Redbeard

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!

@ProDave, I am buying my WF from Ty Mawr lime, but propose to buy Baumit MC55 from my usual supplier. I have signed up for Baumit's installer training at the start of June.

Thanks Dave. I had better expand on this on your thread, I guess, but I will be using Baumit render. I have used Baumit plasters and renders very successfully in the past and like the 'feel' of them. Your experience did take me round a 'loop' (via graphite EPS) until I decided that I really did want to use WF and renders I am familiar with. I will discover whether I can hold a trowel with my fingers crossed.

Been reading the Forum for relaxation for a while but had not joined. Recently stopped hands-on Green Building but 130m2 wood-fibre EWI, new 3G windows and small timber-framed extension to do on my own house this summer. Caught out, as many have been, by long lead-times from quote to delivery, but even more so (and less expected) by long gaps between enquiries and quotes. When not doing this I do retrofit surveys and teach Eco Refurbishment.