Insulating Floor Voids

[padstar]

I want to insulate the ground floor void thermally and the upper floor void acoustically.

Are the below sketches the correct way of doing things and are the depths of insulation given about right.

Is board insulation better than the quilt for both instances and is a vapour control layer required at the ground floor if foil faced PIR boards are used.

 

[JP_]

I only have 10cm joists, and my preferred method is 50mm kingspan at the bottom, and 50mm rockwool on top. Provides great insulation, cheaper than going 100mm kingspan and easier to install.
Any gaps filled with foam and everything taped up. The foil on the kingspan is a vapour barrier, so no need for additional.
Having the PIr at the bottom is easier to install, as you can run supports (I use trellis poles because i had spare) perpendicular, screwed from below, to support the boards.

Problem with first option is that you only need a tiny bit of cold air to get into the void and it will massively reduce the effect of the insulation. Rockwoll insulates and stops drafts, and if you need to run any radiator pipes you could do it here - although mine are all still under everything ...

 

[padstar]

Good idea for teh ground floor. The upper floor is purely for acoustics as the rooms below will be heated.

 

[JP_]

yeah, I think just chuck in some acoustic wool in that bit.

 

[padstar]

Can loft quilt be placed on and around downlight fittings. The void will be peppered with them and always consider the combination a fire risk?

 

[JohnD]

no, you should space off them. you can get "smoke hoods" made for the job, they often have an intumescent lining that swells up to block the passage of fire; or you can make simple boxes out of plasterboard, which is fireproof, and lay them over the lamps to rest on the ceiling, from above. Modern LED lamps do not get anywhere near as hot as the old incandescent (especially halogen) lamps.

Hoover off any dust and fluff before fitting your covers, as it can smoulder or ignite when hot.

You can stuff mineral wool into an irregular gap to block draughts. Board has to be accurately cut and sealed.

Mineral wool does not burn or emit toxic gases in a fire, so is my preference. Remember Grenfell.

 

[Leofric]

Celotex is no good for acoustic insulation anyway.

 

[padstar]

If i used this -> https://www.insulationexpress.co.uk...liKV9Hsgs3Y1J80CY27BryWZ5t7-xLPYaAoi9EALw_wcB could i cut the insulation slabs between the downlights leaving 100mm from each side of the fitting and then bridge over them from slab to slab? How much clearance does the downlight need from the insulation? In reality the lights will only run within 2 of the 8 voids per room so the others will be fully filled.

 

[John D v2.0]

Don't use celotex in between floors it's a waste of perfectly good insulation. The only board acoustic insulation to consider is to overboard with a second sheet of plasterboard. Ideally sound block board as it's heavier. You could also part fill the void with acoustic wool but that has a limited effect and would only help with airborne noise not impact noise.
For impact noise it would be carpet needed to solve it.

 

[Leofric]

If you look on their websites you should be able to find British Gypsum's technical details for upgrading existing upper floors for sound insulation. Insulation companies have technical details for insulating suspended timber ground floors.