Another extension question

Beenie

We have planning permission to build a single storey extension on our bungalow. Due to the area where we live (on London clay or 'terminal morain') we have to have a structural engineering company to bore some soil samples, and then advise on the cost of groundworks.

The extension will be 30sq metres. I know that the costs above ground are roughly £2K per sq metre, but does anyone know the costs for doing groundwork/foundations (could need piling if we are unlucky with the soil and it turns out to be mostly clay).

We are in Essex.

Doozergirl

It can't be guessed.

Have your ground checked and the structural engineer will give you a guide as to the cost of different available options.

A guide of £2,000 per metre is an apparant guide to the cost of building a building, not just above ground. The actual cost is somvariable though becuae there are so many different ways to build in so many different shapes and sizes. Any type of foundation that isn't a bog standard strip is going to cost you more but there's no point trying to guess until it's been assessed.

Furts

I am curious here. I am guessing you have a Structural Engineer on board, or else you would not be ground sampling. But the Engineer should have a gut feeling for the outcome and approx costings. Hence why ask unknown folks on the Forum when the answer is available from a qualified professional who has seen the site?

My curiosity includes your bungalow - if the ground is so bad what detail exists to hold that up? What state is the bungalow in structurally? Plus how will you deal with the joint between new and old?

To cap it all, trench fill goes down to 2 metres or somewhat more when pushed. Which means for a single storey extension, and assuming no trees are present, one would hope this could be the outcome.

I cannot stab at the costings but if you end up with piles, pile caps, ring beams, and a structural floor slab it must be a really viable scheme you are proposing. Many folks would not bother! Or they would demolish and start again from scratch perhaps?

Beenie

We don't have a structural engineer in mind yet. The basic plan for PP was drawn up by a mate, and we are being left to our devices to pursue builders and engineer(s) for quotes.

Our bungalow is built into a hill, and is on two levels (we live on the upper level) and ground level is garage, boiler room etc. It's a fairly unusual home in a nice part of the county. It's worth spending money on an extension as we would never replicate the space and privacy we have here.

Furts

Beenie wrote: »

We don't have a structural engineer in mind yet. The basic plan for PP was drawn up by a mate, and we are being left to our devices to pursue builders and engineer(s) for quotes.

Our bungalow is built into a hill, and is on two levels (we live on the upper level) and ground level is garage, boiler room etc. It's a fairly unusual home in a nice part of the county. It's worth spending money on an extension as we would never replicate the space and privacy we have here.

I realise now that the post is a total wind up! Fair play because you did take me in!

However let us go along with it because fellow forum users might gain knowledge from this, myself included...

You are crazy to be going about matters in this manner. You could end up being taken for an enormous ride. With a split level bungalow, on a hill, in a nice part of southern England I am left speechless. To cut corners now before ever starting work beggars belief. It is not as if you could argue "the project does not warrant it".

Get professional help on board now, get proper drawings produced, engage a Structural Engineer if the advice given is one id s needed, then get a full set of working drawings, a Specification and a Full Plans Buildings Regulations Approval. Obviously services, build overs and every thing else, including CDM becomes part of this package.

Time for a reality check me thinks!

Beenie

I don't think I mentioned cutting corners. We have been steered towards engaging a structural engineer (which we will do) but my point was that our friend is letting us choose the firms we feel comfortable with, not people recommended by him. Several neighbours have given us names of good people to work with.

My OP was to get an idea of likely costs involved. That is hardly an outrageous ask, and it is what this board is for (I thought).

Furts

Beenie wrote: »

I don't think I mentioned cutting corners. We have been steered towards engaging a structural engineer (which we will do) but my point was that our friend is letting us choose the firms we feel comfortable with, not people recommended by him. Several neighbours have given us names of good people to work with.

My OP was to get an idea of likely costs involved. That is hardly an outrageous ask, and it is what this board is for (I thought).

I re-iterate - you are going about matters in the wrong manner. I repeat that I am left speechless at your approach to the works. It all comes across as corner cutting, whether that is you intention or not. In fairness, it could be a total lack of knowledge, but if so then take heed of what people suggest. Alternatively if it is a case of you wishing to plough your own furrow that is fine by me. Accepted, and time proven procedures do not have to be followed. Your alternative approach may turn out OK. But this is arisky scenario for the majority of folks.

Equally, it is impossible to say what the groundworks will cost, and even more so now there is a consultancy involved. The good Doozergirl has told you this, and I am also saying much the same

Since you do not like my observations, it is best that you continue as you are. I wish you well.

Beenie

I don't understand your hostility.

We are at the very beginning of a project. It might not proceed.

We are reliably told that the ground-level building costs are £2K per sq metre.

What I was hoping for was someone who had had the sort of underground work that I have described done, in the south east, and could say 'For piles and concreting to a depth of X and an area of Y, you are looking at £Z per sq metre.'

If that is an impossible question to answer, fair enough. We aren't in the building trade, and have never had an extension built before, so it wasn't unreasonable for me to ask what I thought was a fairly innocuous question.

Doozergirl

It's far too specialised to answer. Piled foundations are not common.

£2k above ground can't really be reliable information either. I mean, it sounds a very safe suggestion and is based more in reality for quailty work than many people's ideas but costing is much more of an art than it is science and we need as much information to work on as possible to even begin to *work* on an answer. There will be more than one option available to you.

As soon as you engage your structural engineer, they will provide some guidance. The firm we use also provide the specialist services to get people out of the ground so they have an actual idea.

Beenie

Thank you Doozergirl.

Our house is real 'one off' in a relatively secluded setting, in a conservation area, and the village is surrounded by NT land.

We want to make the most of this position (other bungalows have been demolished and 5-bed executive styles built on the land instead). At some point I could imagine a property developer demolishing our house and building a HufHaus in its place - but not yet.

It is worth taking our time and learning as much as possible about materials and construction techniques. I look in here at MSE quite often to see what other people's costs are, and I realise that ours is probably at the high end (we have budgeted £150K for a single storey with bi-fold doors).

A final comment, when I said mate, I didn't mean some bloke down the pub. I meant that a friend who is an architectural technician did our basic plan. He says we should get builders round when the specific plan for Building Regs has been drawn, and a structural engineer to do his bit asap. We will do that of course, but were curious about ball-park costs for the (potential) underground works. Not to worry, I have learned a bit more in this thread and hopefully it will be useful for anyone else in a similar position.

Furts

Beenie wrote: »

Thank you Doozergirl.

Our house is real 'one off' in a relatively secluded setting, in a conservation area, and the village is surrounded by NT land.

We want to make the most of this position (other bungalows have been demolished and 5-bed executive styles built on the land instead). At some point I could imagine a property developer demolishing our house and building a HufHaus in its place - but not yet.

It is worth taking our time and learning as much as possible about materials and construction techniques. I look in here at MSE quite often to see what other people's costs are, and I realise that ours is probably at the high end (we have budgeted £150K for a single storey with bi-fold doors).

A final comment, when I said mate, I didn't mean some bloke down the pub. I meant that a friend who is an architectural technician did our basic plan. He says we should get builders round when the specific plan for Building Regs has been drawn, and a structural engineer to do his bit asap. We will do that of course, but were curious about ball-park costs for the (potential) underground works. Not to worry, I have learned a bit more in this thread and hopefully it will be useful for anyone else in a similar position.

Talk about a story slowly evolving, talk about a story changing ...