Brick Workshop Insulation and Damp Proofing ...again

[rjb]

Hi,

I have a brick built garage (single skin) with pitched tiled roof which I use as a workshop. It doesn't get any sun at all because it is in the shadow of the house and it is very cold and damp. The damp is a particular problem because I use a lot of MDF and it swells and even goes mouldy if left for any length of time.

I have read a lot of old posts on the subject, but I still have a few questions.. I plan to batten the walls with 2x2, apply a polythene DP membrane and insulation (Cellotex or Rockwool) and then board over with plasterboard or OSB. Does that sound about right? Do I need to leave an air gap behind the dp membrane? I think if I use rockwool it will be difficult to get it to stay in position unless it's packed in tight i.e. with no air gap behind.

The ceiling is simple enough, but I don't know what to do about the concrete floor as I imagine damp could come through. Would floor paint be effective?

I'd be grateful for any advice.

Thanks,

Richard.

 

[Doug B]

Richard,
I`d be tempted to put a DPM on the base & lay a 2' screed, that will stop any damp rising. Then build stud walls of this screed, 1' off the existing walls. Vapour barrier the back of the stud walls, fill with insulation & then cover with either PB or OSB.
Rockwool do firesafe insulation which is rigid & a good acoustic insulation.
This is how i did my last workshop & it worked very well.

 

[PowerTool]

Can't have had much headroom after a two foot screed - guess you really meant 2".. :wink:

Andrew

 

[Doug B]

Would have taken some troweling as well :shock:
Yes definitely 2 inch

 

[OllyK]

Vapour barrier wants to be on the warm side of the insulation not the cold BTW, so:

Exterior wall, Insulation, VB, T&G or Plasterboard

 

[Deejay]

Hello Richard

Have a look at this thread ...

https://www.ukworkshop.co.uk/forums/view ... hp?t=28009

I agree with Wizers comments about concrete floors.

If you want a wooden floor, you could seal the existing concrete and one metre up the walls with two or three coats of bitumastic paint.

Lay a damp proof membrane on the floor and build a frame of 3" x 2" on top of it. Fill the gaps between studs with something like Kingspan. For a workshop, WBP ply or even shuttering ply would be OK.

Cheers

Dave

 

[MikeG.]

Richard,
Then build stud walls of this screed, 1' off the existing walls. Vapour barrier the back of the stud walls, fill with insulation & then cover with either PB or OSB.

No, no no!!! Don't do this.......the vapour barrier MUST be on the warm side of the insulation. If you use OSB, by the way, it has such a resistance to the passage of vapour that you can dispense with a vapour barrier completely.

Richard,

you ask about using a paint as a tanking (damp-penetration barrier). This would be a very short term measure, and isn't really the right way forward. It would soon bubble off. I agree with the others who have suggested using a damp membrane above the slab, (a liquid might be effective.........."Black Jack"........) and then screeding over that.......

I am always cautious about laying battens or joists on a slab (leaves a great place for vermin and wet or dry rot to take hold).........and if you are going to do a floating floor I would recommend using a T&G ply (no square-edges anywhere within a floating floor!!) rather than chipboard.

Mike

 

[johnf]

Forget the stud walls and 2x2 battening .
celotex directly against the brickwork 8x4 sheets osb inside skin stagger joints with the celotex fix osb with long masonry screws easy :lol: :lol:

 

[rjb]

Forget the stud walls and 2x2 battening .
celotex directly against the brickwork 8x4 sheets osb inside skin stagger joints with the celotex fix osb with long masonry screws easy

Hi,

Thanks for all the helpful replies. I like the above idea as it sounds quick and easy compared to other methods. My only concern is whether condensation behind the insulation would be a problem if no air gapis left?

Thanks,

Richard.

 

[MikeG.]

My only concern is whether condensation behind the insulation would be a problem if no air gapis left?
Richard.

I wouldn't have thought that much moisture could get through those 2 layers of nearly impermeable materials.

My only cautionary note is that you should leave gaps around the OSB sheets (4 or 5 mm) , otherwise it will buckle all over the place.

Mike

 

[johnf]

Forget the stud walls and 2x2 battening .
celotex directly against the brickwork 8x4 sheets osb inside skin stagger joints with the celotex fix osb with long masonry screws easy :lol: :lol:

Hi Richard

This how I lined out my workshop 4 years ago I used 25 mm celotex 12mm OSB it is a realy great way to go.

No problems with buckling or condensation heat retension is good too the only limitation is the lenth of the masonry screw also minimum loss of space is good the 12mm osb is fine for fixings. I cut all the power cables into the celotex before boarding so no surface cables.

No gaps between osb close butt joints 2 coat of white emulsion and job done

this system has proved to be a complete sucess

 

[phil p]

Hi,

my garage is a similar size and I'm going to insulate it early next year when it starts getting a bit warmer.

What I was thinking of doing was glueing some Kingspan or something similar straight onto the wall then covering with some 9mm MDF or plywood.

2 questions though.

1) Would the Kingspan stick, using the correct adhesive of course but I'm still worried it wont stick properly as its a pre fabricated garage and the walls would become damp in winter or should I batten it?

2) Would the MDF or similar get a good fix to the Kingspan with screws and would it be strong enough to hold brackets for ladders, cramps etc?

Thanks for any advice

 

[MikeG.]

Hi,

my garage is a similar size and I'm going to insulate it early next year when it starts getting a bit warmer.

1) Would the Kingspan stick, using the correct adhesive of course but I'm still worried it wont stick properly as its a pre fabricated garage and the walls would become damp in winter or should I batten it?

2) Would the MDF or similar get a good fix to the Kingspan with screws and would it be strong enough to hold brackets for ladders, cramps etc?

Phil,

if you can afford the time and money, wouldn't it be better to do the job now and thus have the benefit of a useable workshop through the winter?

In answer to your questions:

1) If they can glue concrete balconies onto the outside of blocks of flats, there is a glue out there that will glue Kingspan to masonry. I don't know what to suggest, but I imagine some of the builder's gap filling adhesives such as Liquid Nails would do the job OK.

2) Don't line with MDF!!! I would suggest ply, ideally, or OSB (painted). But, no, screws don't work into Kingspan. You will regret trying this forever more!!!

Can't you get a fixing straight into the walls of the garage? If you can, you can screw straight through the OSB and the Kingspan into the wall, or you could batten out with 2x2's (screwed to the wall), insulation between, then fix your lining to the battens (at 600 centres).

If you can't get a fixing into the wall, then here is a cunning plan!

Using 2x2's, make a stud wall......ie sole and wall plate, studs at 600 centres......that is a very tight fit under the roof joists. Bash it into place about 10mm off the wall. At the moment, as a wall, this would be a bit too springy and flimsy.......then the cunning bit!

Spray a bead of expanding foam behind each stud. This will take all of the bounce out of the studs. Obviously, you will have fastened the two plates to the floor and the joists. Wait until the foam goes off, cut off the excess and press the insulation hard up to the wall. The very best way of insulating is to cut the sheets 10mm undersize all round, and using wedges to hold them temporarily, spray foam all around. Again, cut off the excess and screw your OSB or ply lining in place.

Just another tip.....space you studs very carefully to reduce cutting sheet material, and lay your sheets horizontally rather than vertically. Don't forget that most sheet products are sold in Imperial sizes.........don't do the studwork before you have bought your sheet material!!!

Don't forget to insulate your roof, and don't forget to allow airflow under the roofing.

Hope this helps......

Mike

 

[phil p]

Hi,

Mike, youre a star!!

Never even gave that a thought as I'm sure the walls with them being bolted together with 2 foot wide panels, does very slightly bend from about zero to an inch and a half or so from end to end (18 foot).

Ive used expanding foam a few times and know it sets quite solid and robust.

It's certainly food for thought, in fact it could be used in several applications for packing and giving extra support for certain things.

Many Thanks for the tip.