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Whole house build cost vs extension costs - why is an extension relatively so much more expensive?

(31 Posts)
sunnysouthend Thu 27-Apr-17 15:50:06

My surveyor has quoted a rebuild cost for a 148sqm semi (for insurance) as £180k. £1216 per sqm

Architect estimates the cost of a 15sqm extension at £30k. £2000 per sqm

Why the discrepancy? Feeling deflated at costs.

Are costs relatively cheaper the more work you do? Or has surveyor got it wrong??

KatyBerry Thu 27-Apr-17 15:52:14

no VAT on a new build for starters

sunnysouthend Thu 27-Apr-17 15:54:57

Ah, would that include rebuilding a house that had burnt to the ground for example?

Aside from costs of what I want to do I also want to be sure the rebuild cost for insurance is enough...

KatyBerry Thu 27-Apr-17 15:58:05

actually that's a good question and I don't know. The architect figure for your extension sounds like it's for a very high level of finish though - does the surveyor who quoted the reinstatement value have an idea of your level of finish?

JigglyTuff Thu 27-Apr-17 16:00:14

It's much harder to work within the context of an existing building - you have to make sure that it doesn't fall down, you can't get plant and materials into place with machinery, you have to keep noise and dust down to a minimum etc etc.

All those things are expensive

sunnysouthend Thu 27-Apr-17 16:05:18

Well the surveyor has visited the place so I assume (?) they have quoted the cost accordingly.

I was shocked at 30k for 15sqm.

sunnysouthend Thu 27-Apr-17 16:06:57

Yes, jiggly all good points

BrieAndChilli Thu 27-Apr-17 16:13:53

I would imagine that there are some costs that fixed no matter the size of the job
Scales of economy e.g. Buying 2000 bricks is more expensive /less preferential rate than 50000 etc

CJCreggsGoldfish Thu 27-Apr-17 16:14:44

Sounds about right to me unfortunately. I've just paid 28k for a 9m2 extension with a patio, and work to an existing roof. This included the removal of a conservatory too, so it wasn't just a straight forward build. It's to a high standard. I too was shocked at prices though, we originally thought 15-20k, so it took a while to get our heads around the quotes.

sunnysouthend Thu 27-Apr-17 16:22:31

Oh dear, will need to scale back my plans sad

BanjaxedFecker Thu 27-Apr-17 16:25:01

Mines come in at 40k for converting 30m2 but we had a couple of hiccups namely having to add in deeper foundations etc.

sunnysouthend Thu 27-Apr-17 16:26:15

Is it true that it costs relatively less to add a second storey? I read that it would be an additional 50% - so 45k for the same footprint? Or is that an internet myth?

sunnysouthend Thu 27-Apr-17 16:27:34

Do you mind my asking which region you are ban?

I'm SE which obviously affects costs.

BanjaxedFecker Thu 27-Apr-17 18:04:53

I'm NW, Southend, but shocked at the price although everythings been itemised thoroughly and i know they're not up to mischief in terms of pricing.

It's just really expensive! I have to find another source of income pronto - we're on m ajoy austerity measures to pay for it. Originally quoted 30k.

BanjaxedFecker Thu 27-Apr-17 18:08:17

We're making a utility room, plus needed a partial rewire and building control are being massively fussy.


Electrics 3k
Plumbing 0.5k
Fit kitchen 2k
Brickwork 3k
3 RSJ 3K
Plastering 3k
Tiling 2k

plus kitchen cost, I never factored that in, thats about 7-8k

sunnysouthend Thu 27-Apr-17 18:49:14

There must be ways to save money - I guess doing some stuff yourself, not sure I have the courage. But people do do it. Not sure if I'm massively naive...

sunnysouthend Thu 27-Apr-17 18:56:36

Just reading this interesting article about ways to save money when extending - in case it helps anyone else!

namechangedtoday15 Thu 27-Apr-17 19:28:00

NW too and I think everywhere is expensive. Close family member lives in outer London and paid roughly the same as we did per square metre.

I don't think that's unreasonable - what about VAT.

As pp has said, you start with a fresh slate with a new build. No time removing / redoing what is there already. No need to match bricks in, or match floor levels, wall depth. As for 2 storey, its generally cheaper to do a 15sqm footprint but get 30sqm metres because its double storey than a 30sqm metre single storey but not by much! Nowhere near 50% discount (have never even heard that!)

sunnysouthend Thu 27-Apr-17 19:33:02

It was on that homebuilding website that comes top of pretty much any google search for extension advice (centaur media owns the site). Comes across as very knowledgable and trustworthy but I instinctually distrust these sorts of things.

I'm just driving myself mad trying to research unknowns when what I really need to do is chill my boots and get professionals out to look at and discuss things. I'm too impatient...

CountMagnus Thu 27-Apr-17 19:39:00

Adding a second storey costs less per sq m than a single storey as a good part of the costs are in the footings and the roof.

sunnysouthend Thu 27-Apr-17 19:53:03

I haven't even exchanged yet so really need to chill out but...

It is currently a 4 bed with loft conversion (no dormer) and 1/3 width single storey rear extension. I need 5 beds and a bit more living space.

My plan was a single storey extension (the 15sqm) to square off where the existing ext is, adding full width dormer to loft and moving loft stairs - the last two would allow the loft to become 2 bedrooms rather than 1.

But now I'm wondering whether leaving the loft and it's stairs alone, and adding a second storey above the new and existing rear extensions to add an extra bedroom to the first floor would be cheaper.

In the first option I think (and have been advised) that moving the loft stairs would be costly.

In the second option there may be additional cost involved if the existing rear ext does not have sufficient foundations to support a second storey.

I know I need to wait until I'm in and get people around to advise me, but I'm obsessing a little a lot

namechangedtoday15 Thu 27-Apr-17 23:25:12

Is it semi detached or detached?

BornStroppy Fri 28-Apr-17 03:59:51

two things:

1. moving stairs is hideously expensive
2. you need to dig a new set of foundations if going up a storey - this is also a majot cost. i think it takes about two weeks to do and the labout stacks up.

sunnysouthend Fri 28-Apr-17 06:06:39

It's semi.

ChunkyHare Fri 28-Apr-17 06:51:10

I had a kitchen extension 4 years ago, we are in Leeds. The extension costs came in at £1650psqm and I paid the builder £125 per day for his labour plus a skilled helper £80 per day or a less skilled helper £50 depending on what was happening.

So all in the build cost me £11.5k to first fix and plastered. Then I added a kitchen in at around £9k (Ikea units, but more expensive appliances/flooring etc) and then we paid to have the garden dug out and level off a patio area and have it paved.

Our foundations were deeper than expected. The structural engineer didn't even visit us just quoted by email what we needed as it was a standard build of house, that was a mere £160 for their service. It was to embed a vertical steel into the wall rather than have a nib of brick sticking out. We needed load calculations for the padstone the steel had to sit on.

My builder had been in the trade for over 20 years so had a lot of contacts for electrics/plastering etc and tended to use the same people all the time.

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