Attic Floor Insulation - Gap?

gaelicyoda

Hi All,

I'm guessing this MUST be answered here a million times, but be it my search keywords or whatever, I can't seem to find the answer - hopefully someone can help.

I'm going to be insulating the attic pretty soon - it's got 6" x 2" rafters and 9" x 2" joists - I've opted for 100mm Ballytherm rafterlock in the rafters and stud walls, and rockwool between the joists, more for soundproofing really than insulation. The floor will be 8' x 2' T&G chipboard, and the attic envelope itself will be supplemented with 50mm Ballytherm backed boards (38mm polyiso, 12mm plasterboard).

The question I have is - do I need to leave a gap between the top of the rockwool and the floorboards, or can I go for a 6" plus 4" insulation there instead? And do I need to worry about vapour barriers here?

Cheers,
GY

gaelicyoda

62 views and no responses - maybe it hasn't actually been answered before in that case.

Isn't there anyone out there who might have an answer to these questions?

Thanks!
GY

gaelicyoda

Over 100 views now and not even a nibble!

Doesn't anybody know whether or not it's appropriate to leave a gap between the top of the rockwool and the underside of the floorboards?

Cheers,
GY

Unk tantor

Is the attic a 'habital space' i.e is it inside the thermal envelope of the house or is it being boarded and floored for storage use ?

gaelicyoda

Thanks for the response!

It will be used initially for storage because we have no shed, but we've had the plumber run pipes the length of either side for the addition of radiators later whenever we decide to "fully" convert it.

We've also had a fourth heating zone plumbed in for those pipes so it will be properly usable immediately whenever the radiators are added.

Cheers,
GY

Unk tantor

some answers might be found on these threads which related to ground floor suspended timber floors, in short no gaps but a vapour barrier

http://www.greenbuildingpress.co.uk/forum_topic.php?thread_id=271
http://www.greenbuildingpress.co.uk/forum_topic.php?thread_id=304
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2850

smokeyjoe321

There no requirement to leave an air gap under the attic floor but I would recommend using a vapour barrier on the stud walls and up the rafters, (a 500 gauge plastic can be used for this)
Might a suggest using 8’ x 2’ T&G OSB for your flooring, its stronger than chip board and can be got at a building providers for approx €11.50/sheet