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Thanks both of you for the info and advice.

So what are you experiencing? As I said they are flow killers on gravity systems but on normal mains pressure systems they are pretty insignificant

+1 to both through the roof - that's clearly going to be the easiest. They should both go through the same surface so that both intake and exhaust are subject to roughly the same wind pressures, which then keeps the airflow through the machine more-or-less in balance at all times. Intake & extract are generally recommended at least 1.5m apart from each other, but most important is that the intake must be well away from chimneys and vent pipes.

Do both through the roof, do both on the same roof plain with suitable seperation. No need to go through wall.

Hi @-rick-, no, you're not missing anything and I did go down the attic truss route early on. I only found one supplier who could produce something similar with pre-made dormer panels and it ended up at pretty much the same cost once crane and more labour had been factored in, plus put all the risk on me for measurements etc. I think the span (nearly 9m) was the difference maker. The other thing was I wasn't planning to strip the roof out in the way I did. It doesn't actually make much of a difference in hindsight, but when I was planning it, I intended to keep the original tiles on the front for much longer to allow me to get the dormer finished first and then tackle the front. It's probably a mindset thing - if I did it again, I'd have more confidence to go bigger and bolder from the start.

Hi, and thanks for the reply. There is no radon. Or at least that's what the survey and radon map showed. There's also no road fumes etc due to us living on farm land. And I was only thinking of using the void for either fresh air or exhaust. Not both. However, with all that said, by the sounds of it then it's not a good idea either way even if everything is perfect under the floor. I'll just use the duct holes I left in the floor to vent up in to the loft and out from there. Looks like I'm going to have to do some drilling. Roof: Would it be better to draw fresh air through a roof vent then extract through the wall? Or draw fresh from the wall and vent out the roof? Cheers again.

About 14, 15mm or so from memory. Glued in place on concrete screed. Have the same stuff in living room, hall and office. The rug is a woven one, so quite thin

Very bad if the air contains Radon. Otherwise just really bad - air may well be humid with the potential for other contamination depending on location - road fumes, for example. Really because it will raise humidity levels below the floor in general and, in winter, increase condensation in the void. While the floor may have ventilators, the air will often be pretty static, so if you're extracting and exhausing into the same void, that's going to lead to a build-up of moisture and cross-contamination of the supply with the exhaust air. The whole idea is no doubt against Builing Regs too. Through the roof, if you have one. If not, the only sensible option is to drill the stone or concrete. Mine were core-drilled through 450mm of stone & brick within around 25mm of the targeted break-through points, with the crew suspended on abseiling ropes.

🤣🤣🤣 you do realise you put the joists on as you build the wall up not leave pockets out for them. Then you use the joists as a platform to keep building up. Yeh it would just be a right pita to cut and fit pozis to size between ledger plates. They are about 70mm thick for a start. Then your relying and having to install a lot of fixings whereas you just rely on gravity with built in method and the odd wall restraint strap.

Edit: the floor is egger advanced peel clean. See photo

Really? I don't have experience of either method, but leaving all those holes looks a lot more difficult to me, especially when you consider the depth of the holes will need to be more than the height of a block. & with the ledgers, you're not restricted to setting them only at the height of the top of one of the courses of blocks - you can position them where you want to to give floor to ceiling heights that suit both ground floor & first floor. Given the lack of competence of the builder I sacked, if the next guy manages to get my walls to within 10mm of being parallel, I will be celebrating. Aren't the posi joists designed to be trimmed at the ends? Ordering with 20mm or so additional length may be a good odea. If a posi joist ends up being 10mm too short then I suppose a big plywood shim would be an easy fix.

If your plumber can do the install (with some help from you?) for less than about £5000 labour only, then I would think that using the umbrella scheme would be the cheapest (and possibly best) option. The one I used was happy to come to North Somerset, and reccomends Panasonic HPs, which seem to be well regarded.

Hi Yep I'm talking about MVHR. The idea behind using the under floor (or roof) is so I don't have to core drill through 3 feet of stone wall for the incoming vent, and 1 foot of concrete wall for the extraction vent. Cheers.

Are you on metered FIT export payments or deemed? An AC coupled battery won't upset deemed payments but likely will if youre getting metered FIT payments

15kwh battery is unlikely to power an all electric house for a day if that's what your after. We're almost all electric with a lodger in a separate flat and a single 16kwh battery with 91% depth of discharge is flat by tea time now the ASHP is running. Just added a second battery to see us through the winter on cheap TOU tariff 2x Fogstar 16 kwh batteries is £3600 plus Solis 5kw inverter at around £700 gives £4300 for a 32kwh set up.

Thanks for the advice…. Plenty to think about. I’m trying to work out the floor build up. I have posi joists with 22mm eggar protect flooring. For a tiled finish I’m wondering if I should tank the floor with anything, lay tile backer or something like ditra to decouple. Feels like a bit of a minefield so another steep learning curve 👍

If you plan for 2 cat5 cables that should be enough for almost anything you plan. But if you are putting in ducting then the cost of the ducting is miniscule compared to digging the trench so I would always put something bigger in just in case. 50mm ducting is pretty standard IIRC. If running on a surface then normal 25mm conduit should be ok. Worst happens it's easy to add another, but digging a trench, do it once and hope you never touch it again.

Only going from what I've read here do check the FIT regs. You should be able to do what you want but you might have to follow some registration process or ensure things are done a certain way. Can't say more than that as not an area I know that much about.

Very interesting project, but one question stands out to me: Given you have virtually stripped the whole roof and rebuilt it, why not just take the whole thing off and put new trusses on? Yes that would need a crane and maybe extra help to get them on the roof but seems like it would likely be a lot cheaper and quicker than doing it the way you have. Am I missing something?

I think i would want a pv diverter to tell pv to charge up the water tank. How big of a cable and duct is this going to require? Am I setting myself up for problems? I am also considering extending the garage so it adjoins the house. I suppose no duct needed then can just take the cable thru

It was @JohnMo

Yeh i meant to say "crack just anywhere"

Not at all. Never in the house, and only if standing on top of it in the garden, and then it's pretty quiet.

with the eps suspended floor systems the slab kind of has to act as a raft on top of the eps. It can't just crack anywhere You did say that was the floor consruction and I forgot. Yes that makes sense. You mean eps blocks spanning between beams? For the pedantic record, it will still crack, but in millions of almost invisible cracks instead of a few big ones. The mix must be exactly as specified, so leave it to them at the plant... Never, ever, ever allow anyone to add water on site. In fact instruct the contractor and also the driver not to accept any request to do it as you weaken it and have lost all guarantees. And it isn't a raft, just levelling screed. With some systems they want a 100mm or so reinforced concrete slab over, to provide stiffness, but I assume you are following all the instructions.

@G and J Would I be right in thinking you can’t hear it at all?