We have just had the asbestos ceiling removed from our integral garage, and now need to insulate between the joists before fire boarding the ceiling. The bedroom above is cold and musty due to the cold sink of the garage below, so we want to improve that.

There is also a triangle section void above the garage door, as the garage in longer than the bedroom above. This void is formed by a 45 degree slate/lime mortar section of roof, and the plasterboard wall of the bedroom. There is currently no insulation in this void either.

Questions:
What is the best product for between the joists/ below floorboards of the bedroom? Friend recommended thermafleece, which can be handled without Ppe but seems expensive? Standard knaus rock wool type roll? King span?

Should the insulation butt up to the floorboards or should there be a small gap? Edit, joists are 150mm deep.

For the roof void, should I insulate the back of the plasterboard wall (king span?) or the back of the roof slates, or both?

Sorry for all the numpty questions. Cheers!

The floor: depends if you are having to do the work from below or you can take up the boards. If the latter, then it’ll probably be cheapest to fix the fire-rated boards from below, then take the floorboards up and drop in some fleece/quilt type insulation. If you’ve got to fit the insulation from below then a rigid PU board like Celotex or Kingspan could be cut to size and wedged between the joists before you fix the boards under the joists. As the garage is still going to be a ‘cold’ space, I’d leave a gap between the insulation and the floorboards, like I would if it was a roof.

The roof void: if you insulate between the rafters, make sure you leave a min 50mm ventilation gap between the slates and the outer surface of the insulation. For insulating the back of the plasterboard wall then, as above, a rigid PU board would work. If you do both you’ll be warmer.

thanks! Definitely going to be insulating from below. Is the celotex/king span stuff easy to work with/cut to size, or is it a ask/gloves/goggles job?

Little, one off job …. you’ll be fine with a mask. Have the garage door open and just cut it with a saw.

Shop around for it mind …. there can be big differences in price

You need to decide where you want to form your thermal envelope. I decided it was easier to bring the garage inside the insulated area, and internally insulated the walls and fitted 20mm celotex to the inside of the up and over door. My integral garage was also my workshop so it made more sense, especially as the boiler was located there too.

Working over head between the joists is a pain, but doable. I think I’d favour measuring and cutting celotex, but you might be able to get it done quicker with a staple gun and that multi foil stuff everyone seems to use now.

I recently completed insulating my dining room extension with celotex, and found it easier and far less dusty using a kitchen knife. A rip-saw made a hell of a mess.

Friend recommended thermafleece, which can be handled without Ppe but seems expensive?

IMO If you’ve a Friend who knows, rather than one who just read something, then I’d be taking their advice – plus how to fit it.

I had a radiator fitted in the integral garage, that has helped a lot, interested in insulating the up and over door now

s the celotex/king span stuff easy to work with/cut to size, or is it a ask/gloves/goggles job?

Yep.

Cut with a handsaw and shove between joists. Tape over joins with foil tape.

[url=https://flic.kr/p/dzA6MU]8 Dec 2012 14:26[/url] by Ben Freeman, on Flickr

[url=https://flic.kr/p/dzuAj8]8 Dec 2012 17:00[/url] by Ben Freeman, on Flickr

Price up the difference between celotex and regular insulation. It’s REALLY easy to put up between joists, far less cutting than celotex, probably cheaper and the ceiling board you then put up will give you the airtightness. You just need a load of these to hold it in place.
bendy wires

Even if I were insulating the garage (which I would), the cost and ease of putting up some fiberglass insulation is well worth the effort.

On a related note TomB – how much did you pay to have the ceiling removed? I have an integral double garage and want to do the same (including insulation). Thx

If its a cold damp garage I’d be tempted to put some wood fibre or Thermafleece in there – much better moisture control that way.

If it’s a cold damp garage, fix the cold / damp, don’t treat the symptoms.

Garage isn’t damp, just unheated brick box with drafts. The bedroom above suffers due the lack of insulation from below. Great help so far, thanks. OMITN, I’ll dig out the quote and let you know what asbestos removal cost, not cheap but very thorough professional job.

Thanks TomB.

Also pls post up your insulation decisions, as I need to do the same project.

I bought a load of insulation from here when I did my loft… good service, delivered on their lorry… need to insulate my garage roof soon, so will be getting some more: Seconds and co

I bought it all online, used 68 sheets in the workshop…

[url=https://flic.kr/p/dz8YPz]1st shipment of Celotex (38/68 sheets)[/url] by Ben Freeman, on Flickr

[url=https://flic.kr/p/dA3aUA]Plaster Board backed Celotex (PB4050) arriving – two palletes worth![/url] by Ben Freeman, on Flickr

For OurManInTheNorth, the asbestos removal was £700 incl Vat, they plastic wrapped all the furniture/appliances etc, removed the boards, then hoovered out and washed out, leaving it all clean and tidy. Half day, 2 man job. Lot of money, but not a job I wanted to do myself.