2 storey extension - build cost?

WPC123

I have an end terrace house (Midlands) with a driveway to the side. A similar property in the road has recently added an annexe in their driveway position creating a self contained 2 storey 'flat' consisting of an entrance and lounge/diner/kitchen on the ground floor and a bedroom and bathroom on the first floor ~ all with a pitched roof. An extension such as this would be great for me as I have some money to invest (I own the freehold of my end-terraced home) as, if the figures worked, I could let out the annexe at £450 - £475 pm but the return depends upon the build costs.
I have had a look around the outside of the similar property in our road and guess the total extension is around 450 sq ft over the two floors.
I realise I will need planning and building regulation approvals and the cost of the kitchen/bathroom are very variable however I just wonder if there is a rule of thumb for calculating the likely build costs of the 'shell'?
Thanking you.

GreenBee_2

we have just started looking at building costs because we want to do a selfbuild. we got this software that helps you work out the costs of building work and from what I can tell you are looking at a cost of between £40k - £50k for what you want to do, including pretty much everything to make it move in ready. But because this is selfbuild estimate, it probably wont be an exact match - should be close though.

MX5huggy

Back of a Fag packet says £1000 per meter square so £41,000. Or £100 per square foot.

mildred1978

WPC123 wrote: »

I have an end terrace house (Midlands) with a driveway to the side. A similar property in the road has recently added an annexe in their driveway position creating a self contained 2 storey 'flat' consisting of an entrance and lounge/diner/kitchen on the ground floor and a bedroom and bathroom on the first floor ~ all with a pitched roof. An extension such as this would be great for me as I have some money to invest (I own the freehold of my end-terraced home) as, if the figures worked, I could let out the annexe at £450 - £475 pm but the return depends upon the build costs.
I have had a look around the outside of the similar property in our road and guess the total extension is around 450 sq ft over the two floors.
I realise I will need planning and building regulation approvals and the cost of the kitchen/bathroom are very variable however I just wonder if there is a rule of thumb for calculating the likely build costs of the 'shell'?
Thanking you.

Why don't you ask the other owners what it cost them to build?

ormus

the standard formula for budgeting costs, is 1k - 1.5k per sq m.

SailorSam

searchlight123

the other thing to factor in to your calculations are if you intend to move from your existing house at some time in the future the value may reduce as you have turned an end terrace property into a terraced one. that is of course presuming that your proposed build will be adjoining your property.

SailorSam

Utilities and Services

GreenBee_2

ormus wrote: »

the standard formula for budgeting costs, is 1k - 1.5k per sq m.

is there really a standard approach to pricing building work, or is that a sort of figure-of-speech estimate?

WillowCat

It is a fairly standard formula, much quoted. That price has been used for a number of years so I imagine most estimates come towards the higher end now, unless you are in a very cheap area.

This assumes no 'unexpecteds' like bad access or special foundations.

Of course the dreaded VAT must also be added if this is an extension, rather than a new property.

OP - be aware it may be much harder to get planning permission for a self contained property to be let out than for a simple extension of your own home.

WPC123

Thanks All -
mildred1978 - have already asked the question but owners seem reluctant to disclose full figure + their kitchen is way over (spec) to the one I require.
Have been carrying out a bit more research during the day and appears I definitely need planning permission and the Local Authority regard my proposal as a 'new-build' rather than an extension therefore the planning fee is £335 as opposed to £150. Anyone aware that say, if I leave a connecting door in for a while (then brick up later) I can treat this as an extension or is this too much penny pinching (money saving)? Building Control want £153 to inspect plans and £446 for site inspections. All these figures include VAT. Guy drawing up the plans is suggesting around £800 for submission of all drawings (but not previous fees) and payment upon recipt of planning and building control approvals.
As I say thanks for your help - any comments on latest info appreciated.