Construction Tech - Flash Cards - L3
Sub Floor, OL - How was the timber rot identified?
Visual inspection highlighted sagging in the timber floor, upon exposure it was identified as dry rot caused by insufficient cross ventilation within the floor void.
Sub Floor, OL - How did you identify that it was dry rot?
The timber joists in the vicinity were showing signs of weight loss and deep cuboidal cracking.
There was light mycelium growth across timbers - white / grey cotton wool like.
A damp meter was used to identify the moisture content showing a reading of 24%.
Sub floor, OL - What is the difference between wet and dry rot?
Wet rot grown on more saturated surfaces around 50 - 60% and dry around 20-30%.
Dry rot affects timber, masonry and plaster, whereas wry rot only affects timber.
Wet rot fungus tends to be black and dry rot lemon tinge.
Wet rot timber will crumble easily, dry rot timber will show weight loss and cuboidal cracking.
Sub floor, OL - What remedial action did you recommend following the identification of dry rot?
Initially I took recommendation from BRE digest 299 on dry rot.
Due to the smaller size of the room and that we were unable to provide adequate cross ventilation I recommended that the suspended timber floor was removed ad disposed of.
All masonry within the vicinity was treated with a fungicidal wash.
We implemented rapid heating and ventilation to dry out the space prior to installing a new floor.
Sub floor, OL - Why was cross ventilation not adequate?
Over time it was evident that the building had suffered from air brick removal due to a drainage gully being added to the first external wall. The second and only other external wall was receiving an extension so it meaning we were unable to provide adequate ventilation.
Sub floor, OL - If you were to re install a timber suspended floor, how would this be done?
Ensure that there is adequate ventilation from air bricks in external walls, timber installed on joist hangers rather than in the brickwork. Refer to TRADA span tables for timer joist requirments.
Sub floor, OL - Why would you advise a concrete floating floor is installed?
To prevent further issues with timber rot in the room, and because we were unable to provide sufficient cross ventilation required for a timber suspended floor.
Sub floor, OL - What is a floating concrete floor?
A concrete floor which is laid on the ground without any form or anchoring?
Sub floor, OL - How is a concrete floor installed?
Dig out as required, hardcore base, sand binding course, damp proof membrane, insulation, concrete slab, and the floor screed.
Sub floor, OL - What are the key advantages and disadvantages of using a concrete floor?
Advantage - Does not require ventilation, good thermal properties with insulation, requires little / no maintenance.
Disadvantage - Costly / disruptive to retrofit.
Sub floor, OL - What was the age of the property?
Estimated to be late 1800’s to early 1900’s. DPC was required by the Public Health Act 1875.
Sub floor, OL - What building regulations apply to the installation of the concrete floor?
Part C (resistance to contaminants and moisture) - Damp proof membrane must be at least 1200 gauge.
Part L (fuel & power) - 0.18 w/m2k
Sub floor, OL - Are there any risks identified with installing a concrete floor?
Blocking ventilation to other rooms - this was checked prior to specification.
Risk that moisture will travel up the internal walls - this was identified as a risk, however as the void could not be adequately ventilated this risk was observed within the decision made.
Flat roof, HH - How did you identify additional insulation was required?
The roof was surveyed and with the help from a roofing manufacturer a core sample was taken to identify the existing insulation depth. The manufacturers initial survey report identified that the current level of insulation did not meet current Part L requirements (0.18w/m2k).
Flat roof, HH - What regulation is required to be met?
Approved document part L - Flat roof 0.18 w/m2k.
Part H - Drainage.
Part C - Cavity trays.
