G and J

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?

It looks lovely. Have you a cross section of the eaves showing the hidden guttering and associated detail?

At least I do agree with one part of your recent posts.

Oh, and I know most peeps are too polite to ask, but what sort of overall cost (after vat reclaim) are you looking at? We’re following a similar approach on a much smaller scale and actually achieved cost, even when build detail is very different, is informative.

Congrats - looks fab. Would love to see the detail of the rainwear/larch cladding area.

We renovated a cottage in Norfolk and one luxury was some delightful sash windows, which we paid a lot for but we got a Fensa certificate. So when the lights blew after only 7 years we knew we were ok. Except the company had gone bust (i.e. had changed their name and walked away from all responsibilities) and Fensa gleefully told us we should have taken an insurance policy against the company failing, so it was our own fault. Lovely.

If you’ve got I beam joists or posi joists it might be dangerous to add full height timber noggins to do plasterboard under as well as floorboards over. Timber will expand and contract with moisture much more than either of them - but if you have full timber joists it’ll probably be fine.

Having cleared our own site I wouldn’t take it on for anyone else for £3k, but then, I dug up the bushes so they wouldn’t just regrow in no time. You can probably get cheaper but that might mean less professional, tidy and courteous to your neighbours (if you have any).

So, an update. Today I got an answer back from the sea monster: I’m still trying to get spec info. Anything I do get I’ll share.

How about we invent a device that turns excess body fat into electricity. I’d not have to import any leccy for years! 🙂

Methinks fingerless gloves, a thick wool beanie, a Sarah Lund sweater, thermal leggings and moon boots (all matching or at least coordinating, natch) for the eight days a year it’s really, really cold would be a cheaper and more environmentally friendly solution. And on the bright side, the computers will only overheat for three months of each normal year. Obviously not this year mind, so that’s next year’s problem….

Another snippet of info. No response to my email from the eight legged sea creature (why did they think of the name Kraken I wonder) however I had a nice conversation with a sales dude from Hopkins homes. The salient points: * it’s a kind of test, so there’s only a few plots designated to the zero thing on the whole development. * only one available for sale currently is a three bed detached. Internal footprint is ~22’ x ~19’, and the plot concerned has a east/west ridge therefore a due south facing side. I’m guessing this will hold circa 4kW Solar PV max. * T’s & C’s are between the buyer and Octopus, Hopkins are only involved in so much as they build a house to Octopus spec. After that you are on your own! * The premium in a ‘zero’ house over the same design in normal spec. is circa £20k. So, I’m wondering whether this is about distributed storage paid for by the house buyer. Octopus would like to store umpteen mWhours but can’t afford the investment. So they bribe homeowners to pay for and house loads of little batteries….

Welcome to BH. Why are you regretting doing that?