Help me understand /m2 pricing better.

[Ramaya]

I'm trying to understand the economics of a self build better and want to understand how to better predict £/m2 pricing. 

Obviously the complexity, design features, material choices will have an immense impact on price but for the sake of this arguments let me simplify it to a cost for a watertight shell (finished render exterior & doors and windows). 

 

What would be more expensive: 

 

A 200m2 single storey house or 

A 200m2 1.75 storey dwelling with a ground floor area of 100m2.

 

To me the answer is obvious the first will be more expensive due to the larger foundations roof etc. However, by how much? 

 

I am looking at a plot that has planning permission for a rectangular 4 bed 1.75 dwelling (200m2 roughly) and I'm straggling to understand how to price it correctly per m2. 

Location: outside Edinburgh by-pass, preferred construction method: ICF. I've budgeted about £110 - 130k so far for a water tight shell with me working PM'ing a contractor to reach that stage but maybe i'm day dreaming. 

[ProDave]

You would do very well indeed to build that for a total of £200K (£1K per square metre)  Probably £300K is a more realistic total build cost.  You don't hint how much you are expecting to do yourself?  All in turn key and a total bill of £400K would not surprise me.

 

I would say 60-70% of the cost is in getting a complete shell.

[scottishjohn]

5 minutes ago, ProDave said:

You would do very well indeed to build that for a total of £200K (£1K per square metre)  Probably £300K is a more realistic total build cost.  You don't hint how much you are expecting to do yourself?  All in turn key and a total bill of £400K would not surprise me.

 

I would say 60-70% of the cost is in getting a complete shell.

and choice of windows and bath rooms and kitchen can romp up price dramatically

 any of those could be 10 k or 40k+each

same goes for flooring 

£1500 -£2500 sqm would be good estimate figure  in my view  

 don ,t see any one realistically doing for £1000 sqm -- 

[Ramaya]

My intention would be to bring the building to water tight shell and only finish the internals of the ground floor then slowly self-build the second floor as and when funds allow it. 

 

Power float finished floor on the ground.

Velfac windows or similar, budget £15-20k

Foundations/Groundwork £30-40k

Shell build £30k (ICF Assembly)

Internal structural flooring for first floor £10k

Structural roof works £15k

ICF Formwork £20-30k

 

I work in construction albeit in infrastructure still I consider myself clueless in terms of a self-build home. However, I do think I can reduce my groundwork/foundations costs by self managing that stage of the job. I can do all the setting out and surveying myself. And possibly work with trades for putting up the shell ICF's. However, I can not work at the project during the week days.

 

 

Edited September 21, 2020 by Ramaya

[SteamyTea]

Not just the m² that is important, the periphery has to be taken into account. A 10m by 10m square has a periphery of 40m. A 1m by 100m has one of 202m

[Ian]

2 hours ago, Ramaya said:

To me the answer is obvious the first will be more expensive due to the larger foundations roof etc. However, by how much? 

Typically about 15% more.

 

 

[the_r_sole]

In answer to the op, m2 pricing is a very, very blunt tool for pricing. There are far too many variables for it to give you a meaningful cost estimate. 

Generally it's cheaper to build a smaller footprint with more floors

You look like you're fairly well on with things so why not get a qs to give you a budget cost?