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As part of my investigations into the Octopus heat pump deal, and having talked to them yesterday about their quote; they mentioned that we need a valid EPC for them to be able to claim the £7.5k grant - which is obviously quite important.
They also mentioned that if any loft or cavity wall insulation issues are recommended on the EPC, it has to be sorted out before the grant is allowed - which does make sense.

So I set about getting someone to come and provide an EPC. Not sure how, but a random pick from the government list replied in 5 minutes and was onsite at 5pm yesterday - EPC was in my inbox by 7:30pm!!!

I was concerned about the cavity wall part of things, as the 1980s extension bit has cavities which aren't insulated. I thought that retro-fill cavity wall insulation in general had been rather discredited, due to damp bridging, cold spots, settling etc. Especially if the wall receives 'lots of driving rain and heavy weather' which pretty much describes our situation perfectly!
I mentioned it to the inspector as he walked round, and he said he would only comment if it wasn't present, and could be an improvement - so I was fully expecting to be ringing cavity wall suppliers today to see what they have to say.
Much to my surprise, he didn't mention it at all, only mentioned the solid stone walls and the insulated cavities in the new extension from 2 years ago - result!

So I don't need to do anything from the heat pump perspective, but I am now thinking I should investigate if it is reasonable to get some of the 80s cavities filled - the 2 rooms, downstairswith suspended floors and an open fireplace (with chimney sheep fitted) are much colder than the rooms with solid walls. Brief reading suggests that closed cell expanding foam may be the best - unless damp gets into the wall, as it can rot the wall ties. Polystyrene balls can also do the same, and mineral fibre is very much frowned upon now....

Any suggestions?

Do you know what sort of wall ties you have in the 80's extension? When we renovated our current place, the external walls we took down had galvanised steel wire wall ties and cellulose CWI on the house, the attached garage had the same walls but no CWI. I found some wall ties had rotted through completely, some partially and some not at all, but there appeared to be no relationship to location. When we refaced the external wall sections (so we have the same bricks all round) along with any new/rebuilt walls stainless steel wall ties were used. We used a closed cell polyurethane injected CWI on all walls (celulose was removed) and have had no problems at all (but only been in 5 years). Our location in the Yorkshire dales means we do not suffer from strong driving rain (bing surrounded by a hillside on the rear and trees on the other 3 sides probably helps. My parents had injected polyurethane CWI put into their house i(built 1916) n the 1970's and had no problems with damp due to the CWI in nearly 50 years (wasps making a nest in the cavity yes) again location onTeeside meant quite sheltered.

When we bought our house the EPC said assumed cavity wall insulation, well they didn't look very hard, there wasn't any! I used an inspection camera from the loft.
We did have it done since using multi sized balls, that still leaves some gaps for any moisture to drain down.
The outside of the house is rendered and we're in south Devon. So can be a bit damp.
We have been very pleased with it. With this and replacing the old double glazed windows and adding an enclosed porch we gone from 16,000kWh for DHw/ heating to just under 8000 kWh .
We did this just before the grant came in for cavity wall.

Where we had vertical tiles on the outside of the house they weren't going to fill there, so I told them to drill the holes in the internal walls for access needed decorating any way.

richbee wrote: ↑Thu Oct 19, 2023 9:49 am As part of my investigations into the Octopus heat pump deal, and having talked to them yesterday about their quote; they mentioned that we need a valid EPC for them to be able to claim the £7.5k grant - which is obviously quite important.
They also mentioned that if any loft or cavity wall insulation issues are recommended on the EPC, it has to be sorted out before the grant is allowed - which does make sense.

So I set about getting someone to come and provide an EPC. Not sure how, but a random pick from the government list replied in 5 minutes and was onsite at 5pm yesterday - EPC was in my inbox by 7:30pm!!!

I was concerned about the cavity wall part of things, as the 1980s extension bit has cavities which aren't insulated. I thought that retro-fill cavity wall insulation in general had been rather discredited, due to damp bridging, cold spots, settling etc. Especially if the wall receives 'lots of driving rain and heavy weather' which pretty much describes our situation perfectly!
I mentioned it to the inspector as he walked round, and he said he would only comment if it wasn't present, and could be an improvement - so I was fully expecting to be ringing cavity wall suppliers today to see what they have to say.
Much to my surprise, he didn't mention it at all, only mentioned the solid stone walls and the insulated cavities in the new extension from 2 years ago - result!

So I don't need to do anything from the heat pump perspective, but I am now thinking I should investigate if it is reasonable to get some of the 80s cavities filled - the 2 rooms, downstairswith suspended floors and an open fireplace (with chimney sheep fitted) are much colder than the rooms with solid walls. Brief reading suggests that closed cell expanding foam may be the best - unless damp gets into the wall, as it can rot the wall ties. Polystyrene balls can also do the same, and mineral fibre is very much frowned upon now....

Any suggestions?

Geocell foam glass bubbles?

AGT wrote: ↑Thu Oct 19, 2023 9:04 pm

richbee wrote: ↑Thu Oct 19, 2023 9:49 am As part of my investigations into the Octopus heat pump deal, and having talked to them yesterday about their quote; they mentioned that we need a valid EPC for them to be able to claim the £7.5k grant - which is obviously quite important.
They also mentioned that if any loft or cavity wall insulation issues are recommended on the EPC, it has to be sorted out before the grant is allowed - which does make sense.

So I set about getting someone to come and provide an EPC. Not sure how, but a random pick from the government list replied in 5 minutes and was onsite at 5pm yesterday - EPC was in my inbox by 7:30pm!!!

I was concerned about the cavity wall part of things, as the 1980s extension bit has cavities which aren't insulated. I thought that retro-fill cavity wall insulation in general had been rather discredited, due to damp bridging, cold spots, settling etc. Especially if the wall receives 'lots of driving rain and heavy weather' which pretty much describes our situation perfectly!
I mentioned it to the inspector as he walked round, and he said he would only comment if it wasn't present, and could be an improvement - so I was fully expecting to be ringing cavity wall suppliers today to see what they have to say.
Much to my surprise, he didn't mention it at all, only mentioned the solid stone walls and the insulated cavities in the new extension from 2 years ago - result!

So I don't need to do anything from the heat pump perspective, but I am now thinking I should investigate if it is reasonable to get some of the 80s cavities filled - the 2 rooms, downstairswith suspended floors and an open fireplace (with chimney sheep fitted) are much colder than the rooms with solid walls. Brief reading suggests that closed cell expanding foam may be the best - unless damp gets into the wall, as it can rot the wall ties. Polystyrene balls can also do the same, and mineral fibre is very much frowned upon now....

Any suggestions?

Geocell foam glass bubbles?

I used vermiculite, air can gently pass through wicking away any moisture and it won't melt your internal wall electric cables which poly balls can do. After reading some horror stories on cavity wall foam insulation I don't have the bottle to touch it.

I had a look at geocell this morning, looks good. I did required walls with vermiculite.as I said last night. I don't remember geocell being about then. They'd have been a contender if I'd known.

The difference was instant. I also did recycled shredded newspaper blown into loft to top up existing insulation in inaccessible places. That was with a leaf blower and homemade hopper/hose extension. Messy but excellent

I used vermiculite too around the chmimney liners when we installed the stoves, I also used it when I found a space under the floor in the first floor that went all the way to the ground floor, poured bags of it in there.


I think I read about the Geocell on the green building forum a while back and kept it in mind as it doesn’t affect pvc cabling unlike EPS

I don’t have cavities but stone will lath and plaster with gaps so was thinking about this to fill that gap when the need for redecoration arises.

Thanks guys,

gives me some things to look at - the Geocell stuff looks interesting

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?

At the same time I'm planning to fit underfloor insulation, as it is the only suspended floor (1980 extension) and is the coldest end of the house by far - even compared to the 1830s 2ft stone walls & solid floors!

YouTube seems to be evenly divided between using pir boards resting on wooden strips, or lay breathable roof membrane over the joists and fit rolls of loft insulation in the spaces, then cover with dpm & relay the floor.
The pir will have better insulation properties, and maybe less faff to fit, apart from fitting the wooden strips, but the other method may be cheaper, and possibly more breathable around the joists?

- Any thoughts from you knowledgeable crowd?

richbee wrote: ↑Wed Oct 23, 2024 9:41 am 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.