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Insulating a garage roof.

Does what it says on the tin
OLTB
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Insulating a garage roof.

#277622

Postby OLTB » January 15th, 2020, 1:57 pm

Afternoon all.

Before we moved into our house, the previous owners extended over the attached garage making a fourth bedroom (mine and Mrs OLTB's). During our ownership of the property, it is apparent that they cut many corners in every area, which frustrates us enormously. Our bedroom is fairly cold and we think it's the garage underneath with nothing apart from the ceiling and floorboards stopping the cold air coming through.

I have therefore been thinking of filling the gap in between the garage and floorboards, but not too sure whether to lay insulation foam, or squirt insulation expanding foam (is there such a thing?). It would make sense to do the least disruptive thing (hopefully work up from the garage into the gaps rather than take up carpets from the bedroom etc.) and wondered if anyone had experience in this?

Cheers, OLTB.

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Re: Insulating a garage roof.

#277641

Postby fca2019 » January 15th, 2020, 3:28 pm

I have no direct experience of this. However I had fit an insulated roller shutter garage door, which made the garage feel much warmer. Which may indirectly help the temperature in the room above.

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Re: Insulating a garage roof.

#277674

Postby PinkDalek » January 15th, 2020, 5:34 pm

What is the construction of the garage ceiling?

OLTB
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Re: Insulating a garage roof.

#277689

Postby OLTB » January 15th, 2020, 6:28 pm

PinkDalek wrote:What is the construction of the garage ceiling?


Thanks PD - I’m away from the house at the moment and I’ll confirm later but going from experience of the other building work that was carried out, it’ll be cheap plaster board.

Cheers, OLTB.

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Re: Insulating a garage roof.

#277692

Postby Itsallaguess » January 15th, 2020, 6:41 pm

OLTB wrote:
PinkDalek wrote:
What is the construction of the garage ceiling?


I’m away from the house at the moment and I’ll confirm later but going from experience of the other building work that was carried out, it’ll be cheap plaster board.


If that turns out to be the case, then one of two approaches might seem to be worth considering -

1. Overboard the current plasterboard ceiling in the garage with another insulated-board layer.

2. Remove the current garage ceiling plasterboard, fill the exposed joist voids with loft-insulation and secure as required (stapled cloth strips or similar), and then re-board (with an option of re-boarding with an insulated plasterboard) to finish.

I personally think that option two would give the best results with regards to comfort in the room above, and would be relatively inexpensive. Kingspan insulation could be used instead of loft-insulation, but would be more expensive and more difficult to cut to the required strip widths.

Be careful to not insulate right to the outer wall areas, depending on the direction of travel regarding the under-floor voids. Similar to insulating the loft, you usually want to avoid shoving insulation right into the outer-corners/edges of external walls etc. so as to help allow air-flow where required.

I'd suggest trying to avoid any thoughts of 'expanding-foam' solutions completely.....

Cheers,

Itsallaguess

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Re: Insulating a garage roof.

#277711

Postby AsleepInYorkshire » January 15th, 2020, 8:04 pm

OLTB wrote:Afternoon all.

Before we moved into our house, the previous owners extended over the attached garage making a fourth bedroom (mine and Mrs OLTB's). During our ownership of the property, it is apparent that they cut many corners in every area, which frustrates us enormously. Our bedroom is fairly cold and we think it's the garage underneath with nothing apart from the ceiling and floorboards stopping the cold air coming through.

I have therefore been thinking of filling the gap in between the garage and floorboards, but not too sure whether to lay insulation foam, or squirt insulation expanding foam (is there such a thing?). It would make sense to do the least disruptive thing (hopefully work up from the garage into the gaps rather than take up carpets from the bedroom etc.) and wondered if anyone had experience in this?

Cheers, OLTB.


To make it easy to understand I've simplified. There are three types of insulation available.
  1. Fibre quilt (Glass or stone)
  2. EPS (Expanded polystyrene)
  3. PIR (Polyisocyanurate)
In order of the list the cheapest is first. In order of thermal capability compared to thickness the worst is first.

My guess is that the void above your ceiling will be 225mm (9" in old money).

So 225mm of PIR will cost a lot more than 225mm of fibre quilt. But it will be dramatically warmer.

PIR is also available "foil backed". I can't recall if you will need foil backed if used above plasterboard in a garage. Google it (try the British Gypsum "White Book"). If I may gently point out that "Kingspan" is a trade name often miss-used to describe PIR. If you opt to use PIR (and that would be my first choice) don't ask for Kingspan as it's probably amongst the most expensive. There are many makes of PIR.

I would also point out that this insulation is very easy to cut with a saw. It will take longer to install than quilt insulation but the result should be much better in regards to heat loss and the overall cost of "lost heat". Obviously you will have to replace the plasterboard. Additionally there should be no part of the ceiling left uninsulated. Such would cause cold bridging and over time pattern staining. To the best of my knowledge there's no requirement to ventilate the void, noting my comment above regarding the potential need for foil back insulation.

I believe in recent years advances have been made with EPS and there are dense EPS boards available. I do not know if they can be used in this particular element or if they are economically viable.

I think it would also be worth checking the timber to brickwork joints whilst the ceiling is down. Seal them to prevent the passage of air in much the same way as you see mastic around a window frame. This will reduce the passage of cold air dramatically and add to the thermal ability of the finished work.

AiYn'U

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Re: Insulating a garage roof.

#277774

Postby bungeejumper » January 16th, 2020, 9:03 am

Itsallaguess wrote:I personally think that option two would give the best results with regards to comfort in the room above, and would be relatively inexpensive. Kingspan insulation could be used instead of loft-insulation, but would be more expensive and more difficult to cut to the required strip widths.

I'm well above my competence/knowledge level in such matters, but I gather that building regs etc are getting more picky these days about how you insulate the void between a garage and an overhead living area. They're thinking mainly about fire risk, of course, but also about noxious smoke getting through. (Shudder.) I can't think that foam anything would really cut the mustard these days, but probably best to DYOR.

FWIW, our neighbours have just built a triple-width garage with living accommodation overhead, and they finished up with about 15 inches of rockwool-type insulation. (Plus a separate fire escape staircase, but that's another story and not relevant.) Clearly, the OP hasn't got that kind of a deep underfloor cavity to play with, but it did underscore for us that standards seem to be on the move.

BJ

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Re: Insulating a garage roof.

#277789

Postby DrFfybes » January 16th, 2020, 9:38 am

AsleepInYorkshire wrote:
To make it easy to understand I've simplified. There are three types of insulation available.
  1. Fibre quilt (Glass or stone)
  2. EPS (Expanded polystyrene)
  3. PIR (Polyisocyanurate)
In order of the list the cheapest is first. In order of thermal capability compared to thickness the worst is first.

My guess is that the void above your ceiling will be 225mm (9" in old money).

So 225mm of PIR will cost a lot more than 225mm of fibre quilt. But it will be dramatically warmer.


I would echo the above, except that for under the floor the difference will not be as dramatic. If you have carpet then 11mm 'foam' underlay will make quite a difference over thin rubber stuff.

"Heat rises" (loosely termed) so heat loss from the room will be largely through the ceiling, walls, and window. There isn't much you can do about this now without major work so making the floor warmer would be the way forwards. Stopping drafts would be the first start, although it seems there is underboarding anyway (required as a fire break).

Either make the garage warmer (seal the door, warm the space) or insulate under the floor. There may already be something in there so be careful removing the existing boards. Try and prise the nails out (they probably nailed it rather than screwed) so you can re-use the boards. Not because you want to reuse them, but because you might find your local council charges you a small fortune to dispose of them.

You can get 'Rockwool' style rolls cheaply, wrapped "Space blanket" rolls which should be the correct width for the joist spacing and a lot less messy, or semi rigid Slab insulation which pushes into the gap and is (sometimes) self supporting whilst you refit the plasterboard.

First thing is to drop a board and check what gap you have and if anything is in there.

Paul

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Re: Insulating a garage roof.

#277797

Postby sg31 » January 16th, 2020, 9:55 am

The above posts cover the ground very well and I can't add much.

As a quick and easy win there is often a gap between the skirting and the floorboards which can be very drafty. If you have a light coloured carpet fitted this will have a 'dirty' edge around the room perimeter. It's caused by gaps between the floor joists and brickwork among other things.

Pull the carpet back and fill the gap with decorators caulk or similar, then replace the carpet. The room should be a bit warmer until you can get round to the bigger jobs.

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Re: Insulating a garage roof.

#277824

Postby OLTB » January 16th, 2020, 12:07 pm

Thank you all so much for your valued input.

Mrs OLTB has spoken and the first thing we shall do is get a properly sealed garage door as the current one is a cheap metal up and over door with a cm or so gap between it and the brick wall. The garage walls could also do with a layer of something as well, as these are currently breeze block type style walls (painted white) with the brick skin next to them on the outside. I think it will look nicer as well as slightly insulating as we do want to turn the garage into a small games room. Once the above works are done, if the bedroom is still too cold, then the floor insulation will be tackled - and I will do it correctly as I hate a job to be bodged just to save a few quid.

Thanks again for your time to explain things to an enthusiastic, yet inexperienced DIYer.

Cheers, OLTB.


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