Redbeard

I would have said mortar, had I not assumed that you were looking for a very quick fix.

I take your point, but if you look at it in the context of a whole-house plan enacted over a very long period (possibly finished by the person(s) after you), there's still logic in getting the best you can from each element that you do 'enact'. I fully expect my refurbishment to be finished sometime after I am dead! Depending on how much work you are doing yourself the actual 'spend' could be as little as the cost of an extra 50mm. Agree also with 50, not 25mm upstand at perimeter.

You are asking for comments on the TF, but may I ask about the floor? What U value do you get with 100mm PIR? Could you fit 150 in (or even greater thickness and use graphite EPS instead of PIR)? Will you have under-floor heating? If so others will be along to highlight the greater delta T (and therefore the justification for more insulation).

Epoxy, or CT1, which my former colleague claims will stick more-or-less anything to anything! I don't know anything about Soudal Plasterboard Adhesive but wonder if an adhesive made for a dry indoor environment would do well in a wet outside one... (Happy to be proved too sceptical)

Agree with the comments above. I am sure there's more to the process so far than I read, but it sounds like *you* have come up with a compromise so that *they* can get PP. Not sure where the 'balance of power' is there, and agree with others that you should at least look at the issue of future sale now, before development, whatever the 'inducements', even if your ultimate conclusion that it will sell with no probs. It sound like not a fun position to be in - literally - and I wish you luck with the outcome.

The plastic is a Vapour control layer (VCL) which is designed to stop 'interstitial condensation (water vapour condensing out in the insulated wall 'sandwich). Unless you are planning to change completely the 'moisture behaviour' of your Mum's house no, you do not necessarily need to remove it, but if you are adding more insulation internally you might, as you would then install a VCL on the 'warm side' (just behind the plasterboard) of that new insulation. Edit: Was typing while @Crofter typed.

PIV = Positive Input Ventilation, as described by Andehh

ST = Buildhub member @SteamyTea dMVHR. Decentralised mechanical ventilation with heat recovery. Decentralised because he's not talking about 'full monty' MVHR systems which have a central heat exchange unit. dMEV (decentralised mechanical extract ventilation) involves using specifically-designed fans in wet areas (bathrooms and kitchens) which run permanently at very low wattage (perhaps less than 2 Watts). They also have an over-ride (pull-cord or - my preference - humidistat) which kicks the fan in when things get too steamy. They rely on having open vents (often 'trickle vents in the window frames) in all the 'dry' rooms, so that the extract from the wet rooms causes supply air (from outside and usually more dry) to flow in. It's very simple with no complicated 'control interfaces. CV2 is simply the model number of the 'Greenwood (manufacturer) Unity dMEV fans I have bought.

Agree with ST's dMVHR suggestion, but if you want to go a bit cheaper and forego the HR, decentralised mechanical extract ventilation (dMEV) may be an idea. Some have spoken of it highly on here and I have 3 Greenwood Unity CV2 units waiting to go in.

Some would say not. Like base-rails for EWI, some like a 'proper base'. If your upper layer is to oversail the brick slips it will still need a drip at least, to reduce the risk of the worst-case scenario which is water tracking back into the junction of the 2 layers.

I realise these 2 are not using GSHP, but I was answering your 1st post, not your 2nd. Both these use(d) solar thermal. Simple trickle at CAT and, I think, evac tubes in Tony's House. I think he is a member here so he might pop in to the discussion.

Tony Cowling also has ISHS, I think. He described it in a recent AECB webinar. http://tonyshouse.readinguk.org/

Centre for Alternative Technology in Machynlleth did. The basis was experimental (and cheap, I guess!), so it (water-trickle solar roof over black-painted crinkly tin feeding a 100,000 litre - IIRC -thermal store which ultimately leaked) proved the concept very well. The store was a big hole lined with huge EPS blocks and lined with pond-liner. I believe the issue was that the liner used to extrude into gaps between blocks and pop! I believe the short-lived Earth Centre at Conisborough had an inter-seasonal heat store too, but I am not sure how well that worked.

1930s house: some render cracking may (or may not) be indicative of wall-tie failure/degeneration. Lots of firms out there, but does anyone have any recommendations from real-life experience in this (S. Yorks/N. Derbyshire) area? In the past I'd have done it myself but not feasible now. Thanks in anticipation.

There's a great difference between using a bit of air-tight foam for specific purposes such as air-tightness round windows and joist ends and foaming up a whole roof. I think it's the latter application that upsets Bldg Soc's rather than the very reasonable use of small amounts for small applications (though I could be wrong and they may be more twitchy than I thought!)

I had originally taken that as 'walls with a 4" cavity'. I suppose it could also mean ' 2 skins of 4(and a bit?) inch brickwork, with a cavity (width unspecified)'. What age is the house? I don't *think* I have ever come across a 4" unfilled cavity. They tend to be around 2" or even less. (I accept that anomalies exist. If you do have a 4" cavity then with graphite EPS bonded beads blown in you could possibly achieve a U value (unadjusted for (e.g) bridging at cavity closures etc.) of under 0.27W/m2K, which is none too shabby.

Hello! Can we assume that the exg masonry is rendered?

Hmm. Exactly what I was going to ask. I have used it a lot, but always hidden, so I have never tried to paint it. Anyone tried painting Orcon F?

Ventilation... 'Breathing Wall'

As @joe90 says, what you do may depend on whether the mechanism extends down that far and is fixed to that part. If it is not, how about trying to get hold of some 'plastic lumber' (think some park bench seats) and scarfing that in? Wood-rot problem gone, and I for one will probably be dead before the 'plastic weevils' (take that either way) have done their stufff.

I like to use rigid wood-fibre on a lime parge (air-tightness) coat. It's fairly DIY if you are quite handy and good at attention to detail.

Vermiculite boards. Do you live in an urban area? Do you have to travel a long way before you see any neighbouring properties? Do your neighbours have wood-burning stoves which make you cough on winter nights?

Can I ask what the pic above shows? Is it the PIR between the rafters, with tape entirely covering the rafters? I did 20-25 Victorian attic re-fits over the years and they followed a similar pattern: Fit insulation between rafters. BEIS Best Practice now suggests 50mm vent gap as compared to typical 25mm hitherto. So for typical 75mm rafters, 25mm PIR between rafters. Rafters carefully marked at top and bottom. Offer up 1200 x 2400 x 100mm PIR boards and fix temporarily - 3 or 4 fixings max - with long screws using a piece of slate lath as a 'washer'. Tape all joints and perimeters as VCL or, if desired, add a sheet VCL. Then offer up and fit 25 x 50 slate lath (that's what I used). You could take the view that a hole with a screw in it is not a hole at all, or take the more pessimistic view and pre-drill holes and 'gun' with silicone to form a 'grommet'. Then I would add 25 PIR between the battens if I did not want a service void. If I did, perhaps 25 PIR and a 25mm void would work. (??) No time for pics tonight but I will try to find some tomorrow and post them up. I rather more favour wood-fibre now if headroom allows. (It wouldn't have done in most Victorian attics I did). I'll post pics of that too.

I have not llooked at the price for vacuum panels (Optim-R) for a long time, and I had to remind myself re the thermal conductivity too. Kingspan say: ''OPTIM-R is an optimum performance rigid vacuum insulation panel (VIP) with a declared thermal conductivity of just 0.007 W/mK,'' If you really mean 40mm of VIP (not a composite board made of, say floorboard with VIP attached) then that would give you an R value of 5.7m2K/W, good enough for a U value of 0.175W/m2K even without adding in the 'base case' R value. That's not too shoddy! Compares with an R value of 1.81m2K/W for PIR at 40mm (U = 0.55W/m2K). IIRC re the price, though, you may need a mortgage - and (in ignorance of the specifics) I imagine you'd need some sort of (less insulative - wooden?) frame to sit them in. They also cannot be fixed through, or they become NIPs instead of VIPs.

Point tooken, to a degree, but water vapour permeability is often talked of as 'breathability', so the lay-up I described has 2 a/t layers and a 'breathable' construction (Brick/lime/WF/lime). Unless there is an inherent damp issue then in this example I don't feel I'd be risking trapping any moisture (but also I acknowledge myriad ways of cat-skinning!).