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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Building Questions >> Insulation under an old loft conversion floor https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1456414780 Message started by wozzer on Feb 25^th, 2016, 3:39pm

Title: Insulation under an old loft conversion floor
Post by wozzer on Feb 25^th, 2016, 3:39pm

I have been told I need to put 100mm of rockwool or fibreglass under the floor of my old (25 years ago) loft conversion - There is nothing under there at the moment.
Could I use two layers of Cavity Batts instead?
Easier to handle for me as I can put it in a bit at a time?

Title: Re: Insulation under an old loft conversion floor
Post by woodsmith on Feb 25^th, 2016, 5:21pm

I can't see why not, but the bats are quite stiff and may not fill all the gaps around them in the same way so may not be quite as effective.

Title: Re: Insulation under an old loft conversion floor
Post by CWatters on Feb 27^th, 2016, 11:47am

Who told you need to do this and why?

Insulation under the floor of a loft conversion is typically for noise reduction. The other reason might be to stop cold air circulating under the floor.

Title: Re: Insulation under an old loft conversion floor
Post by wozzer on Feb 29^th, 2016, 1:12pm

We are "re-jigging" the existing Loft conversion:
The bungalow is 1961 and has two whopping great purlins running the length of the roof space. Hence, I have an usable area of 9 x 4.2 Metres with no alterations to roofing required. At the purlins the height is 1.4 Metres and at the ridge 3.7 Metres the roof is a simple gable.
Originally 2/3 of the loft was converted - we are extending this to the whole loft. The old conversion floor joists are ok for size and new ones will be added to the remainder of the unconverted area. We will be building new internal non-load bearing walls and splitting the loft into a bedroom and en-suite. We will be having a "proper" staircase installed (presently a space-saver stair with offset treads is fitted).
The new walls will be insulated to present standards and the old room perimeter walls will be replaced too.
The ceiling will be insulated to current standards as a "cold" roof - we do not intend to re-roof. The roof currently has two Velux windows in it and we will be adding a third. The chap doing the drawings for me has advised that there should be sound proofing under the floor.
I am doing as much as possible myself to keep costs down, hence the query about the cavity Batts.