Insulating Bedroom Over Garage

11 Jan 2004
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United Kingdom
I have a bedroom with ensuite over a garage (attached to house). The garage is completely unheated and the bedroom is centrally heated. The roof is flat and recently recovered in EDPM. The roof spaces were filled with rockwool and the cavities have polystyrene beads but the efficiency of these two forms of insulation is unknown. The ensuite has stud walls.

The floor space is empty. The garage ceiling is covered in water, CH, waste and soil pipes.

I was thinking of covering the ceiling and solid walls with 50mm Celotex and pulling up the boards and laying insulation under the floor. Is there any benefit in insulating the ensuite walls?

Has anyone got any suggestions, please?
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the bedroom floor is roughly equivalent to the wooden ground floor in a house, with an unheated void. So it will not be very cold, apart from draughts if there is no carpet.

IMO packing mineral wool between the joists will give ample insulation, and also blocks draughts (which show themselves as black dust stains on the carpet). Pay extra attention to packing gaps around the edges of the room, where draughts are more likely under the skirting. The joist depth is probably about 7". I strongly recommend mineral wool by Knauf which is treated with Ecose to prevent it shedding irritant dust and fibres. It is brown, not yellow. Also sold as an own-brand by some chains, but "Ecose" will be flashed on the packaging.

Assuming the existing floor is chipboard, you could rip it up and burn it, and replace with 18mm ply which IMO is greatly superior. More rigid, stronger, quieter, will resist odd leaks, does not weaken and crack with traffic. If the fancy takes you, you can even stain it with Colron and apply a matt floor varnish, it will then be very easy to keep clean. A multicutter is very handy for trimming. If you take up one or two boards at a time, the room is mostly usable while you work.

If the ensuite is heated, there is no advantage to insulating the partition wall with the bedroom.

If there is a plumbing duct, it is probably a source of cold draughts, and cold air under the bath or shower tray. You can seal round pipes etc with expanding foam, but I think mineral wool will do the trick and is less trouble if you ever want to open the duct.

You can get a bonded plasterboard with Kingspan or Celotex type foam on the back, which is probably less laborious to fit. I have not used it.
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You really need to insulate within the floor void and seal gaps around joists in the void, as that is where cold air is getting in. Not insulate the garage. ceiling.
Cheers, guys. The extension hails from 1970 and the floor is T & G with lino tiles on top, stuck on with what looks like extra strong camel poo.
Given that I will need to get socket wiring altered and have insulation fitted, ripping it up and starting again (I feel a song coming on...) sounds great, especially with 18milli marine ply, but I don't see that being practical, what with the ensuite studding in the way.

Does Celotex sound good for the ceiling and walls? On the wall where the bedhead is, I'm having a lot of lighting wiring put in so instead of Celotex, there will be wooden battens and plasterboard with insulation battens placed in the void.
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Depending which way the joists run, you will be able to stuff insulation under the partition.

WBP ply is cheaper than marine ply, the veneers are not selected to such a high grade. But if the old floor is wood not chipboard if should not be so awful.

In the wall, celotex may be better as it has the insulating power of twice the thickness of mineral wool
Is it OK to just plonk Celotex direct on a wall, screw it in place, skim it and decorate?
I have an idea there are instruction sheets, I have seen them on one of the makers websites, might have been Knauf. You are talking about an insulating dry lining, there are rules about vapour barriers. Might do better on the plasterer's section.
Well, in this case, I was talking about plonking it straight onto the inside of a solid, plastered external wall.
I am thinking more about this and am worrying about the flat roof which was refurbished in October 2009.

The sheet says:

Strip off existing roof materials and chimney.

Inspect timbers for signs of rot and replace where necessary.

Fit new insulation (type, thickness etc not specified).

Lay 18mm ply deck and fully adhere 24m3 of Firestone RubberCover.

Fit black edge trims.

AFAICT from a small hole in the bedroom plasterboard, there is some fibreglass insulation evident in the void.

Suggestions on the 'net are that this type of construction is awkward to insulate from underneath as there are difficulties in preventing codensation; that the insulation should have been applied from above.

Is that correct? Cheers.

How can I supplement the existing insulation without risking build-up of condensation?

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