Crofter

Hi and welcome to the forum. The building regulations don't specify a wall thickness per se, but they do require a certain insulation value (U Value). Different materials have better or worse insulating properties so the eventual thickness depends on what you use. Normally you would set a target U value and then work to that. Just to throw out a very rough number, I think you will find that you would need 150-200mm of insulation to get a low enough U value. Then you have your plasterboard etc on the inside, and whatever your finish is on the exterior. You will find a lot of people (especially on this forum anyway) will tend to specify more insulation than the building regs minimum. In my own house, I have aimed to put my money into the building fabric and then spend less on the heating system. This can be a good tradeoff as insulation is a one-off cost, unlike running your heating. Is your wall thickness constrained by budget or space?

Thinking about this some more. I have to have a horizontal run, both on my own house and if I were to fit something like this on the new house. As Steamy points out upthread, this means the water flowing only along the bottom of the pipe, so probably too little contact area for effective heat transfer. So... fit a simple filter and overflow arrangement. If everything is running clear, then the waste water goes down through the narrowest diameter copper pipe that will do the job (need to work that out of course)- or perhaps multiple pipes in parallel. These are overwrapped with microbore to form the HE. In the inevitable event of a blockage, there is a separate high level waste pipe which can just be normal plastic. Ideally you would have some sort of sensor (float switch?) to let you know when it was backing up, and that is your cue to clean the filter. Or just make the filter easily accessible and remember to check it.

Thanks for the details. I probably don't need to overthink this- the windows go up to within about 60mm of the soffet, which will be about 160mm past the cladding. So it's very hard to see how any water is going to get in from above.

For my own use, I would be looking to use the waste-warmed water right away at the shower, rather than storing it. Current setup is a TMS so I guess I would be feeding this into the cold side, at header tank pressure. However I really need to redesign the entire system and in the long term would be looking to feed at mains pressure into either an electric shower or an instantaneous water heater. Jeremy, what sort of input temperature can your Stiebel Eltron handle?

Thanks, it's all becoming a bit clearer now. Is this is sort of thing I need? https://www.roofingsuperstore.co.uk/product/rigid-eaves-protector-15m-packs-of-10.html And yes I guess the membrane has to go on top of it!

Ah OK. It's basically just a spacer, then? Sounds like you could take some chunks out of it without worry, IMHO.

Bit confused- is this joist at the same height as all the others? Are you saying that the wall it supports is basically putting a shear load on each end of the joist, so there is not the normal compression/tension loads on the upper/lower flanges?

How do you secure the membrane over the plastic guard- just nail through both layers? I think the purpose of the eaves guard is to keep the UV off the membrane at the very edge, where it is exposed. I'm planning a rather simpler design where the sarking board angle remains constant and overhangs the edge of the fascia, so the plastic strips would just be to add a UV layer. Would also help hide the cut edge of the OSB. Haven't considered how to deal with the edge of the box profile- I know you were asking about that very issue so I'll dig up tat thread again...

What about a check valve? That would eliminate the possibility of contaminating the whole mains system in the house, which I agree is a completely theoretical risk anyway. I'm not going to lose any sleep over how this would apply to a bath- I would estimate that less than 5% of our usage is baths, the rest is showers (each have maximum of one bath a month, compared to daily shower).

Thanks for the links, gents. These units all appear to assume a vertical waste pipe. In my house it would need to be horizontal- would this be a problem? I presume it would actually help with heat exchange as the waste water would be in contact with the pipe for longer, albeit only along the bottom.

In a rare idle moment, I was contemplating the torrents of hot water that disappear down the plughole whilst having a shower, and thinking what a huge waste that is. A quick google reveals that heat recovery systems are possible, but I didn't stumble across any off-the-shelf systems. One of these days I fancy building a system myself. Plenty of space under the suspended floor. My initial thoughts are to swap out a length of the 40mm plastic waste pipe for a compatible metal pipe, and then wrap microbore copper around the outside in a close spiral. Encase in insulation, and then feed the incoming cold water in at the low end of the microbore, and feed this in to the existing thermostatic shower. Potential complications: - how will my shower cope with the increased temperature of the cold water feed? - how long will the heat exchanger need to be to extract a useful amount of energy? - will it be practical to make a leak-free joint between plastic waste pipe and the metal section? I think it could work much better if I was able to do something more elaborate e.g. take the waste water and feed it into e.g. 28mm copper, overwrapped with microbore, which should make a much better heat exchanger. Perhaps two such HE in parallel, to ensure adequate flow rate. But I would see this getting blocked with hair etc very easily, and no doubt it would be a nightmare to find a way of connecting it to a 40mm waste... Curious to see if anybody else has given this some thought.

I assume the house has the original 1976 felt and tiles, and I assume that this is non breathing. No sign of any ventilation at all. The retrofit insulation was added before we bought the house, but the previous owners only used it as their holiday house so it was unoccupied much of the time. Once we moved in, we noticed how bad the problem was. I'm sure that if left unattended for too long there would be loads of mould and eventually rot in the roof timbers.

Blimey, how many different types of roofing membrane does the world need! Certainly plenty of competition in the marketplace. Might go with Cromar Vent 3 Pro as it looks nearly as good as the VP400 but significantly cheaper, and has a 4 month exposure rating which is as high as I can find from anybody. On a related note, it seems that I will need to fit eaves guards- guessing that these go between the membrane and the battens?

Breather membrane + no vents has got to be the way to go. It's what I would like to do on my house but I don't think the roof tiles would survive coming off and going back on again.

Our house has the exact problem Dave describes- retrofit loft insulation and masses of condensation. I've managed to pry open the skylight for now, before I did that you would have water streaming down the chimney breast, collecting on the rafters, etc. The medium term solution will be some air bricks in the gables, but in the long term we are converting the loft. The Rolls Royce option would be to strip the roof tiles, fit a breather membrane, and convert to warm roof. But a new roof covering would probably blow the budget completely.

That one may have been Metro Fixings. Tradefixdirect were also good. An additional complication for me is delivery costs- many suppliers offer apparently great prices until you get to the checkout and find they want £30 to send you a tenner's worth of penny washers...

Is this the one about the brickie who built himself a 180m2 house for £80k? One of his big tips was to shop around endlessly. I would agree with this- it is very easy to fall into the trap of just opening an account at your nearest BM and buying everything from the one place. You will pay dearly for the convenience. So far, the biggest price difference I have found was in my joist hangers- some cheeky eBay sellers are asking £15 each, and the going rate seems to be about £6; I got the exact same ones for £2.52 from a specialist online retailer.

Reminds me of this: https://what-if.xkcd.com/91/

That 2300km2 is conveniently just enough to cover all islands from Lewis/Harris (2200km2) down. Not many people appreciate that Lewis & Harris comprises the third biggest island in the British isles. Oh and don't get me started on the bridge

I'm looking up the BBA certs of different membranes. The VP400 is not cheap but so far it is clearly the toughest available. For the extra hundred quid or so it might well be worth going for it, as I don't know how long it will be exposed for. Building a roof entirely on your own takes quite a lot of time!!

No, not there- the sarking stops at the edge of walls, but when the roof covering goes on it will overhang a bit and I'll make up a barge board to support that. That's some way in the future, though. Thanks, I remember you had 11mm osb sarking so if it's good enough for you... I am considering gluing some strips of osb scrap onto the underside, just to bridge the gap between adjacent boards, and more than anything else to help prevent rainwater getting in through the 3mm gaps that I have dutifuly left between each board.

42 degree pitched roof, 6x2 rafters 3.8m long at 600 centres, and then boarded with 11mm OSB as sarking. The sarking is doing a good job of stiffening everything up, but should I install a dwang to support the edge of the sheet? I know that with 22mm timber sarking you obviously don't. It seems a bit weird to have an unsupported sheet edge, though. I don't want any movement across the join between sheets, in case that damages the membrane which is going on next. Just wondering if a dwang would normally be fitted, and if so can this just be a little bit of batten? Thanks

The thing is you are never going to have a 'normal' house off grid. You will have significantly higher outgoings due to battery replacement, diesel, and ongoing maintenance. Or you change your lifestyle to suit and give up the big TV and fridge. So 'worth it' is a tricky one because you can't just look at a cheap site with no access to mains electricity and add a lump sum to cover the off-grid system. IMHO the most promising off-grid system would be hydro, but you would be very lucky to have a resource available.

PV is the easy bit. Storage is where it gets expensive. You can run a backup generator and live with the fuel costs of course. £13k split between two houses isn't a show stopper- my connection was £2k for a single house and represents about 5% of my total budget.

Measure that 12v out, both under load and without any load, and maybe see how it behaves when the system is charging as well. But I would expect it to be much more stable than trying to get 12v direct from the battery.