Iceverge

At a casual glance you wouldn't guess. Very good.

A new house might have a 1:1.25 ratio on internal volume:surface area with 200mm insulation. Running at a delta T of 15 deg maybe. A 15mm pipe will have an internal volume:surface ratio or over 1:400 and runs at a delta T of 30 with 10mm insulation. The pipe has proportionately 380 times more surface area to loose heat, twice the heat difference and 20 times less insulation. The numbers explain it all.

I would insulated the hot recirculation only. If you have a handle on the internal humidity the cold won't condensate. Insulating any other hot's is a bit of a waste of time. Tried to insulate my way out of an issue with 50mm pipe insulation but it still lost all it's heat in 15-20 mins.

The MVHR is very good at dehumidifying if that's running.

Is that a factor of sunshine or is it something else? Having looked at it I think in the British isles you need to burn something to be practically off grid during the winter. A small inverter generator would get you through no?

Good thinking. It makes a difference but not as much as you'd thing at very low pitch angles. Here's the north facing one from PVGIS. Here's the South . The difference is only about 300kWh/year. It'd be easily compensated for by adding a single extra solar panel. @Nic I would consider moving all the PV to the roof in one block. Less lightly to suffer differential shading which I gather it doesn't like unless you have some clever inverter gizmos. Some PV guru's could probably enlighten me.

You could put cellulose in the service void too but it'd mean cutting holes in the plasterboard to blow it in and a second visit for the installer truck. The main benefits would be already had in the main 220mm depth of the rafters. Namely, decrement delay (phase shift, airtightness enhancement and the ease of install around awkward cuts of timber etc. ( Not a huge factor in this roof) Mineral wool is cheap and if you correctly space the counter battens for the service void can be very quickly fitted. As @Nic mentioned budget I am conscious that posi joists are probably 5 times the price of cut lumber and a special order item rather than an off the shelf thing from a merchants. Beware 220mm timber rafters will need intermediate support. Re the U-Value of 0.14. It's just what emerged given the space constraints. The OP is limited in their height build-up to 350mm. Trade off's need to be had between the cost of materials and performance. A 400mm I beam with cellulose and woodfiber sheathing would be ace but probably 3 times the cost. Similarly PIR between the rafters with PIR underneath would appear cheaper and have a lower U value. However it's very tricky to install the PIR accurately. Differential movement of the timbers and PIR over time will result in gaps and thermal bypass of the insulation. There'll be loads of waste from the PIR boards cuttings. It has a worse decrement delay resulting in poorer summer performance. It'll be much much worse from a noise and airtightness perspective.

Here's a suggested roof build up I've gone for a trapizoidal profile metal roof. Far cheaper and less temperamental than standing seam etc. Also a thinner build-up. as you can effectively ventilate under the sheeting with 20*70mm strapping as fixing battens. Then a good breather membrane. Taped at all joints of course. Then 11mm OSB, for rodent protection, solidity, noise, ease of buildability. 220mm rafters ( if ok with the SE) with densepack cellulose insulation. Great for noise, airtightness, decrement delay etc. A Vapour control layer. A 44*70 mm crossbattened service cavity with mineral wool insulation. It would be enough to accommodate flat uPVC MVHR ducting if needed. If you pushed this to a 88mm or 95mm service cavity you could run semi rigid MVHR ducting no problem. If you could a second layer of standard plasterboard or a single layer of 15mm PB would help with noise. NIC roof buildup.pdf

Similar thread here. Have a pursue.....

@Nic Has sent me a PM and I've replied. I'd encourage you to post publicly as people can check my workings and hit me over the head with a metaphorical mallet I'm spouting nonsense.

Very interesting. I'm currently installing a Daikin FTXM25R. It's going at a snails pace mind you. Keep us posted.

It would involve a bit of fiddling but a seperate conrete lintel across the external leaf where it goes into the porch and then insulated it internally would be my preference. Blocks built on top then. Render boards there is only asking for cracks down the line in my opinion. Alternatively you could move the entire porch outside the heated area of the house and have a second door inside. Much easier to detail thermally and for airtightness.

I looked at them for our house but for some reason forgot about them. They did look very smart. Any chance of a few pics?

Welcome welcome. I do like small houses. You could post a few of your plans here (deidentified) and I could have a gander. I did my own PHPP and it isn't too tricky really for simple house. Jeremy's Harris's spreadsheet is probably just as useful in reality. Passivhaus isn't a perfect standard however and it favours larger buildings. Small single story houses can be tricky to meet the standards as they have lots of surface area Vs their volume. Have a look at these examples. https://passivehouse-database.org/index.php?lang=en#d_6778 https://passivehouse-database.org/index.php?lang=en#d_5132 https://passivehouse-database.org/index.php?lang=en#d_2096 https://passivehouse-database.org/index.php?lang=en#d_4466 You'll note that they often need extremely low U-Values for certification. Far below 0.1W/m2K in many cases. No problem in that itself ( I'm all for insulation) but it may not be needed for passivhaus performance. The problem is better explored here. The small passive house problem - a solution? - passivehouseplus.ie The passivhaus 10W/m2/annum was designed around forgoing a central heating system so is rather arbitrary, much like the 20deg living temperature and the assumed occupation rates. It's an excellent standard and I'm a total advocate of the methodology but don't tie yourself to certification without being informed of it's drawbacks.

Its a shame to see the creeping grinding incrementalism. Its like being on a train that stops at every station rather than just getting the express to the destination many of us here have realised. Build a passivhaus out if things that used to be plants and add lots of solar and an ASHP.

The trouble with small projects is that it's often cheaper to slightly overspec a design to save the SEs time and fee for getting everything to the last decimal point. In any case your spec doesn't sound mad. A good builder should be able to give you a feel for if the SE has designed someone sensible and maybe point you towards someone more suitable if they think yours has gone totally overboard. As an aside (without having costed it) YouTube told me recently that Spaz do impact driven screws that could save a good chunk of labour to replace the M20 bolts.

Lidl. Now this is a man on my wavelength. Will keep an eye in the ROI if/when the offer arrives here. In the process of doing an A2A ATM. Will review the situation once it's installed.

Maybe some pics would help if the stage you are at and the access? Would it be impossible for a concrete truck with an unloading belt to back up to the site?

Curved ball here. How about filling the cavity with closed cell polyurethane foam. It'll be more expensive than concrete but no labour for you and make an excellent job of that wall to floor thermal bridge.

Nope! I did a short while of civil eng at uni before bugging out to work at nothing building related. Everything is self thought (occasionally it shows) so please get a second opinion. However when building out own passive house I didn't meet anyone in reality who had more knowledge than I had pulled myself from forums (this one the most) and the internet. With timber buildings there's a lot of info from the USA and Canada. They've been poking around at low energy buildings with 50 years.

No problem. Its an interesting topic. It's annoying to effectively double up on structure, but that seems to be difficult to avoid if you want an oak frame that performs well. The expense also annoys me as the modern equivalent of a steel portal building clad with insulated metal panels is one of the most economical build methods.

I've reinvented the wheel again haven't I! That pic above very much looks like the oak frame is just for show. The I beam frame is raised first, then plasterboarded and then the oak frame. It'd be a durablen if expensive solution though. If they're done it the other way around it'd be a nightmare airtightening the propassive behind the oak frame and the plasterboard would definitely crack too if screwed between the oak and service batten. Pondering this I wonder would something like a hempcrete wall be an option. Its self supporting but not structural so would tie in well with an oak frame. You'd need 700mm walls to get near 0.1W/m2K though.

If you were able to guarantee an excellent job taping the external OSB for airtightness I would have no issue with the above. Replacing the 360mm I joists with 220x44 mm timbers and the Egger DDF with 11mm OSB would be much much cheaper and simple to source locally. Also rotating the 95x44mm horizontals would give a little extra insulation thickness for a very respectable U value.

Here's a quick 3d View. From the outside. 30mm egger DDF 360mm i joists @600mm cc filled with densepack cellulose 44x95mm timbers horizontally also filled with cellulose to hang plasterboard on. 15mm plasterboard 100x20 vertical strapping on 250x250mm oak uprights to allow plasterboard to slip being oak.

Pro's: All you insulation is in the one place with no waste. Egger DDF offers a chance to externally insulate window frames to some extent. The web of the I joist offers a good chance to take screws for external battens. Easy Airtightness details boosted by cellulose would make a great score possible with some care. Plenty of area to run wires etc inside the 44x95mm horizontal battens. Tremendous decrement delay. (Phase shift) Vapour open construction = very safe long term. All you Oak frame is inside the insulation zone making it completely temperature stable and unlightly to move at all Flexible insulation etc so any small movements make no difference. Floating Plasterboard not connected to the lovely Oak frame. making it simple to fit and unlightly to crack. Con's: You're moving into slightly more specialised and dearer materials like the Egger DDF, if you run a board short you won't be able to buy one locally, you'll have to wait for a delivery. Similar argument for the I joists. They are dearer than cut lumber. Cellulose isn't as cheap as some insulants on a £/U value basis on the face of it. However once you take into the account the cost of fitting and zero waste I think it's good value. We have 450mm in our attic. You'd need to somehow add rafter extensions to the I joists if you want to have an overhang of the roof on your walls. Defiantly recommended if you want have timber siding.