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Insulating a pitched garage roof


BudSlater

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Given that Autumn is close by, I'm looking to insulate the pitched roof of my garage. I've got an electric garage door which seals all the way around, so with some insulation in the ceiling, it shouldn't be freezing in the garage!

 

A few years back, npower were doing a really really cheap deal on that horrible glass insulation, but it did the job, so get some of that, some plasterboard up there and happy days!

 

Anyone know of a cheap source for the insulation?

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I'd be tempted to speak to you local builders merchant - to save you some time, given you're local, I found TG cheapest for insulation followed by Huws Gray.  TP were crazy expensive for evertything.

 

Check out the Celotex type stuff.  Doesn't sag, twice as insulative, and dead easy to work with single handed.

 

Don't forget the airflow needed to stop your roof rotting!

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I found Planet insulation on the web were the best price for celotex. As always a mate said he could get it for me trade but the Planet insulation price was cheaper than his trade price. Have used them twice and it turned up when they said it would to the minute. As it turns out they seemed to deliver from my local builders merchant anyway.

 

David

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I'd be tempted to speak to you local builders merchant - to save you some time, given you're local, I found TG cheapest for insulation followed by Huws Gray.  TP were crazy expensive for evertything.

 

Check out the Celotex type stuff.  Doesn't sag, twice as insulative, and dead easy to work with single handed.

 

Don't forget the airflow needed to stop your roof rotting!

The Coyote speaketh the truth....Foil backed urethane foam insulation might cost a bit more, but pound for pound, its the best you can get.

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The Coyote speaketh the truth....Foil backed urethane foam insulation might cost a bit more, but pound for pound, its the best you can get.

I concur also :yes: the only thing I would add is the importance to fit PIR/PUR tightly between the joists to ensure there are no airgaps around the edges of the boards or all the benifits of using it will be lost. This is where the mineral wool insulations have an advatage as they can be compressed and pushed in to provide a tight fit between the joists and are more forgiving if cut to slightly the wrong size.

[pedant]

FWIW Celotex is acutually a Polyisocynurate rather than a Polyurethane

[/pedant]

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Awkward to do in the mineral wool stuff but can be done well and quite cheap, I stapled up poly sheet to retain it.

 

Knauf Eko roll 7mts 100ml is three rolls for  £40 in B and Q, three rolls would do a fairly substantial garage.

 

 

  Jim

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Don't forget the airflow needed to stop your roof rotting!

Good point, any recommendations for what gap to leave?

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Anyone have any thought on insulating a metallise corrugated roof? Obviously it will last forever but the condensation inside the garage in winter is horrendous. Only way I can see is to remove the roof and replace it with sheet ply and roofing felt but I am no expert and if anyone has a better idea than I am all ears.

Ian

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Good point, any recommendations for what gap to leave?

 

Can't claim expertise, but would guess 1/2" would suffice if there is good airflow through soffit vents positioned so that you get through flow.

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Good point, any recommendations for what gap to leave?

Can't claim expertise, but would guess 1/2" would suffice if there is good airflow through soffit vents positioned so that you get through flow.

ideally you want to have the equivalent of a continious 10mm gap on opposite sides along the length of the eaves.

Swish-Building-Regs-Images-.jpg

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That's the great advantage of having a building expert on the site nice one Mark.

 

Bob :d

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  • 6 years later...

Hi

 

Sorry to bump an old thread, but this is practically the same as what I want to do, with the exception that my garage does not have soffits (at least that stick out from the sides).

 

I'm looking at option B from above, with fibre glass roll and poly sheet to keep it in.  The pitched garage roof construction is starts level with the top of the wall construction.  Happy to post a pic if needed.  In this case do I still need to leave a 10mm gap between the insulation and the roof?

 

Thanks in advance

 

Neil

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On 22/01/2021 at 17:39, neil2048 said:

Hi

 

Sorry to bump an old thread, but this is practically the same as what I want to do, with the exception that my garage does not have soffits (at least that stick out from the sides).

 

I'm looking at option B from above, with fibre glass roll and poly sheet to keep it in.  The pitched garage roof construction is starts level with the top of the wall construction.  Happy to post a pic if needed.  In this case do I still need to leave a 10mm gap between the insulation and the roof?

 

Thanks in advance

 

Neil


yes and if you don’t have any eaves you need to think very carefully about how you plan to cross ventilate the gap or you’re going to end up with condensation issues.

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