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[oilstain]

My garage is not warm
I have a insulated roller door on the front and double glazed/insulated door at the back, walls single layer brick, rendered on the outside. I fear most of the heat loss is through the roof which is board and felt over joists.
I'm thinking of adding insulation between the joists either tight to the roof boards or on the joists leaving a 8" gap but with the loss of space I use for storage of "stuff"
The insulation I'm thinking of is 25mm polystrene or Celotex, not the best but price is a factor!
Any thoughts or advice

[ChrisJC]

Is it draughty?, that will have a larger effect than insulation.

My garage has double glazing and a double skinned wall. But the roof is pitched with tiles and felt, and uninsulated. I generally find it retains it's heat pretty well. If it's been a warm day, it remains warm inside in the evening, and if it's been cold for a few days, and then warms up, it takes it a while to warm up inside.

Chris.

[Robin]

I replaced the old corrugated fibre/cement roof on the garage at our old place with insulated box profile steel - well worth the effort as it made it much warmer in the winter and cooler in the summer, but expensive!

25mm Celotex/Kingspan would make a difference, I would think, either stuck to the underside of the roofing boards with no gap for condensation to form, or with an air gap, only needs to be an inch or so, ventilated to stop condensation between the insulation and the roofing boarding.

Bear in mind that standard Celotex/Kingspan is a fire risk, especially if you're grinding etc.
You can get fire resistant Celotex/Kingspan though, and foil covered, which lessens the risk.

Polystyrene would really be considered a no-no, I would think, as it burns really well - I doubt your insurance company would look favourably on a claim if you've lined your roof with polystyrene!

My current 'barn', 72mx32m was built with 3" of fibreglass insulation inside the walls and roof, and the temperature is very stable and is easy to warm up in the winter   

[oilstain]

^^^^
Thank you for the points made
-I dont have any draughts when the doors are closed
-I will not consider polystrene, after your thoughts
- I only have single skin brick walls but the work to remove all the bench's, shelves, fridges, washing/drying machines etc etc put me off that idea

 
So it looks like some 25mm foil backed kingspan type insulation, I will look at the prices

[nathanglasgow]

I recently insulated my 30m2 garage/workshop. Newly built concrete sectional with apex roof. 50mm polystyrene on walls and ceiling then boarded over with 9mm osb. £800 in materials. Biggest heat loss now is the two up and over doors but a 2kw fan heater keeps it plenty warm and dry.

[linesrg]

^^^^
Thank you for the points made
-I dont have any draughts when the doors are closed
-I will not consider polystrene, after your thoughts
- I only have single skin brick walls but the work to remove all the bench's, shelves, fridges, washing/drying machines etc etc put me off that idea

 
So it looks like some 25mm foil backed kingspan type insulation, I will look at the prices

Give this lot a call - https://www.secondsandco.co.uk/headoffice - I have no connection but have bought off them twice over the years. The 20/ 23mm stuff they have should do the job.

Regards

Richard

[alchad]

Another vote for Seconds and Co, have bought from them on quite a few occasions, they are close to us so easy to pick up from ( Mrs Alchad’s horse box has it’s uses at times😀). Check out their special offers on the website as well.

Alchad

[Robin]

And another vote from me 
I got a pallet load from them, 120mm thick sheets, to finish off a cabin - some sheets were actually seconds, with ripples and rounded edges, but 90% of them were just about perfect and I managed to use them all despite defects.

[oilstain]

^^^ I note you have to buy £500+ to get it delivered, I need to work out the best option, perhaps 50mm rather than 25mm.
Time to measure up....

[mrutty]

Go to Jewsons and ask about the rock wall type of insulation. It might be called slab insulation. Its cheaper than Celetex and easier to get a tighter fit. You'll be better off then adding some battens to keep it in place or a thin ply skin. The R value won't be as good as Celetex but you'll have less gaps so the overal roof will have about the same value. Used it in my house roof and then used Celetex in the walls, made a huge difference. If you stick with Celetex then don't forget to tape seal all the way round.

[nickmerry]

I have added a no light infrared heater, which heats the objects etc, not affected by draughts etc, so you feel like you are under the sun.
Herschel for example, do some good ones, not cheap but less cost  to run long term than fan heaters.

[Owen Sparke]

I have just insulated the galvanised box metal roof above my Landy with Celotex and ply/shuttering.
The insulation was bought over 6 months piece by piece from FB marketplace - loads of off cuts and full sheets sold from projects which over estimated requirements and sold cheap. It took time and perseverance  but saved a fortune to get the right stuff.