Extension advice - Where to start?

[Ripper]

Right drawings are in the process of being created and he’s going to confirm whether planning permission is needed. Charging £325. He’s essentially a friend of an architect who was recommended to us, simply a young lad doing work on the side. The recommended architect has said he’ll assist him as needed. Sounds dodgy I know, but I’m going with it. He showed me examples of work and it looked good enough to me.

Anyway, once I’ve got drawings and planning permission what would be next? Would I need structural engineer to come in and confirm lengths of steel etc? Or should that come sooner?

Then would it be confirming quotes with builders?

Where does building regs come in to play?

Sorry if I’m coming across as thick, genuinely don’t know what I’m doing

 

[Peerzy]

Where does building regs come in to play?

Using the order from my original reply - you'll need to get someone (structural engineer) to do all the calculations to meet building control standards at stage 4. Some builders may quote (stage 5) without them as they can roughly work out what's needed (or do the calculations themselves) but most will want them doing before being able to do a full and proper quote (especially on an extension that removes a load-bearing wall.

Once the build starts (stage 6) building control will normally (Covid aside) make the odd visit (occasionally at your request if required) to ensure everything is being done to specification, comparing the calculations to what is being fitted. At the end they'll sign everything off based on the calculations, what they've seen and what has physically been built. They won't be interested in the architects drawings or how it looks aesthetically - just that it is safe and meets the minimum calculations.

 

[Ripper]

Using the order from my original reply - you'll need to get someone (structural engineer) to do all the calculations to meet building control standards at stage 4. Some builders may quote (stage 5) without them as they can roughly work out what's needed (or do the calculations themselves) but most will want them doing before being able to do a full and proper quote (especially on an extension that removes a load-bearing wall.

Once the build starts (stage 6) building control will normally (Covid aside) make the odd visit (occasionally at your request if required) to ensure everything is being done to specification, comparing the calculations to what is being fitted. At the end they'll sign everything off based on the calculations, what they've seen and what has physically been built. They won't be interested in the architects drawings or how it looks aesthetically - just that it is safe and meets the minimum calculations.

Cheers mate, apologies I should have referred back to your original post. Thank you, I'm moving in the right direction then at least. I'll pop and see the neighbours tomorrow to begin the sweet talking process.

We've changed the design slightly now, opting for a larger bi-fold instead of the second window as follows:

 

[tom_nieto]

I can't stress enough how important it is to get an architect involved. Firstly they will bring design ideas to the table that you just won't have thought of and you'll get a much better result than just a box on the back... although I concede that this is not necessarily the most important part of their role. They will also be able to guide you through the planning process and hopefully will also know what the local planning office will like and dislike. They may also know a couple of good building firms.

TECHNICAL DRAWINGS. Get these done as soon as possible. These can wait until after planning permission, but I'd want to have a preferred builder on the end of the phone as soon as the process is completed to get the ball rolling. Without technical drawings of every last plug socket and tap you're opening yourself up to either very varied quotes or committing yourself to a builder and finding out that things were't included in the initial quote. Spending the money now for these drawings will help to budget during the process and avoid too many surprises.

Good luck! I'm sure you'll end up with something amazing in the end, just be prepared for the pain if you've not done this before!

 

[Peerzy]

There is some planning regulation which says you can't have more than a certain % of the extension as glass (or they'll likely reject it), I'm not sure of the exact % and do often see entire rear walls as bi-folds (but they tend to be smaller - 3m wide or so).

Remember - more glass will be expensive (bi-folds are usually at least £1000 per 1m, they also come in set sizes so make sure you design them to be a standard size or you'll end up needing to pay mega money for bespoke sizes. You'll also need to factor in that walls hold the heat in better than glass and can make a room very hot in the summer, so consider your heating / cooling situation.

 

[bayo000]

Cheers mate, apologies I should have referred back to your original post. Thank you, I'm moving in the right direction then at least. I'll pop and see the neighbours tomorrow to begin the sweet talking process.

We've changed the design slightly now, opting for a larger bi-fold instead of the second window as follows:

Unless you have a really nice view out the back and are not overlooked I wouldn't bother with such a large bi-fold.

 

[Ripper]

Right we’ve had our drawings done. Interested to know if people think these are good enough for the builder and whoever else will need them?



Any feedback appreciated.

 

[Scrutinize]

Right we’ve had our drawings done. Interested to know if people think these are good enough for the builder and whoever else will need them?



Any feedback appreciated.

They are ok as high level plans and will initially do for starting the application but you will need more details on construction methods / cross section of wall & roof, drainage, insulation type / u-values, tie-in to existing, site constraints (levels, access etc)

You also need full views of existing property with no extension, to scale location plans plus the application documents. This is where an architect would be providing a complete package for you including the structural calcs + foundation requirements.

Architects can also provide a bill of quantities so you can get quotes from builders.

You need a very good builder if that is all you are giving them.

 

[Ripper]

There are three other drawings he provided, same as above but for current property, and two site plans (close up showing boundary lines, and zoomed out of the wider area).

We’ve since found out it falls under permitted development so will be applying for a ‘certificate of lawful development’.

Fair point on the other things you mentioned. Perhaps I’ll have a chat with the proposed builder and see what he thinks.

 

[Scrutinize]

That's good.

A decent builder can price and build from that drawing but you have no way to benchmark the pricing and construction method unless you get several quotes, all from good builders. You place a lot of trust in the builders this way.

You will need to identify utilities (water/gas/elec) plus where you want power points, lighting etc.

Also does your kitchen design fit within this ok or is that remaining unchanged?

It's not a hard extension but pricing can vary significantly between regions and builders. I could see that in the range of £20k-£60k but realistically it should be £25k-£35k.

It is a very large open span between the old and new space though, previously supporting the floor above and roof so you will need some significant steelwork. I'm not convinced you would achieve that design without a central pillar or two.

 

[bigstevex]

I only linger on these forums and rarely post however this may help as you sound as new to this as we were. Get a structural engineer involved now and get them to consider what the architect has proposed is buildable, as already stated that's looks a crazy span for 1 beam. We had a 7.1m span an experienced architect proposed and original SE laughed at it as not possible without columns mid span and compromise etc, we've shortened down to 6.2M now. Get yourself an older SE too, with age comes grumpyness and moaning but also comes tons of experience and making the structure work how you want it.

Permitted development is good, if you're within 1 or 2m (can't remember) of boundary you have to do the neighbor consultation scheme too. Fyi £325 is cheap but not too cheap that it's worrying. We paid £500 + £200 for measurements (exc VAT), that seemed to be the going rate for a simple single story extension. Don't forget building regs drawings are another costs again of similar/lesser amount, they won't be included in that £325 price (if they are that's amazing haha)

Here's our painful timeline.

Jan 2020, architect measures up house and proposes ~38sq/m ground floor extension for open plan kitchen, larger utility and downstairs bathroom/toilet. We'd assumed build costs of £1200 per SQ/m based on websites and saved up enough based on this, the internet is outdated, looking more towards 1500-1750sq/m easily on every quote we've now had excluding any final finishes.
March 2020, drawings done and an SE was engaged via architect while planning permission went on in the background. SE did a visit due to the complexity of taking out the gable end and corner of the house
May 2020, called SE for an update, he told me he's been busy and hadn't started them. (Failure one, we didn't agree a timescale and assumed it would be quick), agreed a 3 weeks timescale.
June 2020, called SE, again, he'd done nothing with the plans. SE Dismissed from project. Planning permission agreed in background.
July 2020, struggle to find an SE due to lock down finishing and everyone being busy (we should have waited but decided to rush into the below fatal choice).
August 2020, got a new SE, a young and chartered engineer who agreed to a 4 week turn around at a premium price of £1100. He'd done beams etc and large commercial projects before but never something this complex on a house, I stupidly fell into the idea that everyone has start somewhere and being our first extension, surely he can't go too mad!
October 2020, Some delays happened but acceptable, and a structural and foundation design was proposed.
November 2020, start to engage builders on rough designs. Builders claim the SE has made something so over engineered it's crazy. 1 refused to quote.
December 2020, arguments begin with the SE about the buildability of what he proposed yet he stands by what he proposed. Building regs sign off completed in back ground. Fyi, Building control do not do full and detailed checks of calcs, they check they exist and that the beams proposed match the calcs I'm told.
Jan 2021, narrowed it down to 1 builder now who said he can build it but I really need to speak to another SE for a second opinion as he really thinks I'm paying too much for something that's not needed.
Jan 2021, engage with new engineer, older, 30 years experienced chartered engineer who point blank said what has this guy done is not required at all and you're paying 10K extra for steel and over engineered foundations you don't need.
Feb 2021, SE dismissed from project and new one is currently proposing new layout of beams and columns. His price is also a fair bit less than the other at £795.
Feb 2021 - This week, we've now lost our favorite/preferred builder for May as he can't wait any longer for new drawings and has taken on other work (understandable).

All builders are mad busy at moment if they're any good and some won't even come and look at the job as they're booked up till September onward and material prices are changing by the day.

Oh what joy building and extensions are, hope I haven't ruined your night so far sorry.

I slightly disagree on the idea of getting a proper quote until you have you structural calcs/buildings regs drawings, this will affect the price. Granted though you will get a rough idea and that's it, no one will give you a firm quote without the structural side of it being known, especially something requiring a steel that large taking out the entire back wall of your house! Highly doubt you'll get it anywhere near £25-35K either sorry, you've got about 5-10K of velux, bifolds and glass alone depending on what brands and U values etc you go for. That's also an additional load of steel work above your bifolds or sliders, decide now before you get your SE if you want option 1 with the shorter or option 2 with longer bifolds as you will be charged for changing your mind if they calculate option 1 and you want to change to option 2.

Bifolds vs sliders... We've gone down the sliders route now after having hearts set on bifolds, it's a debate that goes on forever but a friend has a set of 2 door 4M sliders and there's so much glass it's amazing, with bifolds you have to add up how many times you'll open them in the UK, we considered 2019 and worked it out to 5 times max. Sliders only downside is that you can't full open the 'wall' to the garden but when they aren't open you dont have 6 doors to look at, just 2-3 large panes of glass with maximum uninterrupted view of the outside space.

Do some due diligence too if you're not getting a soil investigation (750-1000), has anyone else had an extension near you, ask them if they had ground issues, if you find you're on soft ground and need piles, you can add 5K+ straight away just to foundation costs.

One final point I've just thought to add, who's doing your planning application whether full or permitted/lawful development application, our fee to the achitect included prepping and submitting the paperwork; you just have to pay the fee, same with building regs.

 

[bigstevex]

There is some planning regulation which says you can't have more than a certain % of the extension as glass (or they'll likely reject it), I'm not sure of the exact % and do often see entire rear walls as bi-folds (but they tend to be smaller - 3m wide or so).

Remember - more glass will be expensive (bi-folds are usually at least £1000 per 1m, they also come in set sizes so make sure you design them to be a standard size or you'll end up needing to pay mega money for bespoke sizes. You'll also need to factor in that walls hold the heat in better than glass and can make a room very hot in the summer, so consider your heating / cooling situation.

Sorry but that's not quite true. 'Standard' sizes don't exist from what we've found and where they did, they were very similar prices per M as custom sized, the issue is just the lead time changes from off the shelf to ~3-4 week lead time (or try origin who can do 24hours on popular colours); 3.8m by 2.1m tall are coming in at between £3000 and £6500 depending on the brand. Stick with aluminium for bifolds too, tons of info about this out there and how upvc ones need adjusting constantly.

You can have 99% as glass if you want it to be, beware though on how close you are to your boundary, it's the building regs part b that can affect this as it's a sliding scale on how much sq/m of glass you can have before it has to be fire rated. Generally not an issue on rear extension as most gardens are over 6M long which is when you reach the 'no limit' part, this mainly comes into play on side extensions I've found. Check out https://www.homebuilding.co.uk/advice/fire-safety-building-regulations-part-b

 

[Vauxmad]

Watching this thread with interest. We have a 3 bed semi which ticks most of the boxes for our forever home with the only real issue is the small galley kitchen.

We bought it in 2009 for 123K and i was aiming to be mortgage free in 5 years. We had casually talked about an extension in the past but was going to wait til the mortgage was done.

New neighbours bought the house next-door last April fully renovating it and will be building a large extension at the rear this year. Now this has made the other half want to extend ours much sooner!

 

[Scrutinize]

I slightly disagree on the idea of getting a proper quote until you have you structural calcs/buildings regs drawings, this will affect the price. Granted though you will get a rough idea and that's it, no one will give you a firm quote without the structural side of it being known, especially something requiring a steel that large taking out the entire back wall of your house! Highly doubt you'll get it anywhere near £25-35K either sorry, you've got about 5-10K of velux, bifolds and glass alone depending on what brands and U values etc you go for.

Do some due diligence too if you're not getting a soil investigation (750-1000), has anyone else had an extension near you, ask them if they had ground issues, if you find you're on soft ground and need piles, you can add 5K+ straight away just to foundation costs.

One final point I've just thought to add, who's doing your planning application whether full or permitted/lawful development application, our fee to the achitect included prepping and submitting the paperwork; you just have to pay the fee, same with building regs.

Your timeline didn't look fun...

The structural engineering as a prerequisite was already covered but a decent builder would make allowances for it if no calcs provided or charge for getting them done as part of the quote and use of QS services.

The extension isn't that big or complicated.
It's pretty much a single room/shell. Even the steelwork assuming pillars will be ok providing the footings beneath are in the right location.

If anything the costs will be disproportionate to the actual space gained.

Tweaking the design to leave more of the rear wall in and opening up either side could manage costs and structural challenges but obviously not give quite the same openness.

 

[norm]

I only linger on these forums and rarely post however this may help as you sound as new to this as we were. Get a structural engineer involved now and get them to consider what the architect has proposed is buildable, as already stated that's looks a crazy span for 1 beam. We had a 7.1m span an experienced architect proposed and original SE laughed at it as not possible without columns mid span and compromise etc, we've shortened down to 6.2M now. Get yourself an older SE too, with age comes grumpyness and moaning but also comes tons of experience and making the structure work how you want it.

Permitted development is good, if you're within 1 or 2m (can't remember) of boundary you have to do the neighbor consultation scheme too. Fyi £325 is cheap but not too cheap that it's worrying. We paid £500 + £200 for measurements (exc VAT), that seemed to be the going rate for a simple single story extension. Don't forget building regs drawings are another costs again of similar/lesser amount, they won't be included in that £325 price (if they are that's amazing haha)

Here's our painful timeline.

Jan 2020, architect measures up house and proposes ~38sq/m ground floor extension for open plan kitchen, larger utility and downstairs bathroom/toilet. We'd assumed build costs of £1200 per SQ/m based on websites and saved up enough based on this, the internet is outdated, looking more towards 1500-1750sq/m easily on every quote we've now had excluding any final finishes.
March 2020, drawings done and an SE was engaged via architect while planning permission went on in the background. SE did a visit due to the complexity of taking out the gable end and corner of the house
May 2020, called SE for an update, he told me he's been busy and hadn't started them. (Failure one, we didn't agree a timescale and assumed it would be quick), agreed a 3 weeks timescale.
June 2020, called SE, again, he'd done nothing with the plans. SE Dismissed from project. Planning permission agreed in background.
July 2020, struggle to find an SE due to lock down finishing and everyone being busy (we should have waited but decided to rush into the below fatal choice).
August 2020, got a new SE, a young and chartered engineer who agreed to a 4 week turn around at a premium price of £1100. He'd done beams etc and large commercial projects before but never something this complex on a house, I stupidly fell into the idea that everyone has start somewhere and being our first extension, surely he can't go too mad!
October 2020, Some delays happened but acceptable, and a structural and foundation design was proposed.
November 2020, start to engage builders on rough designs. Builders claim the SE has made something so over engineered it's crazy. 1 refused to quote.
December 2020, arguments begin with the SE about the buildability of what he proposed yet he stands by what he proposed. Building regs sign off completed in back ground. Fyi, Building control do not do full and detailed checks of calcs, they check they exist and that the beams proposed match the calcs I'm told.
Jan 2021, narrowed it down to 1 builder now who said he can build it but I really need to speak to another SE for a second opinion as he really thinks I'm paying too much for something that's not needed.
Jan 2021, engage with new engineer, older, 30 years experienced chartered engineer who point blank said what has this guy done is not required at all and you're paying 10K extra for steel and over engineered foundations you don't need.
Feb 2021, SE dismissed from project and new one is currently proposing new layout of beams and columns. His price is also a fair bit less than the other at £795.
Feb 2021 - This week, we've now lost our favorite/preferred builder for May as he can't wait any longer for new drawings and has taken on other work (understandable).

All builders are mad busy at moment if they're any good and some won't even come and look at the job as they're booked up till September onward and material prices are changing by the day.

Oh what joy building and extensions are, hope I haven't ruined your night so far sorry.

I slightly disagree on the idea of getting a proper quote until you have you structural calcs/buildings regs drawings, this will affect the price. Granted though you will get a rough idea and that's it, no one will give you a firm quote without the structural side of it being known, especially something requiring a steel that large taking out the entire back wall of your house! Highly doubt you'll get it anywhere near £25-35K either sorry, you've got about 5-10K of velux, bifolds and glass alone depending on what brands and U values etc you go for. That's also an additional load of steel work above your bifolds or sliders, decide now before you get your SE if you want option 1 with the shorter or option 2 with longer bifolds as you will be charged for changing your mind if they calculate option 1 and you want to change to option 2.

Bifolds vs sliders... We've gone down the sliders route now after having hearts set on bifolds, it's a debate that goes on forever but a friend has a set of 2 door 4M sliders and there's so much glass it's amazing, with bifolds you have to add up how many times you'll open them in the UK, we considered 2019 and worked it out to 5 times max. Sliders only downside is that you can't full open the 'wall' to the garden but when they aren't open you dont have 6 doors to look at, just 2-3 large panes of glass with maximum uninterrupted view of the outside space.

Do some due diligence too if you're not getting a soil investigation (750-1000), has anyone else had an extension near you, ask them if they had ground issues, if you find you're on soft ground and need piles, you can add 5K+ straight away just to foundation costs.

One final point I've just thought to add, who's doing your planning application whether full or permitted/lawful development application, our fee to the achitect included prepping and submitting the paperwork; you just have to pay the fee, same with building regs.

The two structural engineers who you didn't accept their work, how much did you end up paying them? Is it similar to lawyers where you have to pay them by the hour for their time?

 

[bigstevex]

The two structural engineers who you didn't accept their work, how much did you end up paying them? Is it similar to lawyers where you have to pay them by the hour for their time?

The first engineer although he did a site visit; he didn't even ask for payment and he would have been politely told to F off The second one is a little more awkward. We'd paid him as we got through the building regs and weren't aware of the issues we were going to end up with once the builders started to quote on the steelwork and foundation design. Granted it's a lot of money to lose however we're going to save 5-10 times this on the re-design. I'm tempted once I have the redesign to send him a chance to offer a refund before I start looking at legal routes to get money back. I have an extremely busy life though and the extra stress of small claims etc isn't worth the cost to me at the moment.

 

[bigstevex]

Your timeline didn't look fun...

The structural engineering as a prerequisite was already covered but a decent builder would make allowances for it if no calcs provided or charge for getting them done as part of the quote and use of QS services.

The extension isn't that big or complicated.
It's pretty much a single room/shell. Even the steelwork assuming pillars will be ok providing the footings beneath are in the right location.

If anything the costs will be disproportionate to the actual space gained.

Tweaking the design to leave more of the rear wall in and opening up either side could manage costs and structural challenges but obviously not give quite the same openness.

I'll still disagree a little, granted the steel work will be a 'simple' portal steel frame for the opening and beam/another portal above the doors, I agree that's simple, however it's ~11m wide on that drawing, give a little bit for return walls/piers/columns and you're still looking at a 10M beam span which is too much unless you're happy with 400mm+ beams holding it up and the cost associated with such heavy section size steels, that's quite a variable on the build costs. This is definitely the time to start thinking of kitchen design and whether a column mid span to reduce steel depth would be acceptable. We've had some kitchen design options done in the background just so we could have some approx costs to save for however it also allowed to consider a mid span column in the island if it came down to it.

 

[Ripper]

Thanks to everyone for advice so far, it is appreciated.

As an update I’ve been I touch with a few structural engineers and sent them the drawings.

One was very honest and refused the work as he said it seemed too complex and said the architect had drawn something that was ‘unbuildable’. Simply due to the significant size of the steel beam and how impossible it would be to get this in to place given the lack of sufficient access to the rear. I appreciated his honesty, he phoned me to explain everything and I found that really helpful. He also put me in touch with another engineer who may be more up for the challenge.

So I sent my drawings and information to this second engineer, who responded today with a quotes. He said the single beam was possible but really hard + expensive to do and suggested a central pillar. That’s fine, I’ve come around to this idea now. However I wouldn’t mind your help in his quote, it seemed expensive (1200+VAT). Two friends have paid 400 for similar services recently. I’m 99% sure it doesn’t include anything other than design/calculations (I.e no actual steel and I’d have to take his info to the steel shop!). Here’s the wording on the quote, thoughts/advice?:

1. Design and details for steel frame, post and beams to support rear of property.

2. Design and details for pad foundations.

3. Design and details for beam and plate over bi-fold doors.

4. Undertake wind load analysis.

5. Design and details for wind posts as required.

The above includes details and specifications for padstones and all relevant connections.

 

[Scrutinize]

@Ripper it is because the engineer is essentially having to do the architects work too, as well as the structural plus indemnify the work. This isn't a simple rsj calc.

You need to start again with a new architect who will design something buildable and cost effective and appoint the structural engineer.

If you progress further with the current design you will end up with significant cost exposure. You will need the drawings redoing anyway so they accord with the structural engineers proposals for planning and building control purposes.

Write-off the drawing costs accrued so-far. Lesson learned and move on.

 

[Ripper]

I’ve had a couple more quotes from other SEs since, one is now saying £1000.

What would be the disadvantage of going with this and amending the drawings to show the central pillar? That would be the only amendment really? Unless the SE suggests anything else?

I’m not fully against starting again as you suggest, but will that really help me if it’s just the central pillar that needs including/amending? A friend who gave me inspiration for this did his own drawings which were nowhere near the standard of mine, he simply employed the SE, got the steel sorted and it got built

Once the SE has done his work it’s then a case of getting full quotes from builders right? And sorting building control?

Can I apply for a lawful development certificate to prove that it’s permitted development just from the architects drawings? Or do they need the work of the SE first? Peerzy suggested I can get it prior to the SEs work in post #2.