Redbeard

Hi, Have you done a heat-loss calc? What's the worst-case scenario at 21 internally and say -5 externally (or whatever parameters you want to work to)? If less than 16 or 17kW then you are OK for a single-phase ASHP. You probably know you can keep the walls breathable and improve the insulation using rigid wood-fibre, cork or (with a rather worse lambda value) hemp/lime. However if you simply want exposed stone walls then you won't want to cover them with anything. Is the existing render lime or sand/cement based? If lime and not too cracked you could treat it as a parge (air-tightness) coat for wood-fibre.

Would this help? https://www.susdrain.org/resources/SuDS_Manual.html The original CIRIA document is of some age (I knew it in 2008) but there is ref to an update. Hope it helps. I agree re the 'drainage field' and foul, but is this perhaps whatever the 'modern' version of a leach-field is, after a sewage treatment plant?

If it is not for seriously long term, how about turning those studs into Larsen Trusses (spaced studs) and filling with 300 cheapest-you-can-get mineral wool? If you are just wanting it to last a year don't even worry too much about VCLs and so on. You will have to do something to isolate the insulation from the (damp) plinth walls, but I would suggest don't do it with polythene (risk of condensation on the cold side of the 'sandwich'). I would definitely do a floating floor (say T & G OSB on 50 PIR) but then that will be 'dead money' unless you can find a late phase of your build in which you can re-use the materials. Are you going to insulate the ceiling/roof? Maybe that could be spaced studs too. I don't think I would 'do' MVHR in this case unless I found a really really cheap unit.

It suggests that you can have a monopitch roof sloping 2.5-3m, but I would suggest a Planning app to get what you really want, if that does not fall under PD. I did that for my shed. Within 1m of the boundary, 3m @: eaves (and ridge height 4m). No problem (except the 8+ week wait for it to be transferred from the 'in' to the 'out' tray!).

Hi @richo106. You have not attached anything so we cannot see what you want your 'large glass front' to look like.

jimal1969: https://www.google.com/search?q=lulu+'shout'&oq=lulu+'shout'&aqs=chrome..69i57j0i22i30l9.6577j0j7&sourceid=chrome&ie=UTF-8#cobssid=s It was the w-ee-e-ll that did it. ''but surely if treated and untreated is the same price, treated would be a better bet??'' The feeling I have on timber treatment is that it contains stuff designed to kill things and if those things are very very unlikely to be there then it's a chemical I can keep out of the (or at least my, immediate) environment.

We-e-e-e-ll... (no, not Lulu, for those of a certain age) (explanation available on request)... OK, so pressure treatment is no longer CCA (Copper, Chrome and Arsenic) but whatever treatment is there may not be necessary in your circs. My general feeling is that if you are not exposing timber to potentially aggressive conditions you don't need to treat it against them. My timber-framed extension will have no treated timber in, and neither have a few extensions and TF buildings which I have helped build over the last 15 years. I would not buy treated for mine even if it were available at the same price.

Hmm... Strange. However: 10-12 years ago a fairly well-proven rule-of-thumb assumption was about 750kWh/kWp in propitious conditions. Again another rule of thumb is (was) that you could go to SW or SE with a loss of only 5-10%. Outputs per kWp of what we are getting now (I am not up to date, but 850 - 900kWh seems reasonably common) were not, AFAIK, around then. The sums work for me (within a few kWh) if I assume 240W per panel and a 5% drop-off from due S. As to whether the FIT £ is right for that size of array you could 'unwrap' that figure using RPI for each year going back. If I remember rightly the year 1 FIT was 41.3p, rising to 43 (?.3) in 2011.

Hi and welcome from another relative newbie. As intimated by @Mr Punter I would strongly suggest that you do a Whole House Plan (detailing your wishes, target U values, where the air-tightness layer will be, what it will be, *how* it will be) at the outset, even if you have to do a room at a time. I am 35 years into my 'incremental retrofit'! Doing the Whole House Plan allows you to identify the 'edges' - those perimeter bits which the next stage of work will need to connect to when you get round to it in however many years. There are some who believe that 'move out and rip out' is the only answer. If that were the case then 99% of my clients over the last 20 years would have done nothing. You do have to be careful not to leave gaps and potential 'moist edges', but with care (and documentation) it can be done. In particular note that the tighter you make it the less you can rely on 'unintentional ventilation', so design in your ventilation 'system' (even if it's not MVHR) sooner rather than later. Enjoy it; it's fun!

A common approach is to lay the VCL on top of the bottom OSB deck, before laying the insulation on. A not uncommon approach is not to be too careful where the long screws go, between top deck, bottom deck and (supposedly) into the joists/rafters, meaning that the 'sandwich' is mainly fixed between OSB and OSB, leaving it insufficiently fixed down. I suspect this is why the 'deck is pierced with nails in quite a number of places'. In the circs it may be that a retrofitted polythene VCL may not be fitted too 'tightly', and that in these circs the 'VCL paint' might be OK. I normally worry about having gypsum (which, in my view, 'sucks' moisture) in a 'sandwich', but in terms of 2 'evils' the VCL paint may be the lesser. It will also allow you to connect wall VCL with ceiling, which can be very tricky if the VCL is above the bottom deck.

When you say ' I was intentionally NOT insulating between the floors' I assume you mean 'the *walls* between the floors. If so this is what was done a long time ago, but is not common IWI practice now, which is to wrap the entire envelope (preferably externally but sometimes internally), including the interstices between floors. I am a retrofit practitioner, but I cannot claim to be a moisture expert. I defer to WUFI when I can (if I can find a practitioner to do the calcs (leads appreciated!). Have you got pics or diagrams of your situation and your proposals? What thickness of WF are you using? Rigid, hard-to-the-wall, or flexi between studs?

Can you maybe find a union which will fit in the tank tapping (assuming there is one) and then find an in-line tap?

Thanks @ProDave! I had not looked far. I think I just Googled 'Octopus Electricity Prices'. This is what Good Energy say re the Price Cap: Why are Good Energy exempt from the price cap? Good Energy was one of three suppliers granted a 'derogation', or exemption from the price cap, because we support renewables above and beyond other suppliers.

This is Good Energy, so outwith the cap, AIUI. Our current rate is 32.15 per kWh and has been for a while. It made us think of changing, so I (idly) looked at Octopus and found v similar rates.

My gas will be 10.87p/kWh on 1st July, and elec 40.7p/kWh, so I'd be looking for a CoP of 3.74 to break even. As I understand it that not an easy task on a 'slot straight in' replacement. Nothing really complex, but if you are looking to optimise CoP by keeping flow temp really low then you may (may not - it depends) have to replace some rads with larger ones (do you have enough wall?, is the Q in some rooms). 40-45 deg C is perhaps good territory for efficient running. Try turning your gas boiler temp down to 40 once the heating season is on us and see if it 'cuts the mustard'.

Is there a Defects Liability Period? (A Long Time Ago) I used to work for a Housing Ass'n. We had 6-mth periods for refurb and 12-months for new-build (with a retention). All the minor stuff such as nail-heads, beading cracks etc would be picked up at the Defects inspection and dealt with thereafter. Obviously anything serious or urgent would be dealt with as it was reported. At the end of the Defects period and after satisfactory resolution of any issues the retention would be released.

Have you tried Green Building Store? They do a mock sliding sash. I have used their windows as have a number of my clients and we've all been happy with them. Factory painted. Ours went in in 2014 and I don't envisage even considering putting a paint-brush to them for 4 years or so.

Take wall 1, for example. Draw a diagonal line from the words 'dining room' to outside, running between the EWI and the IWI. Although you have shown a (very) slight overlap between IWI and EWI what happens below 'main house floor level'? The EWI and IWI do little, as there is a path through from warm dining room to cold sub-floor void. Maybe take the IWI across the window so that you lengthen the path the heat has to take to escape. You very rarely 'get rid' of thermal bridges, but you can mitigate them.

Hi Well thought-out re the sub-joists for the UFI. Is the cross-ventilation really *excellent*? 'EWI' on wall 2 would work. Remember that any insulation on those walls wants to 'oversail' as much as possible to cloak 'diagonal thermal bridges', same as you'd do for IWI where the ext wall meets an internal or party wall. Haven't got time to look in further detail yet (particularly re junctions, weak-points etc.) but hope to comment later.

In your situation you have to consider the interstitial condensation risk, or at least consider whether there might be one. Adding another layer - in this case separated by a skin of brick - further cools the inside of the external skin. I am a great believer in dynamic condensation risk assessment. WUFI is the only one I am familiar with, but I gather there is another. The BS 'Glaser' Method is a bit of a blunt instrument and makes assumptions which are simply not always true (for example that all the moisture in a 'sandwich' will come from inside). Sadly I think, even now, there is a scarcity of WUFI-wranglers. Some merchants offer it 'free' for buying their materials. I have used the warm batten method a lot, and have 'championed' it (more that it's better than hiding vulnerable battens on the cold side than that it is the bee's knees, and always in the context that I am thoroughly 'sold' on rigid, dense, wood-fibre on the basis that if it functions without a VCL then there isn't a VCL to screw up myself or have subsequent 'generations' screw up for me), but I note now that the BEIS guidance for IWI effectively says 'vapour-open' (wood-fibre, cork, etc) or 'ventilated cavity. IIRC they say 25mm, which strikes me as too small, but that's gut-feeling, not physics. I also worry about 'real-life' situations actually giving you a properly-cross-ventilated, properly 'purged' cavity. Of your 2 possibilities gypliner (which I have never used, BTW) could give you the ventilated cavity.

@jc89, I could not get my head round 100mm of WF giving 0.247, as usually it gives somewhere around 0.3+ on a 225 brick wall. I realise that the figure for Intello seems wrong. The Pro Clima datasheet gives a lambda of 0.04, giving an R value for the 1mm thick sheet of 0.025, not 1.0 as per your U value calc. Think I have got that right....

Thanks! Only ever been a member of one forum before and that doesn't have a PM 'feature'!

@ProDave, can I send you a private message or e-mail? I have searched for how to do a PM but it refers to a drop-down menu which I cannot find.

It's hard to tell why that 'kick-up' occurred. I suspect it'll be fine in terms of being waterproof, but once being aware of it, it would annoy me. Pity the 'stack' (in terms of the lead visible on each side) is asymmetrical, too.

Hi ST. I have taught the Eco Refurbishment short course at CAT since 2008 and spent a lot of years teaching Walter Segal timber frame building, straw-bale building and self-build solar water-heating for a local council adult education dept. I teach for a number of other organisations too. The advent of Covid led to a lot of on-line teaching and a very aching neck!