DIY two storey extension

[Chickenski]

Thanks Dulux

Your reply came just in time. We have prepared everything for tomorrow morning. I fixed battens horizontally and flush between the rafters every 1500mm to be able to staple edge of the foil to them. Wasn't aware that I have to do it. Actis own website and Triso UK website have two different methods of laying it. One recommends horizontally the other one vertically.

They also say it does not matter which side up. Is it true?
I really need to be careful so BC does not reject it on the basis of wrongful installation.

If you are there let me know before the morning please!

Reference rockwool, I just thought it would be easier than cutting Celotex into little pieces (my rafters are around 300mm centres).

Thanks in advance

 

[Deluks]

It gets a bit tricky with multiple layers of fabrics, foils and felts to lay down.

From what I can gather you have laid battens flush between rafters, so that the tops of the rafters are still the outermost part of the roof?

Not sure that was necessary

From here you will... lay the foil on top, then the battens vertically, fixed to the rafter tops, then the breathable membrane (slightly sagging in the middle) then horizontal tile batten, then tile.

...sounds like the way to go.

Then fix celotex between the rafters, flush with the underside, then plasterboard.

This will mean your insulation will be 70mm celotex/80mm airgap/tri-iso, which actually sounds like a really good solution, as you will have that big airspace between the insulation layers.

Plus the triso on top of the rafters will eliminate cold bridging. Top dollar!


Celotex: Very easy to cut, certainly cleaner and less irritating that rockwool. Use sharp knife to score deep both sides and snap, or just get an normal handsaw and saw through it.


Now to confuse things. When you were told there must be an airgap between foil and membrane; who told you that? Cos I can't see what good it would do. That method might only be applicable to foil laid underside the rafters (the room side) Even then it doesn't make sense?

Traditionally, there should be an airgap between insulation and felt, but if this is breather membrane then it shouldn't make any diff, the airgap on that side won't add any extra insulation value either.

Sooooo, you could lay the breather membrane over the top of the foil, then horizontal battens, then tiles. Boarded roofs and walls often have tyvek stapled direct, then the tile battens go on. I can't see what's different in this instance.

 

[Chickenski]

Thanks Dulux. Just in time as well!!!!
Will let you know how we got on. Have a good day