G and J

We are advised that our planners will, rightly methinks, come out and measure if there is a complaint.

So, we put in our planning permission with our design substantially covered in vertical Siberian larch cladding. Separately to this, I read a lot about the war in Ukraine, and I’m very aware of the embargo on Russian products. So why I did not put the two together? Perhaps I assumed that Siberian Larch was a species grown in many places not simply larch from Siberia. Please don’t answer the “question how dumb is that?”. So we are now seeking alternatives. We have to have a fire treatment because we are within a metre of the boundary . We are committed from an ascetic point of view to vertical cladding, preferably 100 to 140 mm wide, and we want something that never needs to be treated because one of our goals is a low maintenance house. We are being directed by several companies towards a product called Ayous. Has anyone on here used that already? Does anybody know anything about its longevity other than the sales staff I’m talking to? Are there any other alternatives we should be seriously looking at? As always help gratefully received.

So, imagine in parallel universes that two almost identical builds were happening. The only difference is that one is going for PH certification and the other isn’t. All build costs are the same apart from PH consultation stuff and PH certification and whatever else is needed to get a ticket. How much extra do the PH certified project cost?

Would be a good name for a care home.

One advantage of being in one’s seventh decade is that ‘forever’ is a different time span compared to when we first built with us both in our 20’s. 😉

I’ve approached this from the other direction. When we started planning our build, (informed by TV programmes like Grand Designs) PH seemed like a daft idea, requiring houses with two foot thick walls, two acres of meadow for the GSHP, and 18’ deep concrete slabs and acres of glass so they looked like an Asda. I suspect that’s still the image a high percentage of the population who have heard of PH have. But I figured there would be elements that would be worth using on our modest home. We were committed to disconnecting gas from the word go, and that meant an ASHP as I’d already learnt that GSHP wouldn’t work for us. Airtightness and MVHR was clearly the way to go, so they were the first elements adopted. I was very keen on a long underground pipe to feed the MVHR but concluded that that wasn’t yet proven technology and wasn’t one that the MVHR suppliers were happy with so ditched that, sadly. Turns out our design had a sensible form factor anyway (2.75 if I’ve calculated it correctly), so that made me smile and feel we weren’t so bad. We’ve not that much glazing and can’t take advantage of solar gain because of the restrictions of the site, but we do have an east/west ridge on our bog standard 40degree pitched roof so south facing solar PV should be productive and offer a quick payback especially with the slate saving. Cold bridging is boiling my brain right now, and I think that’s the area I would fail most on as we will have to have a cheap strip foundation b&b construction and I’ll do my best but it won’t be the same as a polystyrene raft based build. What I’m ending up with is, I think, sort of a PH Lite, on a sensible budget, and where it won’t translate into volume house building is the extra time I’ll put in to airtightness. But as the practices become more widespread and the kit makes it easier and MVHR becomes a basic then I’m sure airtightness will steadily improve. So I’m starting to think that our house will be not an inspirational green build icon, but simply one of the earlier examples of the new basic houses of next decades volume builders.

I tried to engage with Octopus re the zero bills thing and they informed me they aren’t doing zero bills for self builders.

So is this Passivehaus Lite?

So more akin to osmosis?

The window is for passing in sheets of lavatory paper….

Is its behaviour determined by the ambient temperature it experiences? And if so, isn’t it always sort of summer indoors in a well designed house?

I’m using it for thermal performance only. I’m striving to be as informed a ‘buyer’ as possible, but the final answer will be underwritten as a minimum by appropriate professionals. I might be suffering from an inadequate understanding of terminology (amongst other things). When I tried to look it up I thought it indicated that this was moisture permeable. If not then I am royally confused. The good news is that I’m used to being that, but I try not to stay that way.

Well, either the house in Iceverge’s link is rotting away inside the walls as I type or things do dry inwardly, so maybe it does. Standard practice can easily become dogma and that’s generally a good thing if it simplifies and ensures that the majority of projects are ok. But sometimes there might be the possibility of something better if new approaches are tried. Interesting debate, I do appreciate the inputs.

Because I understood the PIR to be vapour impermeable. From what I’ve read you can put PIR outside if the frame if you don’t tape it and maybe leave small gaps, which I would have thought would reduce it’s effective thermal insulation. Otherwise it won’t be breathable.

Now this was in Ireland, I wonder if it would be acceptable in England. If so I think my frame design might benefit from this, assuming I can also get PIR on the outside of the sheathing accepted from a fire resistance viewpoint. There’s a lot of ‘ifs’ there. 😞

Specifically worrying about water ingress into your wall?

Thank you, very illuminating. Hidden gutters do rather complicate things.

So, I’m trying to understand the logic behind this build up. A skin of PIR externally (carefully taped?) presumably does a brilliant job of alleviating cold bridging, and means the frame has to dry inwards. Presumably the breather membrane is to keep rain out, but could be non breathable given it’s proximity to the non breathable PIR. Is the intello membrane primarily for air tightness?

Should I infer from this that you are asserting that frames can’t dry inwards?

On the bright side, I’m already in my seventh decade, and whilst in decades to come I might ask one of my carers to ladle some more polyfilla into the latest soggy corner of my rotting from the inside timber frame (by then) old fashioned house, I’ll not be around to see any really big bits crumble. That’s got to be good news. 🙂

And perhaps that’s the answer to ‘why not?’ Shame that potentially good engineering (which I’m not sure if inward drying actually counts as, mind) has to conform to such norms.

OK, I am very ready to accept that my thinking is muddied, and very slowly clears through our debate, so apologies for seemingly daft assertions and questions…. but… Our houses are designed to withstand peeps who don’t have MVHR and don’t ventilate, those happy with condensation and mould and fug. Such houses are designed to dry outwards for good reason. But my house won’t be like that so why can’t my frame dry inwards?

I’m not, but as you point out, the VCL can be the airtight layer, in this concept a nicely protected one. The presence of MVHR would appear to deliver lower humidity internally. I guess my question could be rephrased as “if we start from that premise can we build thinner and more thermally and cost effective walls?”

Good grief, in hindsight it’s obvious that in many ways I’m describing EWI. So there must be known and defined practices including near to boundaries.

Ok. I’ve now spent many hours pondering this topic for our forthcoming build. And something fundamental has been bothering me. I don’t understand humidity as much as perhaps I’d need to to know to answer my own question, but it seems to me that UK building practice is based on the assumption that most houses don’t have MVHR and so have internal relative humidity (RH) much higher than external RH, so we put the vapour control layer (VCL) near the inside to stop our steaminess rotting our frame. But…. What if I put a big fat layer of non breathable PIR insulation outside of a super airtight VCL, then put the frame and maybe some breathable and compressible (maybe rockwool) insulation in frame inside that. Plasterboard straight onto the frame, service void courtesy of the frame - no vapour permeable membrane needed? Airtightness provided by a continuous and well protected VCL. My frame stays reasonably warm all winter, and as I’ve got MVHR keeping my humidity at reasonably low levels it stays dry enough not to rot. What have I missed? Why wouldn’t this be a good idea?