Rear extensions

[Lmb85]

We’ve found a property were interested in buying and we’re thinking of adding a double rear extension on the back, a 3m ‘simple’ permitted development job. In theory it’ll allow us to have a much bigger kitchen/diner, possibly a study or play room and then upstairs a larger family bathroom with either 2 doubles or 1 master & en-suite.

Firstly, is the general rule of thumb still £1k-2k per square metre for the ground + 50% more for the upper still reliable? And are these figures for a plaster finish with electrics & plumbing or do they include decorating/bathroom/kitchen fitting? I’m going a bit boss-eyed with all the different types of estimate that google throws up & would really appreciate some clarity!

Secondly, regarding permitted development we know the 3m double storey shouldn’t be a problem, but if we wanted to add a conservatory or further single extension later would we need planning permission? If that’s the case I’m wondering if it might be worth just doing it all at once under full planning.

We’re in Kent & it’s a semi detached property. Yet to measure up properly but probably 3x5-6m out from the rear on both floors...maybe 2x3m as an additional single storey if we feel the need.

TIA

I’m in Kent and judging from quotes we were getting for a single storey last year it’s more like 2-2.5k per square metre , maybe it’s cheaper if you are doing a bigger job than we were .

We've just had a 6m wide by 3m deep extension done and it came to £32k.

@bloated1977 where are you? We are in Sussex and to do a single storey 6 by 3.5 with some internal remodelling to include a utility we have had quotes upwards of £72000!!

We are in kent. That included bifold doors, underfloor heating, new windows and a new boiler.

Double storey may not come under pd. How old is the property? Have neighbours done similar? Pd is based on the %increase in the original floorspace so a conservatory or indeed what you are proposing may exceed this. If the property is relatively new (less than 25 years) it may have had pd rights removed.

@bloated1977
That's is amazing, we can't seem to get anywhere near that! Are you pleased with the work? Did it all go to plan?

@bloated1977 I may want your builders number Was that for a double storey as well?!
Looking online so far we’re thinking it could be anything from £50k-70k depending on the finish and fitting. The most common figure I’ve seen is in the £60 area. We won’t need underfloor heating, probably not a boiler either!

@LIZS Yes most of the neighbours have either removed their single storey side building and rebuilt as a double side, or gone out on the back - in some cases both. There are also several loft conversions and single storey rear extensions. Looking at the satellite pictures I’d say about 30% of the houses in the road haven’t been added to or converted in some way.
The neighbour in the set of semis next to the property has demolished their single storey side building (all the houses were built with this) and added a single storey on the back. We’d like to do the same but with a double.