Nick1c

The claim seemed a bit odd to me, but I have no experience of ducting!!!! I may well call GBS tomorrow and get more info. Why would plastic ducting be more prone to bacterial growth then steel? I had assumed it was due to a build up of dust in the ridges, but the incoming air is filtered so this seems unlikely, the dusty (with a large proportion of skin) air will be on the exhaust side. Has anyone experience of both axial & radial systems? If so when is one preferable over the other?

https://www.greenbuildingstore.co.uk/mvhr-dos-donts-ducting/

Would it therefore be possible to use any source of electricity (inc. peak if needed) to keep the pcm liquid locally around the heating element and then Pv or e7 until fully charged?

Most here seem to have taken the semi rigid radial route for their MVHR ducting. If I have it right this is runs of corrugated plastic pipe going directly to/ from a box which has a pipe into the machine (plenum) from/ to input/ extract terminals with no branching. As I understand it the alternative is to use rigid galvanised ducts in which case the norm is to have main, larger diameter 'spines', one supply, one extract, with branches off them to the terminals. From a practical point of view I can see that the semi-rigid variety is easier to install and a radial system easier to balance - but presumably these are one-time events. Greenbuildingstore counter this with a claim that semi-rigid pipe has a life expectancy of 15 years, galvanised 40. As replacing ducting would be a major undertaking in a finished house they strongly recommend the rigid product. As it stands we will have an I-beam floor which I believe allows a fair degree of flexibility in terms of coring out penetrations, there may well be some steel as well which will require advanced planning whatever we use. Does anyone know if the life expectancy above is realistic? If so it seems to be a no-brainer to go for rigid. Would a radial layout work in rigid, or is it a better idea to suck up the balancing difficulties of a branched system?

In the absence of Pv there would be no/ much less point, but wouldn't Pv provide a 'free' boost for a large proportion of the year & E7 a cheap boost for the remainder with the sunamp acting as a low loss store until you need the heat?

I hope that this is sorted out by the time we need to make a decision. The low standing losses and (at least notional) 'charging' flexibility is very appealing. This has been dissected in detail by minds far greater than mine but could someone explain why the following wouldn't work: Pre heat water via an ASHP (Pv if possible) to a temperature that makes best use of the COP. Feed the UFH if needed straight from the ASHP. Use an electrical heater (powered by Pv when possible) to raise this waters temperature to charge the sunamp. In summer if cooling is needed there should be plenty of Pv available so use some for the ASHP in cooling mode and some for the electrical water heater. I wait to have the scales lifted from my eyes....

@MarkyP sorry, my mistake, I remembered it as you describe your tea cosy option. Isn't EPS good in damp situations?

Thank you @PeterW It's sounding quite positive, I didn't realise you could stop worrying about studs. Virtually all the corners will be 90 deg, but a couple aren't - do you just cut on an angle with a (cheap!) skill saw and glue or is that what the router is for? If using beading fit shadow gaps will they work with FST or do they rely on a 'proper' skim coat? Is it tough enough to be hoover proof at ground level, or are you better off fitting flush skirting with a shadow gap above? I have seen examples on here that looked good (criterion industries I think, but they were Australian). Can you hire board lifters? Would pallet loads via TP be the best option & would you get the screws/ glue/ filler from there too? Thanks again.

Try googling 'Tony's house reading' for an example of a solid walled house. If there is a significant flood risk how will you manage it - raising the ground floor? will it be insurable?

If you are fitting insulation between timbers on site I would have thought that push fit (mineral or wood fibre batts) or blown/sprayed (cellulose, icythene or eps) would give the best chance of it performing to spec. (& be quicker). If the U-value needs improving then put rigid stuff over the top. A good job between timbers with PUR would take ages.

AFAIK only for ground floor soil pipes. Water, electricity, phone etc are generally run round the house in service voids.

I am trying to get my head around the best way to line the house in the far, far, future when it eventually goes up. The wall structure, from the outside in, will be rainscreen (timber/render), batten, Proctor Wraptite, OSB (or something more breathable tbc), 300mm I-beam with warmcell, OSB, (?vcl), batten/service void, plasterboard or Fermacell. We will probably go for either a shadow gap to the floor or flush skirting/ architrave with a shadow gap to the walls. As far as I can see Fermacell is a superior product, but you pay for the privilege. Does anyone know what the real premium for using it is? Some of the extra cost must be set off against not needing to plan/ put in extra noggins for hanging, is it quicker/ slower to put up, is taping and using the fine finisher quicker &/or cheaper than skimming? How do the finishes compare, does it feel more solid than PB, does it repair well if dinged? Anything else? Other than cost the downsides seem to be weight when moving it around and unpleasant dust - any others? Sorry for the exhaustive list of questions, but I haven't actually seem it in the flesh.

There are thermal &/or financial costs to any deviation from an ideal form factor with minimal glazing. Budget, plot, planning policy and personal taste determine where each individuals 'sweet spot' is. We are going for an over glazed, cantilevered reverse level house, we accept that it will cost more and be less efficient, but to us, in our specific case, we think it is worth it. As a result the square meterage is less than it might have been & I am doing all I can to minimise the penalties..... Managing the thermal bridges from the steels and overheating are two of the things I am keenest to get on top of. I am hoping for clever ideas from the frame designer & architect to help with the former and relying on external shading of the south facing Windows and rooflights for the latter. If you are going for the cantilever for practical rather than aesthetic reasons you could consider supporting it with posts, that would be cheaper, and more efficient, but less dramatic.

I was reading about this somewhere on here yesterday (God knows why, we haven't even got a slab designed yet!). IIRC the recommended method was to fix the 1st row of boards with a couple of screws per board plus glue & then glue only. I think there was an egger spec sheet on it.

I have been told that a woodburner in the new house is 'non-negotiable'. Whilst I love a fire as much as the next person my concern is that having spent several thousand pounds on a stove it will either not be used or we will be sitting round it sweating! Other than enjoying the flames it would however act as a focal point in the room, what have others done for this?

We put UFH upstairs in our previous house. I battened out the joists and put 50mm cellotex on it, the pipes were then put in and a mix of aggregate and cement (no sand) put in every alternate joist space. The SE didn't think there was enough strength in the spans for a normal screed over the pir. The ensuite had shorter spans so we went for standard screed. The standard screed worked best, followed by the aggregate, you could tell which were the 'alternate' joists. This was in a very leaky house though, with much lower flow temperatures in a more efficient build I am not sure how noticeable it would be (we had t&g solid wood floors). Not sure how this might work with I-beams or posijoists as battening would be problematical.

We currently live in a granite barn. When we moved in it was freezing cold, had condensation running down the walls and cost £10/day in gas (you could still see your breath!). It has multifoil insulation in the roof, underfloor heating on the ground floor, sand & cement render internally was cement pointed and the external window cills were 1cm short on each side everywhere. We ditched the bottled gas boiler for an ASHP, rejigged the slate cills so they wrapped round the reveals, had the walls repointed in lime and the applied Beek BS+. The effect was beyond my hopes - heating bills well down (with a warm house), condensation much reduced. Starting from scratch I would have made the building as vapour open and airtight as possible, replacing the s&c with wood fibre insulation & lime plaster with breathable paint, together with properly insulating the roof & floor as much as I could. Could you not work on improving your floor & roof U-values in order to use breathable wall insulation?

One of the reasons we are considering Gaulhofer for our windows is that they offer an external blind system, much like a Venetian blind which is retractable, this would be a big help with any unwanted solar gain on our south facing window. Velux also offer external shutters, these can be retro-fitted so I plan to just ensure we can get power to the rooflights in case we need them.

I like the idea of combining Pv & wind generation as it dramatically improves the window for providing power. However a neighbor has a turbine installed in his field and it is remarkably noisy, not something that would be tolerated in a built up area. Fortunately we are rarely downwind of it. The (lack of) noise claims made by https://thearchimedes.com/ piqued my interest, but they have gone very quiet, and we would never get PP for it on our new site. I do wonder if district systems based on geothermal heat will ever take off, apparently the conditions in Cornwall are good for it, but I would imagine the setup costs would be prohibitive for the foreseeable future.

Tony on greenbuildingforum built a well insulated high density block house, he also had a website/blog - Tony's house reading iirc (the 'Tony tray' is worth looking at). As others have mentioned a good result can be achieved using any of these methods, which is most appropriate will be specific to your circumstances. Site access and the availability of trades will be key. As far as I can see attention to detail is vital to achieve good air tightness and insulation performance, for this reason I would avoid rigid insulation internally as gap filling would be difficult. Sheathing a building with eps sheets or blown insulation sounds fairly simple to get right.

Living at the end of the country, surrounded by sea on 3 sides is great, but does have drawbacks. One of these is a limited number of local tradespeople with specialist skills in relatively niche areas due to the lack of a sufficient population to support them. I have chosen to build what I hope will be an airtight, well insulated house using I- beams & warmcell with MVHR & as efficient a heating/cooling/hot water system as I can manage. This, I suspect in common with the rest of the country, isn't a common approach so I think it will be difficult to find experienced trades locally. I will have the option of : Importing the labour, with the upside of getting an experienced & efficient worker, and the downsides of having the person responsible a long way away if something goes wrong, not supporting my local economy and paying travel & accommodation expenses. Using local trades who will be slower as they are 'learning on the job' (& time is money...), but nearby if/when things go wrong & I will be supporting the local economy. I would dearly like to use a single contractor for M&E as it will avoid the 'it's not my fault, it's ..(insert another trade)' circular arguments, but I think this will provide the greatest challenge locally. What have others done and how did it turn out?

Thank you @JSHarris. That sounds like a plan.

IIRC there was a kit which allowed extract and supply to be in adjacent rooms. Maybe no good for most houses, but it might work in this situation.

We have had our overhead supply dropped to a cabinet at the base of the pole and an isolator switch fitted. I was planning to have a standard meter fitted, but after reading about @JSHarris use have started to rethink things. Our plans are to build a reverse level house using 300mm I-beams for the walls with a passive slab and 400mm I-beams for the roof with warmcell blown in. There will be 17 Pv panels on the roof facing due south at 22 deg, heating (& possibly cooling) via UFH & an ASHP (with a couple of heated towel rails in the bathrooms), DHW via sunamp(s). A woodburner will be fitted in the living area. If the majority of the use of electricity is on space heating is it sensible to "charge" the slab overnight using the cheaper rate, in spite of the fact that this is when the house would ideally be at its coolest? The estimated energy use is around 19kwh/m2 per year. According to EDF (our current supplier) if over 35% of power is consumed at off peak rates E7 becomes worthwhile, I do however feel a bit twitchy about the limited choice on E7/10 tariffs. What would those better informed than me suggest?

Viking house were pushing a system called FreshR, making all sorts of claims about its efficiency, a while ago. Not heard much about it recently though.