Insulating attic room - advice on plan

serco

Hi All

A few years back we had our attic converted into a room but the insulation and air tightness wasn't done well with poorly fitted solid board between rafters and very poorly fitted vapour barrier. The room is therefore too hot in the summer and too cold in the winter.

I'm planning on correcting the work in the coming months however the rafters are only 100mm deep so I'm restricted in how much I can insulate between them.

Without going into detail, the current plan would be a 50mm air gap between rafters, followed by 50mm of Metac rafter roll between rafters, then a vapour barrier over the rafters taped and sealed at all joins, followed by potentially 50 or 62.5 rigid insulated board installed over the rafters again taped at joins and then plastered.

We are limited on height so I cant go above 62.5mm on the insulated board (the pitch roof height is not standard) and I'm unsure if the rafters could support more.

Would people recommend a different approach to the above?

Also, I've been looking at isover vario vapour barrier but at 200 euro for 60m sqr it seems quite expensive. Are there cheaper alternatives people have used?

thanks for your help

hexosan

Use intello membrane instead I've used both and there's no comparison between the two. Vario is so light and it takes next to nothing to tear it.

Calahonda52

Have a look at this
https://www.nsai.ie/S-R-54-2014-Code-of-Practice.aspx
Who told u put the VB between the two layers of insulation: thats not the right way.
I would also strongly argue that solar gain in room is an issue, PIR and rafter wool won't hack it under the decrement delay heading.
Whats the head room in the attic, does it comply with regs now?

serco

Thanks for the info. It doesn't meet regs as a habitable room, the joist to pitch height is 2m, there are 3 veluxs in the roof facing north. On the vapour barrier thing I believe I saw it referenced this way on many threads here however there was a caveat about it being to the warm side and my current setup may not be meeting that.

Calahonda52

Well if its not meeting regs then don't fret over a few less mm to get it right.