Insulating Detached Garage - have I got the right idea?

[JoshRogan]

Hi All.

I've finished all the structural work on my garage, just got some rendering to do to finalise the exterior and I am now looking towards the inside. I would like to make the garage a little more comfortable for working in the winter and want to minimise moisture forming on the interior - I will be storing my car while I restore it and girlfriends motorbike.

A) Walls (DCBs)
It was suggested to me I batten (studwork?) and line the walls with DPM (to stop moisture ingress) and then place polystyrene next (insulation) and then final with plasterboard - however a dry-lining chap suggested that DPM was not the best move as moisture/condensation may form between the DPM and the blocks, dripping down and pooling at the base of wall. As an alternative he suggested using bitumen paint on the walls instead of the DPM to prevent moisture getting beyond the blocks.

B) Roof (pitched)
For the roof I have a breathable membrane (double roman tiles) and was going to simply use either polystyrene between the rafters (or perhaps rockwool roll may be easier to place, the rafters are 150mm deep) leaving 50mm gap between membrane and insulation for airflow (is airflow needed for A) Walls at all?).

I don't intend to paint or plaster over the plasterboard at all.
Not sure what thicknesspolystyrene will be useful.
The base will be concreted with a DPM underneath.
Walls are DCBs.

This 'sounds' reasonable to me, but i'm a complete novice so if anyone can see any problems or perhaps suggest alternatives they would be most welcome - I've read through a lot of threads and they have been helpful, but I like to try and put my situation forward individually.

Thanks.

c

 

[Deluks]

I wouldn't bother with paiting the interior wall. Just batten out, fix insulation leaving a void, vapour barrier polythene, plasterboard. More insulation the better, especially if you intend to heat the space. polystyrene will be best for walls, rockwool rolls or normal loft insulation best for the ceiling. Leaving a gap between insulation and roof membrane is best practice unless it's a decent breathable membrane like tyvek.

Could you afford to lose 4-5" floorspace all round? Will you be heating it at all?

 

[JoshRogan]

Thanks for that Deluks, so painting is out. What void spacing is required for the walls and would I get the void by using counterbattens? I was going to use 25mm thick (1 inch) polystyrene as I dont want to eat away at the garage space too much, though would something like Celotex 25mm foil backed provide a better insulation at the same depth? It includes the vapour check too and looking at the instructions from the website it appears I only need one set of battens (no counters).

Cost is a bit more at £1 extra per m2 by my rough calcs, maybe its money well spent?

In term of heating, was just going to use portable electric or halogan heaters to take the chill off - so its not going to be a full radiators job or anything like that.

C.

 

[Deluks]

Celotex is better over poly at the same thickness, but at only 25mm, not much better. If you can squeeze to at least 50mm you will probably be much better off. 50mm poly will probably be better than 25mm celotex. I say poly I mean constructional polystyrene that you buy in big sheets, not the packaging your washing machine came in.

My previous questions about floor space: What I would do (will be doing in the future) in my garage, is to build a stud wall spaced about an inch from the outer wall. 3x2 will do for this. Then fill with 50mm insulation and vapour barrier/plasterboard. Will cost around 112.5mm of room space round the perimeter though.
My (future) stud wall will be 6x2s spaced 8" from the outer wall but that's a whole 'nother story

 

[JoshRogan]

I like your idea of stud wall away from the outer wall.

To be honest its a large garage, 4.6m by 6.0m internally, but I want to preserve as much space as poss for moving around the vehicle etc. For me, space and prevention of water is more important than being 'very warm'. I'll be using the 'attic' space upstairs for sitting around more I guess, downstairs I ought to be 'busy'!

With that in mind, can I ask why the void gap between the wall and insulation? Is it to do with condensation or is it just acting like in cavity walls to help prevent water transfering to the internal structure?

I noticed this thread //www.diynot.com/forums/viewtopic.php?t=121768 earlier and it mentions no need for void, but perhaps thats due to the particular application in a small area?

 

[Deluks]

Well then you may as well just fix 2x2 to the wall insulate, and board over. What you have to ask yourself is, if water were to penetrate the outer wall, where would it go? Rendering the outside should prevent this anyway, did you use a waterproofer in the render mix? (2 coats?)

 

[JoshRogan]

Water prevention is one of my main concerns and I am happy to give up a bit of space to prevent against, which is why I was asking about the void - so water that does enter the walls will just enter this void space I presume? This is why I thought the idea of using bitumen paint on the internal walls was a good idea, to prevent water moving beyond that point.

Yes, the external will be rendered with 2 coats with waterproofer, but I remember reading/or have been told, that if you heat a room water will still try and move in and render may not entirly prevent this. I imagine this would be fairly rare situation? perhaps only when the render is wet for a period of time - persistant rain etc - and not given a chance to dry.

Am I being a bit to cautious all about this? It would not be the first time! But I do just like trying to understand. I noticed on th celotex website http://www.celotex.co.uk/downloads/SolidMasonryWalls.pdf that the celotex goes up against the wall, battens hold the celotex on and then you board on the batten leaving a void created by the batten thickness, but this kind of goes against what I said above with water dripping in the void.

Can you see why I am a bit confused?!

Thanks, I do appreciate your effort here!

 

[milton1]

I'd just like to say I am also waiting to insulate a single, solid block wall and am as confused as you are. I hear the best thing to do is leave a 25mm gap; build a timber frame with a waterproof breathable membrane on the outside attached to plywood then insert 50mm Kingspan or equivalent then vapour check plasterboard to prevent condensation from the inside. BUT, if there IS moisture infiltration from the blockwork, Where does it go? Does it just dry up; does it seep under the breathable membrane or is it so little it doesn't really matter. If so, when Polyfoam Linerboard or Kooltherm K18 are resistant to moisture where is the problem of applying these straight to the block with adhesive plaster dabs? This would save internal living space, BUT, Would the case then be, that the insulation properties would not be good enough to comply with building regulations? Yes Josh, you and me both!

 

[and1c]

Water prevention is one of my main concerns and I am happy to give up a bit of space to prevent against, which is why I was asking about the void - so water that does enter the walls will just enter this void space I presume? This is why I thought the idea of using bitumen paint on the internal walls was a good idea, to prevent water moving beyond that point.

Yes, the external will be rendered with 2 coats with waterproofer, but I remember reading/or have been told, that if you heat a room water will still try and move in and render may not entirly prevent this. I imagine this would be fairly rare situation? perhaps only when the render is wet for a period of time - persistant rain etc - and not given a chance to dry.

Am I being a bit to cautious all about this? It would not be the first time! But I do just like trying to understand. I noticed on th celotex website http://www.celotex.co.uk/downloads/SolidMasonryWalls.pdf that the celotex goes up against the wall, battens hold the celotex on and then you board on the batten leaving a void created by the batten thickness, but this kind of goes against what I said above with water dripping in the void.

Can you see why I am a bit confused?!

Thanks, I do appreciate your effort here!

It is worth it to lose a few inches of garage and have it nice and dry so your tools and car dont rust Been there and had to deal with that on a garage I inherited with my last house.(moisture and damp)
You do need a void in the cavity next to the celotex (or what you use) so that moisture does not get trapped in the cavity.

You will also need to put a vent on each end of the garage so that moisture can also escape the cavity and air can circulate.

Its better to be thoughtful as you are rather than rush into it and do it wrong...

 

[wiedzmin]

Hi All.

I've finished all the structural work on my garage, just got some rendering to do to finalise the exterior and I am now looking towards the inside. I would like to make the garage a little more comfortable for working in the winter and want to minimise moisture forming on the interior - I will be storing my car while I restore it and girlfriends motorbike.

A) Walls (DCBs)
It was suggested to me I batten (studwork?) and line the walls with DPM (to stop moisture ingress) and then place polystyrene next (insulation) and then final with plasterboard - however a dry-lining chap suggested that DPM was not the best move as moisture/condensation may form between the DPM and the blocks, dripping down and pooling at the base of wall. As an alternative he suggested using bitumen paint on the walls instead of the DPM to prevent moisture getting beyond the blocks.

B) Roof (pitched)
For the roof I have a breathable membrane (double roman tiles) and was going to simply use either polystyrene between the rafters (or perhaps rockwool roll may be easier to place, the rafters are 150mm deep) leaving 50mm gap between membrane and insulation for airflow (is airflow needed for A) Walls at all?).

I don't intend to paint or plaster over the plasterboard at all.
Not sure what thicknesspolystyrene will be useful.
The base will be concreted with a DPM underneath.
Walls are DCBs.

This 'sounds' reasonable to me, but i'm a complete novice so if anyone can see any problems or perhaps suggest alternatives they would be most welcome - I've read through a lot of threads and they have been helpful, but I like to try and put my situation forward individually.

Thanks.

c

Hi
try this link www.solidwallssolutions.co.uk

 

[JoshRogan]

Thanks for those last few comments, though wiedzmin I dont think I will be adding external insulation to the garage (though I am only down the road from Swindon funnily enough!)

So, AND1C, did you look at the link to celotex? http://www.celotex.co.uk/downloads/SolidMasonryWalls.pdf
Its just that there the celotex is against the wall and then comes the void, surely if I then ventilate that to the outside then there is little point in having the insulation on the wall as i'm letting cold air in (i'm looking at the picture on the backfoot a bit, not the one with fancy mesh and blue things).

I'm getting the picture a bit more though now - its similar to the roof construction. You have the tiles, then battens and felt (breatable membrane in my case), then a void to the insualting material which is ventilated at the eaves and ridge so any moisture (and I guess we ought to think 'vapour' rather than drops of water?) is carried out and surfaces are kept dry.

Cheers