attic condensation

johnnyb6

Hi I am yet another person with a condensation problem. I bought my house about 12 years ago and decided to convert my attic myself. Since doing it I have had problem with condensation on the north facing side of the roof during cold weather. The house was built using the oily felt which isn't breadable. I had stuffed the cavity between the ceiling and felt with rockwool as I didn't realise I had to leave space for air to circulate, so I took all this out and replaced it with 2 inch Kingspan slab with foil on both sides. I got engineer to look at it and he advised me to fit 10 slate vents as near to apex as possible. I thought I had problem solved but with frost the last few nights the felt is weeping again. Has anyone any advice for me. If I put more grills on sophit would this help . Or should I pull out the 2 inch board and leave cavity empty.


Thanking You

Andrew_Doran

Ignoring ventilation for a minute, the moisture has to come from somewhere.

One source I've seen is holes in the living space allowing warm moist air into the attic, which then condenses when it meets the cold roof. Warm air rises, think of the draught from an unused chimney in winter. If I was in your situation I would consider things like socket outlets in the attic room, missing bits of plasterboard in the ceiling, holes allowing pipes or cabling into the attic, holes in tops of stud walls, vents and bathroom fans opening into the attic (should not be done), leaky trap doors and so on.

johnnyb6

Andrew_Doran wrote: »

Ignoring ventilation for a minute, the moisture has to come from somewhere.

One source I've seen is holes in the living space allowing warm moist air into the attic, which then condenses when it meets the cold roof. Warm air rises, think of the draught from an unused chimney in winter. If I was in your situation I would consider things like socket outlets in the attic room, missing bits of plasterboard in the ceiling, holes allowing pipes or cabling into the attic, holes in tops of stud walls, vents and bathroom fans opening into the attic (should not be done), leaky trap doors and so on.

Thanks a lot for your reply. there is a lot to consider. I have pipes running from copper cylinder up to tank in attic , but I have bottom of tank surrounded with rock wool, so I guess its not here. I also use side of my attic for storage and access this by means of small door. Is there any way I can elimate this from the problem .When I was fitting the 2 inch insulation I had to make few holes in ceiling slab and as I covered the ceiling with tongue and groove boards I thought this would stop heat getting true here. Was I mistaken

MicktheMan

johnnyb6 wrote: »

1. there is a lot to consider.
2.I have pipes running from copper cylinder up to tank in attic , but I have bottom of tank surrounded with rock wool, so I guess its not here.
3.I also use side of my attic for storage and access this by means of small door. Is there any way I can elimate this from the problem .
4.When I was fitting the 2 inch insulation I had to make few holes in ceiling slab and as I covered the ceiling with tongue and groove boards I thought this would stop heat getting true here. Was I mistaken

1. Yes there is. Poorly thought out attic conversions can easily cause the problems you describe and generally lead to significant heat loss into the bargain.
2. First off, insulation should not be placed under the water tank but should instead be brought up and over the tank to bring it inside the insulation envelope. This is to help prevent freezing problems during extreme cold weather. Secondly, insulation does not offer a barrier to vapour or air tightness, so if there are gaps between the pipes and ceiling, warm air (moist) will travel easily from the house into the attic.
3. How well is this door (and frame) sealed to the wall? Remember, the other side of this door is effectively outside.
4. Yes.T&G boards offer little resistance to air/vapour movement.

johnnyb6

MicktheMan wrote: »

1. Yes there is. Poorly thought out attic conversions can easily cause the problems you describe and generally lead to significant heat loss into the bargain.
2. First off, insulation should not be placed under the water tank but should instead be brought up and over the tank to bring it inside the insulation envelope. This is to help prevent freezing problems during extreme cold weather. Secondly, insulation does not offer a barrier to vapour or air tightness, so if there are gaps between the pipes and ceiling, warm air (moist) will travel easily from the house into the attic.
3. How well is this door (and frame) sealed to the wall? Remember, the other side of this door is effectively outside.
4. Yes.T&G boards offer little resistance to air/vapour movement.

Thanks for the help. I meant that the insulation below water tank in attic is packed around bottom of tank to keep heat from copper cylinder below it from escaping when it does come up to bottom of water tank. Which helps in frosty nights. The rest I have totally failed on and will have to get onto it in new yeas. Would these small things cause the felt to weep .

MicktheMan

johnnyb6 wrote: »

Would these small things cause the felt to weep .

That and poor roof ventilation.
Btw, the felt isn't weeping as such. Moisture (from within the house) is condensing on the relatively cold felt.