Iceverge

Do the best you can is the only thing I can say. I used PHPP and my own spreadsheet to refine the insulation levels. In terms of money spent to improve energy efficiency it's a little further down the list than you might expect. From memory the best bang for your buck was 1.Airtightness 2.MVHR 3. 3g Windows 4. Roof insulation 5. Wall insulation 6. Floor insulation. The metric I used was payback years. EG an extra 100mm of attic insulation might take 30 years to payback and and extra 150mm might take 50 years. I started at bRegs and worked my way up year by year until everything was at 25 years payback. I stopped there as I was at passivhaus performance and a bit extra. At least I knew then I was spending our cash in as balanced a manner as possible. In the end I had 450mm cellulose in the attic, 250mm EPS bonded beads in the wall, 200mm EPS70 in the floor. I could have probably put 300mm everywhere but in our case it would have been dearer for the same result as the floor insulation was much dearer than the cellulose.

There is acoustic benefits to triple glazing too. Not to be overlooked.

Good air sealing is far more important than U-Value in my opinion. A neighbours new build, with MVHR and good airtighness . Excellent U values of 0.1-0.16W/m2K. However they opted for new sliding sash windows with brush seals. The house was drafty and sitting in the kitchen with the heating on in winter you would occasionally get a little shiver. Whatever you pick, make sure you have good compression seals, joined properly at the corners (not just loosely butt jointed). Preferably 3 layers of sealing and multiple locking points to ensure they squeeze tightly to all sides.

I would argue that absolute humidity tends to equalise rather than travel in any particular direction. Indoor absolute humidity tends to be higher and therefore the trend to migrate outwards. By keeping a layer of continuous insulation outboard of any organic materials like timber then it will remain above the dew point for almost all of the year and condensation cannot happen. As there's only space for 50mm of PIR in this case, below about 5 Deg there is a risk of moisture accumulating on sheathing/PIR interface. This assumes that room air comes into direct and regular contact with the sheathing AKA terrible airtighess. In reality in our neck of the woods we are very rarely exposed to prolonged cold temperatures and if you plan on doing a good airtighess job then the risk is truly minimal as ,like I've said before, almost all moisture gets into a structure via air paths and cracks and not through diffusion through materials. I'm afraid , probably quite realistically in many cases, you've assumed terrible workmanship. Flat roofs go wrong when people take a token (if even that) approach to airtighess internally, have multiple down lighters etc, and token offcuts of PIR jammed between joists as a insulation. We have a cold roof. 450mm blown cellulose at ceiling level. However the external breather membrane was fully sealed so there's no ventilation in the roof. This was only possible because of the really diligent job we did on the airtighess layer below the trusses ensuring there was no way for air currents to take moisture up there. The carpenters were all spitting with indignation when I asked them to do it, telling me our roof would rot . But 4 years on and the timbers are as dry as a bone. Hybrid roofs are also an option if you aren't an idiot installing them and will save a lot on extra long fixings the thicker insulation in a pure warm roof of the same U value.

Not necessarily, I would omit the inner OSB layer in any case as it's not needed and will just add to the thickness which you want to avoid. You may want some Plywood or noggins/blocking if you plan on hanging furniture from the wall etc.im certainly areas. This localised ply inner layer won't be airtight as there'll be many penetrations for wires etc so I wouldn't consider it much of a barrier of any kind.

I would limit any material of low vapor permeability to one layer in a buildup. This will aid "drying", either inwards or outwards. The important thing is to have a good airtightness layer somewhere. This will limit "wetting". It's a tricky concept to get your head around but so long as "drying" exceeds " wetting" you're sorted.

Ah, there's a convention to have a vapour control layer (VCL) inboard of any timber structure in this neck of the woods. It's yet another of those things that based on worse case scenario with terrible workmanship assumed. Applied without thought and understanding is risky. In this case you would risk trapping moisture in the structure between two materials of very low vapour permeability (VCL and PIR). Almost all moisture is carried into a wall via air paths (read poor airtightness). If you were to build with cellulose and an external airtightness layer you could expect to see very good air test results if done diligently and it's simple to implement. Omitting the VCL would allow any moisture to dry to the inside again. Sounds like a good architect. No harm to be diligent however. Those pics are from the kingspan design details which use SIP splines but solid timber around the openings etc. 50mm of PIR outboard of any framing would all but eliminate any bridging concerns.

Just saw the plans, That's a nice house, credit to your designer. It is a very tight site however! I'm going to double down on a stick build plan. You could buy every material at your local builders merchants yard, drop it in an 8x4 builders trailer and hand ball them into place completely eliminating any need for trucks of cranes etc.

For thermal bridging mitigation nothing matches a continuous layer of external insulation for ease of install and performance. Now some issues that are really really important in the practicalities of building. 1. Local and completive availability of materials. 2. Ease of making airtight and wind tightness. 3. Fire resistance. 4. Noise protection 5. Ease of installing services. 6. Lightly hood of finding appropriate tradespeople. 7. Need for specialist equipment. I reckon you should reconsider a stick build with a layer of PIR outboard and not get too tied up by the U value of the individual element but look at the wall as a whole. Or better still replace the mineral wool with blown cellulose. No messing with itchy mineral wool, tremendous airtightness with a taped OSB layer externally and cellulose. Plenty of room to deal with services, good noise performance, really good phase shift (decrement delay) for heat protection. Lots of scope to deal with your chosen merchant for a competitive rate on materials. It can all be installed by 2 carpenters on site with no special materials.

@G and J I've been loosely following this. The essentials are you want a low U-Value Wall, with minimal thickness on a site that constrains the use of high overhead machinery. If you really want to dig into the weeds on this I'd advise that you try thermally modelling the entire wall, not just a simple U value calculator, in order to account for thermal bridges. Once you get towards any acceptable U values thermal bridging becomes really significant. Particularly around windows/doors, the floor wall joint and the first floor ceiling band area. You'd be surprised how the promised performance of a SIP wall worsens, once taking these all into consideration, as SIPS often require solid timber blocking in these areas.

Almost any design can be made into a passivhaus, it just depends how much you want to spend. Have you ran your design through PHPP? Caution this approach. Some natural materials have worse embodied energy than synthetic ones. Again it's a thing of many variables. Much depends on your wall construction, ground conditions etc. in our case strip foundations were cheaper. Properly designed they can be excellent thermally too. Maybe have a shot of THERM. it's a bit of a pig to get used to but can give an excellent insight into thermal bridging.

How much can you afford to drop the ceiling by? Lowering the steel is probably cheaper than replacing the window.

@thaldine Move here to the West of Ireland where for 11 months of the year everything is DAMP DAMP DAMP!!! Seriously though, I would advocate building a passive house. An ERV like this will maintain the humidity at your desired level without having to resort to under-ventilation to raise the RH Levels. (This will bring other issues like high VOCs and CO2) The better you can make your airtighess the better too. Otherwise you'll still be at the mercy of the weather which seems to be making your symptoms worse. Thermal bridge free design should help keep any condensation spots from developing too. This is important because these moist corners are where moulds and insects like to breed. The lack of drafts and cold spots will make the house comfortable at a lower internal air temperature which will result in lower RH levels too.

A picture paints 1000 words. Ok, the slope isn't mega. I had visions of a cliff like fall. Also your access is pretty good. Looking at your sketches I would be concerned about the maintenance of the wood that near to all that vegetation. Also I would be worried that the crawlspace would be a haven for undesirable wild life. Could something like building up the ground into a patio work instead?

Ah, I see the 1.5m. Whatever about getting an engineer I would be inclined to decouple it from your house and discard the ledger board. That way if it slides down the hill of moves in a gale at least it won't pull the wall of your house with it.

How tall are the legs of the piers lightly to be? Will they be visible? What's the ground surface underneath like?

Welcome welcome. It's nice to see new projects getting going. Moving from a bungalow to a two story is an interesting one. I grew up in a two story house but after numerous moves ended up in a single floor cottage before moving back into our two story. 3 kids later I think I'd opt for a bungalow in hindsight. Yes for PH it's a poorer form factor but apart from the ease of living advantages there's lots of maintenance and construction benefits too. Any particular reason for this? Some aren't necessarily any more healthy or less polluting than readily available mass produced materials. Good luck.

Concrete piers? Something like Sonotube they use in the US.

No idea, I've always assumed the were made from a mixture of glue and disappointment.

@MariaD What two rooms are you hoping to separate? What are you hoping to hang on the walls

You'll need to use the thicker 172mm panel for that U value. The absolute thinnest buildup I can think of is essentially a metal skinned SIP. is https://www.kingspan.com/gb/en/products/insulated-panels/wall-panels/quadcore-awp-wall-panel/ Is this going to be a garden room effectively?

.31 ACH. It needs attention to detail mind you.

Take up some kind high electricity hobbies. Maybe smelt some steel or do some evaporative desalination.

Me too. The white book from gypsum is about as close to anything I've found. In any case it depends on as built workmanship. 1. Block air paths for the sound to travel through. 2. Add mass 3. Counter resonance with a fluffy material somewhere in the buildup. 4. Decouple the materials in a wall. A cavity wall can do these pretty well if wet plastered and using a full fill mineral wool insulation. PIR is crap. It doesn't deal with air paths unless you use some something dear like gafotape. Blown cellulose is very good. It eliminates any gaps when done well.

Been there, tried it out, from the car battery on tickover. €200 2kw inverter from eurocar parts. The Modified Sine wave does not play nicely with our Led bulbs or the induction cooker. One bulb started flickering uncontrollably and another smoked and set off the fire alarm However everything else worked A1. I looked at getting a better inverter but a quality brand like Victron was almost the same price as a generator. I bought a loncin LC8000 generator instead. Key start and AVR and enough poke to cook and heat water with.