Garage insulation

[DarkSource]

I am planning to insulate an attached garage as a home improvement project (not as a garage conversion). 3 of the walls are external single layer brick. The other is internal breezeblock.
I am trying to achieve the best U value I can without going crazy with the insulation (something around 0.7 looks achievable). The garage is 5.4 x 5.4 m and will have electric underfloor heating with tiles over the top. This is the only form of heating I am intending to use, so it needs to insulated enough to keep me warm in winter.
I also need to be able to hang things off the wall, including bikes, lawnmower etc. Hence dot and dab does not look remotely sensible.

Does the internal wall need insulation? I have seen both views expressed.

Having done some research, I am wrestling with the best method to insulate the 3 outer walls.
Option 1:
Treated timber battens (75mm deep) with 75 mm celotex between and plasterboard over the top. Since it is a garage would I need moisture resistant plasterboard? Does the celotex provide a vapour barrier on the warm side and a breather membrane on the cold side or do I need to add them? How significant is the heat loss through the battens?

Option 2:
Treated timber battens (say 25 mm deep) with insulated plasterboard screwed over the top. Again I could use celotex for this, but with 60mm insulation under the plasterboard I can't see how the wall would be strong enough for heavy items (without battens directly below the surface).

Any advice / other options welcomed.

 

[big-all]

heeelllooo and welcome darksource

electric costs 3 times as much to heat a space compared with mains gas
there is a large time lag between turning on and the room fully heating with underfloor

 

[DarkSource]

Thanks Big-all!
I had initially wanted to extend the central heating system to add radiators or wet underfloor heating. As you say gas is a lot cheaper than electricity. However the local council informed me that this would turn my project into a garage conversion, requiring it to pass building regulations (which would be costly). Hence I have to use a separate heating system, which leaves electric UFH, gas/electric space heater or electric rads.

When I did the calculations for the U values on the proposed insulated floor, ceiling and walls, I worked out that 1.5 kW is enough to keep the room warm, in all but the worst conditions. I was therefore planning to heat the room for a set number of hours a day, modulated to reach 15-20 degrees air temperature. This works out at about £1 per day. I can live with that.
How long do you think it takes to warm up the room using UFH?
I am not committed to using UFH just yet, so there is time to think about it.

Equally I would still like to insulate the garage well, so that whatever heating method I use, the losses are minimised.

 

[drpepe]

I don't think you have mentioned the door. If you have a standard garage door, it hardly seems worth insulating or heating.

 

[DarkSource]

Yes, there are 2 up and over doors, which I will replace with insulated roller shutters and then have a push in 'slab' of 75mm celotex to seal them off (during the winter).

 

[big-all]

at say 12.5p a unit you will get around 5hrs heating for a pound
underfloor will take 2 or3 hours to bring the temperature up
i personally would expect it to use perhaps 25-50% more than your calculations

 

[chappers]

Personally speaking I would just extend the heating system if that's what you want to do, who's to know, one thing to be aware of though is that your roomstat in the house may be switching the heating off before the garage gets up to the temperature you're after in the garage.
With regards to hanging stuff on the wall, consider fixing a strip of ply all round where you may want to hang things in the future, behind the insulated plasterboard

 

[DarkSource]

Thanks to all so far. In summary I have two things to sort out; insulation and heating.
Would welcome any experience on the original questions relating to the type of insulation, vapour barrier, breather membrane, air-gap, plasterboard with insulation vs separate etc.

I have seen strong arguments for and against UFH, irrespective of wet vs electric and the costs involved. I have seen / been offered systems where the electric heating elements are right below the tiles (well 5 mm anyway) with insulation beneath. I would be surprised if this takes 2-3 hours to warm-up. Does anyone have any real data?
Does anyone have electric UFH in their garage and how well does it work?
Equally if not, who has used what they think is a better solution (for a regularly used garage)?

No point in re-inventing the wheel

Thanks folks!

 

[big-all]

it doesn,t take 2 or 3 hours to warm up the elements its the fact they are so low powered it takes hours to make any difference to the surrounds
in other words 1kw heat loss 1.5w elements = 0.5w off heat to the room
3kw element in the same situation 4 times the heating at 2kw
underfloor heating is designed for low heat loss areas and more constant use as its more off a trickle off heat left on fairly constant rather than rapid heat when wanted
if you had say 2x2kw fan heaters that would be 3kw or 6 times the heating to the room so what would take 3 or 4 hours would take perhaps 10 mins as it overcomes the heat loss far far quicker

 

[oldbutnotdead]

Back on point (insulating walls etc)- you'll get better thermal efficiency with 25mm battens up the wall then full sheets of insulation fixed to battens then plasterboard (if you really want plasterboard- thermal efficiency is shocking and it is a garage so what's wrong with seeing a foil faced board). As long as you use foil faced board and tape the joints then that'll be your vapour barrier (by the way, the Celotex jointing tape is much stronger than the generic no name aluminium foil tape from Toolstation)

You can do the studs and insulation between them but the insulation has to be a snug fit between the studs which is a fair bit of fiddly work cutting the stuff straight. Timber is quite a good insulator but any airgaps between insulation and timber will drop the thermal efficiency massively.

For hanging stuff on the walls, frame anchors and battens (3 x 2 or 2 x 1) would do with maybe strategic shuttering ply or plasterboard to protect the insulation. PIR boards are quite good at dealing with distributed load but rubbish with point loads. Plasterboard is better at point loads but not much better and thermally is rubbish.

Heating- dunno. Are you planning on insulating the ceiling (you really should, lots of heat goes that way). Not sure if wet UFH is going to be cost-effective for a garage plus your tiled floor will restrict the floor loading somewhat. I'd just chuck a couple of radiators in once BCO has signed the build off and maybe have a big electric fan heater available for some instant boost. Don't be tempted by those gas powered space heaters- yes they chuck out a LOT of heat but also chuck out a LOT of water vapour which will condense on cool surfaces and be a frigging nuisance. And they need a good air supply......

 

[roboughton]

I assume you are going to use the room as a workshop in the winter?

I did mine (all be it not attached to the house) 1inch battens 20mm kingspan between and I think it was 75 or 80mm board over the top with sheets of Ply covering that. Make sure you tape the joints!!!

As for heating I fitted a 2kw wood stove based on the premise of if I am in here and using it then I would light it and not waster electric via UFH or storage heaters/convection etc. Although its cold when going in it soon heats up with the log burner.

One thing I regret and more due to practicality and time was not pulling the floor up and insulating even just with 10mm insulation to help keep the heat in. I have 10mm on a internal floor in a renovated room with tile and it makes a huge difference against the non insulated tile.

 

[DarkSource]

Thanks again for all your tips and ideas.

Some answers to the various points raised.
Will I insulate the ceiling? Yes. There is already a ceiling there with storage space above (garage has a high pitched roof). The joists are 70-90 mm, so I'll fill them with celotox and then cover with plasterboard. Filling the voids is better than lowering the ceiling even more by adding insulation backed plasterboard onto the underside of the joists.
Regarding the floor, I was going to use 30 mm of celotex underneath the UFH to minimise heat loss.

I agree that insulation onto battens is better than inbetween. I would like to have plasterboard to finish with, as I intend to paint it. Although it is still a garage, it happens to be the only place in the house I can work and escape to, so I'd like to make it feel like a professional workshop.

Oldbutnotdead - by frame anchors and battens for hanging stuff, do you mean..... attach battens to wall and then attach insulation to that. When I need strength, fit a batten at 90 degrees directly to the wall battens and fit the insulation around it. Hence heavy items can be hung off a visible batten, hence no load on the insulation?

Will have a further think about the heating.

 

[roboughton]

if your putting 30mm insualtion in the floor why not buy the boards with the groves for pipes on wet UFH, don't plumb it in until the BC have signed off and hide the tails somewhere. If you are going to all the trouble of insulating etc it seems daft that BC wont sign off as it uses part of the CH system to heat it.
But then the council BC do a lot of daft things haha.

 

[DarkSource]

Thanks Roboughton - because it is not a garage conversion (doors still remain) that makes it officially a "home improvement" project. Hence I am not expecting to need any inspections or certificates.
Equally I am not building in new power or lighting circuits, just replacing the exisitng sockets and light fittings, hence no electrical certificate either.
I am coming to the conclusion that I may just go for wet UFH and have isolators should anyone want to check.

How does that sound?

 

[roboughton]

I'm pretty sure the council cant stop you heating your garage even if it is using the CH system, at the end of the day you aren't going to do much more than store stuff and work on projects and if they ever wanted to check they could.

My new garage (we now have two) after our renovations (although not finished) has 150mm of insulation in the ground so it can have Electric UFH to keep it at a higher temp than normal garages so it can be used as a work shop and cars will be kept in it during the winter. Having said that it will be set to something like 14/15 deg c so not like it would be really warm.

In all honesty I would do the work then if you ever did want to change it to be part of the house (conversion) you would need minimal work other than certs from BC and Electrical. I'm sure a garage conversion comes under permitted development these days but you should ask the BC officers that.