Loft Coversion condensation?

[fordy4]

Hi all, Im new to here and here with my first post.

Ok, so im converting my loft space into a small bedroom. My rafters are 70mm and the roof felt is unbreathable. I bought 50mm kingspan and put them between the rafters but now I have alot condensation between them.

Which is the best way to tackle this? Is it to fit soffit ventilation and then a vented roof tile between each rafter? or maybe to remove all the unbreathable roof felt and replace it with a breathable membrane?

Would finallly sealing the room with Tyvek air/vapour guard also help?

Thanks

 

[freddiemercurystwin]

Doing this under Building Regs or on the QT?

 

[fordy4]

QT... Building regs require alot of insulation, which then would leave no space....

Cheers

 

[JohnD]

does anyone drape wet washing around the house, or over radiators?

How do you ventilate this illegal development of yours?

 

[fordy4]

yes radiators are on with washing.... vetilated with a window in the loft.

Any ideas how to solve the issue?

Cheers

 

[freddiemercurystwin]

QT... Building regs require alot of insulation, which then would leave no space....

Cheers

Doh! I wonder if the regs for ventilation are a bit daft too?

 

[JohnD]

if anyone drapes wet washing around the house, it will make a vast amount of water vapour. This is lighter than air so it will rise up through the house until it either escapes, or finds something cold to condense on.

You can never have a dry house if it has wet washing in it.

Sorry.

 

[fordy4]

freddymercurystwin - It would leave no space so would be no point in doing it, I think they require around 400mm with an air gap. Im doing it instead of moving to a four beroom house.

Would Tyvek deal with the problem? at the moment I have just the insulation in place. Acting as an air and vapour guard?

Cheers

 

[freddiemercurystwin]

I think they require around 400mm with an air gap.

Nah, try about 150mm Celotex instead.

Where is this condensation occurring? What stage is this 'conversion' at? There are no plasterboards up yet right?

If you have condensation occurring beneath the insulation then the issue is too much moisture in the air, soffit vents won't help there, as they won't be connected to your inside space will they. Obviously ventilating the void between the felt and the insulation is another story!

 

[fordy4]

I have read and been told many things and im no builder.... Just trying to make the best of what I have for little money. I know its not everyones way but hey...

I have had the floor done to a great standard and also the stairs, but I thought id try and do the insulation myself, to save more money.

I have put the insulation between the rafters and it is really wet between the insulation and the lining. I only have a 20mm gap between. I presume wet as no air can get between the lining and insulation.

Someone mention using tyvek, whilke another said replace the lining with a breathable membrane.

Thanks for you replys so far...

 

[fordy4]

how do you add pictures?

 

[freddiemercurystwin]

Upload photos with this dubious guide //www.diynot.com/forums/viewtopic.php?t=129539

OK so you have condensation between the insulation and the felt. First thing you should have is a 50mm air gap between the underside of the felt and the back of the insulation (not 20mm), this allows for any sagging to occur with the felt etc. That aside continuous ridge vents and soffit vents are the appropriate solution. You can't replace the felt with a breathable membrane without taking all the tiles off. You could remove the felt altogether (ie rip it down) that would cure the problem also but this goes against the grain and seems like a sacrilege as the felt is your back-up should a tile slip etc.

 

[fordy4]

 

[fordy4]

sorry for the large photo...

yes thats sounds like a better solution... I can add batons to add depth to the rafters to get that 50mm air gap... Then a roofer to pop the continuous ridge vents.

 

[fordy4]