Wall insulation bodge required!

[Duncan Lees]

I'm in the process of buying a house which has a narrow kitchen extension built with just a single brick thick walls. Obviously I want to insulate the walls to make the place warmer in winter. Ideally, I'd want to use something like 50mm of Celotex, with dry lining fitted to wooden battens on top. Unfortunately I can't afford to loose anything like that much width along the extension. There's only around 64cm from the walls to the internal doorway, and I need to fit kitchen units and appliances along the walls. The units take 60cm depth, so I've only about 40mm of space before they project into the doorway.

So I require a bodge! My thinking is to strip the walls back to the brick, fit 25mm or so Celotex between some thin battens, and nail plywood or similar over the top. Then tile/paper directly to the plywood for the final finish. I know it's not pretty, but does this sound feasible at all? I'm after maximum insulation for minimum width.

Any helpful comments welcome :)

-Duncan

[Lee Blaver]

Subject to planning and appearance concerns, you could insulate the outside instead... Of course, it may not be cost-effective, or pretty if you don't like rendering ;)

Lee

[Duncan Lees]

I have considered exteral insulation, and the house is already rendered, so that's not a problem. But the extension has a pitched roof (the extension is effectively shared with the neighbours on one side of the terrance, with the apex of the roof along the property boundary), and I don't think there would be enough scope to extend it further down. It's already very low, and so would have to be even lower to accomodate the extra wall thickness. It's an internal bodge or nothing!

-Duncan

[Lee Blaver]

That sounds exactly like my brother-in-law's house, except that he has an ancient cast iron gas boiler in the kitchen which throws off enough heat to compensate for the lack of wall insulation...

Lee

[BigWallop]

If you can afford to loose around 24mm on the internal size, then why not fix two layers of normal 12mm plasterboard sheets. The thermal insulation of plasterboard alone should lift the atmosphere to a comfortable level. Screw fix the first layer, and then dob and stick the second layer on top.

[Duncan Lees]

According to the Celotex web site, plasterboard has pathetic thermal properties. They list 12.5mm 'Gypsum wallboard' has having an R-value of

0.08, while 12mm of their stuff is 0.50. Plasterboard would only offer a reasonable level of insulation with a full air gap behind, which I can't afford to have. IFAICS, I need to use the maximum thickness of top qual insulation, with the minimum of finish thickness on top that I can get away with. Would just using plywood on top of the insulation be okay in this application?

-Duncan

[Duncan Lees]

Perhaps I should just fit an argour (sp?) cooker instead? :)

-Duncan

[fred]

In article , Duncan Lees writes

Not a bodge at all, sounds like a fab idea. If your walls are anything like mine, the plaster will be an inch thick so you will lose very little width at all.

To save you any possible disappointment, I would recommend you use a heat loss calculator from one of the major radiator manufacturers' sites to assess the likely improvement. Say 3kW loss reduced to 1.5kW and it will be toasty, only down to

2.5kW & it's hardly worth the bother.

btw, I think inside is def the place to do it & celotex the best option.

HTH

[Duncan Lees]

Thanks for the advice. I'll do some sums and see what difference it will make. I'm pretty sure it'll be worth doing, but the thickness I'll have will only be half the 50mm a builder recommended to do the job properly... I'll use the full 50mm plus cavity on the end wall, as well as insulating the roof above. So overall I should be okay...

-Duncan

[Christian McArdle]

25mm of celotex and 9.5mm of plasterboard would provide a very worthwhile increase in insulation. The difference between a single skin wall and the proposed thickness of insulation is massive. Plasterboard is cheaper than plywood and paints better.

Personally, I would decide where the kitchen units are to be mounted and screw 25mm thick battens to the wall where the wall unit fixings are to be. Then insulate around them. Put the plasterboard over the top of all that and screw the wall units through the plasterboard into the battens. The plasterboard should be fairly strong in compression, squeezed between the units and the battens. Don't run the battens any longer than they need to be for structural reasons, as they provide less insulation than the celotex. Use lots of screws.

You could replace the plasterboard with plywood if you like the extra strength, but it is harder to decorate and not as fire safe.

Christian.

[The Natural Philosopher]

Don't Panic.

Remember that kichen units themselves have large pgaps at the bak, and a nice enclosed airspace.

This is what I'd do

mark out where units are going, and glue celotex slabs wherever there is room behind. OK appliances will have to go back against teh walls - but nothings perfect.

Then fit units and worktop. But NOT high level cupboards.

Batten out the walls 1.5" adding nice load bearing noggins wherever cupboards need to be screwed, and reqire using steel boxes where you want the leccy stuff to go, and stick celotex evereywhere, and then plasterboard/MDF or whatever. Mount cupboards on top of that once decoretaed and tile. OK you lose a little depth but...

Yes, exactly, but remember cupboards are a moveable feast, and provide SOME insulation, worktops and units are standard width BUT can be tapered back to clear dorrways etc, and provided you have about 900mm walkspace minimum you can operate effectively.

I battended out the wall about an inch in parts but still mounted the cupboards to the existing wall, and clad under them. Its unnoticeable without a measuring stick.

makes it easy to add sockets too,.

[The Natural Philosopher]

Totally agree. Over single skin brick (damn. Lost my building regs book) ISTR its about 10:1 thickness for thickness) I even had a noticeable effect using 3mm cork tiles on one single brick kitchen. 25-50mm celotex and single brick is up to full modern regs insulation.

Plywood is fine to skin, but why not use MDF? plasterboard ain't bad either. And its CHEEP.

[Duncan Lees]

Really, I only thought of using boarding instead of plasterboard simply because I could use the saved thickness for extra insulation. I could most likely use 30mm insulation plus 5mm plywood over 25mm insulation and ~10mm plasterboard. Perhaps I could compromise and fit the kitchen units right up to the insulation, and fit 9.5mm plasterboard around it afterwards? That way I'd only loose a bit of work surface and still get a nice finish. It doesn't matter what the finish looks like behind the washing machine, and it would still be insulated.

-Duncan

[Duncan Lees]

No reason really. To be honest I don't really know the different merits of MDF, plywood, chipboard, etc. Whatever does the job best really. I think plasterboard fitted around the units would fine, while keeping the insulation where possible. I don't want to create any condensation traps behind the units if I can avoid it. However, there is also another problem with the boiler also being on that wall. I think I'll just leave it where it is and build a frame around it and make it look like a cupboard. How much would it cost to have the boiler taken down and replaced anyhow? Probably not worth the effort if I can avoid it.

-Duncan

[Duncan Lees]

No reason really. To be honest I don't really know the different merit of MDF, plywood, chipboard, etc. Whatever does the job best really. I think plasterboard fitted around the units would fine, while keeping the insulation where possible. I don't want to create any condensation traps behind the units if I can avoid it. However, there is also another problem with the boiler also being on that wall. I think I'll just leave it where it is and build a frame around it and make it look like a cupboard. How much would it cost to have the boiler taken down and replaced anyhow? Probably not worth the effort if I can avoid it.

-Duncan

[Christian McArdle]

I've only ever seen 25mm insulation, not 30mm. Make sure you use Celotex or Kingspan, though, not polystyrene. Quite frankly, the difference between

25mm and 30mm isn't that important. The difference between 0mm and 5mm is much bigger!

and it would still be

I think I'd prefer having the plasterboard between the celotex and the appliances. Some appliances get rather hot and Celotex isn't that brilliant as a fire proofing material...

Christian.

[Christian McArdle]

What boiler is it? Some boilers can't be boxed in. Not without sufficient ventilation, anyway. If it is open flued, boxing it in will probably lead to death.

Christian.

[Duncan Lees]

They list quite a range on their web site for "Celotex tuff-R? Zero GA3000Z" - 12mm, then 20 to 90mm in 5mm steps. Getting a stockest might not be quite as straight forward... But yes, I think 25mm would be a good starting point, and if I can use anything more I will.

Good point. Perhaps some thin MDF behind the units where required, just in case.

-Duncan

[fred]

You have got this sussed haven't you ;-)

Only thing I would do differently is to go for 12mm ply, reckon 6mm is for Rolf Harris wobble boards & nowt else.

[Duncan Lees]

I'm not sure. I think it's a modern condenser. I'll have to wait a bit longer until I get the keys.

-Duncan