Hi Guys, I advise people about dampness and condensation problems in the home and I've a house thats got me stumped!
In one part of the house it has mono pitched roof at quite a low angle the ceiling when first built, followed the roof line then someone leveled the ceiling creating a loft space, at that time it developed a condesation problem and there were a row of high level windows that were cut of by this work that part were replaced by louvre panels to provide ventilation.
I dont know if this cured the problem byt the exisiting owners had to replace the copper roof with a mineral felt, at the time of this work it was discovered that the roof joists were rotton, possibley dry or wet rot I will plumpt for the later. so now thw roof joist are exposed to the loft area and the roofer used damp treated chipboard to board the roof and I imagine insulation then the felt application. Then I was called in after this work as he now had a condensation problem, there was evidence of condensation on the under side of the chipboard and at the time the client had downlighters and i advised that these be removed and sealed, One year on he called me back, he had removed most of them some were now not used and coverd with insulation, the louvre panels were covered and an extract fan fitted to this area and now there is an extensive condensation problem to the extent that there are water drops forming on the boards. The ventaltion that is or was present was at the front, continual soffit vents and the louvre panels at the back that may not have been enough when I first visited the house but assumed at the time the downlighters were causing the problem. Now the ventilation has been reduced and the problem is worse. I advised him he may have to have vents fitted to the roof itself for better quality ventilation but unsure if this would solve the problem and now for my question if anyone can answer this is the chipboard itself in this situation may not be suitable for this application as it looks like it lands itself to condensation forming having a smooth surface. Sorry if this is a long winded post but this is bugging me.
I even have a problem with my own house which remedial work hasn't fixed yet.
If there is condensation forming on the underside of the flat roof it is unlikely that insulation has been fitted (and it should not have been fitted). From your description the problem is probably due to high levels of moisture in the loft area - cross ventilation is important. Also have a look and see if moisture is getting into the loft from a bathroom/showerroom (have these rooms got extractors) and have a look at the CH header tank - is hot water being pumped over the vent pipe?
Condensation only happens when warm air meets cold , from what you have said it is and can only be warm air as stonyboy has said entering the roof space check around pipes from airing cupboards, and loft hatches, central heating vent pipes and cracks around ceiling levels. If no insulation has been fitted to the underside of the roof sheets then you should insulate the ceiling overlay the ceiling with insulation on the loft side to, building regulations minimum 250 mm. But you must ensure the loft space above this is vented. All areas must be insulated and tucked well into the eves sections provide ventilation to the eves using vent grids in the soffit boards and eves cavity vents in between the roof joists, if this can not be done you could always insulate the exterior of the chipboard by removing the felt and putting some warm deck panels over the chip board and then re felting the roof, I believe a vapour barrier does not need to be fitted on this type of insulation, and the loft space does not need to be vented as the warm air will not condense on the now insulated boards, however the soffit sections will also need insulating from the fascias down along the soffits to where it meets the ceilings. The disadvantage with this method is you are heating this space from bellow the ceiling level. You will also need building regulations approval for this method.
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