Garage insulation?

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I've done an extensive search here, but still confused about how to proceed...

Single block construction, pitched roof slated garage, rendered on the outside and painted.

IMG_5020.JPG



Looking to insulate my garage to make it more comfortable as a workshop and to prevent rust on tools etc.

The roller door is an issue, I was going to replace this with uPVC doors, unless anyone has a cheaper suggestion? I'm guessing trying to insulate it is wasted effort?

With the pitched roof, I was just going to put celotex 50mm or 75mm between the rafters and ply over it leave it at that but do I need to leave any air gaps between that and the roof membrane that is already there? Or is anything else required like vapour barrier?

With the walls, I was going to create a wooden batten frame, directly to the walls and fill the gaps with celotex also and then plywood as I want to hang things on the walls. Do I need a vapour barrier between the celotex/battens and the ply or the wall? Or any air gaps within this?

Thanks for the help!
 
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Insulated sectional doors are available, they don't roll up, they end up horizontal at ceiling level like an up n over. Might also be able to get an up n over and insulate it or buy one already insulated

The rest of your plans seem fine, you could use wool in the ceiling held in place by roofing felt (stapled)

You don't need to worry about moisture too much because garages don't really have activities going on inside that generate it, and ventilation rate is typically higher than a house
 
Insulated sectional doors are available, they don't roll up, they end up horizontal at ceiling level like an up n over. Might also be able to get an up n over and insulate it or buy one already insulated

The rest of your plans seem fine, you could use wool in the ceiling held in place by roofing felt (stapled)

You don't need to worry about moisture too much because garages don't really have activities going on inside that generate it, and ventilation rate is typically higher than a house

Thanks, I'll look into the sectional doors and the felt/wool option sounds easier.

Should I leave an air gap between the exterior walls/roof and the celotex/wool?

And if I tape up the joints in the celotex, I don't need a vapour barrier?
 
Id be inclined not to bother with air gaps for aforementioned reasons of low moisture generation, and the fact that the wood (the only thing affected by moisture) is in contact either side with surfaces that are reasonably vapour-open. Wool is permeable too
 
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Ok, so moisture in a garage not a huge issue by the looks of it, how does this plan look then, in order to save time and money.

Roof - Celotex inbetween the rafters, sealed with foam where needed. Thats it. No need to tape the joints?
Nothing on top of it for now, could add another layer of celotex on top of this later if needed or plasterboard down the line. Do I only need to tape the joints when I get to this stage?

Walls - battens, straight on to the block, Celotex inbetween and OSB on top. Tape the joints for this one?

Thanks for the help!
 
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Moisture is produced everywhere, and if you have no heat to hold it in the air, then it will condense on cooler surfaces. The only way to deal with it then is to ensure that air is moving - so you do need ventilation
 
Moisture is produced everywhere, and if you have no heat to hold it in the air, then it will condense on cooler surfaces. The only way to deal with it then is to ensure that air is moving - so you do need ventilation

Thanks for the reply. figured I'd leave the air gaps anyway, as I don't need the space and I will be heating it also. Was looking at upvc doors with air vents as well....

I'm just not sure now if I need to tape joints or not? As per the above plan?
 
The exteranl wall will not be water proof. You should fit a membrane (polythene) up the wall first and then construct your frame and insulation layer.

Then, as everything should be tight with no air gaps and there is no true timber frame to protect, then you wont need to take any further precautions by taping joints.
 
The exteranl wall will not be water proof. You should fit a membrane (polythene) up the wall first and then construct your frame and insulation layer.

Then, as everything should be tight with no air gaps and there is no true timber frame to protect, then you wont need to take any further precautions by taping joints.

Ok so, what I'm getting from all this is that a good plan would be:

outside wall
Basic DPM - polythene sheet
battens with insulation between - still with an air gap between the polythene and the insulation
tape the joints anyway
osb or ply

sound good?
 
No air gaps!

Ok, understood!

Just one more question, the roof. (yip, I'm gonna mention air gaps again...)

From the photo in the OP, there is a membrane in the roof already, battens and then the slates. Insulation right up against this also? Or do I need the... u know.... gap

Thanks for your help, very much appreciated!
 

A quick Google came up with this https://www.boards.ie/b/thread/2057334577 :eek:

Is it ok before you cover it up.

With that type of non breathable membrane it may be best to have a vented gap between the insulation and the membrane. 50mm is often recommended, but 25mm minimum should be ok. But this relies on having continuous ventilation along the eaves and ridge.

Otherwise, again you could full fill the roof with insulation tight up to the membrane - and in this case no gaps anywhere are even more important. The concept is to stop any moisture getting into the roof via damp air, and condensing on the cold membrane.

In both cases tap all joints and across the rafters.
 
Walls - battens, straight on to the block, Celotex inbetween and OSB on top.

Fireproof wall and ceiling linings, i.e. plasterboard, have obvious advantages in a garage, and may be required by building regs.
 

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