vacant and unventilated, I suspected this could be a possibility
In option 1, how would you have issued the variation for additional rot remedial works?
- I would have detailed the extent of any implications caused by the additional works to the contractor and asked for a price for the change
- I would have then assessed his price with a QS and if reasonable, issued a written contract instruction
How would you have determined the value of the provisional sum to include for the unforeseen rot remedial works?
I would have assessed the implications this may have caused with a QS and estimated a value, however as the provisional sum would have been undefined, the risk would have lied with the client and was one of the reasons I did not advise on taking this route
If the unforeseen works would have been covered by a provisional sum, what kind of provisional sum would it have been and why?
Undefined, as the full extent of the works could not have been established
In option 1, why would the additional cost for delays post-contract be greater than those caused pre-contract?
Because pre-contract there would have been no contractor on board, whereas post-contract the contractor may have been entitled to claim loss and expense
How did you establish the new area of rot?
- With the report now in my possession, I carefully walked around the building and compared the areas highlighted in the report with those visible on site
- I noticed the floor in a corner of one of the rooms appeared to have sunk slightly, and pulling back the carpet I noticed the timber floor boards were beginning to rot, which had not been identified in the report
By revisiting the building and undertaking further investigations yourself, did your client have a problem with you disobeying his instruction to proceed with option 1?
No, they commented that they appreciated my professionalism the additional advice I had sought to give them
Why could you not have stuck to the programme and then issue a tender amendment once the revised dry rot report had been received?
I felt the dry rot report and the extent of the remedial measures was critical for the tendering contractors in order to plan their works and price accurately, and ultimately may have deterred contractors from bidding if this information was tentative
How was the client able to keep extending the end users’ current tenancy?
I believe the transparency of information within the client’s team was not sufficient and information was not updated regularly, causing my contact to think there was less flexibility in the programme than there actually was
Why did you receive the dry rot report late?
- I requested a copy of the report at the initial site visit with the client, who said they would send it, however as the works did not form part of my scope of service, the client and I did not prioritise this information
- The client implied the report had been undertaken recently and in hindsight I should not have relied on this information and should have emphasised seeing a copy of the report earlier
If the client had included the dry rot works in your instruction, how could this have improved matters?
- This would have led to me identifying the full extent of the remedial works within my design information, which could have been submitted in one tender rather than relying and waiting on third party information
- This would have also meant the main contractor was not limited in programming his works around another contractor and would have also made health and safety on site easier to manage
