large extension - whats the process?

Wait for the recession to kick in & all trades will bite your hand off for the work?

Other than producing a very large sum of money, what’s next?

call kevin in, get pregnant, go massively over budget, find a spare £500k to finish the project?

Have you not employed the architect to draw up the building warrant package (or that just Scotland?)to send out for tender? I would expect structural engineer stuff to be done as part of that.

I’m not sure if we need a sturctural engineer before we go to builders, or if the builders cover that off as part of their service?

Either - just get the builder to have a detailed brake down of costs inc structural engineer fees and compare.

how do we get fair\comparible quotes across different builders?

Couple of methods, design and build where the builders will look at your basic drawings and quote from them but you may get a larger variance between the difference between quotes as the builders may use different materials and construction. No further architecture fees. As the details and budgets by the builders is given, you can change spec and budgets with the builder on things like bathroom suites etc. Or you can give this detail yourself to the builder before the quotes are provided.

Or

Speak to your architect about completing full drawings and specs and put it out to tender. Architect may also be able to recommend builders. Means the quotes will all be based on the same specs and design but youll have further design fees.

Other than producing a very large sum of money, what’s next?

...double what you think is a very large sum of money!!!

We've just knocked an extension plan on the head as we felt it wasn't value for money.

Re builders - speak to your architect. If it's a big job you don't want Dodgy Dave and his mate doing it for you.

If it were me I'd write a detailed project scope document detailing the exact level of finish required for fit out as well as the design of the extension; wall finish painted or papered. Number and location of Rads. in ceiling spots or pendant light fittings, bathrooms tiled or panelled, design  / brand bathroom suite chosen and detailed etc. Make sure it's comprehensive and written down. Once issued accept you & your wife cannot alter this.

Once you've agreed the scope issue out to builders and terms and conditions (I use NEC4 for framework for work, but may be more appropriate one for house builders) and get them to tender for the work.

All tender responses should be consistent and easy enough to compare against.

Have you got full architects plans or just planning drawings?

The former will contain most of the answers to your specification questions, the latter will be floor plans and external elevations.

I’m not sure if we need a sturctural engineer before we go to builders, or if the builders cover that off as part of their service?

They'll go to the same people you will find, only they will charge a markup for the priviledge. Plus if that comes after the quoting process, the quote will be for a worst case, rather than what actually is needed. Get your full plans and engineering done before you go near a builder's price quote.

If you're home counties, send me a PM, we do architectural plans and structural engineering, tailored to what you need.

producing a very large sum of money

and then producing some more.

For getting started the only thing I can suggest is get word-of-mouth recommendations, go visit the properties they've previously worked on, and then be prepared to wait for them to become available. It's absolute pot-luck just googling for builders in your area for what I'm assuming is well north of £100k of work.

Have you not employed the architect to draw up the building warrant package (or that just Scotland?)to send out for tender? I would expect structural engineer stuff to be done as part of that.

ah sorry, should have stated that up front - south east england.

Couple of methods, design and build where the builders will look at your basic drawings and quote from them but you may get a larger variance between the difference between quotes as the builders may use different materials and construction. No further architecture fees. As the details and budgets by the builders is given, you can change spec and budgets with the builder on things like bathroom suites etc. Or you can give this detail yourself to the builder before the quotes are provided.

Or

Speak to your architect about completing full drawings and specs and put it out to tender. Architect may also be able to recommend builders. Means the quotes will all be based on the same specs and design but youll have further design fees.

thanks! we've got a few recommended builders in the area (it used to be mostly bungalows, so we know lots of people who've had building work) - finding an architect was much harder.

from a spec perspective, we know the brick & roof/floor tiles in use on the house already (and want to match them), we're adding one en-suite and a utility, would it just be a case of picking something out (to get fair quotes) for each of those, or is there more "spec" in the stucture of the building to think about and compare?

…double what you think is a very large sum of money!!!

we're currently budgeting for £3000/sqm (of ground floor footprint, its a 2-story extension). are we way off?

not planning on doing much ourselves, maybe a spot of light decorating

How does the size of the extension compare to your house as it is? Then imagine doing that proportion of the house all in one go. When we extended our house, I planned to do all the painting then realised with the amount that needed doing it'd be at it for ages. Far better to have it as part of the building work- once the constructions done, the rooms will be ready to use in no time and it'll be a small % of the overall cost.

Re builders – speak to your architect. If it’s a big job you don’t want Dodgy Dave and his mate doing it for you.

This - after seeing what our next-door neighbours are going through, you want to ensure you get the very best you can afford – theirs is supposed to have been finished last week but it's still insecure (no windows in half the build and they have only just ordered them), the flat roof is still not watertight (just plastic sheeting) even though they are fitting the new kitchen, the quality of the build is shocking (loads of stuff out of square, the pointing is shocking, messy patching).

When we did it our architect produced a full report on the construction method / how the roof works / insulation requires etc.

I just went out to a few builders after that and got fairly widely varying quotes from £80k - £120k. This was in 2018 so expect those costs to be higher now - this was a single story wrap around extension with one wet room and large bi-fold doors. The £80k was effectively ‘mates rates’ from a friend and we went with that with all the potential pitfalls but upsides that can have.

In the £80k we had the builder quote labour to fit the wet room but we went out and bought all the materials for that separately as you probably don’t want to just leave that to the builder.

In terms of hidden costs just check if anything runs under where you’re building over - I had to get our gas and electricity meters moved which was a pain in the arse and quite expensive. I also had to go to the water company about potential ‘build over agreements’. We had to effectively prove we weren’t going over anything before they’d commit to saying we didn’t need one.

Would also use a private firm for building control - easier to deal with than local council ones.

from a spec perspective, we know the brick & roof/floor tiles in use on the house already (and want to match them), we’re adding one en-suite and a utility, would it just be a case of picking something out (to get fair quotes) for each of those, or is there more “spec” in the stucture of the building to think about and compare?

Insulation (walls and roof), wall thickness, interior finish (paint, wallpaper, linings, which wall etc), damp proofing materials, flooring, ceiling specs and finish, lighting, electrical spec and position, doors (internal and external), windows, heating, ventilation...... Etc etc etc

You might be OK at £3000 / m2.

We were quoted £40k to £50k for 25m2 by 3 builders. So £1800 ish /m2, but we'd have to finish the inside at that and get plumbing sorted. No fancy bi-folds or anything like that either.

That was just for a 7m x 3.5m single storey 'box' off the back of the house. We've decided to buy a better shed to put the washing machine and dryer in that and spend the rest on holidays! 🙂

Have you got full architects plans or just planning drawings?

The former will contain most of the answers to your specification questions, the latter will be floor plans and external elevations.

just planning drawings at this point

If it were me I’d write a detailed project scope document detailing the exact level of finish required for fit out as well as the design of the extension; wall finish painted or papered. Number and location of Rads. in ceiling spots or pendant light fittings, bathrooms tiled or panelled, design / brand bathroom suite chosen and detailed etc. Make sure it’s comprehensive and written down. Once issued accept you & your wife cannot alter this.

ah see this is the kind of thing I hadn't thought about (light fittings, rads etc). I recon we might be able to DIY the spec choices at this level though, so I've just ordered the haynes extension guide to see if they have a list of what you need to spec.. such as

Insulation (walls and roof), wall thickness, interior finish (paint, wallpaper, linings, which wall etc), damp proofing materials, flooring, ceiling specs and finish, lighting, electrical spec and position, doors (internal and external), windows, heating, ventilation…… Etc etc etc

🙂

How does the size of the extension compare to your house as it is? Then imagine doing that proportion of the house all in one go. When we extended our house, I planned to do all the painting then realised with the amount that needed doing it’d be at it for ages. Far better to have it as part of the building work- once the constructions done, the rooms will be ready to use in no time and it’ll be a small % of the overall cost.

ahh yeah good tip. It adds about 70% to the size, but there'll be decorating that's trashed I think in about 30% of the existing house (rooms being extended/stairs etc) so yeah, its a LOT. Thanks.

I just went out to a few builders after that and got fairly widely varying quotes from £80k – £120k. This was in 2018 so expect those costs to be higher now – this was a single story wrap around extension with one wet room and large bi-fold doors.

out of curiosity, how much size were you adding? We're just outside brighton so I'd assume that a lot of the costs are broadly similar here

In terms of hidden costs just check if anything runs under where you’re building over – I had to get our gas and electricity meters moved which was a pain in the arse and quite expensive. I also had to go to the water company about potential ‘build over agreements’. We had to effectively prove we weren’t going over anything before they’d commit to saying we didn’t need one.

our house is a newish build (bought off-plan 7 years ago), so the location of most things is fairly well known. There's nothing under our land, and the gas/leccy meters are both in a location that won't be affected (I think)

out of curiosity, how much size were you adding? We’re just outside brighton so I’d assume that a lot of the costs are broadly similar here

The bit on the back of the house is one room - 4.5 metres x 5.5 metres. Then there’s the bit down the side of the house which is an awkward shape as it’s up against a boundary which isn’t parallel to the house - starts at about 1.8m wide and goes narrower to 1.2 metres (enough for the front door).Quite long though - 5 metres ish. Call it 32 square metres. So £2500 per sq metre plus the cost of bathroom fittings and flooring on top.

It’s really nicely finishes to be fair - the wet room has really good quality tiles / merlin bi fold shower doors / wall hung rimless toilet / sink sat on a floating oak shelf etc etc

Bifolds are 3.5m long (3 doors) and have electric blinds inside the double glazing unit etc.

Thinking about it the guys also built a patio and repaved round the house too - although we bought the materials on top for that.

In the middle of a build right now. roughtly 5mx7m single story. About half via removal of existing walls and half new build to create a kitchen. I hope to bring it in around £100k

Our route:
Architect drew up plans, gave us a rough estimate (very wrong), submitted to planning
Architect gave us contact details for structural engineer (2 of them, one tried to take the piss with the estimate. other one was half the price...) and 3 builders (who all eventually provided very, very expensive quotes)
I put the structural plans through building control before I engaged with builders. We have 9 steels going in so I wanted to be bloody sure it was right
The spent 6 months trying to talk to builders / chase for quotes / waste my time showing builders round who then vanished or told me they are busy for two years.... quotes that did come in were massive, and as well as paying for labour there was a 20-30% markup on everything. They get a sparky in for you? 20% on top of his day rate. They buy the bricks? 20% more expensive. 20% more when you are already spending £100k is ALOT.
Eventually found a local builder who had done recent work for my boss, and is his best mate. No fancy sign written van, no big elaborate quotations, no advertising. Very good reputation. Had a small window to fit us in due to a cancelled job. Prefers to work on day rate not fixed price (his view is he will just quote a large number to cover his risk)
So, despite what everyone will say on here, we went with him. As the other builders were simply pricing to the stratosphere and unless you have a personal recommendation or contacts you are essentially trying to decide based on the quote and from one or two conversations whether the guy is a cowboy or not
So far very happy. In fact as I type this I can hear them lifting in the 4th steel. Couple of horrors found during the ground work which meant all the drainage had to be rerouted, and we will need to underpin a 1950s section of the house ("appears to have been built on a patio"). Plus foundations needed to be 1.4m deep. Ensure you have contingency budget.
One thing that could be better is coms, and he is clearly juggling a few jobs. There have been two occassions were stuff has just turned up (muck away, steels) which I wasn't expecting - I knew it was coming 'sometime' that week. Luckily I WFH so its fine.
The worry with day rate rather than fixed is it feels a bit open ended. However comparing his rough estimates (which so far have been spot on) with the fixed price we have nearly £50k difference. That can cover alot of overspend. So I figured we take the risk, with the expectation of maybe half that difference being overspend

Appears to be no slow down for the building trade in our area. Our builder says he is pretty much booked now for the next 2 years on a couple of big jobs.

Oh and shop around for kitchens, they seem the same as builders wildly massive quotes. We will be using diykitchens. Cookers have been a pain in the arse to source, and prices have been increasing super fast (bosch series 8 has doubled in price since xmas). Stock is very limited so you need to jump on it when you see something in stock.

Erm. what else. having your electrical spec, plumbing spec and heating spec all designed and planned upfront is a good idea, but unless you have lots of experience of this its not all that easy to do. Getting a decent builder in means you can have a conversation about these things and agree the best solution. I prefer this as it means both of us have thought it through, rather than with my lack of experience I've made all the decisions.

and...I had to get the gas meter moved. Expensive and long lead time, so if you need to move any utilities get on it asap as it could hold up your build.

Good luck 🙂

oh. if you are excavating within 2m of your neighbour you need to take a look at party wall legislation and see if it applies to your build

The worry with day rate rather than fixed is it feels a bit open ended.

this would be my biggest concern, as well as a lack of control if the builder just goes awol. I think for a £50k saving we'll consider it, if its £10k, probably not.

oh. if you are excavating within 2m of your neighbour you need to take a look at party wall legislation and see if it applies to your build

*mild panic*

after a bit of reading, the key thing is within 3m of a neighbours structure. Our new wall will be 3.3m from their garage, so assuming the foundations aren't more than 30cm further out than the wall (it seems like 1-200mm is common), I think we'll be ok. *phew*

Its nothing to panic about, it just means more £££. You can still do the work but you need to get surveyors involved and such like.

On the contract, there is nothing to stop a fixed price builder going awol either. Every builder we spoke to wanted some level of cash up front - most 50% of first phase. I'm told this isn't common and normally builders will work without deposit and then payment on completion. This wasn't my experience, with the 9 I managed to speak to.

Its all very stressful spending big bucks, but think about the outcome!

bear in mind most builders quotes will be re-measurable at the moment as prices for materials are fluctuating (going up) alot.

so you 80k quote might easily cost £120k down the line.

leave a good 25-30% contingency in your budget - never ever ever disclose to a builder, or architect, how much money you actually have to spend. the job of the builder is to extract as much of it from you as feasible while doing as little as possible.

be prepared to get cheaper stuff temporarily, or do stuff yourself, if needed if build costs spiral.

some builder partner with architects/engineers, some dont. get the builder to separate out fees and get quotes to check costs. professional fees will be small fry compared to materials and labour though.

I wouldn't consider any major building work at the moment, prices are sky high and being passed straight on (understandable) if they keep going up.

so you 80k quote might easily cost £120k down the line.

leave a good 25-30% contingency in your budget

That's why we abandoned our project. Our money is sat in the bank from an inheritance and with us in our mid 50's we're not going to the bank to borrow again if it ran massively over.

Don't pay any money upfront. If the builder can't afford to buy the materials then do you really want to be working with him? When you do your valuations/monthly payments or however you are doing it don't pay for anything that's not on site.
Consider getting a QS involved, he'll save you more than his fee if he's any good.

Don't forget VAT, so on £100k is....you know the maths £20k plus fees plus contingency, be realistic, it will cost more, best to TRY and sort out your sped/quantity and quality now, any change from plan costs money, it's worth it in the end but eyes open. Try for local builder who can show examples and has good references, like example earlier, if you don't know then get a good plan/spec.
Does the work involve changing kitchens/bathroom, i.e. will you need temp facilities? try and work out all angles and get ahead of decisions, you don't want a decision needed on the day...where will sockets go, what lights and where, as mentioned above, these all change cost. Good luck, show us designs we'll love to comment;)

Don’t pay any money upfront. If the builder can’t afford to buy the materials then do you really want to be working with him?

It's quite common to pay something up front for development of something with high materials cost. Happens in engineering happens in building industry.

If you are getting 10k of materials delevered to your house it's not unreasonable to be asked to pay for them.

Pay for materials actually on site but never ever pay in advance. The builder goes bust and you kiss your money goodbye. We’ve just awarded a building contract worth £6.6 million, not a single penny will be paid upfront and unless any materials are actually on site or otherwise in our possession then we won’t be paying for them either. It’s monthly valuations as well so the builder needs to be financially stable and able to carry the cost until the valuation is agreed and paid. If he’s not prepared or unable to do that then I’d be looking for another builder.
That’s how building should work (under a JCT or NEC-4 contract anyhow) and even for a relatively small domestic job I’d be looking for a proper contract.
We are a team of six technicians, a senior architect and a QS. In the five years I’ve been there every single one of our projects has come in under budget. That because of a good contract, a nailed down specification, decent drawings and a good QS. We’ve not bankrupted any builders either 🤣🤣

All very well saying don’t pay up front. No builders I spoke to in 6 months would work without a deposit of some level.

50% upfront 50% on completion by phase was the most common approach

Most of our materials I have sourced and paid myself, some materials the builders pick up as they go and I reimburse when I see the receipt (for instance a bunch of joist hangers today). Bit of an admin pain in the arse, and some trade companies don’t like talking to me direct on a supply only basis, bifolds in particular were a challenge, however if you shop around you’ll find companies that will. Most of the materials have been via builders recommended contacts, and I have used his trade discount without markup.

So there are guys out there that will work without squeezing you for every penny. One quote included professional cleaning of the extension on completion, at 2k plus vat plus markup. £800 for a toilet on-site. £8k for a management fee, plus vat £1k on scaffolding (it’s single story )etc…. You can see very quickly how you get massive quotes

Structural work should be complete on ours next week and roof complete week after. That’s the main work needed, still a bunch of other internal stuff to sort, but that should be easier to forecast so should be able to see if I’m bringing it in budget or not.

Btw it’s easy to bring something in under budget if you quote a bloody massive number and cost in loads of risk

Used to be a PM, not construction, but budgeting and forecasting is the same approach. I’m 3 days behind schedule which I don’t think is bad given the unforeseen stuff. Keep expectating delays with materials but so far, touch wood it’s been fine. Biggest bugger was everyone going on holidays, so I’ve got another rejuggle as the muck away guy is away to Friday and we can’t work on the section we had planned to.

Oh and if you buy the stuff yourself you can use a cashback credit card and get a decent amount back, it all makes a difference if you have a tight budget!

We’ve just awarded a building contract worth £6.6

I get what you're saying but a 6.6 m deal is a different type of builder to a domestic extension.

cashback credit card

As someone who does use credit cards that is a good idea and gaming the system to your advantage top job

oh. if you are excavating within 2m of your neighbour you need to take a look at party wall legislation and see if it applies to your build

Doesn't cost anything just print off a party wall agreement and ask them nicely to sign it. Have been on both sides of it three times now. Total cost £0.

The agreement isn't really worth the paper it's written on and doesn't guarantee anything, just a very cheap hoop you jump through.

When we did party wall our architect explained it a bit differently to that. With our neighbour we paid to have a party wall survey done on their house so that we had the condition of their house before we dug foundations. That way if they said we’d done any damage to their house we could prove we had or hadn’t based on the condition prior to starting.

Glad we did it as the photos showed they had some cracking inside the house in places which we couldn’t have proved wasn’t anything to do with our works if there’s raised it after.

The survey option protects both parties in the party wall situation.

we’re currently budgeting for £3000/sqm (of ground floor footprint, its a 2-story extension). are we way off?

You'll be fine for a single storey. Oh...

As for paying up front, if you don't then the builder will price in the risk of you not paying and/or arguing - we paid for materials as delivered to site (in our name). TBH as someone else said, I'd be waiting for the economy to settle down a bit before committing to a large project, unless of course cash isn't an issue AKA you can run over 'budget'.

When we did my Mum's place (100sq m renovation - basically take down to a couple of walls and start again) the builders tenders varied by a factor of two and we ended up using the one in the middle AND I'd used them on a work project, so had a good idea of their capability. All builders were local and all were also bringing in additional trades to cover areas that they didn't do - so their ability to project manage was key.

Delivered on budget and to quality - late on time, but we were comfortable with this.

Have you not employed the architect to draw up the building warrant package (or that just Scotland?)to send out for tender? I would expect structural engineer stuff to be done as part of that.

ah sorry, should have stated that up front – south east england.

You will need to get building regulation approval in that case.

https://www.gov.uk/building-regulations-approval/how-to-apply

For that, you’ll need a full set of plans drawn up (this may require the services of an Engineer to calculate certain things as part of the process, but not necessarily). Your architect may/should be able to prepare these. They will contain the technical detail of the build (what size floor joists, what they’re made from, insulation (thermal and noise) details and calculations, ventilation calculations, window area, lintels, etc. etc.), rather than the cosmetic details. You may have to make changes to your ideas in order to get approval (you may not be allowed large areas of glazing, for example).

I wouldn’t approach a builder until I had building regs approval as the scope of the work is undefined IMHO - YMMV.

(35m^2 ground area 2 storey extension ~17 years ago!)

ETA Decent summary about what is covered by building regs here:

https://www.homebuilding.co.uk/advice/building-regulations-for-extensions

I wouldn’t approach a builder until I had building regs approval as the scope of the work is undefined

absolutely this as a minimum.

the more unknowns the builder has at pricing stage the more it will cost.

yep, agree I didn't approach builders till building regs approval. However, trying to find a builder was such a long and painful process for us, if I was to do it again I'd run in parallel. I thought planning was going to be the difficult bit !

When we did party wall our architect explained it a bit differently to that. With our neighbour we paid to have a party wall survey done on their house so that we had the condition of their house before we dug foundations. That way if they said we’d done any damage to their house we could prove we had or hadn’t based on the condition prior to starting.

Neither myself nor neither neighbor bothered with anything other than the form itself. I don't know anyone in the street who bothered with a survey either.

When one of my neighbours applied for planning, some ambulance chasing party wall survey company mailed me a brochure explaining how my neighbour's extension 'could' collapse my house and I'd better insist on getting them out to dig up half the garden. Just binned it as totally unnecessary. If the builder knows what they're doing, which they did, the odds of causing any damage are minimal and even if they do, they'll just have to fix it.

ok so I have a structural engineer who's done some calcs, and an architect who is meant to be tying this in to a building reg submission..

I'm now being told that the roof design is a bit complex so can't be done with trusses (fair enough - this is from a truss manufacturer) - and as a result the contractor can just design them as he does the work. It seems that this would involve quite a lot of calculation that as a layman I don't expect would normally be within the remit of a general builder. Am I right? will I even get through building regs without roof structure design?

I’m now being told that the roof design is a bit complex so can’t be done with trusses (fair enough – this is from a truss manufacturer) – and as a result the contractor can just design them as he does the work. It seems that this would involve quite a lot of calculation that as a layman I don’t expect would normally be within the remit of a general builder. Am I right? will I even get through building regs without roof structure design?

I had a structural engineer want to duck complexity - not sure if he just didn't need the headache, couldn't do it, or just didn't like the (what I thought was straightforward) job on offer. I found a different engineer - who was mate of the joiner who was doing the work...

call kevin in, get pregnant, go massively over budget, find a spare £500k to finish the project?

Is mrs_5lab pregnant yet?