EPC and cavity wall insulation

[richbee]

I Haven't made much progress in the last year obviously!

I'm now thinking about avoiding cavity insulation altogether and just fitting insulated plasterboard inside the room - it's a pretty big room, so losing a few inches here and there won't make a huge difference. The end wall could stand 62.5mm board, but the window wall would be much easier with 37.5mm board to minimise problems with radiator /sockets etc. I know this doesn't meet building regs, but according to my heat loss calcs, the 37.5mm board would still reduce heat loss by 50%,so is definitely worth doing,and I'll do it myself.

- Any recommendations for tricks & tips - things to avoid?

I did this Richbee when we first bought this house and fully guttered it.

Reason being it was fully electricslly heated by the previous owners using panel heaters and the EPC said the annual running costs were £2500/annum, back in 2010!

Id have fitted central heating, given thats my game, but no gas in the street, and no existing pipework/rads so quite an expense. Gas company wanted £36k for laying a new main. SWMBO's fault wanting to buy the house in the first place.

Anyway, i used insulated plasterboard and 'dot and dabbed' it directly to the existing plaster wall finish, after scrapping all the existing paint off and PVA'ing the walls first. Its been there 13 years now and not a single 'dab' has come adrift. The difference its made is unreal. All uninsulated solid floors in the house and no damp anywhere.
As you are 'thickening' the walls as such with the additional covering you will find the electrical sockets will most likely not have enough 'length' in the existing wires to remain in the current location - as my cable all drop from the loft above, i simply moved my sockets up the walls a couple of inches to ensure the wires reached. You can get socket backboxes that are designed to sink into the plasterboard/poly, so it was a simple case of cutting the new hole a little above the old sockets and pulling the wire through into them. A crap explanation but really simple to do.
Give some though to window boards needing to be wider possibly, and the method to refix your skirting boards back on (if using screws they will need to be v long), i just used gripfix type stuff and braced them inplace till set.
Doorframes are interesting to work around. They will need the frame either 'widening' or you can just run the insulated sheets upto them, rebead, and lose the extra width as per photo below. I didnt fit architrave around frames afterwards and finished frames as per picture. Bit contemporary i suppose but i like it.
I did the same around my whole house, every external wall, inc Kitchen where i hung some tall wall units. Had to use some 150mm wall anchors to fix those due to the lack of strength of the poly backed board, also used twice as many, so give some thought to this sort of thing if hanging anything heavy on an insulated wall. Photos/pictures etc, not so essential to go to such extremes.
Didnt affect me as my house was fully gutted, but think about any existing carpets. You wont want those or grippers etc under the now thicker walls, else will be a pig to replace in the future.
Also ensure you have somewhere dry to store the boards, and store them flat - some of mine curled a little, which needed sorting when putting them up so best avoided, dont buy to far in advance like i did.
Get yourself a hesvy long straight edge to tap them all flat to each other as you work around the room.

Took me three months worth of weekends to do this work and reskim the lot afterwards, but id do it on any house i ever bought again, and once started it was actually quite intuative and good fun.

Thanks Resybaby,
That's really helpful.
Fortunately there are no doors in the walls in question, but will need the windows & sockets & curtain rails etc dealing with.
Floor wise, it's oak topped laminate - I'm perhaps being optimistic to think I can pick it all up & then refit afterwards, taking account of the reduced width. At least we've a few spare packs left, due to my hoarding instinct - they'll come in handy one day