Cold loft or warm loft

[britishboy7]

Am currently clearing out the loft on our 1930's semi, and its a fairly large space, ideal for storage. My original plan was:

remove all old loft floor insulation (its black with dust and ripped anyway)
replace with new Earthwool or similar (leaving gaps at eaves)
board entire loft floor with 18mm chipboard sheets
insulate rafters with Celotex or similar


We want to use the loft for storage of all sorts, seasonal clothes, suitcases, electrical goods etc so thought a warm loft better, for the winter months. If so, should i not both with the Earthwool under the new loft flooring? Was only going to be 100mm put down anyway, between the joists

 

[cwhaley]

I did the same with my loft re. insulation --took out the decades-old stuff and replaced with new then boarded over on stilts. Didn't insulate the rafters though so it's a cold (in the winter) draughty, dusty, airy loft which I like. It means no condensation or mold and I cover everything with sheets from the dust.

I'd leave it and work on the insulation instead, but make sure you put in more than 100mm - 270mm is the current recommended level. Keep the rooms below warmer and the loft well-ventilated. Keeping heat in a loft is likely to increase the chances of condensation.

 

[geraldthehamster]

There is little point in insulating both the loft floor and the rafters. Usual practice is to insulate the rafters if converting to a habitable room, or the floor if just using for storage. So I'd insulate the floor. That way you are saving money on materials (rock wool is cheaper than Celotex), saving the energy you're not wasting on heating the loft, and reducing the likelihood of condensation in the loft (provided it is well ventilated).

 

[britishboy7]

Thanks guys (sorry for the late reply, had several other jobs take priority over the loft this last year)

I'll keep it as a cold loft, for storage etc but would like to board over the rafters anyway so its a little less 'loft-like up there. Have put a 5ft LED strip light up there and want it to look a bit better. Should I just board straight onto the rafters (leaving air gap at top and bottom), or put some kind of waterproof barrier between the rafters and the board.

Also, what board should i use to board it out? The only loft Ive boarded was a warm loft and we use plasterboard onto the rafters but that was so it could be plastered

 

[Leofric]

Should I just board straight onto the rafters (leaving air gap at top and bottom), or put some kind of waterproof barrier between the rafters and the board.

Why leave air gap top and bottom unless you are using the 25mm thick ' foil and bubble wrap ' stuff which requires a 25mm air gap above and belowIs there breathable roofing membrane over the rafters For insulation between rafters you would need a 50mm ventilated air space above the insulation and a vapour barrier on the warm side of the insulation. The ceiling finish could be foil backed plasterboard. Look on some insulation company websites where they show recommended construction details for insulating roofs.

 

[britishboy7]

I thought you had to leave a gap top and bottom of any boarding if you'd insulated the loft floor, to prevent condensation? (I may be wrong though...)

Its a 1930's build, theres no membrane between the rafters and the tiles. Should I just pin a breathable membrane to the rafters, then board over it? (Was thinking 3mm ply, just to hide the tiles and rafters, and to reduce the spiderwebs)

 

[Leofric]

Not clear to me whether you are talking about insulating the loft floor or the roof

 

[britishboy7]

Sorry Leofric, I should of said. The loft floor is already insulated with Earthwool and boarded over with 18mm chipboard.

I'm wanting to board over the rafters (so it looks better when you go up there), not fussed on insulation as happy for it to be a cold loft. I'm asking do i need a breathable membrane on the rafters before i board over with 3mm ply (and is 3mm ply the best to use?)

 

[Leofric]

A breathable membrane would go over (on top of ) the rafters and you would have to remove the existing roof finish and battens to do that.
You mean boarding under the rafters just for appearance presumably .A breathable membrane under the rafters wouldn't serve any purpose.

 

[britishboy7]

Thanks Leofric, yes thats what I mean. So dont bother with the membrane and is 3mm ply best to board under the rafters?