I have a small site with outline planning for a pair of small semi detached houses.

Its in an area where house prices are not particularly high but I would like to build a couple of houses to Passiv Haus standards but I am concerned that it will be uneconomic.

Does anyone have an idea of what a typical premium there would be to build to that standard over and above the building regs requirements.
I know building costs vary geographically and I would say build costs in this area are about average.

Thanks

There seem to be more and more masonry cavity builds in this sector, I presumed because the skills are in more supply and thus lower cost.

I would like to avoid brick externally as brickies are in very short supply locally.

I presume it’s possible to build in block and insulate externally otherwise block cavity and render.

Do windows have to ph certified or just to ph specs?

I have access to triple glazed European windows but they are not ph certified.

The world is changing and it is all about good management now.

My house sits way below PH energy use, not certified, no heating system, repair or maintenance costs etc

Do you need certification?

Are you costing only the build or the ongoing costs too?

Cheapest simplest approach is solid blocks with 200 or 300 EWI and any cladding you like.

They always used to say 10% extra for PH but Exeter City Council now do it for the same cost but get a far superior product and it looks like Norwich are following:-

https://www.theguardian.com/artanddesign/2019/jul/16/norwich-goldsmith-street-social-housing-green-design

Posted By: nigelLooks like the way to go is solid block and EWI, with some other cladding as well to break up the render.

+1 for block and EWI

What they do here to break up the appearance of the render is to add 20mm extra EPS about 150mm wide around the windows (fixed to the base EPS with the same adhesive) to stand out as a relief and when the final colour render coat is applied the relief is done in a contrast colour, typically a pastel shade for the main part and white for the relief.

Take a look at Passive House Plus magazines's online archive of projects - which are excellently detailed and costed.

tony mentions Exeter City Council, which have adopted PH v widely incl currently for giant leisure centre under construction. Some years ago they gave £1400/m2 cost for small mixed PH social housing projects - typically say 12 units, mixture of terraces and flats, saying that was same cost as 'mere' Bldg Regs standard at the time. But that cost would be with advantages of scale - a larger project than yours - but possibly also by same token additional complications.

If you're developing for sale, you might get a premium for Passive House, but I'd have thought you'd need the Certification to support that. In a build for a private/user client, Certification is a cost that can be saved. Or indeed full-PH standard itself - a super-decent job can be done without going all the way.

On construction, a lot depends on the Planning requirement for external finish. It looks like in your case render finish is OK? That leaves all methods open. Advice here seems to be single skin blockwork EWI'd, but I'd have thought that a pair of simple-shape semis would be ideal for prefabricated timber frame. If it's good enough for the big housebuilders .... Denby Dale was driven by the Planning requirement for natural rubble stone finish.

Single skin blockwork - Building Regs deemed-to-satisfy is 190mm thick, which means 215 blocks laid-flat in practice. That is far more than necessary - get a Structural Engineer to design it, can be mostly 140, even 100 blockwork.

For small PH, the EWI will be at least 300 thick. That gives you walls nearly 600 thick overall with the blockwork solution, but only 400ish thick with timber frame, as the frame's thickness is useful insulation. On a tight site, thick walls may mean less internal floor space, and/or increase the effective 'footprint' for £/m2 calculation.

With blockwork you'll likely be driven more to conventional trenched foundations, though can be done with PH-preferred 'floating' slab solution. With timber frame the latter is the way to go.

Thats useful information, we intend to design it ourselves (daughter is part qualified architect) but happy to pay for hand holding on first one.
Will order book and have contacts with PH designers and a very sound structural engineer who has worked on a lot low energy housing.

I am not a big fan of render but if its used sensitively and broken up it can be done. As these are going to be small properties then it isn't such a slab effect.
I have considered TF but access isn't great so a crane may be out of the question and there are boundaries so too much timber cladding will fall foul of fire regulations.

Posted By: tony
https://www.theguardian.com/artanddesign/2019/jul/16/norwich-goldsmith-street-social-housing-green-design

Thanks for that link, Tony. I hadn't come across that project before and it looks very good. There's one bit in the story that seems odd to me:

"Passivhaus means windows have to be raised up around half a metre from the ground"

Anybody know what that is all about? (speaking as somebody with windows to the floor in a passivhaus)

And yes, central government policy about council housing is a big mess.

There's another article at https://www.architecture.com/awards-and-competitions-landing-page/awards/riba-regional-awards/riba-east-award-winners/2019/goldsmith-street that has more detail. It mentions the main contractor was RG Carter, who IIRC were involved with North Kesteven's straw bale houses.

That's handsome - the first pic of it we've seen? How did you support the balcony without thermal bridge? What's that little notch top right and the bulge lower right?

So the balcony depends on L-rigidity of the column/deck joint? Must make the balcony pleasantly 'live' underfoot!

The two poles are under the centreline of the balcony. Sorry if that is not apparent from the photos. Steel is pretty rigid stuff. It just feels solid. As do all the balconies cantilevered out from the side of buildings I've ever been on, for that matter.

PS sorry if we've hijacked your topic a bit, Nigel :(

But you don't have to insist on high window cills - go low if it would be life-enhancing but be prepared to compensate with extra measures (and costs, because non-optimised) elsewhere.

My philosophy is to make construction method as easy as possible, geometry to minimise surface-to-floor area ratio, and other optimisations, thus saving costs - which can then be spent on the 'frills' and non-optimums which make life worthwhile!

Posted By: djhSo it's not a requirement, just an optimisation.

Yes exactly that.

There is, of course, an exception to the rule. In as much as anything going all the way to the ground (and with a head height of 2m) can be counted in PHPP as extra floor area without increasing the envelope. So a way to increase the treated floor area ratio if you really need it (though they argue you shouldn't be grasping at those extra few sqm to meet the target anyway).

Depending on depth of walls, this can add a square metre or so in places. So doors are the best way to get low level glass to 'pay for itself', but this will be offset by the solar gain/heat loss mentioned above. Definitely avoid a sill of, say 150mm off FFL, as this would be the worst of both worlds.

The Ecology Building Society will certainly provide mortgages for PH, to name one source. I expect there are others.

Yes I am aware of them. I am aiming to build them at a lowish cost and not aiming for the top end of the market therefore I really want to do something that mainstream lenders will recognise and lend on.

The problem being that most will only lend where external envelope is brick or block. To build in that will make the walls very thick.