Partial cavity wall insulation

garydufley

Hi all, I am a ftb (so new at this)

I have had an offer accepted on a property, however through (probably my own) bad planning I only got confirmation of the EPC a few hours before the property went to best and final and gave me a deadline

the EPC is lower than the EA expected, the details on it are partial fill cavity walls (assumed). after some time googling I’m now aware of what partial fill is along with some reason why it might be done. I think driving rain/weathering is the main reason along with potentially the physical width of the cavity

looking at the EPC for the rest of the houses in the road, most are assumed full cavity but there are some are assumed partial. there is a mix of 2/3 bed semi and terraced in the street so it could be the assumption is correct

after looking at CWI/EWI it seems to be a good idea in theory, but practice could be an entirely set of problems, depending on the cavity width may even rule it out as an option anyway

currently I’m trying to gauge how ‘bad’ only partial fill is in terms of energy efficiency and whether this should put me off, whether there is any scope to improve it in future (without causing more issues) or whether I am focussing on this far too much

I guess a bore scope would be the only way to get more information but I’m not sure what that information would signify even if I had the results

advice of more experienced people would be welcome

thsnks

ic

Might it be a partial CWI because of some walls being solid construction rather than cavity?  This was the case in my last house which was built 1897 - the walls facing the side and road were Accrington brick with a cavity, while the kitchen and bathroom at the rear were common brick and solid.  I eventually internally insulated the solid walls at the back of the house, and it made those rooms much warmer - more so than those that had CWI!  The brick bond and the thickness of the walls will give away whether there's a cavity or not.

Can you consider internally or externally insulating affected walls (admittedly without a survey hard to say).  Even without support schemes at the moment, insulation will quickly pay dividends given energy prices.

anselld

The EPC cannot be relied on at the best of times and these are assumed statements anyway so meaningless. 
If it matters to you and you want a definitive answer you will need to instruct a surveyor or expert to make a detailed inspection.

FreeBear

ic said:

Might it be a partial CWI because of some walls being solid construction rather than cavity?
...
Can you consider internally or externally insulating affected walls (admittedly without a survey hard to say).  Even without support schemes at the moment, insulation will quickly pay dividends given energy prices.

Also have a mix of construction here - A late 1920s semi with a ~50mm cavity on the ground floor, and solid brick on the upper half. Quite easy to spot of you a familiar with the construction method.

The corbelling at the junction between the red brick and render is a pretty good indicator of half & half cavity and solid. The section of wall between the upper & lower bay window is likely to be lath & plaster internally with lath & render externally. The gap is highly unlikely to be insulated, nor will the bit of roof over the bay. If I were to purchase this particular property, internal wall insulation would be number 1 on the list of things to do before moving in. 75mm Celotex/Kingspan on (most of) the exterior walls along with ~150mm around the bay - Done internally, the walls would be nice and flat for any wallpaper or paint. I'd also rip down the ceilings, pack the space between joists with fibreglass to kill any cold spots under the eaves. 25mm of Celotex/Kingspan wouldn't go amiss under the suspended timber floor at ground level (just need to be careful not to compromise ventilation).

Edit to add - Have (partial) cavity wall insulation, and to be honest, it has made zero difference to energy efficiency. Have completed wall insulation internally on one upstairs room, and that has made a big difference. Much easier to heat with a smaller radiator, and no more condensation on the walls !

garydufley

thats interesting thank you. I assumed that it just partial width sheet insulation bonded to the inside leaf as oppose to different walls. I guess it can be both

I've just done a little analysis on 20 or so EPCs on other houses on that road, EPCs in general seem to be inconsistent with the ratings. Presumable their weightings have changed over time but they dont seem to agree with themselves

I saw internal insulation mentioned when I was looking last night but I didnt really explore it. I think it would move any potential dew point out of the cavity which is good. and may be less involved than external. it could be an ideal option!    

FreeBear

garydufley said: I saw internal insulation mentioned when I was looking last night but I didnt really explore it. I think it would move any potential dew point out of the cavity which is good. and may be less involved than external. it could be an ideal option!    

External wall insulation requires moving of downpipes & foul water drainage from bathrooms/kitchens. The window sills need extending out, and detailing around the windows can be problematic - If you have bay windows, it can look piggin' ugly. Detailing around the roof line can also be an issue, particularly if you have a gable wall. On the plus side, you retain the thermal mass of the walls, so rooms take a while longer to cool down (but also take longer to heat up).

Insulating the walls internally means sacrificing a bit of floor space. Window boards need to be replaced/extended, but you have the opportunity to insulate around the reveals which cuts down on cold spots. Extending the insulation down into the void between ceiling & floor needs to be done to avoid cold spots in that area - There is a risk that moisture gets trapped around the end of the joists which might promote rot. Bathrooms & kitchens would need to be gutted which adds to the overall cost.. One big factor to consider - Hanging heavy objects on walls that have had IWI needs careful consideration. For kitchens, it is prudent to put good quality plywood on in place of plasterboard and use additional mechanical fixings through to the brickwork to secure the ply in place. No dot'n'dab unless you want any wall units falling down. Done right, the rooms will heat up quicker, but without the thermal mass of brick, they will also cool down marginally faster. But the heat requirement will be lower, so you can get away with a smaller radiator.

One final advantage of IWI - You can do it room by room, so can spread the cost and do it as part of a program of redecorating/refurbishment. EWI, on the other hand, needs to be done in one hit.

garydufley

FreeBear said:

garydufley said: I saw internal insulation mentioned when I was looking last night but I didnt really explore it. I think it would move any potential dew point out of the cavity which is good. and may be less involved than external. it could be an ideal option!    

External wall insulation requires moving of downpipes & foul water drainage from bathrooms/kitchens. The window sills need extending out, and detailing around the windows can be problematic - If you have bay windows, it can look piggin' ugly. Detailing around the roof line can also be an issue, particularly if you have a gable wall. On the plus side, you retain the thermal mass of the walls, so rooms take a while longer to cool down (but also take longer to heat up).

Insulating the walls internally means sacrificing a bit of floor space. Window boards need to be replaced/extended, but you have the opportunity to insulate around the reveals which cuts down on cold spots. Extending the insulation down into the void between ceiling & floor needs to be done to avoid cold spots in that area - There is a risk that moisture gets trapped around the end of the joists which might promote rot. Bathrooms & kitchens would need to be gutted which adds to the overall cost.. One big factor to consider - Hanging heavy objects on walls that have had IWI needs careful consideration. For kitchens, it is prudent to put good quality plywood on in place of plasterboard and use additional mechanical fixings through to the brickwork to secure the ply in place. No dot'n'dab unless you want any wall units falling down. Done right, the rooms will heat up quicker, but without the thermal mass of brick, they will also cool down marginally faster. But the heat requirement will be lower, so you can get away with a smaller radiator.

One final advantage of IWI - You can do it room by room, so can spread the cost and do it as part of a program of redecorating/refurbishment. EWI, on the other hand, needs to be done in one hit.

thanks for the explanation. its good to know that I would have options and room by room sounds more financially palatable. I only have one 'cat to swing' (to use the bizarre expression) so 100mm from each wall would not be the end of the world.... apart from it being an involved process

FreeBear

garydufley said:

FreeBear said:

garydufley said: I saw internal insulation mentioned when I was looking last night but I didnt really explore it. I think it would move any potential dew point out of the cavity which is good. and may be less involved than external. it could be an ideal option!    

External wall insulation requires moving of downpipes & foul water drainage from bathrooms/kitchens. The window sills need extending out, and detailing around the windows can be problematic - If you have bay windows, it can look piggin' ugly. Detailing around the roof line can also be an issue, particularly if you have a gable wall. On the plus side, you retain the thermal mass of the walls, so rooms take a while longer to cool down (but also take longer to heat up).

Insulating the walls internally means sacrificing a bit of floor space. Window boards need to be replaced/extended, but you have the opportunity to insulate around the reveals which cuts down on cold spots. Extending the insulation down into the void between ceiling & floor needs to be done to avoid cold spots in that area - There is a risk that moisture gets trapped around the end of the joists which might promote rot. Bathrooms & kitchens would need to be gutted which adds to the overall cost.. One big factor to consider - Hanging heavy objects on walls that have had IWI needs careful consideration. For kitchens, it is prudent to put good quality plywood on in place of plasterboard and use additional mechanical fixings through to the brickwork to secure the ply in place. No dot'n'dab unless you want any wall units falling down. Done right, the rooms will heat up quicker, but without the thermal mass of brick, they will also cool down marginally faster. But the heat requirement will be lower, so you can get away with a smaller radiator.

One final advantage of IWI - You can do it room by room, so can spread the cost and do it as part of a program of redecorating/refurbishment. EWI, on the other hand, needs to be done in one hit.

thanks for the explanation. its good to know that I would have options and room by room sounds more financially palatable. I only have one 'cat to swing' (to use the bizarre expression) so 100mm from each wall would not be the end of the world.... apart from it being an involved process

Don't forget that it is only the external walls that need insulating. And if you remove the plaster from those walls first, your total loss of space need not be excessive.

For example, when I remove the plaster from my walls, I gain ~20mm. Using an online u-value calculator, I only need ~65mm of Polyisocyanurate (Celotex/Kingspan type) to reach the minimum target u-value of 0.30W/m²K. Add another 15mm for plasterboard & skim, I've only lost 60mm of floor space. Actually going for 75mm of insulation, so loss of floor is up to ~70mm.

Already done one room (a small box room) with two external walls. The loss of space is not noticeable, and there is still room to swing the proverbial cat, dead or alive. Budgeting £1-1.5K per room to insulate, plaster, and fit new windows - Also adding extra sockets & moving radiators away from under the windows. Doing the bulk of the work myself is the only way to keep costs down and improve on overall savings.

garydufley

that is good value if you are doing it yourself. I never really understood why radiators got put under windows, I would have figured that probably the worst place even if you have A rated ones with carpet on them

thats also a good comment on making it effective, I'm sure the eventual energy saving could recover the cost but a project like that could spiral out of hand  

garydufley

Ive just found some info on age bands for EPC. I suspect (hope) that the actual algorithms are more complex but it suggests that houses built in the 80s are assumed partial fill, and houses built in the 90s are full fill

given that out of 27 EPCs that are in the register for that road, the fact that 3 are assumed partial and 24 are assumed full fill seems a little out of line with itself. 

drilling a whole is going to be the only way to save myself the what if mental anguish that Ive put myself through over the last couple of days

I had also found some reports that if modern carbon/graphite BPE beads are installed by a good installer than that does drastically reduce the possibility of future problems although there are a lot of assumptions about location/weather which make it still far from guaranteed

complicated this house stuff!

stuart45

Houses built in the 80's had higher U values than those built I the 90's. Either could be part of full fill as long as they met the target. Some.of the ones I worked on in the 80's had no insulation in the cavity, but wider AAC blocks on the inner skin.