Ok, got that; not sure 80mm-ish of insulation would be worth the effort and expense. Oh well.
I’ve always considered the kitchen extension to be a flimsy (and therefore chilly) edifice; I’ve even thought of enclosing it entirely inside a new structure, with insulation of course. Have people done this…?
I had noticed that your ground floor extension was grossly increasing your form factor. Careful planning of extensions can minimise this and in some cases they can even improve it (such as filling in a void in the original structure).
If you want to enclose what you have then you need to do as I hinted earlier, build a new and fully insulated roof (maybe over the existing one, maybe a replacement) that overhangs the walls by enough to allow EWI into the soffit, thus giving continuity of insulation without any thermal breaks. The EWI needs to go down to the footings, so waterproof below the damp course and with adequate drainage. If your insulated footings go at least a metre down you could avoid insulating the floor, unless it is suspended. Most extensions have solid floors, so need excavating (
) and a new floor needs to be constructed with adequate insulation.
It is a major task for just one room as the effect on the rest of the house will be minimal unless the task is part of a greater plan.
Edit:
Is it single brick or cavity? From the photo it doesn’t look solid double brick.
If cavity, what is the state of wall insulation?
What insulation is there in your “new” roof?
What type of floor structure do you have?
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Thanks for that. *The kitchen extension is brick cavity-wall. *Recently filled with blown-in EPS (I’m about to do a few ‘after’ infra-red photos with the heat-camera) *the flat roof has a layer of mineral-fibre insulation, not thick, and also comprises a hefty Knauf board I had fitted internally, to help retain heat *floor is suspended-timber, with the usual airbricks (no underfloor insulation.)
Initial impressions are that your roof is the best bit, thermally speaking. It’s just not large enough to cover EWI. I can understand your reluctance to work on it again.
Provided your thermal survey is ok the walls are probably not your immediate priority either.
My guess is that airtightness and floor insulation are the priority areas.
Kitchens are notorious for air leakage as plumbers and electricians drill “ample” holes for their pipes and cables and never seal properly afterwards. It took me years to track down some of my leaks before I had access to thermal images. There are probably also leaks between walls and ceiling/floor, particularly if the walls are dry lined with plaster board.
What air leakiness terrors await under your kitchen units? I found sections of floorboards missing under mine. That also explained how mice were getting in!
Before spending too much effort on airtightness of the floor and floor/wall interface give some thought to how you will insulate under the floor. You don’t want to be destroying one to do the other. This is a summer job. Particularly if you enjoy salad. We spent a couple of months without a kitchen while sorting out ours.
If your subfloor is shallow you could follow the AECB recommendation and after water/air/radon proofing fill with insulation with a screed or board floating floor. Remember the insulation upstands around the floor.
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Great, thanks. At least I got one bit right then, basic draughtproofing - when we had a new kitchen fitted several years back (before I knew anything about airtightness etc), I carefully tracked down and mortared all the ‘ample’ pipe fittings you refer too.
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That looks good. I hope that you mortared both sides of the wall, so that there was no additional air movement introduced into the wall cavity.
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Another idea could be, replace existing staircase (embedded in the large external wall) with a free-standing cast-iron one, thus removing the embedded stairs and the awkward under-stairs cupboard; then do IWI on the resulting large uninterrupted wall surface, apart from the electrics services (in current under-stairs) which could instead be overlapped by a proportionally-small area of EWI ‘behind’/outside that bit of the wall.
If you were to move the stairs away from the outside wall I would also move as much wiring as possible away from it too. Your electrician can move anything after the meter.
Remember the overlap between IWI and EWI should be at least 1 metre in all directions or you will get thermal bridging.
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I’ve now put this idea to People Powered Retrofit, via their very-helpful enquiry/advice platform; however, they say they would not advise on an IWI job on any wall ‘inside’ of a cavity-wall-insulation job, because of the dew-point hazard (that @Frank_Reif has referred to); might this not be over-cautious? Surely a large proportion of the 20m+ UK houses are now cavity-insulated (like ours) and some of those will have meagre roof-overhangs (like ours) which would rule out effective thicknesses of EWI; these would therefore need IWI, would they not?
All IWI a subject to risks. Those risks can be managed. I’ve seen some projects where they’ve put 200mm of wood fibre, with a smart membrane, on a brick solid masonry wall, on the first storey, south-westerly face, with no overhangs (in London).
However, to do so, they used archimetric data such a flux monitors, local weather stations, to tune their modelling software, then use embedded monitors into the wall to verify the results after 7 years.
Whatever you do with IWI with cavity walls, it will be less risky than IWI solid wall projects. As the cavity should be a continuous drainage plane that eliminates any liquid water from wicking into the internal leaf of the building.
Air tightness reduces moisture transport to the briefly cool surfaces down to the low single digits.
Vapour pressure is easy to manage unless you go to very high levels of thermal resistance and in very cold climates. Your internal block leaf will accumulate a small amount of moisture over the winter months, but it is effective at storing, and redistributing, that moisture with an internal parge coat. The moisture content won’t remain high enough for long enough to be of a major concern in the vast majority of cases.
We obsess about vapour pressure and “breathability” when there are many more important concerns. This is true of many building professionals.
The answer to retrofitting at scale is a government backed scheme of deep outfitting our building stock, that will be in use for 3+ generations, which includes over roofing to create the overhangs necessary to provide the depth for EWI.
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Thank Frank, very useful. So our cavity, now stuffed with EPS beads, should still drain away most moisture before that would cause condensation problems at the inner leaf?
I would therefore still consider IWI; however if People Powered Retrofit do not wish to advise on it (for reasons of caution, perhaps), then I’m short of a suitably-qualified/experienced person. Would you be interested in having a look…? (Manchester city-centre area.)
I’ve studied this independently since it’s related to the mechanical design needed to decarbonise heat which is what I’m primarily interested in, so I’m not technically qualified. Im active in the forum to practice the Feynman technique more than anything.
To my knowledge, EPS beads are water tolerant and free draining. You would be able to check by surveying the moisture content of the internal block wall to see if regions of the wall have been compromised. Or remove an external brick and check the insulation itself and the environmental side of the internal block.
CWI does eliminate back ventilation, therefore the bricks will remain wetter for longer, which may result in additional/accelerated freeze thaw damage once extra thermal resistance is added internally.
Modern bricks are more resistant to freeze thaw damage and most climate zones in the UK are not very cold. Usually softer mortar mixes and methods of pointing allow for sufficient expansion of the brick face before failure.
I am not surprised this isn’t recommended, as there is no code to refer to to limit liabilities.
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Ok, thanks. (Feynman technique always a good thing!)
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Without knowing the expression I have certainly found that answering other people’s questions and delving into their issues has helped me more than asking things for myself.
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