Loft insulation and plasterboard

[mtkdaly]

I have been doing some diy work in my loft which has an up and over roof.

I have stapled insulation foil over the rafters and then put plasterboard directly on top of the insulation foil - which I now think was a major mistake.

Before I had a feeling that I made a mistake, I had the loft plastered and it has just finished drying. Yesterday, I noticed a bit of a damp patch appear near the bottom of the pitch (in the eaves) and it got progressively worse throughout the day.

In the evening, we noticed the damp patch started drying up.

I wanted to ask people's oppinion about the work I have done and what the possible cause of the damp patch could be.

- Did I make a mistake by laying the plasterboard straight over the insulation?

- Should of I battened over the insulation and then put the plaster board on the batten so to create a bit of an air gap

- Do you think the damp patch is condensation due to the insulation not being able to breath? Or could this be a bit of left over moisture from the recently dried plaster (it looks completely dried to the eye, but may not be behind)

- If the problem is that the plasterboard is on top of the insulation, is there a quick rememdey for this? Or will it be a case of removing it all and starting again?

Thanks in advance[/list]

 

[stef99]

Sounds like you need to start again.
did you use a roofing membrane under the roof tiles first?
This is designed to catch any water thats comes through the roof tiles.

You always need a 50mm gap from the insulation to the roof tile.
Otherwise water gets under the tiles and get stuck.

What sulation did you use? please don;t tell me you used the soft rock wool type stuff?

as for the tin foil, directly under the insulation, the insulation should have come with the tim fiol stuck to it? (I'm not sure what you have used here.

As for plaster board, I would consider using water proof boards. but thats not essential if the insulations has been installed correctly.

It's hard for me to advise anymore with the info you have given.

 

[mtkdaly]

Hi, thanks for getting back to me.

Here is a little more detail with regards to the current set up:

- Roof tile on outerside sitting on battens
- Then a layer of breathable felt under the battens
- Then we have the 2" roof rafters

On the inside of the rafters I have stapled the foil insulation and then screwed plasterboard directly on top of it.

So, we have a 2" gap between the felt (on the outside of the rafter and the foil insulation on the inside of the rafter.

I was just worrying incase I will have a damp or condensation problem because I haven't left a gap between the inside foil insulation and the plasterboard.

Any further advice you can give would be great.

Thanks

 

[freddiemercurystwin]

If you mean it’s the multi-foil layer insulation then it’s pretty rubbish to be honest. Anyway no problem with what you’ve done.

 

[mtkdaly]

This is the insulation I used:

http://www.screwfix.com/p/airtec-double-insulation-1-05-x-25m/21112

Do you think the lack of breathing space between the insulation and plasterboard will cause condesation? or is this completely fine?

 

[freddiemercurystwin]

It won’t cause any condensation issues. Provided the membrane under the tiles is definitely breathable. It’s still pretty rubbish though.

 

[mtkdaly]

Thanks for the feedback. Which part is rubbish? the whole job or just that I used the foil insulation?

 

[freddiemercurystwin]

Foil insulation, its equivalent to about 50mm polystyrene at best. which ain't a lot. And that's if you have an air gap each side which is really how these are designed to be used. But then you gets what you pays for.

 

[mtkdaly]

Yeah good point. I probably should of got some advice from other tradesmen before proceeding with the work but it is all finished now and I don't want to take it all down and start again!

Do you have a link to insulation that you would of used? Also what method of installation?

Thanks

 

[freddiemercurystwin]

Celotex or kingspan or other PIR rigid insulation. Assuming your rafters are only 50mm deep I’d have stuck 25mm rigid insulation between the rafters (retaining a 25mm air gap) and then a continuous layer of say 50-75mm underneath. Then plasterboard underneath. Wouldn’t want to go much more as your rafters are so slender. But that kind of insulation costs more of course. But then it resists heat flow more so will retain more heat reducing the heating bill.

If this were a proper loft conversion you would be looking at something like 100mm Celotex between the rafters and 40mm continuous layer beneath.

Your single layer of foil insulation is equivalent to about 30mm Celotex.

 

[stef99]

Oh Christ mate, that insulation is heat insulation which you put around hot objects to stop them burning the walls.

You need proper wall insulation.. like kingspan or celotex.

The buliding regs recommend 100mm insulations which is £40 per sheet.

http://www.wickes.co.uk/Celotex-50mm-High-Performance-Cavity-Wall-Board-450x1200mm/p/190546

It will be freezing n your loft if you don;t use it.

As it happens, none of this will cause condesation. (in my opinion).

but I suspect there was holes in the breathable membrane which were not fixed when you did the install.

That way, water is finding it'self running down the back of your tin foil insulation and into the cracks, were it's soaking into your new plasterboards.

 

[geraldthehamster]

Oh Christ mate, that insulation is heat insulation which you put around hot objects to stop them burning the walls.

No it isn't.

Cheers
Richard