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cost of house extension

Mep

Well-known Member
I know this is potentially a "how long is a piece of string" type question, but I'd be grateful for a ballpark estimate (nearest £5k) from anybody in the building trade or who has had something similar done.
We are looking at a property that has potential to extend out to the side, over the attached garage. This would basically give one of teh bedrooms an en-suite shower roomand make another bedroom larger. I believe the garage would also need work to support a second storey.

Very grateful for any thoughts
 

Alan_W

Active Member
We did this last year.
I know nothing about DIY/building so sorry if this is a bit simplistic!

First thing to do is to check the foundations of the existing garage to make sure they will take extra storey. Need to dig big hole down to expose foundations. Needs surveyor to approve foundations.

The floor was just suspended on timbers above the existing flat roof. Walls were quite cheap. Most of the expense was the roof and the inside. We had to extend the existing roof out, as opposed to having a flat roof, or a sloping roof with dormers. Just when I thought I had contained the cost, my wife insisted on choosing the bathroom :eek: :eek: :suicide:

My advice is to think about the roof carefully. I had a friend who is a builder who gave good advice, and a good idea on price as opposed to another friend who is an architect, and drew up some plans but whose price estimate (even before my wife) was hopeless.

The expense set my plasma back 6 months :(
 

Knyght_byte

Distinguished Member
if the garage needs work, then for an average size extension of around 12ft x 10ft you'll be looking around £15k......plus or minus £3k for variables.....of course that also depends on if you can get an honest builder in...also just how much plumbing you need.....

this doesnt count interior decorating......so you could be adding another £2-5k or more....

i'm basing this on knowledge from my dad who was in the tool trade and has often asked clients he dealt with on advice for extensions......

if the garage was sound to take a room above it, tbh £2.5k would do it, just need materials and machines....build it yourself to save another £5k.....heh

but if the foundations need redoing to support it then its gonna be more expensive....

otherwise you looking at subsidence issues.....heh..believe me, not what you want come selling time in the future....
 

Mep

Well-known Member
many thanks for all the info chaps, I'm pretty sure the garage will need the foundations doing..........was hoping for a max of 25k which looks like it may be possible.
It's one of those tricky things of trying to get an idea of costs before I decide whether or not to buy the house.....need to find a friendly builder now I guess.
 
A

av2diefor

Guest
Paul, how you doin?

RE your proposed extension,

You will need about 1k to get it off the ground for planning fees, building regs and the cost to have the plans drawn up.

If its a pretty standard size garage 2.4m by 7m with a bedoom over its likely to be around 30k inc vat.

This takes into account a pitched roof tying into the existing house, electrical and the provision of a radiator or two.

Bear in mind the scaffold alone will be around £600!

The existing garage is normally only 100mm brickwork and cant support a cavity wall over and we normally underpin the exixting founds and widen them.

You can get over that by building piers and slinging rsj's through, this normally works well as they go at high level and dont restrict internal space in the garage.

We do approx 20/30 of these a year and the price indicated is the going rate for a contractor to do the lot.

If you want to go ahead i suggest you put your PHD8 in the for sale thread;)
 

Solomon Grundy

Distinguished Member
We extended the back of our place (a bungalow) last year for a new living/cinema room 10m x 5m and it cost £16,000.
 

Orson

Well-known Member
I've just (well, almost) completed the same as you're contemplating. I had an attached garage, and the paln was to build on top. I dug down & exposed the footings (and also exposed how unfit I am), and got the local Building Control Officer to come along and look at my hole :oops:, which he did, free of charge. Although mine was okay to build on, the brickwork was double skin, but didn't have enough of a cavity between (same as the rest of the house) to satisfy modern building regulations. This would have meant lining the internal wall , and an unsightly detail where existing met new, so I opted to take the lot down & build new. The other benefits to me were I could build exactly where I wanted (slightly different to the original garage size), but best of all, it meant I could re-use the bricks & roof tiles from the garage on the front of the new extension, therby matching the existing brickwork excactly.

As regards price, you'll want aroun £1000 for plans, applications & permissions etc. I had a few quotes for mine, ranging between £30k, & £69k :eek: .

I've had a pretty interesting last few months, but it'sll be worth it!
 

Mep

Well-known Member
av2diefor said:
Paul, how you doin?

RE your proposed extension,

You will need about 1k to get it off the ground for planning fees, building regs and the cost to have the plans drawn up.

If its a pretty standard size garage 2.4m by 7m with a bedoom over its likely to be around 30k inc vat.

This takes into account a pitched roof tying into the existing house, electrical and the provision of a radiator or two.

Bear in mind the scaffold alone will be around £600!

The existing garage is normally only 100mm brickwork and cant support a cavity wall over and we normally underpin the exixting founds and widen them.

You can get over that by building piers and slinging rsj's through, this normally works well as they go at high level and dont restrict internal space in the garage.

We do approx 20/30 of these a year and the price indicated is the going rate for a contractor to do the lot.

If you want to go ahead i suggest you put your PHD8 in the for sale thread;)


:D thanks for that Graham (doing fine by the way thanks) reckon I may need to put the wife and kids in the classifieds too!.....
 

Mep

Well-known Member
Orson said:
I've just (well, almost) completed the same as you're contemplating. I had an attached garage, and the paln was to build on top. I dug down & exposed the footings (and also exposed how unfit I am), and got the local Building Control Officer to come along and look at my hole :oops:, which he did, free of charge. Although mine was okay to build on, the brickwork was double skin, but didn't have enough of a cavity between (same as the rest of the house) to satisfy modern building regulations. This would have meant lining the internal wall , and an unsightly detail where existing met new, so I opted to take the lot down & build new. The other benefits to me were I could build exactly where I wanted (slightly different to the original garage size), but best of all, it meant I could re-use the bricks & roof tiles from the garage on the front of the new extension, therby matching the existing brickwork excactly.

As regards price, you'll want aroun £1000 for plans, applications & permissions etc. I had a few quotes for mine, ranging between £30k, & £69k :eek: .

I've had a pretty interesting last few months, but it'sll be worth it!

thanks mate, I prefer the lower quote which ties in nicely with av2diefor's estimate too.
 

Mep

Well-known Member
Decadence said:
We extended the back of our place (a bungalow) last year for a new living/cinema room 10m x 5m and it cost £16,000.

the place i'm looking already has a room suitable for HC luckily......obviously that is number 1 priority with little details like bedrooms and bathrooms coming further down the list :D
 

Mr_Wistles

Distinguished Member
mep said:
I know this is potentially a "how long is a piece of string" type question, but I'd be grateful for a ballpark estimate (nearest £5k) from anybody in the building trade or who has had something similar done.
We are looking at a property that has potential to extend out to the side, over the attached garage. This would basically give one of teh bedrooms an en-suite shower roomand make another bedroom larger. I believe the garage would also need work to support a second storey.

Very grateful for any thoughts

Basically all you will be doing is adding a bathroom. No extra rooms, only making an existing room larger.

I would be suprised if your outlay would be more the price increase of your house.
 

Mep

Well-known Member
Russell_Piper said:
Basically all you will be doing is adding a bathroom. No extra rooms, only making an existing room larger.

I would be suprised if your outlay would be more the price increase of your house.

it would make an already very nice property ideal and I think yo are right...it should pretty much pay for itself on paper
 

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