Insulation between ceiling and floor

How cold is floor in the room above the garage compared to other floors above heated rooms?

I guess you have sealed any gaps you can see?

Would it be easier to replace the underlay in the room above if you have a carpet with a thicker option? Or put a huge rug on the floor above if it is a hard floor?

Is this possible?

Unlikely, an ex tried to do it.
She eventually took the ceiling down and did it properly.
Which (unfortunately) involved a lot of dust (old house) and scraping a load of expanding foam out from the void. (What her dad had suggested.)

No idea what the eventual outcome was.
Would it be easier to insulate the garage?

I've done it successfully and it made a significant difference to the room above. You can see how much I took out from the ceiliing. I used rolls of rockwool loft insulation that came in a plastic liner so that its not itchy.

You’re either taking the ceiling down or floor up. You need to make sure the new insulation is continuous to not get cold spots. Also worth working on airtightness at the same time. These combined will make a significant difference to the room above.

How tall is your garage roof? Could you put a false ceiling in and insulate between?

You try fitting insulated plasterboard to the existing garage ceiling but the best way is as already said "take the bedroom floor up or remove the existing garage ceiling" if the latter I would still use insulated plasterboard when replacing the garage ceiling.

Bear in mind that above a garage fire protection is paramount so you must use non flammable insulation (usually rockwool as foam, plastic wool and wood pulp based insulation are flammable).

I think that building regs have something to say about the type or extra installation conditions on the plasterboard above too.

non flammable insulation

rockwool loft insulation is non flammable

And I can’t use Rockwool because the dust would be abominable.

I've  used 'earthwool' (recycled glass bottles) insulation and its not as fine/fdusty/fluffy as rockwool - a fair bit denser making it a good sound insulator as well as providing thermal insulation - you can get it in various width slabs so if you know the spacing between your joists you can get it in a size that will just push into place and its firm enough to stay put while you re-sheet.

Watching as have exactly the same issue.

How cold is floor in the room above the garage compared to other floors above heated rooms?

Cold.

I guess you have sealed any gaps you can see?

Also yes. Builders had not bothered insulating around the exterior French door, I did that. Garage has an insulated Hormann door with gaps sealed, and additional Kingspan crudely taped to the inside.

Would it be easier to replace the underlay in the room above if you have a carpet with a thicker option? Or put a huge rug on the floor above if it is a hard floor?

It's hardwood flooring, and given that it's my daughter's room simply tidying it up enough to gain access would be far harder than removing the whole ceiling!

I used rolls of rockwool loft insulation that came in a plastic liner

This is exactly what I thought I wanted but I couldn't find - do you have a link or something I can search for?

Taking the ceiling down will be a massive ball-ache as the garage door is installed on the ceiling and there's a lot of stuff piled up in there.

you can probably blow insulation into the gap like you would retrofit cavity wall insulation. Effectively they just use little polystyrene balls that fill the space up - I think they apply a slightly sticky coating to ensure they don't settle later but in your case that might not be needed.

Effectively they just use little polystyrene balls that fill the space up

I'd be less than keen to have a quantiy of that under a floor. Flammability isn't really an issue within a wall cavity but thats a lot o combustable material and air mixed together (and a source of toxic fumes)  to have under a living space

do you have a link or something I can search for?

I got it from B&Q but they don't seem to do it anymore. Their 'earthwool' is non itchy though https://www.diy.com/departments/diall-insulation-roll-l-6m-w-0-37m-t-100mm/3663602481812_BQ.prd

Could you just screw insulated plasterboard to the existing ceiling? Not as much insulation as filling the void, but would be a lot easier.

In a similar vein, is it worth inuslating under the floor on our ground floor? It would mean getting in to the crawl space and shoving rockwool in a confined, dusty space.

I always thought that as heat rises there's little point.

Have you made a test hole in the garage ceiling to see if it's insulated?  The room above the garage will always feel cooler as it's not benefiting from downstairs heat rising through the floor.

If your garage is double skinned alternatively you could change the door for an insulated uPVC french door and then heat the garage, bedroom will then benefit and you get a warm garage!

Only worth it if garage is not going to lose all the heat though, and suspect there might be a building regs issue if adding a radiator to the main heating system.

If you don’t want to do any damage to the ceiling of floor then screw a celotex type insulation of whatever thickness you think will be sufficient to the garage ceiling . Just need some long screws and penny washers

In a similar vein, is it worth inuslating under the floor on our ground floor?

Yes, as much heat is lost down as up.

Assuming floor up, and false ceiling / overboarding are out your only real choice is to take the ceiling down.  As its a garage it might not be plastered, if thats the case it would be a few hours work to get it down.  you may even be able to remove the existing screws and reuse the stuff afterwards

If its plastered it is a bloody messy job removing, cleaning up is 90% of the job (I've replaced 3 ceilings now).  Also getting rid of the waste costs as you can't just chuck it in a skip or take it to the tip

As suggested up there, make an inspection hole, big enough to get your head in to take a look (keep the cut out, its fairly easy to refit and fill).  Or you could do an endoscope thingy, I had a cheap one from amazon but it was rubbish.

How old is the house? Even into the 80s the fire resistant garage ceiling covering might still be asbestos, and if AIB then is really nasty stuff and notifiable if having removed.

If it is just plasterboard, you can get blown rockwool so both fire proof and can be inserted through openings rather than ripping the lot down. And an insulated and rubber sealed front door would help (sectional or side opening).

I did this to our room above the garage. I did it by taking up the floor of the garage floor and insulating that way with 100mm of celotext. Also took down the (room) ceiling, insulated that with 120mm celotex and insulated the walls with insulated plasterboard. The room is by far the warmest room in the house now!

Was fairly straight forward - if you do it from the bottom you need to make sure it's still fire protected (e.g. two layers of plasterboard or fireproof stuff).

Note that doing this will likely require building regs sign-off as you're upgrading a thermal element which is a notifiable event. Sounds scarier than it actually is - they were actually quite helpful (they come round before you start and then as many other times as required - think mine only came twice as i had lots of photos) - they'll also say if they're willing to reduce the U values you need to achieve if you're worried about headroom etc. Also means no awkward questions when you sell and you can get your ECC rating improved.

I would love to insulate under the floor. I don't mind crawling about but I think I'd need to knock a hole in the brick wall round the side of the house...