(yet another) integral garage thread

[desperate-unbodger]

I've read a lot of threads like this, but don't think I've found quite my answer yet (which probably just means I haven't found the right thread yet).

I've got an integral garage on my 1930s house. The previous owners constructed over the top of it so our en-suite and half of my sons bedroom are over the garage. The construction is a steel frame supporting the upper cavity walls (which i have the structural designs and building regs for), but it appears to me the floor/ceiling between the garage and the rooms above are just to "internal" standard. 180mm joists, what looks like acoustic rockwool type insulation and plasterboard (I can see from below because there's holes in the plasterboard ceiling where the waste pipes exit from the bathroom.
The rooms above the garage are much colder than the rooms not, and I assume this is the reason.

The garage is tiny - way too narrow to get any modern car in, so I don't want to convert the garage into a habitable room (it would really be a habitable corridor!). What I would like to do is:

1) add some insulation to the ceiling to stop the rooms above being so cold
2) make the garage a bit more useful as a workshop/ storage room by putting up an insulated stud wall on the inside of the garage door (no heating)

For #1, a suggestion that had been made been made by a builder was to overboard the ceiling with something like 50mm PIR and another layer of plasterboard. Does this sound sensible and would I need building regs for that?

For #2, would that need anything? There will be no heating in this room. In fact all the external walls will remain single skin and the floor will remain an uninsulated concrete slab.

I'm also am unsure if door between the garage and the house is a fire door - how could I check that?

Any advice very much appreciated

 

[^woody^]

Block the garage door up and you will need consent for the conversion work.

Also consider home insurance being void for undeclared or unauthorised work

PIR to the ceiling would be OK. Better would be PIR fully between the joists and on the underside. Either way, if the joists are built in, you really should deal with any gaps or holes as they are the main cause of heat loss.

Fire doors are at least 44mm thick, have a coloured peg on an edge, intumescent strips on the edges or frame, self closer device, three hinges, and thick stops on the frame.

 

[desperate-unbodger]

Block the garage door up and you will need consent for the conversion work.

Also consider home insurance being void for undeclared or unauthorised work

PIR to the ceiling would be OK. Better would be PIR fully between the joists and on the underside. Either way, if the joists are built in, you really should deal with any gaps or holes as they are the main cause of heat loss.

Fire doors are at least 44mm thick, have a coloured peg on an edge, intumescent strips on the edges or frame, self closer device, three hinges, and thick stops on the frame.

Thanks Woody, very much appreciated.

I spoke to planning previously about doing a proper conversion on the garage and they said I didn't need consent. Is that what you mean on the first point? I'm still not sure if I understand if there's something that isn't a garage, but also isn't a habitable room I can have as part of my house, or If I'm stuck with either a garage with a garage door, or a fully converted room?

On the second, I'm happy to do any new work above board - presumably my home insurance can't be voided by stuff the previous owners did 9+ years ago? So do I need building regs to put additional insulation on the ceiling? Any idea how much I need? Unfortunately the pipework from the bathroom above only really gives me room for 50mm PIR, but we could drop the pipes if need be (there's plenty of headroom). I also wasn;t sure if I'd need to use fire rated plasterboard or something.