How to calculate overall cost per m2

[Gone West]

I hope this is in the right category if not please move it.

What is the standard way to calculate the overall cost of a build per m2? Do you use the external dimensions multiplied by the number of floors or the internal dimensions? If it is the internal dimensions do you subtract the area of the internal walls?

[Jeremy Harris]

As I understand it, it is the gross internal habitable floor area, so the area of all the internal floors inside the external shell.  Non-habitable area is subtracted, so in our case the "loft" space down the eaves is subtracted, as the first floor is in the roof and so has a smaller floor area than the ground floor.  Space taken by internal walls is not normally excluded, though.

In our case we have 75m² of gross internal ground floor area plus 54m² of gross internal first floor area, with an external footprint that is around 86m².  This is why I'm concerned about ensuring that the VOA use sensible data, as if they just use the external footprint and use their normal rules to calculate the internal volume they could easily assume that it is around 150 to 155 m², rather than the true figure of 129 m².

I've done our costings on the basis of 130 m², as at the time I started doing them I hadn't refined the true gross internal floor area as built.  We are now at around £1380/m², a bit higher than I initially predicted, but we've added a few things that pushed the cost up.  I budgeted on £1300/m², so being around 6% out doesn't seem too bad given what we see on the TV house build programmes!

[Alex C]

I think the reality is people probably choose a method to suit their needs.

[Gone West]

Thanks Jeremy. To clarify one point, is a porch a non-habitable area. Mine is around 4m2 double glazed and insulated.

[joe90]

My builder has just quoted me a figure of £1200 per sq m for a completed build.

[Stones]

+1 on gross internal floor area. I think your porch would / should be included as internal habitable space.

[Stones]

2 minutes ago, joe90 said:

My builder has just quoted me a figure of £1200 per sq m for a completed build.

Not unreasonable, a LOT depends on the final finish and design.  Chatting to my own builder about this, he said he does build (to quite a high spec) for £1000 sq m, but that means either a room in roof or 2 storey design (so less foundation and roofing cost).

[ToughButterCup]

Excellent question Peter. And in the calculation of this number hangs a lot of hidden jiggery pokery. And dancing on the head of pins. 

Here's too much detail on how the 'professionals' work it out from this url

For ease of use, I attach the pdf 

Code_of_measuring_practice_6th_edition.pdf

[Gone West]

Thanks for the link, it is useful seeing it in drawing form.

 

[Gone West]

Yet another related question I'm afraid. To calculate the cost per m2 do you include paperwork such as SAP, air leakage, architects fees, BC, planning, etc?

[Jeremy Harris]

That's a very good question!

I used all the costs incurred, so included planning and BC fees, SAP registration etc, but we didn't use an architect or planning consultant so didn't incur those costs.

I'm not at all sure what the calculators in the self-build magazines use.  I suspect they may well use a lower figure, perhaps using just costs that fall within the VAT zero rate or reclaim rules, as those calculators often seem to be a bit optimistic to me.

[PeterW]

I had this conversation yesterday evening - when it comes to the full cost, I can't see how they include items such as building control, warranty or insurances as there are too many variables. 

I expect that the models include basic tiling in bathrooms, no floor coverings and a coat of white/magnolia everywhere, uPVC double glazing and minimum spec insulation

 

 

[ToughButterCup]

53 minutes ago, PeterStarck said:

Yet another related question I'm afraid. To calculate the cost per m2 do you include paperwork such as SAP, air leakage, architects fees, BC, planning, etc?

Peter, it's nitty-gritty stuff like this which I realised wasn't  always included in the calculations that made me start and maintain this entry in my blog

Re-reading the entry -and some of the comments, this thread too- makes me all the more sure that cost per square meter is a rough and ready guide. No more. 

It depends on what's measured, or not. Additional phone calls? Petrol nipping to the BM? Overnight stay for a trip to the NSBRC (.... doesn't count because  we had a nice trip down to see friends as well)? And anyway, I needed that SDS drill......I'll keep it after the build.

[PeterW]

1 minute ago, recoveringacademic said:

Peter, it's nitty-gritty stuff like this which I realised wasn't  always included in the calculations that made me start and maintain this entry in my blog

Re-reading the entry -and some of the comments, this thread too- makes me all the more sure that cost per square meter is a rough and ready guide. No more. 

It depends on what's measured, or not. Additional phone calls? Petrol nipping to the BM? Overnight stay for a trip to the NSBRC (.... doesn't count because  we had a nice trip down to see friends as well)? And anyway, I needed that SDS drill......I'll keep it after the build.

So that's where it gets a bit odd - your builder has invested over time in his tools. A self builder has to go and buy theirs at a cost which will either be a lost cost or an investment - neither can be included in the cost of building. 

As a rule of thumb I've included everything the mortgage would cover - this is more than the VAT reclaim as it would include kitchen appliances I expect 

 

[Gone West]

I haven't included the cost of tools or paperwork but have included landscaping. It's coming out at £1634/m2 at the moment.

[Jeremy Harris]

If I add the landscaping (so far, drive pavers, patio stone, turf, stone walls, fencing, stone and paved paths, raised beds, etc) then it increases the total by around £80/m². 

However, when we bought a new house there was no landscaping included other than just the paved drive, the path to the front door and the boundary fencing.  We had to pay extra to get the garden turfed, a summerhouse base laid, paving laid around to the back door and a paved parking area alongside the garage to store my yacht during the winter.  As sold, the house just had a sea of mud roughly levelled all around.

On that basis, I think that it's only really the drive, essential paths and boundary fencing that should be included in the build cost.

 

[Alex C]

I think you can only use a method that suits your needs on the project. The really low figures per m mentioned are very unlikely to include any professional fees or much in the way of landscaping. I have worked on a total project budget figure and also a separate m2 cost as for me the total project cost includes all fees including arranging borrowing and also demolition of an existing house which I wouldn't normally include in a m2 build cost.

[Ferdinand]

I think that we should encourage all Planning etc costs to be included, as otherwise it is possible for heaps of bureaucracy to be piled on top and to pretend that it is not a real cost.

If you are dealing with largish sites they include everything even covering Section 106, roads, adoption costs etc because it all has to be paid for out of the sale price of the finished houses.

They also talk about e.g. floor space per developable hectare as a measure of density, and iirc some countries give Planning Permission in these terms.

On our project at one time the buyers and out reps were arguing about whether local new build prices were 2000 per sqm or 1900 per sqm, and working backwards from there to argue about price.

Ferdinand

[curlewhouse]

"I think that we should encourage all Planning etc costs to be included, as otherwise it is possible for heaps of bureaucracy to be piled on top and to pretend that it is not a real cost."

 

That is a good point Ferdinand - the biggest surprise (shock?) to us by far was the sheer cost of paying for the shiny bottomed trouser brigade to sit on their *rses in offices and look for objections and ways to squeeze cash out of you before we even put a spade in the ground - you expect the planning charges, but things like extra copies of the plans for the "Dark Skies Officer" (oh, no, I kid you not! -  a special joy of National park building) are just one example, exploitation by solicitors and so on  - mostly of the surprise costs are utterly pointless (like insistence we pay an archaeologist to watch every bit of digging for a site that's actually had a proper dig archaeological done on it 5 years ago and found absolutely nil) , but all these extra whims have to be paid for by the self builder and add up to a not insubstantial 4 figure cost that is certainly not mentioned in the magazines and books and I am sure will have choked many a would-be project off before where money was tight.   

Edited August 1, 2016 by curlewhouse

[2104GJ]

I find it deeply depressing reading some of the m2 costs that people are quoting-where do you all live? We are in Hampshire, within the new SDNP, where house and land prices are astronomical. To add to this, as curlewhouse noted, planning, additional reports, planning appeal consultants and more, all add many thousands to the end cost.  But the biggest barrier to building here is the m2 cost- from £2.5-3,500 per 2m.  Have we just met the wrong builders?  But i THINK not as we have spoken to many and house builders who say £3,000 per m2 is becoming the norm.

[Mikey_1980]

We have built in Rural hampshire this year, our cost per M2 without factoring in the land cost was around £1550, I think alot depends on what is required to get this site in order, build method and finish.  We haven't gone for a vast amount of technology in our house, but have spent money on things like a made to measure kitchen and good quality shower fittings etc. We managed our project in conjunction with our Builder and the timber frame company.  I did bits and pieces on the house as it progressed, mainly painting which wouldn't have significantly reduced the over cost per M2.

[Bitpipe]

26 minutes ago, Mikey_1980 said:

We have built in Rural hampshire this year, our cost per M2 without factoring in the land cost was around £1550, I think alot depends on what is required to get this site in order, build method and finish.  We haven't gone for a vast amount of technology in our house, but have spent money on things like a made to measure kitchen and good quality shower fittings etc. We managed our project in conjunction with our Builder and the timber frame company.  I did bits and pieces on the house as it progressed, mainly painting which wouldn't have significantly reduced the over cost per M2.

 

We're not far off that ourselves (excluding land). We're in a largish Berkshire town just off the M4.

 

About 380m2 and total build cost is around £550k inc the basement & single garage, may be a bit more when external groundworks and landscaping are finished. That's to a near passive standard with very decent windows and doors, German kitchen & bathrooms. Like Mikey, we went pretty low tech (aside from cat cable everywhere) and I did the MVHR install (saving a few grand) and a bit of general labouring but not a whole lot else. 

[jack]

I haven't had the time (/nerve!) to do the final calcs yet, but we're in a suburban area on the Surrey/Hampshire borders, and I'd say our house came out at between £1500 and £1600 per m2, excluding landscaping.  That was with an MBC foundation and frame, and us managing follow-on trades (mostly using local tradespeople).  Oh, and that includes the cost of an attached double garage and workshop/store, which I haven't factored into the floor area when doing the calcs

 

The kitchen was from a local supplier, based on Crown carcasses (they use Blum hardware).  We have 2 ensuites and a family bathroom upstairs, polished concrete floors throughout downstairs, MVHR and an ASHP.  The MVHR was installed by us, and the ASHP was installed by us with the help of a very handy electrician.  Most everything else was done by tradespeople rather than us.  Windows and doors are high quality German triple glazed.

 

Looking back now, there are areas we could definitely have cut some costs with better knowledge of the process, but overall I don't know that we'd have come in much below £1500/m2 unless we drastically changed the spec.

 

I also have no idea what our VAT rebate will look like.  The numbers above assume that will be zero, but I suspect it could reduce the cost by a few quid per m2.

[Bitpipe]

1 minute ago, jack said:

I haven't had the time (/nerve!) to do the final calcs yet,

 

 

That made me laugh - I know what we've borrowed and roughly what savings we've used up but also have the 'one eye closed' approach to budgeting at the moment. Also prepared for the VAT return to be underwhelming - I started a spreadsheet but it fell by the wayside early on and I just have a big box of paper to wade through!

[jack]

5 minutes ago, Bitpipe said:

That made me laugh - I know what we've borrowed and roughly what savings we've used up but also have the 'one eye closed' approach to budgeting at the moment. Also prepared for the VAT return to be underwhelming - I started a spreadsheet but it fell by the wayside early on and I just have a big box of paper to wade through!

 

I could easily have written that paragraph (except for the bit about starting a spreadsheet!)