Can you confirm what they are insulated with and the thickness?The floor of my attic is insulated between the joists with an added layer running perpendicular to this. The trap door is also insulated.
That doesn't necessarily follow - the back roof surface may be colder.The front of the house faces south so naturally the back of the roof space is colder.
Normally the problems with condensation seem to arise with warm sunny days being followed by night frost.It is only a problem when we have frost at night followed by sunny days as we had recently.
Heat on the outer surface of a south facing roof is unlikely to cause moisture to build up in and of itself - it may warm up the air in the attic so it absorbs more moisture.Heat is building up on the front slope of the roof and this is causing moisture on the underside of the bitumus membrane on the cold, north facing slope of the roof.
The points to moisture laden air not being properly vented from the attic and/or there not being proper vapour-checking from the habitable rooms below plus the decreased temperature in the attic due to the insulation.When I checked the attic during the frosty period the membrane was quite wet and there were a few drips on top of the insulation.
Are you suggesting the soffite of the eaves is concrete?There are 2 ridge vents in the roof and they seem to have helped the membrane to dry out but I would appreciate suggestions as how this can be prevented in the first place as I am concerned about the moisture rotting timbers and affecting the performance of the insulation. Are extra tile vents or possibly insulating between the rafters the answer and how would be the easiest way to do this? The soffit is concrete so unfortunately air cannot get through there. As I say, this problem only seems to occur on frosty/sunny days but is something I would like sorted.
your two vents are not adequate, install more vents, preferably close to the eaves to create air-flow in the attic spaceAre extra tile vents or possibly insulating between the rafters the answer and how would be the easiest way to do this? The soffit is concrete so unfortunately air cannot get through there. As I say, this problem only seems to occur on frosty/sunny days but is something I would like sorted.
do you have an airtightness/Vapour barrier on the ceiling? if not then you have moisture rising up from your house (from cooking, drying clothes, and heating our climates generally high RH, oh! and breathingThe attic is insulated with 200mm Space Blanket between the joists and 170mm Knauf insulation rolled out over this. At first I thought the condensation was coming up flom below but I don't think this is the case.
yes this works both ways, warm in summer, cold in winter but regardless its ventilation you needI only noticed it for the first time last winter when we had all the snow on the roof and recently when we had a few nights of frost followed by sunny days when the fromf of the roof heated up. I could feel the heat on the underside of the membrane so this is why I think this is the cause.
yes cover tank and then insulate, with a rigid PIR type product (kingspan or similar approved) + pipeworkWe have a water tank in the attic too so could the water in it be heating due to the sun and causing vapour? I think perhaps the tank could have a lid fitted and insulated - it is already insulated around the outside but not underneath.
the B'regs call for 10mm continuous ventilation around the eaves, so IMHO (without a visual) you should be installing more than two vents..When I say the soffits are concrete or something similar I mean they are solid and have no vents and it would be impossible to install vents in the soffit so I think extra tile vents will need to be fitted in the slope of the roof. Would it be sufficient to install 2 in the back or would they be needed in the front also?
while the insulation reduced the heat escaping into the attic. this is not your problem. your problem is a lack of ventilationWe only insulated the attic a few years ago and did not have this problem with the uninsulated attic. However the house is much warmer with the insulation -just a pity it has given us a new problem.
Warm moist sir generated during the day lodging in an attic space condenses on coldest roof surface as the structure cools.I could feel the heat on the underside of the membrane so this is why I think this is the cause.
No, not unless you have the tank situated directly under a rooflight where the sun could get at it.We have a water tank in the attic too so could the water in it be heating due to the sun and causing vapour?
An insulated cover and sides will assist.I think perhaps the tank could have a lid fitted and insulated - it is already insulated around the outside but not underneath.
You could possibly install vents in the roof slope just above the level of the quilted insulation (so they are not blocked).When I say the soffits are concrete or something similar I mean they are solid and have no vents and it would be impossible to install vents in the soffit so I think extra tile vents will need to be fitted in the slope of the roof.
You seem to have super insulated the attic without installing a vapour check to reduce moisture migrating through the insulation into the space.Would it be sufficient to install 2 in the back or would they be needed in the front also? We only insulated the attic a few years ago and did not have this problem with the uninsulated attic. However the house is much warmer with the insulation -just a pity it has given us a new problem.
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