Building Costs
As a very rough rule of thumb, in average parts of the UK the cost of house building (excluding the land and excluding design fees) will vary between about £800/m² for a very simple design with no frills up to about £1,800 for a house with quite a high design standard and a high specification of materials and finishes. Of course it can go way higher than that if you get carried away with your imagination!
As another rule of thumb, half of this cost will be in materials and half in labour. All these costs will increase maybe up to 25% in areas such as central London and will decrease somewhat in cheaper parts of the country. The cost per square meter is based on the total floor area inside of the external walls and includes the internal walls area.
This is the sort of cost builders might come up with if you asked them to do all the work. (although there is the other approach they may use of - ‘think of a number and double it’ - which can sometimes work surprisingly well). Depending on how much of the organising and manual work you do yourself, the cost will reduce proportionally.
There will be extra costs for any ‘features’, green or otherwise. These can vary tremendously. The figures from the Passivhaus institute indicate a very small increase for Passivhaus construction of between 2% and 4%, partly because a Passivhaus is so energy efficient that it does not need a central heating system and therefore makes a saving which is offset against the higher amount for insulation (however Passivhaus construction is not yet established in the UK so the costs of an innovative standard could initially be considerably higher). Extra insulation is almost always a low expenditure item. At the other end of the spectrum is photo voltaic solar collection which might easily be £15,000 to £20,000 for a 2kW installation, in other words more than a 10% increase on costs.
This is a useful way of getting an initial idea of the cost of the project but unless money is no object it makes a lot of sense to do detailed calculations on the whole job before starting. However, you (or your architect) can employ a quantity surveyor to do more accurate costings once design work is in progress.
The Homebuilding and Renovating web site forum gives an indication of the wide range of costings that people come up with.
When it comes to pricing fairly standard items, such as brickwork, trenches, pipework, etc. it is possible to use pricing books such as Spons but for anything slightly unusual you need to get quotes from subcontractors.
