Budgeting for our self build project

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Image: ThreeOak

Pinning down the costs of a self build up front is notoriously difficult. There are just too many variables, starting at the very beginning with the purchase cost of the plot, and then the ground works, and don’t talk to me about hedging!

So how have we gone about trying to understand what we can build?

After realising early on that you couldn’t get a price for a build “just like that”, we finally understood that a series of iterations would be needed, each with more detail than before, gradually homing in on the price.

The trick was to ensure that each iteration produced enough of a justification for proceeding to the next iteration, and eventually you get to ask someone to build the house.

That was the theory. In real life the iterations overlapped each other but only because I couldn’t believe just how difficult it is finding out how much money you need to build what you want. If someone had written down for me what I’m writing here, the whole thing might have been a bit less stressful!

We feel as though we’ve been through 5 iterations. Do you actually need so many loops? As ever, it all depends. We were influenced by the Grand Designs standard story line of runaway budgets so we’ve put more effort into this than perhaps we needed. On the positive side, it has meant we’ve learnt a lot of things to do with building houses in a short space of time.

Iteration 1 – Timber Frame

We started off like a lot of people looking at the advertised prices of a timber frame from a variety of suppliers websites. Several of them also included indicative costs for completing a build. We went to speak to a couple of suppliers and one even sketched out a possible design.

Build costs were expressed per square metre of floor space and ranged from £1000 to £1300 depending how the build was managed. So we were able to confirm that a self build based on a timber frame was at least possible for the money we had available.

However we thought a house of 175m2 would be nice giving us a build budget of between £175,000 and £227,500. Bit of a leap from the £30-40k for the timber frame alone, we thought.

Iteration 2 – Main contractor

Over the next few months we did more research. Housebuilding shows, websites, magazines, books – the lot. We discovered build cost calculators in various magazines. They let you identify a build cost per m2 by matching up your build approach, floor area, number of floors and the part of the country you’re building in.

We also spent time thinking about the work we could carry out on the build, eventually realising that we would be liabilities on most building sites unless we just made tea and tidied up the site after work had stopped for the day. I can hang a shelf with the best of them but basic DIY is about my level. This really meant we should be aiming to employ a building contractor which pushed the budget upwards but meant the house would stay up.

This decision then encouraged us to think small-er. We don’t need a lot of rooms, but the rooms we want need to feel generous. We lowered our sights to the 150m2 mark.

Now going back to the magazine calculators, we found the right line on the grid and got a number of either £995 or £1261 per m2 depending on the quality of the finishes.

Sample of the build cost calculator from Homebuilding and Renovating Magazine

Sample of the build cost calculator from Homebuilding and Renovating Magazine

Still ok-ish (under £190k, but only just) but now we needed to understand what an “excellent” finish consisted of and did we really need it? Did we have to say goodbye to the Grohe taps?

Iteration 3 – Housebuilder’s Bible

For a further level of detail we used Mark Brinkley’s Housebuilder’s Bible. Throughout the book, Mark identified costs down to a remarkably fine degree of detail. Best of all, he expresses those costs per square metre.

So for example to cost the block work and render for your walls, you just pick up the relevant line in the table and drop it into your own spreadsheet, multiplied by the area of the walls. And so on though all the elements of the build. He has sample building budgets you can use as the structure for your own.

External Claddings costs from Mark Brinkley's Housebuilder's Bible

External Claddings costs from Mark Brinkley’s Housebuilder’s Bible

All very well, but by now we had decided on a designer and timber frame supplier who would also supply a whole range of the materials for the house. How would that be reflected in the budget?

We also spent some time considering finishes, kitchens and bathrooms. We have identified a number of affordable tiles and flooring options, and we have costed bathrooms and kitchens. We have yet to make final choices on these but we know what it will cost to cover at least the basics to meet our tastes and functional requirements.

We then plugged all the known information including a likely cost for the timber frame kit into our spreadsheet and came up with a cost of around £180,000.

The four remaining unknowns were

  • the cost of the heating system using a heat pump and ground source,
  • the cost of erecting the frame as far as starting first fix,
  • the real cost of using a main contractor,
  • and how competitive was it to buy building materials such as insulation from the frame supplier?

Time we felt to find out.

Iteration 4 – Firefly Wood

By now we felt committed to Firefly Wood for the design of the house. We knew we would be very comfortable living in one of their houses so we used their Moraig design as the basis for our costings from this point onwards.

With Andy Black we worked through a SAP calculation for the building and then, using some of the figures from this calculation, in a further set of sums worked out the peak heating load of the house. This told us how big a heat pump we needed. At the same time we asked a small handful of renewable heating specialists to quote us for the supply of the heating system. Happily their calculations and ours coincided, and the price of heating became a known quantity. The budget was starting to creep back up towards the £200k mark, and still some unknowns.

So, just frame erection and building supplies left to pin down.

Iteration 5 – Builder quotations

Well, at some point you have to commit to some expenditure to move things on.

We worked with Andy Black to finalise a design which we could send to a number of builders for quotations. Andy through his Firefly Wood business has a fixed price approach to getting through design, planning consent and building control. This way you know up front what it’s going to cost you to get to a point where someone can tell you the cost of building the design.

And that’s where we are. The plans have been drawn up, planners and building control are OK, and tenders have been issued.

And now we wait.

We are greatly encouraged that each iteration produced a build cost of a similar amount, albeit derived from different directions. We don’t think we’re going to be too surprised by what comes back from this stage but time will tell.

And the Grohe taps? Don’t hold your breath! And as for the hedging ….

 

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