Two story extension sip house

[AndrewFitton]

We built our own/ organised the building of our own SIP/oak frame house 12 years ago. It’s a simple two story 12m x 8m rectangle internal oak frame, SIP and then clad in rendered block. There is a single story 2m x4m “lean to” housing a downstairs toilet and utility. The block clad wall of the gable is full- ie you could take down the lean to and the gable wall incl block cladding would still be complete. 

 

We have planning permission to remove the lean too and replace it with a two story apex 7x3.5 extension. It would be sip but no oak frame and rendered block. It would house the utilities and two bathrooms but as the drains and utilities exit / enter by the existing lean to, supply shouldn’t be a problem. 
 

Having got planning permission I’m finding cost estimates challenging. The surveyor seems to just quote checkatrade but I can’t even make sense of that myself. I can fit out myself needs be - I’ve been storing lime quarry slabs long enough!! 
 

Added to that I’m in Hexham which is in the Northeast although we tend to get the Hexham price here - as it’s an affluent enclave prices shoot up for NE44, 45 and 46.

 

For what in principle should be a very straight forward two story box 25m sq per floor of a ground and first floor - incl foundations and beam and block floor SIP, block and rendered can anyone hazard a guess as to how much. Assume fitting out bathrooms, decor and floor covering not included. 
 

many many thanks.

 

 

[Iceverge]

£100k I would have said. 

 

Plans would help. 

[Alan Ambrose]

As long as you have a spec and some drawings - maybe get a QS to do some calculations for you. You can then check the QS calc detail against contractor's quotes a they come in as a sense check.