Insulating floor of bedroom above garage

We had a builder construct an extension about 3 years ago, comprising 2 single bedrooms over an existing garage. The floors of the bedrooms sit on 5" joists with fibreglass insulation between the joists. The ceiling in the garage comprises of pink (fireproof?) plasterboard. The problem is that the front bedroom is very cold in winter and also soundproofing between the bedroom and garage is very poor. The back bedroom is not so bad because it is half over the kitchen. The garage isn't actually used as a garage, more a small workspace/ store. I suspect the builders have skimped fairly seriously on the fibreglass and I'm wondering what the best way to improve matters is. I'm thinking along the lines of (a) taking off the plasterboard and adding more fibreglass, (b) removing the fibreglass and putting 75mm Kingspan between the joists (c) leaving the ceiling as is and fixing sheets of 40 or 50mm Kingspan below it Not sure how (b) and (c) fit in with building regs even if the garage will never see a car!
TIA for any advice Gelf
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Best to remove ceiling and the fibre glass and install rigid Rockwool bats 4" thick. These are superior in sound and heat insulation. Cut them slightly wider than the joists to give a tight fit. Available from Wickes. Then put 25mm of Kingspan under the joists. This will eliminate cold bridge to the room above and increase thermal insulation even further. Then add plasterboard over. Use prefinished Fermcell which meets the fire regs and can be DIYed easily enough. http://www.fermacell.co.uk
Important: make sure there are NO air leaks between the garage and the room above by ensuring the Fermacell is well fitted. Any cables running through, seal with silicon sealing.
If you feels rich, replace the garage doors with sealed and insulated doors. This has great benefits all around.
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wrote:

Thanks for the comprehensive reply. I feel a project coming on! Gelf
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Talking of garage-conversion/upgrade projects .... anyone recommend a good make of electric garage door? My fold down one won't fit anymore with my new car parked in forwards as the boot is too high (the garage is about 10cm longer than the car ... a close fit indeed!) so I have to rather awkwardly reverse in, then hop across the seats to get out.
Going to seal the concrete and walls at some stage and paint them, then put in lots of shelves and maybe a low roof storage type thing.
a
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wrote:

Garador do sectional doors. Good quality, but not easy to fit. They have an electric opener option.
Mark
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Cheers ... I've asked for a brochure :o)
a
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al wrote:

B & Q warehouses are selling a Wayne Doulton (US) sectional electrically operated door which may meet your requirements. Price was 400 IIRC. Construction looked to be galvanised, painted steel, without insulation. Very thin.
    Regards     Capitol
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