Extension costs

[oolaroola]

We have seen a house we like but it's too small. Can anyone advise what the cost per square foot for building a double storey extension might be?
Have seen some estimates of £75- £150 per sq foot, but this seems quite low.
Just need to do some sums, so we can think about our top limit.
Thanks in advance....

[Pendeen]

Extensions I have designed within the past 2 years have ranged in cost from £600/m2 to £3,600/m2.

The cheapest was a simple, rendered blockwork flat-roofed 'box' (not one of my finest achievements I admit but exactly what the client wanted). The upper end of the scale was a 2 storey stone and Delabole slate extension to a Grade 2*listed farmhouse including a structurally glazed link, purpose made hardwood sash windows and an oak door.

Prices for Cornwall so add quite a bit for the south east of England / London!

Incidentally, £100 p sq ft is (very) approximately £1,000/sqm

[oolaroola]

Glad it was all worth it. Sounds hectic, but you got through it.
Thanks for the info on SIP, will look in to all this further. Got a second viewing on Sunday so will get my hard hearted glasses on to look for all the snags and expensive problems.

[Potterer]

A SIP is a structural insulated panel, like a ready built wall, with insulation inside it. It saves on labour costs as it goes up quick but for such a small build we went with the usual block and brick route.

[Talkinpeace]

oolaroola
The builders arrived on January 2nd and left on September 18th.
Only one room in the house did not have a knock through.
We had no hot water for 4 weeks,
I'll not comment further
except to say
It was worth it

[oolaroola]

Thanks Potterer, all good facts and advice, but what does SIP stand for?
Talkin, that looks amazing and a really clean finish. Was it all stressful?

[Potterer]

Right my kitchen extension has literally just been finished. I had an amazing builder.

I had a 2.5m wide by 3.3m long extension with a roof that just slopes from the back of the original house to the end of the new kitchen with a massive velux in the roof (I think it is 1m square)

I paid £11.5k for it to be finished and plastered, but I paid the electrician separately as I was having other work done apart from just new kitchen lights and sockets. I also paid the kitchen fitter to move the original pipework so my cost from the builder was literally for a shell that was insulated and plastered.

My house is only 14 years old but we live on a hill and we slope from back to front so that £11.5k included some serious digging for foundations, we didn't have strip foundations as our house is built on a concrete raft (because of the hill) so we had to have a huge hole dug out and filled with hardcore, metal reinforcing bars and a huge amount of concrete.

I read 18 months worth of Home Building and Renovation for info on SIPs/heating/costings etc to see which would be the best route for our build. I can highly recommend it, plus we went to the Home Building and Renovation show in Harrogate (we are in Yorkshire) to get as much info as possible.

The kitchen plus appliances, flooring, worktop, upstands etc then cost another £10k and then we paid the fitter on top of that.

Oh and I didn't want a big lump of wall sticking out where the original back of the house was so we had an extra steel thing put in so although we have a steel across the ceiling, we have a completely flush wall. I will sort out uploading pics onto my profile in next few days.

[Talkinpeace]

NB
We used a LOT of steels : each one added around £10,000 to the overall cost, but the fact that the spaces are open and airy and there is natural light in every room has made it so, so worth the extra up front cost.

That price also includes the solar thermal hot water system that means I get free hot water from April to October.

DH did our tiling as tilers were sillily expensive but I had all the decorating done for me.

Photo of the kitchen part on my pictures

[oolaroola]

Thanks Talkin, the more examples we have the easier ir is to construct a budget I reckon.

[Talkinpeace]

ours was £1500 / sqm right through to putting the furniture in - 2 storey extension 6 years ago

[oolaroola]

Thanks for getting back to me.
Potterer: I'm almost certain there would be unforeseen problems. It's an old place and my thoughts have already gone to issues with foundations and unmarked drains etc...
So I'd better get used to talking in meters instead of feet.
Do either of you know what level of finish that price includes - is it literally bare walls? Or does it include any plumbing and/or electrics?
Also interested in any experiences of self build or more unconventional building methods like straw bale or timber frame.

[MrsAMerrick]

We rececntly had an extension built, single storey. We were told to budget £1500 per square metre and it worked out almost exactly to that. That was fully finished - flooring, walls, central heating etc but not fittings - we put a kitchen into ours so that was an expense on top of the build costs.

[Potterer]

General rule of thumb is the £1000 psqm absolute minimum, my single storey rear extension cost £1400 psqm and I'm in Yorkshire.

Don't underestimate the possibility of complications (mine came in the form of foundations) and the stress of building work, my builders were amazing but it is nice to have the house back to ourselves

[LadyKooKoo]

Not sure about square foot as everyone we speak to speaks about square metres and that is anything between £1000 and £1300.