Is temporary / partial internal wall insulation worth doing?

DRP

We have an unheated garage/utility which is leaching heat from our single storey kitchen extension in the winter.

The extension was built last year, on the same footprint as the ‘family room’ (conservatory) in the attached floorplan. The original garage plans from c2004 stated 100mm blockwork except for the adjoining wall which is cavity with 85mm rock wool. Therefore we didn’t additionally insulate the connecting wall, which may have been a big mistake!

Long term we would like to bring the garage up to spec by adding full internal insulation. however this is too costly and disruptive to consider at the moment, so my cheapo alternative is to directly bond 25mm PIR boards to the utility side of the wall (the highlighted section). Any thoughts on whether this is a worthwhile, temporary enterprise to make the extension room easier to heat? (Utility/garage is fully plastered and decorated, but we’re not worried about the ‘look’ of PIR on that wall).

FreeBear

I'd go 65-75mm, either warm batten or insulated plasterboard - There are two types, one with polystyrene, the other, PIR/PUR. Use the latter as it has a higher u-value. Do a proper job rather than just a temporary one. It will reduce the amount of heat being sucked out of the main house, but won't make the utility any easier to keep warm.

If you shop around for materials, you may be surprised at how little extra it will cost to insulate the entire space - The biggest cost is labour, so if you can do the work yourself, you could probably do the whole lot for £500 or so.

ThisIsWeird

DRP said:

We have an unheated garage/utility which is leaching heat from our single storey kitchen extension in the winter.

The extension was built last year, on the same footprint as the ‘family room’ (conservatory) in the attached floorplan. The original garage plans from c2004 stated 100mm blockwork except for the adjoining wall which is cavity with 85mm rock wool. Therefore we didn’t additionally insulate the connecting wall, which may have been a big mistake!

Long term we would like to bring the garage up to spec by adding full internal insulation. however this is too costly and disruptive to consider at the moment, so my cheapo alternative is to directly bond 25mm PIR boards to the utility side of the wall (the highlighted section). Any thoughts on whether this is a worthwhile, temporary enterprise to make the extension room easier to heat? (Utility/garage is fully plastered and decorated, but we’re not worried about the ‘look’ of PIR on that wall).

Why is the shared garage wall shown as being thinner that its outer walls, if the former is the 'cavity' type?', and the latter single-skin?

Your kitchen/family room was built to current building regs? What heating do you have inside it?

ThisIsWeird

Anyway, to answer your Q, I think I'd keep one eye on the future, and work out what insulating material you intend to use elsewhere in the garage to bring it up to spec, and - if it's, say, 3 or 4" PUR - then buy that now and simply screw (or use the plastic fixings you can get for this) it flat on to that internal wall as a temp measure.

It'll be relatively undamaged (a squirt of exp foam and a patch of ali foil tape will make good the wee holes) so can be reused, and fixing them will be a breeze. Or, just cut the sheets to fit snugly betwixt t'floor and ceiling, and tap them into place - no fixings required. It's temp after all.

I have a suspicion, tho', that the garage - if it is cavity/rockwool - is not really 'leaching' heat from your family room, but that the FR is just not being heated enough (or has other insulation issues).

What sort of design is the room? What kind of roof?

Nobbie1967

I also think the issue is not with the garage wall which already has a cavity with rock wool in it and is protected from wind and rain by the external wall. Are the garage doors well sealed? Eliminating drafts would be worthwhile. Looking at the family room, there seems to be a lot of glass which even when double glazed is likely to leak a lot of heat.

casper_gutman

Nobbie1967 said:

I also think the issue is not with the garage wall which already has a cavity with rock wool in it and is protected from wind and rain by the external wall. Are the garage doors well sealed? Eliminating drafts would be worthwhile. Looking at the family room, there seems to be a lot of glass which even when double glazed is likely to leak a lot of heat.

OP says: "The extension was built last year, on the same footprint as the ‘family room’ (conservatory) in the attached floorplan." I don't think the room there now has all the glass shown on the floorplan.

ThisIsWeird

A proper 'garden' room should be ok to heat.

DRP

Hi, thanks for all the comments.

To answer some of these:
the new extension is built to regs: render/breeze/50mm cavity with 25mm PIR/thermalite/75mm PIR internally/plasterboard (unusual construction as we reused the existing foundations). Roof is flat warm roof with 100mm PIR.
Compared to the picture, there’s now a single opening in the room, 4m wide at the back with 3.2 sliding door and 0.8m window. There are 2x 1m square roof lights , triple glazed. 
We have about 7000 btu in 2x rads in the extension, and another big rad in the old dining room (doors to ext have been removed, versus what’s shown in the picture). 

The utility/garage has double upvc doors at the front (ie. Not a garage door). The utility is very cold and is not heated (ie. It has a big radiator but we do not see it worthwhile heating a single skin room).

The room seems to lose heat quickly.

The door connecting to the utility is a standard internal door. We have put foam strip around it, but additional draft proofing is certainly something to look at. 

We aren’t considering insulating the whole utility right now because there’s a fitted kitchen in there, radiator, electrics etc, which would mean thousands £ compared to a few hundred to diy that wall.

ThisIsWeird

7000btu is around 2kw, so I'd have thought that would do the job fine.

Are you saying it doesn't get up to temp when required? Or is it just that you 'sense' it loses heat quickly once the rads are off?

How is the temp in there set - where is the room stat? And do the rads have TRVs on them? What type of rads are they - standard doub-pan finned? And.. do they get properly 'hot'?!

frostysaver

I've considered something similar for our home which has an internal unheated garage.

One concern for exposed PIR or polystyrene is the fire load - it's extremely flammable once ignited. For this reason I believe insulated plasterboard should use some mechanical fixings, so the plasterboard acts as protection in a fire.

ThisIsWeird

DRP, if you intend to properly insulate the garage in future in any case, then I see no harm in buying some insulation sheets now, of the thickness you intend to use for this. Fit them snugly on that wall as I suggested. I doubt, tho', it'll make a noticeable difference to the new kitchen room, as - from what you describe - the existing kitchen-garage wall shouldn't be leaching heat. But, what's the harm?!