Greetings,

Looking for a bit of advice on insulating a spare room which is over the garage.

I've gone to a lot of effort to insulate the loft and also the walls of the timber-framed dormer extension this room has. However, being over the garage its freezing (even with a PVC garage side door and well-sealed main garage door).

So before we carpet (which comes next week) I'm thinking of pulling up some floor boards and insulating underneath the floor between the room and the garage beneath.

That make sense?

I was thinking of using space blanket (the insulation in a plastic/foil tube) as it would be easier to stuff under the floor and pull through with out having to remove ever single floorboard.

There is cabling down there which is lying on the plasterboard not clipped to the joists (should it be clipped?).
Where practicable, would you go above or below the cabling? (Below seems the obvious answer).

What's wrong with this plan? I'm sure there's plenty of things!!!

Thank you!
James


EDIT: By space blanket, I don't the thin foil stuff. I mean like normal glassfibre(?) loft insulation but it's in a tubular bag with a silver top.

[Edited on 15/12/20 by James]

[Edited on 15/12/20 by James]

I have heard that the space blanket insulation is not that good, but I have no experience of it myself.

Cabling not clipped to joists is fine for existing installations - new ones require cables being supported in a way that prevents them dropping down on firemen in the event of a fire.

If you insulate over the cables, they will be trapped between the garage ceiling and the insulation and will not be able to lose heat as easily. That means that the cables have to be de-rated ... however, depending upon size, they may still meet the requirements for the circuits' ratings. Cables on top of the insulation (as long as it is not tight up to the floorboards above), will still be in air, so should not need de-rating.

What is on the garage ceiling? Overboarding that with celotex would be a very simple solution.
Otherwise stuffing rockwool into the floor void would be a simple solution.
For reference, a 2.5mm cable will carry 17A above a plasterboard ceiling with more than 100mm of insulation. So fine for a ring circuit. If concerned, get some trunking, even that corrugated split stuff so there is an air gap around the cable, it helps.

Also, do not underestimate the advantages of quality underlay. Rubber crumb is very good stuff (but carpet fitters hate it as it is so heavy) or a proper contract underlay.

Is there not fire regs for houses with rooms above garages? Instead of ripping up the floor, how about adding insulation to the garage ceiling? plaster board faced Kingspan would be easy to install and only loose a couple of inches headroom. Saying that, a good quality underlay and heavy carpet and you'd probably feel the same difference.

I have plastic/foil rockwool between floors. It trashes wifi transmission, if that's a concern.

However it does certainly keep heat in rooms well, you can get 200mm of it between floor and ceiling nicely. It would be better to use full-board celotex type insulation if possible, because you won't get cold-bridging by the joists if you keep them entirely on the warm side.

I don't think it would upset building regs but it is worth looking at the fire regs for sure.

[Edited on 15/12/20 by coyoteboy]

Recently converted our integral garage into a bedroom. The walls, sloor and ceiling were all insulated with Celotex fitted inbetween the joists and the plasterboarded over. It transformed a dry, but cold garage into probably the warmest room in the house. Easy to do as it was the Celotex was fitted before the plasterboard and floorboards.

In your case it would mean taking up the majority of the floorboards to fit the celotex effectively. The other approach would be to fit it from belo by removing/refitting the garage ceiling.

I don't know what the regulations are for wiring above or below any insulation. However, I'd think about access to the wiring for any alterations/repairs. Will it be easier for you to get to it from above or below?

It wasn't possible to access below my floor boards (ground floor) apart from a small crawl space with lots of supporting brickwork here and there so boarded products would not work for me. The house was fully floored with hardwood and carpet but full of draughts blowing up from below.
I lifted a small section under 1 carpet and then used space blanket from below between rafters and held in place with stapled in builders orange barrier fencing. This made a massive difference to the heat retained and got rid of most of the draughts too.

Careful when pulling it through it rips really easy it catching anything so have plenty of brown tape to hand.

best of luck

Pete

James,

My house was built this way, and bizarrely My spare room over the garage is warmer than the main one over the lounge!

In my old house, one small bedroom, really a large cupboard went out over an outside utility / store room, and i filled under the floor boards with a polystyrene type of balls, ive done a search for the stuff, and am unable to find it

Basically it was an enormous bag of balls ! that i removed a couple of floor boards, and poured them in, kept pushing them around, in fact an air compressor would of been better, but they seemed to be quite good at levelling them selves

From memory two whole bags were used, and pretty well filled the void, boards back on, underlay and carpet, job done,

steve

quote:

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Originally posted by Mr Whippy
Is there not fire regs for houses with rooms above garages? Instead of ripping up the floor, how about adding insulation to the garage ceiling? plaster board faced Kingspan would be easy to install and only loose a couple of inches headroom. Saying that, a good quality underlay and heavy carpet and you'd probably feel the same difference.

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quote:

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Originally posted by coyoteboy
I have plastic/foil rockwool between floors. It trashes wifi transmission, if that's a concern.

However it does certainly keep heat in rooms well, you can get 200mm of it between floor and ceiling nicely. It would be better to use full-board celotex type insulation if possible, because you won't get cold-bridging by the joists if you keep them entirely on the warm side.

I don't think it would upset building regs but it is worth looking at the fire regs for sure.

[Edited on 15/12/20 by coyoteboy]

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quote:

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Originally posted by steve m
James,

My house was built this way, and bizarrely My spare room over the garage is warmer than the main one over the lounge!

In my old house, one small bedroom, really a large cupboard went out over an outside utility / store room, and i filled under the floor boards with a polystyrene type of balls, ive done a search for the stuff, and am unable to find it

Basically it was an enormous bag of balls ! that i removed a couple of floor boards, and poured them in, kept pushing them around, in fact an air compressor would of been better, but they seemed to be quite good at levelling them selves

From memory two whole bags were used, and pretty well filled the void, boards back on, underlay and carpet, job done,

steve

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Ok, thanks all of you!

LB brilliant as always!!!

The carpet shows up on the 21st! so I really need to get a move on.

So I bought a couple of rolls of 1200mm rockwool at lunch time, and I'll have a delightful evening I'm sure ripping up floorboards and stuffing it underneath as best I can! The gap between my joists is only 350mm so 1200mm rolls will mean I can cut it to size fairly easily with a saw through the whole role hopefully!

Thanks for the advice all!

James

Rockwool is normally "perforated" at 400mm intervals, so you may be able to squeeze that width in. Be nice and tight when it puffs up a bit.

do use a really good underlay, money very well spent.

quote:

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Originally posted by cliftyhanger
Rockwool is normally "perforated" at 400mm intervals, so you may be able to squeeze that width in. Be nice and tight when it puffs up a bit.

do use a really good underlay, money very well spent.

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Originally posted by James

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Originally posted by Mr Whippy
Is there not fire regs for houses with rooms above garages? Instead of ripping up the floor, how about adding insulation to the garage ceiling? plaster board faced Kingspan would be easy to install and only loose a couple of inches headroom. Saying that, a good quality underlay and heavy carpet and you'd probably feel the same difference.

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I'm sure there are fire regs. The only one I know of is the ceiling has to be double-boarded but bound to be plenty more.

If I haven't been clear (and I usually haven't!) the garage and room is integral to the house.

The garage projects forward of the front of the house by about half it's length and has (had!) a pitched roof that leads up to the pitch of the main roof.

It's within this pitched area that we've built a full-width dormer so gained about 50% more bedroom just for the cost of a dormer!


As you suggest I initially thought of going under the ceiling of the garage. However, the ceiling is already slightly too low for a 2400mm sheet of material/timber so I don't want to make that worse!

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Originally posted by Charlie_Zetec

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Originally posted by James

quote:

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Originally posted by Mr Whippy
Is there not fire regs for houses with rooms above garages? Instead of ripping up the floor, how about adding insulation to the garage ceiling? plaster board faced Kingspan would be easy to install and only loose a couple of inches headroom. Saying that, a good quality underlay and heavy carpet and you'd probably feel the same difference.

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I'm sure there are fire regs. The only one I know of is the ceiling has to be double-boarded but bound to be plenty more.

If I haven't been clear (and I usually haven't!) the garage and room is integral to the house.

The garage projects forward of the front of the house by about half it's length and has (had!) a pitched roof that leads up to the pitch of the main roof.

It's within this pitched area that we've built a full-width dormer so gained about 50% more bedroom just for the cost of a dormer!


As you suggest I initially thought of going under the ceiling of the garage. However, the ceiling is already slightly too low for a 2400mm sheet of material/timber so I don't want to make that worse!

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Rooms above a garage have to have a double-boarded ceiling totalling 30mm - which equates to two-off (minimum) 15mm thick sheets of plasterboard - the lowest one of which has to be fireboard. I opted for 15mm fireboard as the outer skin, and 15mm of acoustic board above that, mainly as I used 100mm thick Celotex in between the 8" tall joists, cables sat on top. Celotex is a much better insulator than rock wool/mineral wool in terms of similar thickness, but the latter offers a better noise resistance (hence why I used acoustic board) - and a lot less itchy!

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Originally posted by cliftyhanger

15mm fireboard? that would be flippin heavy! 12mm stuff is horrendous to handle. Accoustic boards are not much better. Makes normal plasterboard seem light.

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As others say, Rockwool.

They have a product specifically for this purpose called Safe and Sound but it may be a pain to install. I believe regular Rockwool has the suitable fire ratings as well.

The standard for a 60 minute fire resisting ceiling seems, now, to be 2 x 12.5mm fireline boards (or equivalent), with staggered joints , taped and skimmed, or 1 x 12.5mm wall board plus 1 x 15mm fireline board again staggered etc..

This I believe is based on 8" x 2" joists at 600mm centres with a 22mm chipboard floor.

But what would I know?!

Wyn