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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Building Questions >> Reroofing and loft insulation https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1422298919 Message started by Sarah on Jan 26^th, 2015, 7:01pm

Title: Reroofing and loft insulation
Post by Sarah on Jan 26^th, 2015, 7:01pm

Hi there

Sorry if I break any etiquette or rules but I'm a newbie!

I'm looking to get quotes to have my roof reslated and I've read that it's most likely I'll need my insulation upgraded in my loft. I'm also looking at getting my loft boarded out but I just wondered if my loft was boarded out, would I have to get up the boarding to add more insulation or use an alternative? There isn't a great deal of head height in my loft so I don't really want a massive thick insulation and then have to use spacers and board over it. This is the reason I thought of boarding it first, then doing the roof if I can get away without having new insulation.

Thanks for any help in advance!

Sarah

Title: Re: Reroofing and loft insulation
Post by thescruff on Jan 26^th, 2015, 11:53pm

Have a word with the roofer/builder you may be able to use 100mm Celotex or similar between the rafters

Title: Re: Reroofing and loft insulation
Post by woodsmith on Jan 27^th, 2015, 9:23am

Im assuming the boarding is so that you can store things in the loft, the trouble is that if you insulate under the boarding the roof void becomes particularly cold and even with a lot of ventilation you can still get condensation forming within the roof space. I am just working at a house where the owner has just discovered the photos she has been keeping in the loft have glued themselves together and become a sticky ruined mass. If you really want to store things in the loft and you are having the roof re-tiled you would be better off creating a warm roof where you insulate under the tiles rather than over the ceiling of the room below.

You should be able to ask you builder about the pros and cons of having a warm roof.

Title: Re: Reroofing and loft insulation
Post by CWatters on Jan 29^th, 2015, 6:59pm

You could move the insulation to between the rafters but I would use far more than 100mm. I have 150mm and wish I had more. Part of the problem is that the rafter bridge the insulation and it's very hard to fit it tightly between the rafters so there are gaps. Sure these could be filled with expanding foam but that's a messy job and not that easy to do well - how do you get it into a <2mm gap? If the membrane isn't vapour permeable you also need to form a 50mm ventilated gap between it and the insulation. If you want to go this route I would put a layer of insulation under the rafters as well as between so boards can be butted together and joints taped.

Personally I think it's best to beef up the insulation at ceiling level and use stand offs to support the boards. Seal up any holes between the warm humid house and the cold loft, particularly where pipes from the bathroom enter the loft. Ditto the loft hatch. Ventilate the loft well to the outside using eaves trays.

Title: Re: Reroofing and loft insulation
Post by CWatters on Jan 29^th, 2015, 7:03pm

PS: If you have less than 4" of insulation British Gas will (should?) upgrade it for free...

https://www.britishgas.co.uk/energy-saving-products/home-insulation?campcode=EONSEA&source=ECO-PPC-Free-Insulation&cid=PPC&mkwid=sdqYfIZj5|pcrid|39840911633|pkw|british%20gas%20free%20insulation|pmt|e|pdv|c|&_$ja=cgid:5859089993|tsid:64723|cid:127642793|lid:12270272232|nw:g|crid:39840911633|rnd:562522262092533447|dvc:c|adp:1t1

Title: Re: Reroofing and loft insulation
Post by Lectrician on Mar 3^rd, 2015, 6:40am

A lot of new houses these days have insulation in between the actual roof timbers, as well as the ceiling timbers. Usually cellotex or similar. Cellotex takes up less space than the save Rvalue in cosy wrap.