Insullation on a single skin extension

[JGralton]

Hi all,

I have recently moved in to a house with a single skin extension. After a cold winter I want to add some insulation to the extension wall on the inside. After some research I decided to use a thermo board (e.g. Fermacall - other recommendation welcome). At first I was going to use a dot and dab technique to fix the boards to the walls, I then read that this might not be the best approach especially as I want to hang a radiator off the board and as I have not used dot and dab before it may be a little more difficult.

So now I am looking at putting a wood batten framework on the wall and attaching the thermo board to the battens. I have looked around but can't find the answer to the following questions. Any comment/help is much appreciated:

1. What size battens should I be using to fix the thermo board to?

1. Is it best to attach the battens to the wall with screws and how much longer should the screws be than the batten?

2. I plan on using a 30 or 40mm thermo board, how long should the nails be, which are used to attach the thermo board to the battens, or should I be using screws here?

1. I was to be able to decorate directly on to the thermo board without needing to skim any recommendations on a board manufacturer I should use? Or is this a bad idea and is there another type of board I should use and then plaster/skim?

Thank you very much,

Jimbo

[TMC]

If you are fixing battens to the outside wall then you would need a waterproof barrier between them and the single skin wall

The thickness of the battens may be determined by the type and thickness of insulation that you put between them but also by how much you are reducing the space in the room

When I have done this sort of job in the past I have done the following

Construct a 4 x 2 frame spaced off of the existing wall with a waterproof membrane on the existing wall side Insulate within the frame with rockwool or polystyrene and face with plasterboard

Not sure if it meets current standards however

Tony

[JGralton]

Hi Tony,

I wondered if I would need this. There is no barrier there at the moment at none that I am aware of yet we have had no problem with damp or anything. Will this become a problem when I add the insulation and that is why I will now need a waterproof membrane?

Well that is part of the problem I want to reduce the size of the room by as little as possible while still achieving the best insulation. That's way I was looking down the thermo board route. I wondered if 2x1 frame packed with rockwool and then 30mm thermo board would be ok. Would your suggestion offer the same insulation (need to reduce my gas bill - lol)

Do you have any idea on the length or screws/nails I should be using?

Cheers,

James

[TMC]

I guess that the wall has presently nothing on the inside of it i.e. is just bare brick or block

Any dampness penetrating the brickwork would dry out from the inside

If you were to seal this wall as you originally suggested then this damp would be trapped in the wall & penetrate the board and decorations

When cavity wall houses are built a lot of care should go into keeping the outer skin and inner wall as separate as possible e.g by avoiding mortar bridges on wall ties and having moisture/thermal barriers where there are windows and doors which bridge the cavity.

Where I have seen bungalows built with wood frame inner and blockwork outer walls they were insulated in the way I described

In terms of increasing insulation and reducing gas bills the thicker the better so a 2 inch wall with rockwool is better than nothing but a 4 inch wall is better that a 2 inch

As to nail length I would use 65mm galvanised nails as the next size down

50mm does not for me have enough into the batten, others may disagree

If you are going to fix 2 inch battens directly to the outer wall then I would use

[TMC]

Just picked up on your suggested batten size

I would not use 2x1 batten need to be at least 2x2 especially if as you suggested earlier you want to hang a radiator off of it

Tony

Tony

[Guy King]

The message from [e-mail] contains these words:

You might also consider adding cladding to the outside. uPVC cladding on cross-battens with rockwool behind would improve things quite a bit provided you make the framing so there's no howling gale round the back of it.

[The Natural Philosopher]

Agreed. My old place had a converted garage as a room..they used about

2x2 and rockwool over a plastic membrane. It was pretty warm and cosy.

Made rigging cable easy too. Holes and coathangers could thread most of what you wanted behind the plasterboard..

[Lobster]

I'm doing the same job at the moment, and using 2"x2" to make a stud frame 1" away from the brick wall; am putting 2" slabs of Kingspan solid foam board within the frame, then will cover the lot with insulation-backed plasterboard. Kingspan is much more efficient than Rockwool for a given thickness, and easier to position within studwork IMHO. Obtain cheap but perectly adequate 'seconds' quality from

David

[JGralton]

Thanks for everyones help here it is very much appreciated. A couple more questions:

How far in to the wall should I screw the 2x2 battens (i.e. how long should the nails be)

Also what is the reason for putting the battens an inch away from the wall?

Cheers,

James Lobster wrote:

[The Natural Philosopher]

As far as you can for good connections. I would screw rather thannail.

I assue we are talking dry lining rahther than exterior?

I suppose someone is worried about damp or condensation in the insulated wall rotting the studs.

Mostly I have seen a polythene layer applied to the bricks and the studs screwed straight through it. However this puts the vapour barrier at the cold side of the insulation.

The other way is to use a foil backed plasterboard and hope that the natural breathing of the bricks keeps the outer skin dry. The foil will prevent internal moisture causing condensation.

It pays to remember that although the regulations are very fine and if followed correctly lead to structures hat should last 200 years or more, much extension work should be considered as probably only in the range of 15-60 years. A little damp and rot will take that long to eat through a bit of timber.

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