Single-skin wall insulation - thick Celotex

[finster]

Hi all,

I'm currently converting my (attached) garage. My plan for the long external wall is: -

• 
  (Existing external single leaf brick wall)
  Breather membrane
  100mm Celotex (sealed to form vapour barrier)
  50mm tanalised softwood horizontal battens at top and bottom, plus vertical battens to coincide with each lining board joint

The total depth of the wall needs to be 150mm so that I can put some insulation over a brick pier in the middle of the wall.

My issue is how the battens should be attached to the wall - I would require extremely long fixings.

My only other thought is to create a stud wall instead of the battens.

Does anybody have any other suggestions of how its usually done?

Thanks.

 

[ColJack]

stud wall is the way to go.. means you can fill between the studs and perhaps leave an air gap behind the insulation..

 

[freddiemercurystwin]

You could follow this thread: //www.diynot.com/forums/viewtopic.php?t=233260

We wait with baited breath for Olduns magic revelation tomorrow!

 

[finster]

You could follow this thread: //www.diynot.com/forums/viewtopic.php?t=233260

We wait with baited breath for Olduns magic revelation tomorrow!

Thanks, that's interesting, I hadn't seen that thread.

stud wall is the way to go.. means you can fill between the studs and perhaps leave an air gap behind the insulation..

Thanks, looking at the Celotex website I think the idea is not to have an air gap so that air can't circulate back there (but I'm no expert!).

The only problem I can think of with the shallow stud wall is that to fix the sole plate to the concrete floor, I'd have to puncture the DPM which my BCO didn't seem too keen on. Is this usually the way to do it?

Thanks.

 

[freddiemercurystwin]

I really don't know what all the fuss about is, this is some official blurb from Kingspan http://www.insulation.kingspan.com/uk/pdf/refurb_booklet_2009.pdf page 15 or 16. I've used this spec in plenty of garage conversions and it gets approved every time.

 

[finster]

I really don't know what all the fuss about is, this is some official blurb from Kingspan http://www.insulation.kingspan.com/uk/pdf/refurb_booklet_2009.pdf page 15 or 16. I've used this spec in plenty of garage conversions and it gets approved every time.

Thanks, yeah, I agree - the Celotex, Kingspan and Xtratherm websites all seem to say something slightly different though - here's an extract from the Celotex PDF: -

* Ensure that existing walls are permeable. Strip any gloss paint or vinyl wallpaper.
* Install a breather membrane where brickwork is only 103mm.
* Use the Celotex Insulation Saw to cut the 1200mm x 2400mm Celotex GA4000 boards to it the loor-to-ceiling height of the room.
* For optimum thermal performance, the unprinted foil surface should face the batten cavity.
* Fix horizontal battens over the insulation at the top and bottom of the wall to hold the boards in place.
* Seal all board joints to create a vapour control layer ( VCL) using the Celotex Insulation Tape.
* Add further vertical battens over the insulation at appropriate spacing to provide adequate fixings for the selected lining system. Ensure that a batten coincides with each lining board joint.
* Apply an appropriate sealant around the perimeter of the insulation to provide a vapour seal.
* Additional battens are required around all openings to provide fixings for linings and grounds for skirtings etc. Battens should be minimum 50mm x 25mm treated softwood.
* The batten depth must be increased to take account of the conduit, if cabling is to be located within the cavity created by the battens.
* Use independent horizontal battens for heavy wallmounted components. Longer fixings may be necessary to it heavy items to the masonry, independently of the battens.

This seems to suggest that I need the breather membrane with no cavity...

 

[theoldun]

Sorry, taken so long to answer your question.

What we call fir band is galvanised fixing band, 1mm thick by 20mm wide by 10m long pre drilled for nail and screw fixings over the whole 10m length. We use a lot of it for strapping and tying together different components. Goggle galvanized fixing band.
It would appear that you have done a fair bit of reading on the bringing up to current U value standards of a single half brick wall. Will try to give you more information.
Celotex used to specify 25x50 battens fixed to the wall, then celotx then 12.5mm plasterboard, however if using 55mm celotex this would only have given a R value of 2.884 and a U value of 0.35 Now if you are fixing 55mm celotex, 12.5 plasterboard and you require a fixing depth of 20mm into the timber grounds, this gives a length of screw required of 87mm. Problem is that there are no course thread gyproc screws available between 75mm and 100mm. To overcome this you have to increase your batten size to either 38x50 or 50x50mm, which is not a major problem.
As the celotex print out in the post in Building Regulations, Celotex have changed their system. Now you temporary fix the 55mm celotex to existing wall and hold it permanently in place with horizontal 25x50mm batten top and bottom with vertical studs at 600mm centres, centre horizontal stud, and additional studs for skirting and any fixings that you may require. You then fix your 12.5mm plasterboard to the studs.
This then gives you a 25mm low emissivity cavity between plasterboard and celotex to increase the R value to 3.549 and the U value to 0.29 Two disadvantages to this system. All half brick walls to garages have either one or two number one brick piers to the long wall, so you have the hassle of forming the insulation and plasterboard round these piers, plus if the existing wall is out of plumb, cupped or bowed, then your insulation and plasterboard will be the same shape.
We did state in our other post to use 47x125 to make up studwork, but after doing some calculations we suggest using 47x150, to give a clear 50mm cavity between 100mm celotex and external half brick wall. According to our calculations this should give a R value of 4.48 and a U value of 0.22, how ever running it through celotex software they give a R value of 4.16 and a U value of 0.24, but this is on a combined method whereas ours is on a elemental method.
Where your plasterboard runs over piers, place 50mm celotex in the cavity between brickwork and plasterboard and this will give you a R value of 2.44 and a U value of 0.41, however running it through celotex calculator they give a R value of 2.668 and a U value of 0.37.
Cost wise doing it the celotex way, using figures that you should be able to buy 55mm celotex and 50x50mm battens, will cost you approx £10.90 metre square.
Doing it our way with 100mm celotex and 47x150 studwork will cost you approx £20.97, metre square.
On average the back and side wall of a garage is approximately 21ms, so our way material wise will be £210.00 dearer, but it will only take half the time to erect.
Plus if you took the payback on energy prices over a ten year period, you only have to save £21.00 a year to break even.
Sorry post is so long, hope it is of use to you.
oldun

 

[aarondown]

Oldun,

Your advice is very detailed and you seem like a font of knowledge, so.....

I am insulating an existing single brick double garage to form a workshop, by building a partition half way along the length of the garage and dry-lining the existing walls. the plan is to use a breather membrane, Celotex 55mm, 25x50mm battens, then plasterboard. I am also insulating the existing concrete floor with 1200ga DPM, 65mm celotex then OSB boards that I already have. A few queries if you have a minute to spare:

Can you suggest a breather membrane and maybe a website to get it from?

How should the breather membrane be fixed to the wall?

I understand that the celotex is fixed to the wall by a top and bottom batten which can be drilled, the board removed, the wall plugged and then the board and battens replaced and screw fixed. However, once these boards are fixed like this, how do I secure the vertical battens and horizontal noggins?

Should the floor build-up run to the external wall and then the wall build-up sit on top of this or vice-versa?

Final one, what is the fixing band in reference to?

Many thanks for any help you can provide.