Olf

Tony tray Like on the drawing, first layer on the OSB Do a Tony tray trick : continue the membrane under the overhang and then over with the same continuos piece of the membrane. Cutting and sealing around joists is a bitch, hours of faff with the tape not worth £5 spent on extra stretch of the membrane.

Towel rail in the bathroom, maybe some backup fan heater when Jack the Frost comes. But it depends on whether you like bedroom warm or cold and how much heat escapes through the fabrics (via insulation and droughts losses). You mentioned new 1st floor and roof, so the latter is all up to you. In border cases the heat you generate may cause the upstairs to overheat, as documented here

28kW Combi, but with addition of UVC to be reduced to kind-of-system (no DHW calls). Everything planned with ASHP in mind, though no timeline on that. Will research, many thanks! That will be exactly the situation for the next few months. I'm ok with separate leg for the rads, without fitting the valve on it.

OK, sounds like you occasionally need a barbecue, @Tempmentioned using gas bottles for that. Try https://forum.buildhub.org.uk/search/?q=gas ashp&updated_after=any&page=2&sortby=relevancy&search_and_or=and Not sure if there is any thread with specific figures, as it is all very relative (even a case study, with members of buildhub doing a lot of diy, may not be representative for general analysis) but you'll be pointed in the right direction with discussions like https://forum.buildhub.org.uk/topic/21583-cost-difference-between-gas-boiler-and-ashp or https://forum.buildhub.org.uk/topic/23106-get-rid-of-gas-replace-heating-dhw-boiler-with-what

+1 Depending on the insulation of the structure, you may not need upstairs UFH at all - read through the forum, there is a specific thread on that. You should include airtightness strategy for the new build, which seems to be wrapping the original bungalow anyway. Even if a building is leaky, MVHR will still provide benefits: mostly by filtering incoming air and delivering/extracting at constant rates in targeted areas, just less of heat recovery element.

go through the forum, there was a thread exactly on that matter - basically depending on the cost of installing gas line vs savings of using it, depending on assumed payback time it is just a matter of calculation what wins. That ignores environmental as well as comfort (this being very individual) factors though. Have you ever tried induction? This summer we had to use gas hobs in the rented apartment - what a waste of summer time it was...

Yes, but they draw from the same source of heat. My thinking is that UFH is zoned anyway, so the delivery of the heat to specific areas will be controlled at manifolds (one for each floor)

Downstairs 70sqm UFH (40sqm house, 30sqm extension), upstairs 40sqm now rads (though running at 40C only), but UFH happening probably next year. The plumber insist each floor should be a separate zone (so together with UVC that would make 3 zones/S+ plan) which I think is overkill and unnecessary installation and maintenance burden. When would you split space heating circuit into zones?

I'll join the thread with my question. Similar setup: extension, Rehau patio door 3600mm wide, block & block wall with 150mm cavity, thermally broken lintel. Lintel tech support categorically forbid drilling in the lintel, suggested getting brackets that reach to the inner leaf. That would however require about 400mm long brackets (150mm cavity + 100mm lintel + 100 mm over the edge to the middle of the block + leftower length of the bracket), whereas the longest Rehau makes are 250mm. Do I really need to attach to the inner leaf to preven flexing, or - considering sides and bottom are going to be bolted to the outer leaf - I'm ok with attaching the brackets to the inner leaf. That will work prefectly well with 250mm brackets. The wall will be rendered, so they won't be seen.

I get it now So in effect tops up the TS via DHW side of the combi in the process

Thank you, that is an interesting concept! How exactly is the secondary circuit connected, if your DHW goes through combi? And can combi really modulate so low, that it even with TS at 40-ish deg it does not complain when only low flow requested? I guess that below some cut-off point it will just pass lukewarm water from TS?

Draughts (aka airtightness)? If not an issue, lift the wool and check how much light can you see. I had massive gaps around light fittings, around chimney and where all the pipes use to go. Not to mention the attic hatch itself. Oh and skeilings with 0 insulation, right above the rads, to dispose of the heat asap....

You did the right choice: XPS have twice the compressive compressive strength of PIR and does not degrade in contact with water

This is 'efficiency' from SAP score perspective and have little bearing on thermal comfort. Also efficiency is one thing, maximum output available (needed do maintain desired temperature) another: dial heat pump temperature down to improve COP and on cold morning it will not maintain comfort any more. Dial it up on a frosty day and even if flat out (and rubbish efficiency) it may not be enough to bring in more heat than comes out.

As you'll at least be moving water connections, the job will fall under Building Regs anyway. First question form BC you'll get will be about structural engineer's assessment for demolition of the wall. We can give you plenty of ideas, but if the roof collapses (or any other shit happens) it will be all on you: no insurer will pay a penny because 'buildhub folks told me so' Get an SE

What is the rationale for the size of the house? Bedrooms 1, 2 & 3 are large, but will that space ever be used? You could probably trim a good meter without any loss of function. 10sqm less > £10k saved? You will likely be asked to provide parking space for 2 cars, is there enough room at the front? Interesting to see the space for heat pump pre-planned, I wonder how much it will cost vs straight wall.

If that is the relative humidity of your local microclimate, MVHR will struggle to get much lower than that. PIV will not make miracles neither. Possibly you mean enthalpy heat exhanger? Yes, it can recover moisture from the exhaust, but its purpose is exactly opposite to what you want to achieve: to keep the moisture inside, when drawing cold air would further dry it by warming inside. For that reason, despite higher price, even the UK distributor does not recommend it. Dehumidifier. If aircon based, you get cooling for hot periods for free

It is hot air that due to lower density moves upwards, carrying heat (convection) . In case of screed, the energy will travel radially from the pipe through the volume, identically in each direction (conduction). The island itself will act as as insulator, so if you were to put UFH underneath, it will not be able to pass a lot of the heat out, and so it gives little benefit. By the same measure, any losses from the loops around not heated island will be negligible, as the island itself will insulate. Considering you're likely have collisions with other services going to the island, not having UFH pipes only helps

Why not using a remote switch? I installed NineLeaf Portable Mini Wireless Switch from Amazon in place of bli%&ing string in a bathroom, 30 minutes job and it has not failed me once. Battery powered (or for few quid extra you can get kinetic ones) so zero chance for electric shocks risk mitigation. And of course no running of the cables, making holes etc!

To start with, planners aren't bothered if it can be build or if it colapses the moment scaffolding goes down, as long as it looks nice from local planning perspective. BC on the other hand could not care less how ugly it is, as long as ticks all the required boxes of building regs. Of course it makes sense for the design to be decent enough to be used for both and be stuck to, but clearly it is not the case here. With the planning do check what exact conditions were stipulated: it may be pitch of the roof, but it might be max height only - either as a dimension or in reference to the existing building, that may or may not give a bit of flexibility. SE calculations are based on the plans he got, so if they showed 45', he would use that value for the calcs. Ultimately it is a blame game: BC is happy to accept stock solution, anything custom (like your roof) and you pay SE to do calcs and put it on his policy. Ultimately should anything went wrong, it is you being affected - and can get out with less of a problem if you can prove wrongdoing of SE or BC. So if you're happy to change the pitch so be it, but the 1st thing anything went wrong, the SE would wash his hands away (and so BC). It feels like the architect is a bit light on sticking to detail, maybe check the initial spec of the drawings - if he ignored the need to follow the pitch of the original house, surely he needs to do something about fixing it. At the end of the day he took money, so the blame game ball lands on his half.

And for that reason alone you should keep it: the house may not be airtight, bit that means the draughts happen likely not where you want them. MVHR lets you suck the humid air where you do want. And then you get some of the effort put in heating that air it back. Makes sense, especially with uninsulated ducts in the attic: this will act as a preheater on sunny days. Loft insulation is always a good idea, and will help with MVHR ducting. Considering the age of the unit I don't expect high effciency, I'd get some modern unit off ebay for few 100s and interface it with the existing ducting.

So you need to speak out your objectives because but that depends on the circumstances. I assume you already narrowed the chocie down to these 2 routes, as there are other options available - though making your hands dirty (be it ink for the drawings or dirt from the build itself.

All the beam and block floor and wall junctions are. You can mitigate it with adding internal wall insulation (if going PB with service cavity route), the higher it reaches, the better - and contributed to wall U value. Or make a thermal break at the slab perimeter insulation level with Thermoblock or alternatives. Depending whether you use UFH or radiators the rationale may change a bit - with rads these cold bridges are of less penalty, as the floor is relatively cold, with UFH they'll turn some of the effort of warming inside into heating the foundations instead (perimeter insulation helps, but only so much as 25-30mm can, and then unprotected wall sponges the heat and takes it to teh dungeon underneath). Saying that, most people just move on and live with the standard detail as on your drawings. Calculating losses due to psi values is a bit more esoteric than U, so it is harder to get return on investment in extra insulation/thermal break calulation.

It wasn't so rosy with BPC in my case: the 'design' shows locations of the ports only, nothing more than what I already knew. Only when nagging I got the flow values. They wanted to sell me what they preferred, rather what I wanted (eg 160>125mm reductions and 125mm ducting as they only stock 125mm system) and overcharged by £20 as the 100+vat design fee returned on order, in the words of the sales person couldn't have the vat component refunded... Hopefully your experience can be better, I'm staying away.

+1 As long as you follow the colours and do it right, it is a basic mechanical work. The electricians like to charge professional prices for that though.