Insulating room over garage with flat roof

[HelenofSparta]

Title says it all really! We have a very cold room over our garage (also damp, but looking to remedy this first). New baby due in March so will need it as a bedroom at one point next year.
So it has three outside walls, windows other end. No insulation above as no roof space. Anything we can do to insulate above an indeed below - insulation in floorboards below? Any thoughts/ideas gratefully received!

If the exterior walls have a cavity then you can get the walls insulated from the outside by getting foam pellets injected. The only way to insulate you roof is either pull down the ceilings (cheaper) or remove the flat roof and install insulating foam, the same can be done with the floor either from the garage ceiling or by lifting the floor (whichever is the cheaper).

Our 1 year old sleeps in room above garage which unfortunately is coldest in house. DH has lifted the floorboards and laid insulation underneath which has made some difference. Next steps we are replacing double glazing and looking into cavity wall insulation as we don't think it exists on that side of the house as it is part of an extension. DS doesn't actually seem to mind though.

Thanks. We are also thinking of fitting an extra radiator to the outside wall to warm it up a bit more.....

Flat roofs don't last very long, so next time yours needs to be relaid, have lots of insulation added under the decking.

If the roof will not need to be relaid for a long time, find a local plasterer and ask how much he would charge to take down the old ceiling and put up a new one, and if he would be willing to put insulation between the joists too, or would you or someone else have to do it. Ask for foil-backed plasterboard which will prevent water vapour rising into the void. This is also a good time to run cables for any new ceiling lamps.

Thanks Piglet. Flat roof is only two years old (we moved in a yr ago), so the replaster suggestion sounds good

Depending upon the thickness you decide to insert you will probably need to ventilate the space above the insulation.