Iceverge

In my view the primary objective of airitightness is building health by stopping drafts carrying damp internal air into the structure. Badly fitted insulation is solved relativly easily. Just use a blown product like cellulose of EPS beads OR fit board insulation over a flat surface like with warm roof or a floor.

Ok with that in mind I will revise your blockwork build spec accordingly. The U values your architect has specced are pure fiction. Floor construction: U Value = 0.13 W/m².K 100mm powerfloated concrete with embedded fibers and UFH. 500g. Polythene separation layer 100mm PIR from Seconds&co or 100mm EPS70. ( I prefer the EPS) Polythene DPM 100mm Pir From seconds & co or 200mm EPS. (I prefer the EPS) Concrete beam & block floor to manufacturer's design DON'T USE BOARDS IN THE WALLS. TERRIBLE IDEA!! My suggestion. Render 100mm 14N dense blocks. 200mm full fill cavity with EPS blown beads (or mineral wool batts) and stainless steel wall ties. 100mm. Dense blockwork. 15mm Sand cement render. 5mm skim. The roof requires some thinking about. I have come to the conclusion that it is far too varied and complex to make a good job of it unless you take the airtightness layer to the outside of the rafters. It'll be easier to build too. Get rif of the cold loft. Roof tiles 38x50mm. treated tiling battens 25x70mm. treated counterbattens. Screwed into the plywood deck with 200mm screws. Roofing membrane 50mm PIR joints taped layered over the rafter tails. 100mm PIR with joints staggered from above layer. 100mm rafter tails screwed into the true rafters with 175mm screws. 18mm ply with all joints taped and returned to the wall airtightess layer at the wall plate and eaves. 140mm rafters with 100mm of mineral wool insulation. 40mm service space 2 x 12.5mm plaster board layers Gypsum skim. This approach would require stub rafters to be screwed to the top of the existing rafters for rafter tails and overhangs. AKA this video. I would change some of his details though. This is a really risky approach unless you are hyper on top of your airtightness. Also it's tricky to joint to the pitched roof. I would more or less copy the above detail. However I would include ventilation below the deck as I don't like the deck straight on top of the insulation. It is very failure intolerant. EDPM 38x50mm. treated across the rafters. 25x70mm. treated counterbattens. along the rafters. Screwed into the plywood deck with 200mm screws. 53mm ventialted space with mushroom vents throught the deck and continious with the pitched roof ventilation. Roofing membrane 50mm PIR joints taped layered over the rafter tails. 100mm PIR with joints staggered from above layer. 100mm rafter tails screwed into the true rafters with 175mm screws. 18mm ply with all joints taped and returned to the wall airtightess layer at the wall plate and eaves. Tapered firing pieces to create 1:40 fall. 140mm rafters with 100mm of mineral wool insulation. 40mm service space 2 x 12.5mm plaster board layers Gypsum skim.

Passivehaus really isn´t about minimum costs (althought it can make finantial sence) , but rather a comfort, building longevity and efficency. Ok I´m going to throw a spanner in the works here. I don't think if you build a blockwork house you'll get better than 3ACH on a blowerdoor test. I read many times that before we built our house that most airtight house builders had abandoned masonary as it was just too hard to get a result. None the less I pressed ahead. We ended up with a blowerdoor test of 0.31 which I was pleased about. HOWEVER, i spent 4 years researching the topic to an obsessive level of detail. I was off work during covid so I was personally able to do all the detailing myself. I spent days on end with a DIY blowerdoor fan and a tube of airtight sealant assessing every crevace and corner. The amount of time and effort that went into it was huge. It would be completely unreasonable to expect any normal houseowner or builder to go down this route. If you want a truely airtight house I would consider other methods. Timberframe liek MBC's twinwall or ICF would be much easier. There is one possibility through. A product called Aerobarrier will use an airbourne caulk to improve your airtightness. I've seen videos and a few patrons of the forum have used it. It may be worth a look.

Similar route here. We have a block built passive class house. It's been running abour 17 kWh/m2 per year since we moved in. I was hoping for better but some of the bridging details around the windows etc aren't mega. During the build there was some things that you just give up on. We've just installed an A2A unit which has reduced our heating usage to about 1/3. Prior to that we were just using a single plug in resistance heater. In short if you make a very good job of the fabric you can forego a conventional central heating system. Its an approach I woudl only take if I was all over the airtightness and thermal bridging details however.

Most of North American houses are built this way. It's nice and clean and most can be done by carpenters which cuts down your spread of contractors. Blocks however are quite cheap and can take sand+cement render which lasts an era. Some on an unpainted Westerly facing farm building here is in excellent condition after 70 years with zero maintenance. I don't know the projected lifespans of synthetic renders.

At the risk of making @Indys life more complicated would you mind starting a new thread concentrating on the fabric as it's a slightly different issue than the heating/cooling and it might keep things a bit tidier.

Well done.

Fairly easy to calculate. All you need is the specific heat capacity of the screed to get a rough estimation. @TerryE has chapter and verse. However it was far down the line of perfections at the end of a very very low energy demand house.

Show me the triple compression seals please!

1. Yes 2. You can charge the slab on TOU tariffs and allow it to slowly release through the day. Beware this is unlikely to be a successful technique if you don't have a passive class house. 3. Jeremy Harris did some numbers on this. Beyond a couple of mm it makes almost no difference. When it comes to keeping a house warm without the heating switched on it's almost entirely down to airtightness and insulation. Otherwise castles would be notoriously warm.(Spoiler, they're not)

Your choices. A. Get a proper chaser with proper dust extraction for a morning. B. Use a grinder and spend 3 years getting the dust out of your house and get silicosis for you trouble.

If I behaved like that in my job I wouldn't last a month.

Was this because you had carpets? I think @Indy has wood and tiles. Fan cools run at about £300. I reckon it'd work out more expensive than UFH.

The internal walls aren't too critical if you model them. Of course it's no excuse and frankly accepting any easily preventable heat loss is negligent in my view.

He's right. The meaningless phrase "thermal mass" isn't hated by people just out of pedantry. It's a term used to con those who don't understand physics out of their hard earned money. It really is a hateful expression that has resulted in too many honest people being conned. It's snake oil of the highest order. Phrases like "heat capacity" "thermal battery" and "energy store" "decrement delay" all actually mean something and can have quantifiable numbers attached to them.

Agreed. Whoever drew these up would be using basic details from 20 years ago.

Another option is to include UFH on the first floor.for cooling mainly . What is it constructed from timber or concrete? As an aside do you have more drawings. The suggested roof methods may not be the best.

The design appears to have bifold doors and a chimney still. My advice is to change these to a pair of french doors with fixed side lights and to get rid of the fireplace. You'll save thousands of pounds and the house will be far less drafty.

Sorry for not picking this up earlier. The thread got a bit hijacked and I must have skipped it. Ok. I'll do my best, you'll have to widen the wall slightly but it'll save you thousand's and perform much better. 1. Standard MVHR. 2. Monoblock ASHP to UFH ground floor only. Cooling if possible. 3. UVC as you say is ok. Bigger is better. 4. UFH on ground floor is good. 5. I don't like fan coils. Unnecessary complexity in my opinion. Provide space for A2A is easier in my opinion. 6. Don't know. 7. No wet UFH upstairs just UFH electric under tiles. On ground floor bathrooms too. 8. Include an electric spur for towel rads if you want them . ASHP runs too cold to do much with them. 9. Don't know. 10. No thermostats in individual rooms. Build well and the house will all be similar temp. Architect is talking nonsense and spitting out Celotex's imaginary U values from their sales book. Floor 0.13W/m²K 65mm screed. Separation layer. 200mm of PIR or 300mm of EPS insulation DPM Block beam. Walls. 0.18w/m²K Sand cement Render. Dense concrete blocks. (13N preferably) 200mm cavity full fill with EPS beads or mineral wool batts. Stainless steel wall ties. Dense concrete blocks. Wet plaster Skim Pitched roof. U value 0.12 Roof tiles. 38*50mm tile batten. 25*50 batten up the rafters. Glidevale vp300/400 membrane taped at all joints and sealed to outer wall woth render over expanded mesh over membrane. 11mm OSB sheathing 220mm rafters full fill with blown cellulose insulation or mineral wool. Airtighess membrane 50mm or 75mm or 100mm battened service cavity insulated with mineral wool. 2 x 12.5mm plasterboard and skim. Pitched roof with insulation at ceiling level. U value 0.12 Roof tiles. 25*38mm tile batten. 25*50 batten up the rafters. Glidevale vp300/400 membrane taped at all joints and sealed to outer wall render with render over expanded mesh over membrane. 11mm OSB sheathing. 150mm rafters. Invented loft space. 22mm Caberdeck or OSB flooring. 450mm blown cellulose or mineral wool insulation. Airtighess membrane. 22*70mm service cavity 2*12.5mm plasterboard and skim. Flat roof Construction U value 0.11. GRP 18mm OSB deck. 38*50 batten across the rafters. 25mm x 50mm battens up the rafters. To create 63mm ventilated space. Breather membrane 11mm OSB sheathing. 220mm full fill rafters installed with 1:40 fall with cellulose/mineral wool. Airtight membrane. 100mm service cavity full fill with cellulose/mineral wool. 2 x 12.5mm plasterboard.

Is there time to change much of the fabric spec. This will perform worse in reality than on paper.

Is this built? Someone has been wined and dined by the celotex salesman🥴

I chased our whole house with a 9"grinder. I would prefer to have a house with no electricity than do that again.

If you're going to the effort of re plastering you could use the time to insulate the wall too? If you don't want to I would hire a proper wall chaser and dust extractor for a day and chase it that way. There's some rules on where the cables run. @ProDave will have chapter and verse.

Provided you have adequate internal mechanical ventilation I wouldn't sweat it as moisture won't be trapped in the timber. It's the susceptibility to rodents and insects, the shrinkage of the boards, the fire performance, the performance loss over time, the thermal bridging through the foil, the waste and dust when cutting are the the reasons I that I don't like PIR.

Out of interest, I've done this with lots of combos. I think A2A and solar PV plus divert is probably the cheapest lifetime install for a building that is well enough insulated not to need central heating.