Garage insulation

[tony359]

Hello all

As many others on this forum I'd like to go ahead and insulate my garage. However, I am going to use it as a DIY workshop - I do not intend to live in there. The garage is a double garage single skin brickwork and it's currently as cold/hot as the outside temperature.
I am not looking for 20°C and sitting down watching telly - I am just trying to be able to bring the temperature up to a reasonable level while I am there tinkering with my hobbies.

I know that insulation is kind of binary: either you do it fully or it's a waste of time. But I read somewhere that if I insulated the ceiling it would be a great improvement and maybe I can then move from there. Shutters are metal ones so those would require replacing as well and all the walls would need to be done - I'm just trying to see if I can obtain an acceptable result by doing the ceiling and seal gaps only.

Please see below a picture of the roof structure.

I was wondering what the best course of action would be. Celotex or similar between the rafters or just board the joists and put some celotex/rockwool in between? Boarding the joists seems the best idea as the ceiling level would be much lower and I guess the heat would fill up the room quickly.

As I may not be using the correct technical words, I've made a quick 3D sketch.

Green: boarding the joists and add rockwool/celotex. Advantage: lower ceiling, easier to warm up - Disadvantage: no access to roof structure

Blue: insulate rafters and board. Advantage: access to roof structure (do I really need that) Disadvantage: Gables will also need to be insulated, more space to heat, trickier to realise.

In the end I want be able to use my garage when it's freezing outside. If the ceiling is not enough, I'll go on and do the walls and the shutters.

Thanks for your help!

 

[garyo]

Can you go for the green approach and leave yourself a large access hole with ladder? As you say it'll make it far easier to warm up, and what you want is rapid response from your fan heater for those times when you're just popping in for an hour or two. You wouldn't even need to fit a hatch - just get an old 1M x 1M piece of board or 50mm PIR insulation and pull it over the top of the hole when you're not going up there.

 

[motorbiking]

love the drawing, but you don't need to do both.. Assuming you want to use the roof space for storage/ mezzanine, I'd just infill the roof with GA4050 or rockwool, standard loftroll or similar and then either board over wiith plasterboard or insulated plaster board (e.g. PL4040 or 4025),

 

[tomfe]

What's your budget?
I'd plaster board and insulate between and over the ceiling joists with dimple cheap rockwool/fiberglass.
If you use the space intermittently put any insulation inside the thermal mass.

 

[motorbiking]

If you do the walls with PL4025 that will make a big difference - also you could make up a screen for the garage door using hinges and batons to avoid replacing the door.
I'd do roof, door screen and walls in that order..

 

[tony359]

thanks all!

Motorbiking,
No, green and blue are two separate options. I am going to do either green OR blue! Could you please elaborate the door screen further please? That sounds interesting!

Tomfe
well, the budget is whatever is required to be able to work in that place without spending an arm and a leg - possibly. But I don't want to invest on something that then has to be removed because it does not work.
What do you mean exactly with "put any insulation inside the thermal mass"? You mean not to insulate the brickwork from the outside?

Thx!

 

[motorbiking]

On the option of blue vs green comes down to a flexibility vs volume compromise.
flexibility - insulate the roof to retain the space for storage
volume - minimise the heated area.

On the insulation screen - Imagine a bifold "door" made out of 2" x 1", in filled with celotex and then covered in sheeting. e.g. (without the wheels.) Make it so it can fit snug inside the opening.

 

[tony359]

thanks Motorbiking
that sounds like a good idea. I'll see how it goes with the ceiling and then I'll move forward. I may decide to replace the shutters with insulated ones.
Ok, thanks for all your inputs. I guess I'll go with the ceiling joists option - maybe boarding the top as well so I can still use the area for storage.

What timber do you recommend I should use? Drywall may be cheaper but I'm concerned about damaging it. I have looked into timber to board my loft area and it seems a tad expensive for some chipboard!

 

[John D v2.0]

Before you do any insulation sort out the air leakage. It's impossible to heat a very leaky space, but even a tent can be heated.
Once you've done that work it's worth getting some insulation, but for cheap use polystyrene or glass wool rather then celotex. 50mm polystyrene is much cheaper then the equivalent celotex if thickness isn't an issue.

 

[tony359]

Air leaks: Absolutely. Even though it may be tricky because of the way the roller works. But I'll sort that out.
Polystyrene: it's a good point. I've also read that Celotex will slowly lower its R value to match the polystyrene one after several years! Anyway for 25m2 B&Q would ask £347 of 100mm Celotex - I'm ok with that if that is the best insulation solution possible. Same B&Q would ask £243 for 100mm Polystyrene. I am happy to invest the extra £100 if that is doubling my insulation strength! (But thanks for the idea).
I'll try finding something cheaper than B&Q BTW. B&Q is seldom the best place to purchase stuff.

Edit: I found this one which seems interesting. They sell "B-Grade" panels. Half the price than B&Q approx.

http://www.secondsandco.co.uk

 

[motorbiking]

I was suggesting the Blue option would give you access to the loft space. Not the green. If you go green then you need an insulated hatch/door. to get to the roof space.
Polystyrene is cheaper, but not when you consider that width for width celotex is twice as thermally efficient. Noting that this does degrade over time.

If you are going green, I'd go with standard fire resistant roof roll.

 

[tony359]

Yes, I understand that the blue option would leave me more space but to be honest I won't be using that space too much and I can still use it if I put an access door as you say.
What's the amount of degradation that I should expect from a Celotex-type material over time? I did not know about that. I am happy to spend a little more (it's only 25m2 after all) to do that right but if the Celotex degrades to the same level of some rockwool in 5 years time then what's the point?

 

[John D v2.0]

Celotex won't degrade noticeably, not sure who came up with that. You aren't supposed to leave it exposed to the sun, but that's about it. Don't worry about it!

 

[tony359]

I read somewhere that the Celotex would degrade to the same level of Polystyrene in 5-7 years while Polystyrene would not degrade. Then Motorbiker confirmed that Celotex would degrade so I assumed that what I read was correct. I'll do some research.

 

[tony359]

Hi there!
Just a follow up. I have now completed the ceiling with Celotex 75mm, it just needs some boarding. I am thinking of 9mm OSB as if not mistaken it won't need any coating. In the end I had the roller doors replaced with insulated ones. I thought I would never be able to do a decent job with the existing ones and my DIY room is a big part of my spare time so I open the wallet for that - but they were much more expensive than I thought.
I've also applied waterproofing liquid to the external brickwalls.



I must say I am pleased with the outcome. Clearly the heath escapes from the wall and the floor but I can now reach a dry, comfortable temperature of about 15°C with -2°C outside which I can maintain with my electric heater set to half (1500W). When temperature is over 5°C things are much more easy. Only main downside is that temperature at floor level is much lower than head level!!
I am now looking for a heath pump air conditioner - I understand that it uses far less energy to generate the same amount of BTU an electric heater does - and I'll think of insulating the walls maybe next year but I'll do some research, I'd like to keep the thickness of the insulation to a minimum to maximise the usable space.

Thanks for all your help so far!