extension costs?

[Hudson1984]

anyone here a builder?

one of the many projects we're considering at the new house...

at the moment there's a daft sun room on the side of the house, connects to what we're using as a gym. I'd like to extend and knock out the party wall (so there would need to be a big steel bar holding the roof up - that portion of the house is a flat roof though with no upstairs)

dimensions would be:

3.36m x 4.78m

but only two walls would need making as two would be the exisiting house.

Then cover it with flat roofing.

Be interested to know what the cost would be roughly

 

[Geoff_S]

There are a few websites around that will provide a ballpark estimate. They seem to suggest anything from £1500-£4000 per square metre, dependant
on location, type of build and quality of materials.

But so many things can affect the price. When we had a small extension, very similar to yours by the sound of it, we had to have 1.6m of
concrete foundation because of tree location, which made a big difference.

What was eye watering were the ongoing costs. For example, the building estimate we received assumed 2 sockets and 1 light fitting. It was
all above board, but of course we wanted more than that, so that was extra.

Does the estimate include decorating? Does it include plumbing? What type of flat roof, felt, rubber, fibreglass? etc etc.

Your questions is quite difficult to answer. I think the only way is to spend time preparing a detail plan of your requirements and get some
builders estimates. And try to include everything that you can think of. It's sometimes easier to cut back than it is to find the extra.

I apologise if I am telling how to suck eggs.

By the way, I am not a builder, but have been a customer too many times, good and very, very bad, and hopefully the last just recently with our extension.

 

[NickN]

at the moment there's a daft sun room on the side of the house, connects to what we're using as a gym. I'd like to extend and knock out the party wall

:shock: I assume (and hope) you mean partition wall (exterior wall of house plus wall of gym)? Knocking down party walls could get you in trouble with the neighbours... :mrgreen:

but only two walls would need making as two would be the exisiting house.
Then cover it with flat roofing.

Sounds as if the sun room is just a wooden or plastic structure, so no proper walls, even dwarf ones? Which could well mean digging and placing suitable foundations for any new block/brick walls, plus both walls would need to be tied in with the current structures each side, ultimately you may find not much difference in cost between that and a simple four wall new structure. Whether you use block + render or brick makes a difference to price, and being between two structures means having a think about roof slope direction, and the feasibility of lead flashing on the two existing walls, or making the new roof higher to drain onto one side or the other.
These days EPDM rubber roofing is widely recommended (and having used several times myself, it is the way to go, stands up to a lot more abuse than felt).

Very difficult to estimate any prices though, as Geoff says, without knowing a fair bit more detail about various aspects of it. But extremely roughly, just for construction assuming double skin and foundations needed I'd say you should budget a minimum of 10k, with electrics, decorating, plastering, flooring etc. on top. I'm no professional builder either but have had plenty of work done over the years and done a lot of work myself too.

 

[novocaine]

it's outside permitted development so you'll need plans and as it involves removal of external walls you'll need structural calcs done too.

1300 quid ish for that excluding changes and amendments post approval by planning office.
1500-3000 per square metre as said above is about the going rate round here depending on what you want and what you consider to be final fit and finish (for me it's up to plastered walls. Others want tiles, paint, doors the whole caboodle), also depends on who manages it.

guess it's a "how long is a piece of string" question. ask around for a trusted local builder and get him out for a quote and to talk about what you can and can't do, they normally know, ask him about an architect or drafter for the plans, he'll know someone.

 

[Lons]

I'm a retired builder but there's no way I would ever have given a ballpark estimate or any indications without a site visit and full details of a customers requirements and expectations.

There is little detail in your initial post so it's difficult to envisage what you're describing. You need to get out your tape measure and a pencil and paper and draw it out, doesn't need to be architect standard for estmate purpose, just accurate as far as measurements, existing construction, and what you want included by way of electrics, decor etc. Nothing to stop you posting drawings and a few photos on the forum and you might get some opinions on cost from a few members.

If you're knocking through an outside wall it is most likely cavity, builder will need to know if the cavity is insulated, whether and obstructions, tree roots, drainage close to the new foundation areas and a lot more besides.
Note that it sounds as if you intend to convert the existing sunroom into a habitable room and there are regulations regarding construction and insulation as well as probable electric work and heating so you will need building regulation approval.
That area of flat roof won't be cheap and it's likely you'll have to alter it substantially to accommodate insulation so one suggestion is to get estimates for a pitched tiled roof as an alternative and compare the difference. Apart from being a better solution it usually adds value and makes a property more saleable than a flat roof. You may need planning approval but in many cases not so would need to check that.

Get at least 3 estimates based on your drawings and make notes as the builders will offer suggestions and alternatives, I would ask more than 3 builders as some might not turn up, get recommendations from friends and family and if you do decide to go ahead do some careful research into the ones you choose.
If any are significantly cheaper than expected there's a reason and you'll get what you pay for, any significantly more expensive may be overpricing as they don't need or want the job. Make sure there is a written detailed contract outlining exactly what they will do and query anything not listed before work starts. It's not unreasonable to be asked for a deposit but don't pay for the job upfront to protect yourself, a reputable company will accept that but expect to be paid promptly on completion.

Cheers
Bob

 

[MikeG.]

"How much is it going to cost, Mr Architect?"

"I don't know until we've got a design."

"I don't want to get a design done unless I know I can afford the building work."

 

[treeturner123]

In my experience, the hardest thing at the moment is GETTING a quote from a builder

(Said with feeling after chasing up 2 builders who have the plans, seen the site and still don't seem inclined to comeback with any price).

Phil

 

[Keith 66]

We built a big extension 15 years ago, the lower figure of £1500 per sq m was surprisingly accurate. I ran the job & got a friend who is a builder to do foundations walls & basic structure. Other trades such as sparks, plasterer, roofer were engaged as required through recomendation. I worked alongside & troubleshot as required (quite a bit) much cash was dispensed & this bought the price down. A surprisingly big cost was muckaway, a little trench or oversite clearance turns into an almighty pile of dirt. Our builder had budgeted for 8 grab lorry loads. In the end it took 18 loads at £150 a time. But we saved on other bits so it equaled out in the end. If we had had a builder to run the whole job it would have cost over twice as much. And we are still friends with our builder, Bonus!

 

[Hudson1984]

cheers all that's really useful. I'll "budget" toward the £1500 per m2.

Think what i'll do is live here a little longer lol, see what we really definitely need and do a few sketchup plans and then get them drawn up properly. Least I'll have something to show a builder then.

but could all be a flop if we didn't get planning permission - so have to look at the paper side of stuff first

 

[RogerS]

I think £1500 per m2 is optimistic TBH. I'd go for £2500

 

[Lons]

In my experience, the hardest thing at the moment is GETTING a quote from a builder

(Said with feeling after chasing up 2 builders who have the plans, seen the site and still don't seem inclined to comeback with any price).

Phil

I'll never really understand that either Phil but it's very common. As I said though depending on your project it isn't just a few minutes to work out and if sole traders these guys are probably out on site 6 days a week.

My reputation meant everything and I never took a job for anyone I didn't know or where I hadn't been recommended, any calls I got from people ringing around were politely refused although I did visit one or two I felt sorry for on the clear understanding it was to offer advice only. It did help however that I was never short of work.

I would always visit a site if I had agreed to and if I didn't fancy the job would say so there and then giving my reasons, if a was going to quote then I would say how long that would take. The practice of overpricing a job because you don't really want it is imo sharp practice. Builders who keep people hanging on are harming their reputation although the reasons are understandable as for a small business like mine it's pretty daunting after a long hard day to come home to paperwork and return phone calls and then needing to spend time producing proper estimates which as I said are time consuming unless you take the risk of applying standard square metre figures. I worked mine out properly so that first I was sure I would make adequate profit and second the price I estimated was as accurate as possible for my customer.
I built up a good reputation and several long term customers never wanted a price as they knew I wouldn't rip them off.

cheers
Bob

 

[MikeG.]

cheers all that's really useful. I'll "budget" toward the £1500 per m2.

Think what i'll do is live here a little longer lol, see what we really definitely need and do a few sketchup plans and then get them drawn up properly. Least I'll have something to show a builder then.

but could all be a flop if we didn't get planning permission - so have to look at the paper side of stuff first

Blimey. That really is optimistic. As a broad-brush budget figure just to set the parameters for the design you should allow at least £2000 p/sq/m + VAT.

 

[MikeG.]

In my experience, the hardest thing at the moment is GETTING a quote from a builder

(Said with feeling after chasing up 2 builders who have the plans, seen the site and still don't seem inclined to comeback with any price).

Phil

I'll never really understand that either Phil but it's very common. As I said though depending on your project it isn't just a few minutes to work out and if sole traders these guys are probably out on site 6 days a week.

My reputation meant everything and I never took a job for anyone I didn't know or where I hadn't been recommended, any calls I got from people ringing around were politely refused although I did visit one or two I felt sorry for on the clear understanding it was to offer advice only. It did help however that I was never short of work.

I would always visit a site if I had agreed to and if I didn't fancy the job would say so there and then giving my reasons, if a was going to quote then I would say how long that would take. The practice of overpricing a job because you don't really want it is imo sharp practice. Builders who keep people hanging on are harming their reputation although the reasons are understandable as for a small business like mine it's pretty daunting after a long hard day to come home to paperwork and return phone calls and then needing to spend time producing proper estimates which as I said are time consuming unless you take the risk of applying standard square metre figures. I worked mine out properly so that first I was sure I would make adequate profit and second the price I estimated was as accurate as possible for my customer.
I built up a good reputation and several long term customers never wanted a price as they knew I wouldn't rip them off.

cheers
Bob

Most builders I get involved with use a QS to do their pricing for them. This costs them about £600 for a typical domestic extension & alteration, and much more for bigger jobs. This is one reason why I seek interest first from builders before going out to tender, and why I never ask more than 3 builders to quote for a job. In comparison with a builder's estimate, a QS price is fantastic, with itemised and individually costed elements making things clear both for the customer, and helping in the contract valuations every month.

-

One of my favourite local builders is booked up until late 2019. Most others are almost as busy. Now is not an easy time to get builders to quote, and this will be reflected in the prices that people can expect to pay.

 

[HOJ]

I would initially find a builder, preferably one who comes with recommendations, and someone you can work with, they will be able to give you guidance as to what can be done and will probably know the local area, with regards any known issues with soil types which will dictate the type of foundations required, too many times I have seen assumptions made, only to find the site is on impermeable clay with a high water table and trees, inuring considerable costs, for instance.

They may also be able to give guidance on the suitability of the existing building/footings for any additional structural loads that you will add.

Whilst this is only a relatively small project you need to establish an affordable budget, again I have been to many potential projects where the budget just wasn't realistic enough, speculative meter rates are fine but it is all too easy to spend money on designers, planning applications, Structural Engineer's and building regulations only to find the cost to build is prohibitive.

 

[MikeG.]

I would initially find a builder.........

And the first thing he'll say is "have you got any drawings?". Start with an architect, not a builder.

 

[ScottGoddard]

It really depends on how complex the build is. We are currently / planning an extension and refit of our kitchen. The extension will replace a small conservatory, knock down a couple of walls. . I manage to get a quote without drawings (although these are being commissioned in the next week or so, through the builder's contacts). So it can be done, he was happy doing this because he has done lots of these types of extensions.

Quote below - He wasnt the cheapest but he was recommended and we got on well through our discussions.

Schedule of works to be carried out (Extension 4.4m x 2.2m) - total cost about £38k...

- To remove and dispose of existing lean too roof and parapet walls as discussed

- To dig new footings for extension 600mm (w) x 900mm (d).

- To fill foundations using a gen1 concrete mix 600mm (w) x 250mm (d)

- To build out of the ground up to D.P.C Level using 7N trench blocks up to DPC level.

- To construct concrete slab firstly by laying down 150mm of sub base hardcore compacting sub base, followed by 25mm of sand blinding, then a D.P.M must be put down, followed by 100mm Celotex insulation and then pouring slab using a pq1 concrete mix 150mm (d), finished with 60mm of screed.

- To construct new extension 4.4m x 2.2m up to wall plate level using cavity walling system, using face brickwork to match property on the external layer and using 100mm thermalite blocks to internal skin, cavity to be insulated using 70mm celotex insulation boards taped with aluminum foil joint tape, door reveals to be closed using cavity closers.

- To supply and put in steel beams complying with structural engineers calculations to span the opening in new extension, all steels to be treated with red oxide primer and to be sat on a minimum of 300mm load bearings.

- To construct lean too roof to new extension according to plan and specifications using 8x2 treated timbers, all braced with truss clips, and wall plates to be strapped every 1800mm to comply with building regs.

- To supply and fit two UPVC Velux S07 roof windows with flashing kits.

- To provide tiled roof to match the property, laying down a breathable membrane and laying tiles onto 2x1 treated battens, roof to be insulated using 150mm of celotex insulation and also roof to be vented for added ventilation and to be sealed with code 4 lead works where roof meets existing building.

- To finish extension with new fascias, soffits and guttering in UPVC

- To run any new drainage works for extension

- To knock out walls according to plans to provide a large open planned kitchen/dinner, supporting upper walls and floors every 6ft using ackro props and then installing structural steel UB’s to take the load of upper walls and floors. Steels to be sat on concrete pad stones with a minimum load bearing of 300mm and to be primed using red oxide primer.

- To box in steels using 1 hour fire rated plasterboard and skim using multi finish plaster and to patch up and make good where needed.

- To plasterboard and skim new extension to a smooth finish.

- To provide new skirting’s to match the property to new extension, priming, undercoating and glossing.

- To self level existing floors into new extension to provide a better finished floor.

- Client to pay for finishing exterior doors to extension

- To supply and fit new upvc back door to utility area.

- All electrical work to be carried out according to plans and to comply with building regs. All electric work will be carried out a NIC registered electrician who will sign off the electrical work and supply a certificate for building control.

- To supply and fit 22 chrome fires rated spot lights to comply with regs.

- To move any sockets and light switches where demolition is taking place.

- To install 15 new PowerPoints in total and electric points to new kitchen area to clients choice.

- To supply and fit TV points in new extension to client choice

- To provide 2 new outside lights feeds, client to supply finishing lights

- All waste will be disposed of via skips and recycled.

- To decorate rooms in colours to client’s choice and all wood work to be primed, undercoated and glossed.

- No allowances have been made for any external patio or paths around new extension but can be arranged.

- To finish floor with either tiles or solid wood flooring to extension and kitchen throughout to clients choice. (Client to supply all tiles or Flooring).

- To get gas safe registered plumber to relocate any gas supply to kitchen or cap off

- To provide protective sheeting throughout property whilst work is in progress

- To block up existing kitchen doorway and plaster both sides of doorway

- To remove and dispose of existing kitchen, tiles and to make good any walls where tiles have been removed.

- To take down ceiling in kitchen, dining area and dispose of to allow for relocation of proposed electrical and plumbing.

- To allow for electrical under flooring heating and digital stat, allowing for latex self-levelling floors to protect wiring before tiling.

- To allow for the fit of new radiator to proposed dining area (Client to supply Radiator and Valves Only)

- To allow for the relocation, alteration or renewal of gas, and water supplies according to kitchen layout and to allow for providing water feed for proposed new fridge.

- To completely tile kitchen floor using tiles supplied by client, using rapid set flexible adhesives and grouts.

 

[user22161]

I can't believe the prices being quoted. Although not a builder by trade I've done quite a few extensions and a couple of self-build houses just paying brickies and plasterers. The last job I did was extending my garage to get workshop space.

The 17' x 4'6" extension is a continuation of one roof slope, 3 single brick walls, sloping down to 5ft, toothed into original brickwork, with an rsj supporting the original wallplate. 4 ft deep foundation took quite a bit of concrete as bad ground and would easily take cavity wall. Bricky paid day rate, I mixed and laboured some days, did roof, wiring etc. myself, mate and I did the foundation with mini digger and powered wheelbarrow hired for one day. Major single cost was skips to get rid of old brickwork and ground/foundation spoil.

Total cost £3,200. OK, the OP's extension will be higher and cavity wall + plastering etc. but that shouldn't more than double the price as the major cost of foundation, roof, skips etc will remain the same. Didn't use architect or surveyor, did drawings and planning application myself and no building regs. on a garage.

 

[Geoff_S]

I can't believe the prices being quoted. Although not a builder by trade I've done quite a few extensions and a couple of self-build houses just paying brickies and plasterers. The last job I did was extending my garage to get workshop space.

The 17' x 4'6" extension is a continuation of one roof slope, 3 single brick walls, sloping down to 5ft, toothed into original brickwork, with an rsj supporting the original wallplate. 4 ft deep foundation took quite a bit of concrete as bad ground and would easily take cavity wall. Bricky paid day rate, I mixed and laboured some days, did roof, wiring etc. myself, mate and I did the foundation with mini digger and powered wheelbarrow hired for one day. Major single cost was skips to get rid of old brickwork and ground/foundation spoil.

Total cost £3,200. OK, the OP's extension will be higher and cavity wall + plastering etc. but that shouldn't more than double the price as the major cost of foundation, roof, skips etc will remain the same. Didn't use architect or surveyor, did drawings and planning application myself and no building regs. on a garage.

Sounds about right for what you have described. If you're able to do most of it yourself, then that makes a huge difference.

Believe the prices on here if you're going to get a good builder to do it.

Yours was roughly 7 square metres, so at £1500 cheapest, that would be £10,500 if a builder did it, including plumbing, electrics, cavity wall & insulation, ceiling & insulation, damp proofed and insulated floor, plastering, painting and decorating. Add a door, window. drainage, it soon adds up if you are
not a DIY'er and you want to live in it.

Decent chippy round here, £200 day cash. Plumber, electrician £300+ a day through the bank. A man and his digger round here is £500+ per day!

Makes me feel dizzy, but there it is.

 

[MikeG.]

I can't believe the prices being quoted. Although not a builder by trade I've done quite a few extensions and a couple of self-build houses just paying brickies and plasterers. The last job I did was extending my garage to get workshop space.

The 17' x 4'6" extension is a continuation of one roof slope, 3 single brick walls, sloping down to 5ft, toothed into original brickwork, with an rsj supporting the original wallplate. 4 ft deep foundation took quite a bit of concrete as bad ground and would easily take cavity wall. Bricky paid day rate, I mixed and laboured some days, did roof, wiring etc. myself, mate and I did the foundation with mini digger and powered wheelbarrow hired for one day. Major single cost was skips to get rid of old brickwork and ground/foundation spoil.

Total cost £3,200. OK, the OP's extension will be higher and cavity wall + plastering etc. but that shouldn't more than double the price as the major cost of foundation, roof, skips etc will remain the same. Didn't use architect or surveyor, did drawings and planning application myself and no building regs. on a garage.

A garage is hardly comparable with a house, and you did a chunk of the work yourself. A single skin wall only 5 ft high isn't a useful guide for an insulated double skin plastered wall 8' high per storey. A garage doesn't have any 2nd fix carpentry. I would give a budget figure for a straight-forward garage on ordinary ground at £750/ sqm....and I know this is right because I've just had the tenders back on Friday for a garage I drew before christmas.

Really, I do this stuff for a living, and people having unrealistic budgets is a big problem. It may well be possible to reduce the costs somewhat by doing certain elements yourself, by managing sub-contractors rather than having a main contractor, but at the stage the OP is at £2000 /sqm + VAT is a reasonable starting point for the conversation. I've had smaller projects recently amount to over £3000+VAT /sqm.

 

[user22161]

O.K, I see where you're coming from. I've never employed a main contractor for anything, I do what I can myself and pay other trades in cash (bricky, plasterer, sometimes roofer if large) when necessary. The mini digger and powered wheelbarrow hire for footings only cost £100 for the day and retired mate drove the digger for free

The price I quoted was for this photo below. Add-on cost if it were a house extension would be extra 3 ft of face brick - plus backing up with block, ties & insulation and plasterer, windows would also be extra. The rest (plumbing, wiring, flooring etc.) I would DIY. Price quoted obviously didn't include the paving.