which insulation?

[Hudson1984]

Hi all,

so, I've now finished the walls in my garage - used 50mm polystyrene for this.

But - now I want to do the ceiling (I know, bad order to do this in however I needed the ceiling exposed for cables and the walls completed for sockets)

Now, I'm only going to insulate between the rafters - not between and on top, mainly because there are places already complete and I want it all to be level.

So, I understand celetex to be a superior insulator but will I actually notice the difference as of course the cost difference is quite large.

I will be using 75mm insulation and have the option of polystyrene (£26 a sheet from Local store) or Celextex at £55 a sheet, now of course I can use thinner Celetex and get the same thermal efficiency as the 75mm poly but may as well use the thickest I can.

Just wondered if in reality I'd notice the difference.

I will only be using a single 2kW heater, this is installed into a thermostat plug which is controlled via an app, so I will be maintaining the room at around 13 degrees all the time, then at "peak times" (i.e. when i'm home) i'll push it to 16/17 and then bump it up if I intend to be in there for a longer period - if i'm working on something for example.

So, I need the 2kW to be sufficient - no point using 2kW of heat when 3kW is escaping!

some calculators say 1600W would be ok, some say 2.5kW (18m2 room) so I'm hoping what I have will suffice.

So, should I opt for Celotex or will I be ok with the polystyrene?

 

[StephenStephen]

I'm curious - why maintain at such a high temperature when you're not using it?

 

[Hudson1984]

tbh that figure was pulled out of my arse! essentially I just want to maintain "a" temperature, rather than a specific one.

Just a case of keeping if from being frozen, so when I come to warm it to a workable temperature/comfortable temperature, it's already got a head start rather than my little heater trying to get it from 0 - 18. By the time it gets there i'll be out

 

[SFK]

you could also Use loft insulation / rockwool.
It is cheaper, quicker to fit, reduces noise and fire resistant.

 

[Hudson1984]

what do I then do with air gap etc - essentially I was going to put a breather membrane against the ceiling. Cover with board, cover that with vapour barrier, then plaster on top. leaving an airgap between insulation and ceiling.

With Rockwool I assume I wouldn't bother with the air gap, but would I need the membranes?

 

[StephenStephen]

tbh that figure was pulled out of my arse! essentially I just want to maintain "a" temperature, rather than a specific one.

Just a case of keeping if from being frozen, so when I come to warm it to a workable temperature/comfortable temperature, it's already got a head start rather than my little heater trying to get it from 0 - 18. By the time it gets there i'll be out

I'd probably go for something like a 6 degree standby, and use a timer or remote switch to get it up to temp before going in there.

 

[Hudson1984]

that's fair. I can do that for sure, it's all controlled via an app anyway - bit like hive but for electric heaters.

 

[paulrockliffe]

I would use the celotex, but I would buy what you need on Gumtree and get it for the price of your polystyrene. There's always one or two people getting rid of small amounts at about £30 a sheet near me. Secondsandco will supply close to that price, though you don't need much so delivery will bump it up. 18sqm is not many sheets so your cost difference isn't very much even if it is a big percentage difference.

 

[Hudson1984]

yeah more a case of if i'll notice a difference in performance more than anything. If my polystyrene will do the job great, if the rockwool will do it so be it.

I just don't want to finish and thick "wish i'd used the other"

 

[paulrockliffe]

You'll never really know. If the garage is too cold you won't know if it's because of the insulation or simply because you're asking too small a heater to heat too big a space over too short a time. On that basis better to go for the Celotex, but like I said if you're patient you'll get enough cheap enough that the polystyrene becomes irrelevant.

 

[Hudson1984]

just looked at the thermal resistance values.
Celotex 75mm 3.4m2K/W
Polly 75mm 1.97m2K/W

so 60 odd % better it seems. Might go for that with the extra cost. seems like it would make the most of any heat I put in.

 

[pilsbury]

Insulation of any kind will help but I’ve been told draughts are far worse than lack of insulation for loosing heat. Is your garage sealed from draughts?

 

[Leofric]

what do I then do with air gap etc - essentially I was going to put a breather membrane against the ceiling. Cover with board, cover that with vapour barrier, then plaster on top. leaving an airgap between insulation and ceiling.

Breather membrane against the ceiling isn't right . From ceiling upwards it should be skim, plasterboard, vapour barrier,

insulation.​

you could also Use loft insulation / rockwool.
It is cheaper, quicker to fit, reduces noise and fire resistant.

Yes, for what it's worth I would go for Rockwool.

 

[JP_]

Insulation of any kind will help but I’ve been told draughts are far worse than lack of insulation for loosing heat. Is your garage sealed from draughts?

Why do we have trickle vents if drafts are so bad?

 

[Leofric]

Why do we have trickle vents if drafts are so bad?

Air tightness on one hand, background ventilation on the other - trickle vents are controllable though