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Timber Frame, Passive Slab Build - Costings for Seperate Elements


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Hey all.


The design I'm planning for my build has shifted towards a twinwall or i-beam timber frame with a passive slab. Just seems the most tried and tested way of getting a good thermal envelope on a budget.


My question is, has anyone got any costings for seperate elements of a build like this (passive slab, external walls, internal walls, roof, e.t.c) that they'd be willing to share. I appreciate that prices fluctuate over time, i just want to get a ballpark so i can create a plan that is roughly affordable before i draw it in detail and start getting formal quotes. I dont want to put off the builders by asking for a load of quotation work on a design that is still completely up in the air.


My build involves a huge, full height room that occupies half the footprint of the house so trying to work out costs on a traditional all-in £ per m2 of floor area just isnt cutting it as there is a huge proportion of external wall & roof per square meter of floor.


The spec & cost breakdown that Viking/MBC have on their website (http://www.viking-house.co.uk/selfbuilder-package.html) would be exactly what i need if they just gave the dimensions of the house they were building for that money so i could compare.


Any help appreciated as always.



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Quick tip, Viking House are no longer connected in any way with MBC Timberframe.  Sadly, the owner of that website is using photos I took of our house without my authority and with misleading, and in some places wrong, information.  I won't air the rest here, suffice to say I'm taking action to sort it, as he refuses to stop using my photos, despite several requests.


Take a look at the MBC website here: http://mbctimberframe.co.uk/  They are now based in Gloucester in the UK and I contracted with them, and them alone for our build, and was extremely happy with their service.


Costs have increased since our build, by a fair bit, I believe, primarily due to the material cost increases that have been hitting all builders recently.  However, if you want to adjust costs since 2013, then our passive slab foundation, weatherproof insulated frame, guaranteed PassivHaus standard airtightness (with air test), delivered and erected in West Wiltshire, cost about £420/m² (net internal floor area - so the sum of the ground floor and first floor room floor areas), IIRC.  That cost also included ground floor underfloor heating pipes in the slab and all the foundation prep work, except for the rough levelling of the site and the basic level of coarse stone over the house footprint that our ground works chap laid. 


Our house was structurally a bit more complex than standard, as it was room in roof and so had rafters hung from a large laminated timber ridge beam, with a similar ridge beam out over the gable, and because I wanted the entrance hall to be the full 6m height of the inside of the house, there were some additional costs involved in engineering the frame to allow this open space (essentially just extra timbers and reinforced concrete beams for two internal load bearing walls).  It may have been as much as £30/m² cheaper if we'd had a standard truss roof, I believe.


That price includes all the internal stud walls, with door openings, laminated timber lintels over a couple of internal doors to take loads from above and all the internal service void battens (50mm x 50mm in our case).  That price also includes the roofing membrane, counter battens and slate battens, to the pitch I gave on the plans to suit our chosen slates.


I'm not sure how helpful the above is, as I don't know for sure how prices have changed since 2013, other than they've gone up a fair bit.


If you want to know a bit more about our build, then I tried to keep a running record of it, here: http://www.mayfly.eu/


PS: The photos of our house on the MBC website are being used with my blessing, it's the other place I'm having an issue with over copyright misuse

Edited by JSHarris
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Thanks for the reply. Your blog is actually one of the few sources of info I'd been using to put the build together but havent read it start to finish yet. Helpful to have you explain the costs in more detail. My build plan is similar - room in roof & large void with the roof held up by a large laminated ridge beam.


Appreciate the tip on the two companies. Without wanting to rake up too much, who is running the show at MBC since they parted ways? Who would you recommend speaking to there about specifications and quoting?

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Give them a ring and ask to talk to Joe Blair, he's great on the phone, not so great on email!  There's also a very good AT working in the office, Trish, and sh'll find Joe wherever he happens to be (he spends a lot of time on the road, dealing with customers face to face).


I'll PM you with more, rather than post it here.

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There's a few companies offering an I-Joist structure, although only one I'm aware of that offers a package with a Passive Slab (or insulated strip foundations) which are who I used - Touchwood Homes.


To save on typing, I made a few comments in this thread regarding my experience:



My build is complicated by being a barn conversion with an existing steel frame, but I found, from the various different suppliers I got to quote, the I-Joist Structure was slightly less expensive than the twin-stud option, but required a slightly more complex periphery detail on the slab to achieve the same "cold-bridge" free junction at this point.


In truth, there is a simple slab solution for the I-Joist that gets ~95% there. It does require a level of accuracy on the slab that general ground workers do not build to and as I was choosing to use local ground workers I went for the more complex option that allowed a little more tolerance on it's sizing.


With so many factors effecting cost you're best going out to all the companies and getting them to quote.

Edited by IanR
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