Still confused about this insulation

Could some please confirm which of the following options i should do with my solid (brick, no cavity) external wall to give the best insulation and comforming to all building regs etc. i have read alot of topics but still seem like too many options.
i already have the following materials:-
25mm Celotex (1200x2400)
12.5mm Plasterboard (1200x2400)
Treated softwood baton (25x50mm)

option 1
fix baton straight onto wall at 400 centres
celotex between baton pieces
sheet of membrane
plasterboard

option 2
celotex straight onto wall (tape up the seems)
baton onto celotex at 400 centres
plasterboard onto baton

I assume option 2 is the best because it gives me a service cavity and should be better insulated because of celotex covering the whole wall as opposed to baton.

Where did you get the info' suggesting that 25mm celotex is thick enough to satisfy building reg's regarding a one brick thick wall?

60mm minimum would be closer.

I am not a trade professional person so this advice is just from my experience with my own work.

Option 2 is ok if the walls are straight and plum as the whole sheet of cleotex will be in contact with it, also doing this way you don’t have to cut up the cleotex into sections to fit in-between the studs.

If the wall is not straight then you can shim out the 25x50 to get it level and plum, but you have to then cut each piece of cleotex.

Hope this helps

It not a new build
the wall is two bricks thick (215mm) but with no cavity & the insulation was intended to go inbetween the baton hence 25mm thick. however i just would like to know which option is preferable and most efficent with the materials i already have. cheers

thanks paul,
unfortunately being a 1930's house the brickwork doesn't look as straight and plum as maybe it should be, so i guess im going with my original option 1 and shim out the baton to get it right.

unless there are any other suggestions

just had another thought.

option 3
baton the wall
celotex over the baton (not in between)
then plaster board.

Would this be advisable, providing i fix horizontal baton anywhere that i am going to hang kitchen units etc

jamriggsy said:

It not a new build
the wall is two bricks thick (215mm) but with no cavity & the insulation was intended to go inbetween the baton hence 25mm thick. however i just would like to know which option is preferable and most efficent with the materials i already have. cheers

Click to expand...

'One brick thick' refers to a wall that is 215mm or twin skin and no cavity. Similarly, a half brick thick wall refers to one built with a single leaf (105mm).

If you are going to go to the trouble of renovating, insulating etc, you may as well do it so that you will prevent condensation issues in the future.
I would suggest doubling up on the 25mm.
Fix 25mm battens to the wall. Fit insulation between AND across the battens. Tape all joints with foil tape on both layers, then plasterboard across the lot.

I might treble the celotex to 75mm or buy some EPS to augment the celotex. Why not go for 100mm in total?

Ok, thanks for that, it does sound like for a little extra cost it would be worth doubling up to 50mm.
one more thing though, would i just cut a section out of the insulation between the batons for wiring etc. thanks

Hi

Your not making any structural modifications so Building Regulations will not apply, however, as already mentioned 25mm is minimal, I would always recommend 50mm and this could be achieved by fixing battens to wall, infilling with 25mm insulation and then overcladding with 25mm insulation and finish off with plasterboard.

I am assuming that as this is a celotex insulation board that it is a PIR board in which case you could do without the vapour barrier.

With regard to energy efficiency, I have a general rule that each 25mm thickness of PIR insulation reduces thermal losses by approximately a half.

In your present situation the heat losses through the brickwork are around 2.1W/m2C therefore adding 25mm will reduce this to around 1.05W/m2C and adding the further 25mm will reduce to 0.5W/m2C.

The ideal thickness is 75 - 100mm which could be achieved by using 50 x 50 tanalised battens and infilling with 50mm between battens and 25 - 50mm over the face of the battens which would give a heat loss rate of around 0.25 - 0.18W/m2C.
In some respects it all depends on how deep your pockets are and the available room space you are prepared to loose.

Another action before you do anything else would be to work out the pay back time for each scenario, and if the pay back time is over say 15years then that option may not be worth bothering about!

I would finally mention that other forum members have used 25mm and have noticed the improvement it makes.

Regards