Remove loft insulation or leave in place.

[conny]

We are looking at getting a loft floored and boarded out into 2 separate rooms, (a bedroom and study).
Currently it has 300mm of rockwool type insulation. One layer between the joists and the top layer laid at right angles across the joists. One of the builders giving an estimate has said he will remove the two layers where the room floors will be, and run it up between roof joists, so allowing heat from downstairs to penetrate and keep heating costs down. Another has said he will leave it all in place and floor over it, (squashing it down to joist level), then fit cellotex inside the stud walls and between all the roof joists.

Which way is the correct method or is there a third option? I should say, the floor joists were sized to the correct dimensions when the bungalow was rebuilt in 2017/18

 

[^woody^]

It won't squash, that will blow the plasterboard ceiling.

The requirement is 100mm of Rockwool or equivalent similar acoustic insulation, not thermal.

You don't use Celotex or any thermal insulation in stud walls. Acoustic insulation is required.

 

[cdbe]

Is this a proper (to regs) loft conversion or just a dodgy lash up? The celotex man is closest. By stud walls do you mean dwarf walls? I would probably leave one layer of insulation where it is and redistribute the rest to the eaves as a top up unless the conversion has any flat ceilings where it could be used. If by "roof joists" you mean rafters I'd avoid the one who wants to stuff loft insulation in there.

 

[Wayners]

With my bungalow loft conversion the void above ground floor ceiling ( below above bedroom floor) had to be filled with rockwool.
For insulation and fire protection

 

[conny]

So, if I have this right, it's remove the top layer of rockwool but leave the stuff between the ceiling/floor joists?
The dwarf walls to be insulated with rockwool/acoustic insulation, NOT Celotex type?
At the moment, there is no insulation between the roof rafters, just a breathable membrane under the battens and roof tiles. There will be no 'flat' ceilings as the ceiling will rise up from both sides off the dwarf walls. Should Celotex type be used between the rafters instead of rockwool?
We are looking at having 2 Velux windows installed which are top hinged, rather than central hinging, to allow us to fit some form of insect screening to keep out the bugs when they are open.
It's certainly not going to be a 'lash-up'. Will be done to BC regs. I just want to get it clear in my head what should be right. If it happens, (which we hope it will), it won't be getting started till late autumn as we have to wait for certain legal proceedings to take place, so not rushing into it. Just want to know as much as possible before it starts.

 

[RandomGrinch]

Will be done to BC regs. I just want to get it clear in my head what should be right.

The attached guidance document helped me get my thoughts straight - it looks to have been revised in 2016, insulation requirements are stricter now I believe...

...and certain regs are different in Wales!

 

[^woody^]

Insulation location

 

[Koolpc]

Insulation location

View attachment 307277

Pure artistry there!

 

[^woody^]