G and J

Agree with both of these!

Definitely the way to go....in a very small way we did something similar. We bought a very tired bungalow, which was a probate sale. Our plan to demolish and build a house on footprint with similarities to house next door. We shared design ideas with the immediate neighbours before planning, and then just before planning went in we did a letter drop to the road "we are......we're planning to.....doing it to become our home.....appreciate will cause you disruption.......contact no.s" etc The reaction was mixed, inc. no reaction from some and did generate some subjective objections, but also was a great way to get to know the new neighbours, had coffee with a number, on chatting terms with more way before actually starting (we still haven't demolished) so was definitely a positive. The other thing we learnt is that the "quiet ones" are sometimes the most vociferous in their WRITTEN objections and whilst welcoming feedback its' best not to position your plans in terms of it all being open to change (you will have some basics that are red lines for you and you won't necessarily be able to please everyone......at one point each if our neighbours were pushing for the ASHP to be on the other boundary!) Finally don't take it personally, whatever the reaction now, when the dust settles people will respect you for having done it. Hope it goes well

Not sure but I think that means it’s circa £16/m2 (exc.) at 140mm which is the same as I found nyrock frame slab for, and that has no installation costs (as a little old and round bald guy will be running round fitting the nyrock for free!). I'm guessing the shredded stuff would be good for deeper frames but looks like the bats will work well for me. Next question though is what do I use for the 50mm inboard of the frame. I’m assuming rolls would be better to reduce gaps. Is there a clear market leader?

Materials. The insulation and VCL and maybe the inner layer of OSB we will be doing. Understood - but we are prepared to invest the time (2 retired types here) so that does change things, but it is a point well made. We built in '91 in 5 months when we were both working full time and still found the time to do stuff ourselves (some including labouring, electrics, plumbing, roofing, painting) and whilst we don't want to take forever we aren't going to push it through as quickly this time as we are older and we don't have to. (We had two mortgages going at once back then - v stressful!).

On the face of it it looks like the same lambda but only 75% of the price. - So, thank you.

Will investigate. Ta.

Is there an easy rule of thumb for the cost per area/volume of this and will I need more than the VCL to contain it while it sets, as if it needs another layer of OSB inboard then it will hurt.

If I have a wall build up with Frametherm that hits u=0.18, changing to a mineral wool which has a lambda of 0.035 changes that into a wall u=0.19! Ouch. I think that's another 15mm of mineral wool to compensate. But I do like to save cash so will look into it.

OK, that's good to know, thank you.

So to be clear @sgt_woulds, what heating should I build into my new house when I install it next year? We have close neighbours either side, gas is already at the bungalow we are demolishing, and low running costs is an important factor or us.

In the beginning there was plan A; and plan A was marmite because plan A used PIR and thus got us a decent average wall u-value (circa 0.15W/km2) for a thin-ish wall and at a sensible cost and lo, we thought it was good - but there are those who though of PIR was the anticrust. And behold, the heathen (G&J in this case) listened and paid homage to the almighty (Jeremy) spreadsheet and asked it for guidance. At which point we realised that given how airtight we were going to be and the insulation levels in floor and attics the precise wall insulation level didn't really make that much difference, within reason. So, that means we could contemplate relaxing to a wall u value of circa 0.18. Which means we can contemplate mineral wool instead of PIR. (Plan A is: 120mm foil backed PIR in frame 25mm PIR layer VCL 20mm service void OSB, then finally plasterboard and skim.) Off to Ubakus we went to play with 140 Frametherm32 in the timber frame plus..... what exactly? We could do as plan A but with a thicker PIR layer inboard of the frame. But how about we put yet more mineral wool inboard? Something like: 140 Frametherm32 in frame VCL (is this condensation I see before me?) 50mm battens with 50mm mineral wall between, then OSB, Plasterboard and skim. Is this a good plan? Will we get a wet VCL? Will the service void be OK filled with wool? Is it better to do the 50mm battens horizontally to reduce bridging? Is there a better alternative to mineral wool for the inboard layer? (I probably should apologise for coming back to the forum for yet more help with our wall build ups, but in reality it is the cumulative affect of BH groans at my planning to use PIR that has driven this, so in a way, it's BH's own bloody fault lol) Responses and thoughts gratefully received.....

Oh dear. So after a few months my new neighbours won’t like my noise one bit - once they’ve got to know me.

Ah then that’s the answer. My ASHP is going half way down the garden. My man cave is at the bottom of the garden, and will have a nice big sound bar connected to my smart tv. So I solve the ASHP noise issue by getting to enjoy some serious beats to exercise too. Brilliant. 😉

Is that the forum equivalent of a blank look?

Because they ‘know’ heat pumps are worse because aunty Enid’s friends neighbour’s son in law lived in a council house with a huge noisy heat pump dumped right outside their bedroom window which ran 24-7 but the house was still cold with luke warm rads and a electric bill they couldn’t pay.* (*A fictitious account based on real life early ASHP installations in social houses that I’ve seen first hand).

Survey done. I find the whole attitude to ASHPs fascinating as we talk to different peeps re our plans. I know my new neighbours would much prefer us to keep gas. Ho humm.

Is t Is the floor plan 2500 sqft? if so not sure the figure above ?

Ah......is to be joined to the house, block not TF, slab fall towards road but......

I was thinking of a 1:100 slope down towards garage doors......not a good idea?

+1 With a passion.

Bet they said that about asbestos once, long ago. When one embraces relatively new technology, or materials, or indeed design practices, one is taking more of a risk. That’s the good news about being a wrinkly self builder. Mistakes will only be a bother for a small number of decades, tops.

I’ve no experience to offer but intuitively as the majority of the year the bedroom supply vents will be moving very slightly warmer air into the bedroom I struggle to see why a perceptible draught would be created, given the low flow rates involved. Like you that would reduce duct runs and for me it would reduce the number of penetrations in our airtight membrane, so we’ll done for a brilliant idea. I think I’ll keep the bathroom extracts in the ceiling though.

From what I’ve read (yep, I’m yet another poster who masks guesswork with confidence) MVHR is only energy efficienct if a fairly good level of air tightness is achieved. That would seem to indicate that a centralised system is not ideal. Reducing humidity is likely to increase the heating bill whatever system you go for but in your position I’d look at things like extractors or dmev. Nowhere near as sexy but cheaper and easier methinks.

Ok, so a trained hamster in a nappy.

Cleaning! I thought MVHR meant I never had to dust or vacuum again? Being serious my current plan is to have limited access to the manifolds and thence continuous duct from manifold to terminal. Will I be sending a trained hamster with a duster through my ducts? Or in reality is cleaning a very rare event?