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how do you go about extending a house?

(24 Posts)
tranquilitygardens Mon 12-Sep-11 17:21:39

Hi, I have chopped and changed my mind so much about housing, I have now decided that I am going to buy a small older house.

I would like to extend it at the back, I know you have to get plans drawn up, and apply for planning etc.

Roughly how long does that take and cost?

Then you have to get some builders quotes and get the work done, again how long does it take to wait for builders and the work to be done and what sort of costs am I looking at?

I know it is a bit of a how long is a piece of string question, just a rough idea would be good!

I was thinking of an extension with back wall knocking down, so rsj's on that, and a sloping roof, left with high celing, two sky lights, and white upvc bifolding doors out the back. I was thinking of the extension to be about 20 x 15 old money!

twotesttickles Mon 12-Sep-11 21:47:21

Okay, let's start from the beginning. You can extend any non-listed building by 10% of its volume without planning consent providing it is single story (or I think under 1.8 metres - google it). Unless you live in a conservation area.

If you do need planning consent you get plans drawn up by a builder or architect. Then you submit a planning application which costs about £250 plus the cost of the plans. That will be decided within about six weeks.

Builders quotes take a couple of weeks. GOOD builders will not be available very quickly though.

What you have scoped out will cost between £20 and £30K depending on materials all in. You could at a push get it for around £15K.

tranquilitygardens Tue 13-Sep-11 14:14:39

twotest, thank you for the response, it was really helpfull.

So the slow bit then is organising people to do the work and waiting for plans to be accepted. The painfull bit is the builders dust and paying the money out, one big ouch!

tranquilitygardens Tue 13-Sep-11 14:15:42

Just thought of another question, should you pay the builder a deposit and how do you organise a contract and schedule of payment so that you don't get ripped off by a builder?

Pendeen Tue 13-Sep-11 16:34:25

Cost: can be between £800 and £2,500 per square metre.
Time: can take (on site) anywhere from 8 to 20 weeks

all depends on size, complexity, locality, access and a million other things.

Look here for guidance about what you need as regards statutory consents:

Interactive House

Here for information on the implications of building on or near boundaries:

Party Wall Act

Here for a typical building contract for the smaller / domestic projects:

JCT Contracts

or.... (now for the self-serving commercial)

take the easy way and use an Architect who will guide and help you as well as creating a delightful addition to your home:

RIBA Website


SparklePrincess Tue 13-Sep-11 18:30:22

Sorry to hijack. blush Approx how much would an architect charge to draw up & submit plans for an extension like this? The one were planning on is about 14ft by 11ft with a pitched roof. Nothing special...

ChitChattingWithKids Tue 13-Sep-11 18:46:48

If you don't have a builder in mind, you could just get an architect to draw up a plan. It cost us £1,000 and if we wanted the detailed drawings for Council another £800. Council approval here cost £650 (just 1 room upstairs, but the roof needed to be altered hence planning approval).

We did it under Building Regs, but TBH next time I would just spend the extra getting the detailed drawings done up by the architect and not go under building regs - just those drawings approved by council, the council fee is no more.

When you submit a plan for planning approval you get inundanted with builders contacting you, both small and large. It is a quiet time at the moment for a lot of builders. Just because they are chasing work doesn't mean they are not good builders! Chasing planning approvals is cheaper than advertising.

Ask to see photos of previous work, and ask if they would mind you talking to some previous clients. If they object, stay away.

Best to get a local builder, because if a problem crops up they are better able to deal with it, have established links with suppliers, subcontractors, etc.

Very iffy if they want a deposit. A good builder should have trade accounts and they don't need to pay in advance. They do, however, need to pay for things as the job progresses if it takes awhile. They also need to pay subcontractors. The only one that I would say might need some deposit would be the plumber because copper piping is pretty darn expensive at the moment!! So you need to set up a schedule of payments, and a job list which can be ticked off.

Make sure the builder does a DETAILED price list. A one liner doesn't cut it I'm afraid. Way too easy for them to say 'oh, you didn't say that's how you wanted it done. That will cost £x more'. Put what you want in writing, and give it to them, and insist it is included with the quote they return to you to make sure that is what they are quoting on.

SparklePrincess Tue 13-Sep-11 18:57:43

Very interesting.. Thanks ChitChattingWithKids. smile That sounds v expensive!! Im surprised you said builders will contact us when we go for planning, as this wasn't the case when I was with my ex & we put in for planning on an extension a few years ago. Nobody contacted us at all. Perhaps it is because it was a very complicated design. My ex father in law is an architect & drew up the plans. I remember him saying it was the most complicated thing he'd ever designed. LOL! In the end the extension was never used by us as the ex built it himself brick by brick over 3 years. sad We moved house on its completion & split up soon after.

ChitChattingWithKids Tue 13-Sep-11 19:00:48

Our planning approval came through a month ago and we have had a constant stream of brochures and letters!

SparklePrincess Tue 13-Sep-11 19:02:52

Cool! I hope its the case when we move to Surrey & go for it. Currently in East Sussex. smile

ChitChattingWithKids Tue 13-Sep-11 19:19:38

Have PM'd you!

SparklePrincess Tue 13-Sep-11 20:42:08


twotesttickles Tue 13-Sep-11 21:23:06

Sorry wandered off. It is best to get a written contract with a builder, you can get free sample contracts online if you google. I personally go for traders who are approved by your local authority because they are followed up so if they go bad they are quickly kicked off the list. Contact your local trading standards (Age concern do a similar list but you can use it at any age).

A good builder will give a schedule of payments upfront which will not require you to pay more than 30% upfront. Be very honest when you get the quote about what your expectations are and ask 'are my expectations reasonable' - people have some very funny ideas about what is possible. For example, don't expect to put up an extension in September and not have some delays to allow for drying out because there isn't time between storms to build the walls AND make the place totally watertight.

If you are minded to manage the contractors yourself for goodness sake build at least 30% contingency in, the first time you do it you will fuck up. smile Do not allow your DH to measure anything and take his word for it and advise him to do the same. Mine ordered a bath which would not go through the door and the builder believed him because he was a bloke hmm

Architects, someone asked. Yes £1000 plus £800 is about right (ours cost £4k all in to do some quite detailed drawings and an extensive planning application including listed buildings and conservation area work).

tranquilitygardens Tue 13-Sep-11 21:51:02

thanks, it all sounds a bit of a night mare, arrgggghhh!

There is loads of info there.

How did you get the bath situation sorted in the end Twotest?

I will be the only adult in the house, which makes me feel quite vounerable about attempting to do this, and I have never had an extension built previously, so a huge novice.

SparklePrincess Tue 13-Sep-11 21:53:10

WOW! That sounds expensive. At that rate we wont be able to afford to do an extension. It's only a small basic single storey thing, nothing complex. I was sort of thinking 20k all in... We currently only have 15k added on to our proposed mortgage & intended to save more & probably get it done in a years time. At this rate it will be more likely to be a conservatory or something smaller coming under permitted developments. sad

twotesttickles Tue 13-Sep-11 21:58:24

Returned the bath for a 20% restocking fee hmm

Was. Not. Impressed. Confiscated all tape measures forthwith.

It's okay actually. The important thing is to start with a list: I want X and it has to be this size, shape and positioned here. It will have a window, here and here and the roof and walls will be made of Y. I want these doors, I want the fabrics used to be Z and A. Building control regs govern a lot of the stuff you used to be able to get shafted on. Basically you want safe, insulated and useable. Anything else is just bonus. Do interview a couple of builders though and don't just take the lowest price, go for the one which gives you confidence s/he will do the job well.

SparklePrincess - it is possible to build small extensions for £10K, but obviously they won't be as high spec and then you tend to spend quite a bit adding bits (flooring, lighting etc.) which you held back from paying for to start with. Conservatories do not last forever either, even plastic ones after 30 years start to fall down.

SparklePrincess Tue 13-Sep-11 22:25:37

I don't really want a conservatory anyway twotesttickles. Heard too many stories about people finding its an unusable room most of the year. We want the new space to be our main living room ideally. What you have said helps me think maybe it is possible after all. smile I suppose ill have to wait till were in the house & get some quotes.

ThePrincessRoyalFiggyrolls Tue 13-Sep-11 22:38:02

OK, think planning depends on the local authority as far as price is concerned - we are doing this at the moment. Architect depends on what you are doing - we have paid a fair amount for ours but he is also doing the project management so that is why it was expensive. Planning consent can take as little as 6 weeks - ours hasn't had any issues apart from bats, we have had to check this out with someone who is "qualified" (we are rural) and have to pay someone to check the trees too <sigh> irritatingly we have had to pay more than most for some of these things because the local authority have been twatty and our home used to be a business which they hadn't changed on their records - but if we didn't pay then a) it wouldn't have gone through and b) they were threatening that they could evict us for misuse of property (we blame our sodding solicitor for this "oversight" - twat) (and previously had sodding planning permission for what we wanted to do <hear my sigh>)
We then put out to "tender" with a date that builders had to get their quotes back to us and if not then they wouldn't be considered. They are a variety of builders - one architect uses regularly and lives close by and one that we have used before, third decided he didn't want to quote because of proximity. However both builders are trustworthy as first is used by architect regularly, 2nd as I have said has already done loads of work for us/family/friends so will be a real decision for us on price and timing. 1st isn't so busy at the moment and wants work close to home, 2nd got lots of work on.
Should point out that architect is family too but setting up on his own so we are paying him. Also you don't have to act immediately on your planning permission as they last for 7 years. most local authorities are happy to give planning, neighbours aren't always though so bear that in mind and you may have to pay for updates/changes if this happens. But it is a little like saying how long is a piece of string grin. You can also set a budget for your architect. However if you are buying somewhere smaller to extend it is more likely to be cheaper to do this than to buy the perfect house. Also if you do buy somewhere perhaps live in it for a little while to make sure this is exactly what you want to spend your money on.

Sorry for soliloquy

It is a long process

Pendeen Wed 14-Sep-11 10:08:23


If you look at my comments above, you will find some useful links including an industry-standard form of agreement suitable for domestic projects.

As regards charges for architectural services, these vary widely depending upon the level of involvement in a project. This can be from simply 'drawing plans' right up to full design, contract administration and supervision of the work.

The basic 'drawing plans' service would be to produce a drawing for submission to the local council to obtain building regulation aproval and (if necessary) planning permission and maybe listed building consent. That would be the end of the Architect's involvement unles there were any technical queries.

Foe a simple flat roofed 'box' extension with no issues (e.g. no planning consent required, listed building, unusual construction, lots of trees, etc) I have charged as little as £400 to produce site and location plans, floor plans, elevations and sections.

I have to say (and not wanting to talk you out of using a fellow Architect) but, there are many other people who are capable of providing a service for simple work - architectural technicians / technologists, etc. or even some builders will offer a 'design & build' service.

Just don't expect much in the way of creative thought or design flair!

<awaits flaming> smile

ThePrincessRoyalFiggyrolls Wed 14-Sep-11 16:53:09

Pendeen, am with you, we did a loft conversion and used the builders architect as they do them day in day out and they were included in the whole price anyway smile so it worked, you are right it is all about what you want to achieve from your extension, for us we have the building already and want to convert it - it is still cheaper to know exactly what we want to get from the building to the floor print that is already there - however if there is no structure there then it is a blank sheet smile

jeanjeannie Wed 14-Sep-11 17:14:18

twotesttickles has pretty much said what I was going to say re: hiring builders. They should have trade accounts. They should also have a contract of their own which they then thrash out with you - so that both of you don't get ripped off! My DH has suffered with doing work and then the client not which time the trade account bills have started to come in.

Staging payments also gives you chance to assess the work - talk about any changes, hitches etc and move forward smoothly. One top tip - be as precise as you can with what you want from the outset....changes cost time and money smile

tranquilitygardens Wed 14-Sep-11 17:28:25

This is so very helpfull, thank you.

SparklePrincess Wed 14-Sep-11 21:22:08

Yes, very helpful. Thanks. smile

Doozie Sun 18-Sep-11 09:35:44

tranquilitygardens this is our thinking as well. Bigger houses with the layout we want all seem to be beyond our budget so we are thinking of buying a smaller house with plans to extend. I have no idea how much it will cost, but I'm wanting an open plan kitchen/dining room/living room to open out onto the garden. Has anyone made these types of changes and how much did it cost?* The above info has been very helpful as a starting point.

*I love MN - I would never ask someone how much something cost in RL!!


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