Extension advice - Where to start?

[Scrutinize]

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.

You are asking structural engineers to design on a design that isn't cost effectively or practically buildable at the moment.

The one who turned you down is the best structural engineer you could have appointed.

The other at £1,400 was very realistic pricing as doing the architects work for them and allowing circa up to 2 days design time plus 1/2 day for dealing with project matters and liaising with you etc.

Structural engineering is a very precise discipline. Achieving chartered membership to the institute of structural engineers is a significant task.

Given the advice you have had from the 2 SEs, and the issue with your design I wouldn't recommend going for the lowest price, go with the best SE. At £1.4k the SE is factoring in your design and use of an arch tech rather than qualified architect so knows how much of a problem project this can become.

You will still need building regs and a certificate of completion issued. For this you need the design and structural work to be correct so it can be built correctly off plan.

Suggest you use JHAI as they are a good value independent building inspector and much quicker than council building control.

Applying for the certificate of lawful development under permissive rights is a separate matter to the SE / Design. Feel free to progress that independently and I suggest you do show an amended central pillar.

 

[DB_SamX]

My charge out rate as a chartered engineer (and I do domestic work as well as multimillion £ work) is around £95-100 an hour but I do work for an SME, but it does mean my work comes with a good level of insurance, all of my work is QA checked by a colleague and a certain standars is achieved. Going for a "one man band" could be cheaper.

The work listed above would take me at least a day to a day and a half, so £1000 to £1200 + VAT sounds about right.

What the other engineers have told you is correct. Roughly 6m is reasonable to lift and install in a small domestic property. Anything longer is a pita. You won't be the first client of mine who has been advised by an architect to have a massive opening, because they haven't considered the cost of the beam or the practicality of installing one. The longer it is, the more likely it needs splicing, which means extra fabrication cost, plus columns/pads at both ends.

Happy to answer any specific SE questions. I know a bit about planning, but it's not my expertise.

 

[Ripper]

Hi DB_SamX (and anyone else), thoughts on this quote I’ve had from a different SE? I’ve been waiting for this quote for a while as a few friends have used him, and he’s come out cheaper + provided a more ‘in depth’ quote from my limited understanding. See image below, is there any detail missing do you think? Anything additional I should ask him before agreeing to the works?

Spoiler

 

[Ripper]

And also, any rough estimations of steel cost?

 

[DB_SamX]

Hi DB_SamX (and anyone else), thoughts on this quote I’ve had from a different SE? I’ve been waiting for this quote for a while as a few friends have used him, and he’s come out cheaper + provided a more ‘in depth’ quote from my limited understanding. See image below, is there any detail missing do you think? Anything additional I should ask him before agreeing to the works?

Spoiler

Yep, quote looks reasonable to me, as easily 1-2 days of engineering and drawings there. I'd guess he's self-employed or working for a very small company for that price. As long as he's chartered with the ICE/IStructE, I'd be happy though. It's not clear if the site visit is included though...I'd guess not from the last sentence of paragraph 3. For completeness, you could ask him for his PI insurance, but I suspect that once you agree his fee, he will send his T&C's your way.

Don't quote me on that but steelwork is closer to £2k/tonne these days, once you account for fabrication and installation.

 

[Ripper]

Is it the ‘done thing’ to ask if he’ll accept cash? Or will I then potentially leave myself without any comeback if it’s not done through the books?

Or am I better off not taking the mick and just going with it? Just trying to reduce costs as much as possible that’s all.

 

[Scrutinize]

Is it the ‘done thing’ to ask if he’ll accept cash? Or will I then potentially leave myself without any comeback if it’s not done through the books?

Or am I better off not taking the mick and just going with it? Just trying to reduce costs as much as possible that’s all.

This is the wrong type of project to constantly be trying to cut corners and do deals on.

Appreciate the need to minimise costs but the way you are going about this could easily cost you 10k-20k more than you need to spend.

 

[Ripper]

Appreciate your honesty. I’ve tried to re-read everything you said previously to remind myself of yours and others previous comments to help, but why do you think it will cost 10-20k more than I need to spend? I’ve now opted for the central column so shouldn’t that help achieve what I’m looking for?

We’ve since had a couple of kitchen quotes and designs which have given us a clearer idea of how it will work.

 

[DB_SamX]

Is it the ‘done thing’ to ask if he’ll accept cash? Or will I then potentially leave myself without any comeback if it’s not done through the books?

Or am I better off not taking the mick and just going with it? Just trying to reduce costs as much as possible that’s all.

It makes no difference if you pay in cash. Won't mean they'll do it for cheaper. The odd domestic client do pay us in cash. You'd still get an invoice, etc. If anyone tried to do it off the books for tax reasons, they would be going against the ethical code of their overseeing institution.

As said, you don't want to cut corners on this; your home insurance could be invalidated if things are not done properly.

 

[Scrutinize]

Appreciate your honesty. I’ve tried to re-read everything you said previously to remind myself of yours and others previous comments to help, but why do you think it will cost 10-20k more than I need to spend? I’ve now opted for the central column so shouldn’t that help achieve what I’m looking for?

We’ve since had a couple of kitchen quotes and designs which have given us a clearer idea of how it will work.

If you go to a proper architect and give them a budget, they will design the extension to suit. This includes using appropriate finish and materials.

They will also provide a bill of quantities so your builder can accurately price.

They can even suggest how to save significant money ie retaining some rear wall mid span and using existing structure that rather than a pillar. You would be surprised how nice the room and space will be even with a 3m-4m opening either side.

Your design is going to be very costly for a nominal space gain even with a mid span pillar.

You will gain more usable space from a deeper but half to 3/4 width extension for example, but still with a vaulted ceiling and bifolds etc.

I say this in the context of you trying to save money at every opportunity. What you are trying to achieve can easily be done but at a fairly high cost relative to the limited gain.

 

[DB_SamX]

If you go to a proper architect and give them a budget, they will design the extension to suit. This includes using appropriate finish and materials.

They will also provide a bill of quantities so your builder can accurately price.

They can even suggest how to save significant money ie retaining some rear wall mid span and using existing structure that rather than a pillar. You would be surprised how nice the room and space will be even with a 3m-4m opening either side.

Your design is going to be very costly for a nominal space gain even with a mid span pillar.

You will gain more usable space from a deeper but half to 3/4 width extension for example, but still with a vaulted ceiling and bifolds etc.

I say this in the context of you trying to save money at every opportunity. What you are trying to achieve can easily be done but at a fairly high cost relative to the limited gain.

Agreed. If the client is flexible, a good design team will suggest small modifications which can save a lot of money.

 

[Ripper]

They can even suggest how to save significant money ie retaining some rear wall mid span and using existing structure that rather than a pillar. You would be surprised how nice the room and space will be even with a 3m-4m opening either side.

Not sure I have much flexibility here? As there is no wall in the middle currently as the area sticks out currently as a living space as part of the kitchen/diner already. I’m basically knocking the middle section down completely and rebuilding by knocking out the left and right parts of the wall that exist in order to open it out. Hope that makes sense, hopefully if you look at the original sketchup in the opening post (the left side drawing) you can see the current setup.

 

[Scrutinize]

Not sure I have much flexibility here? As there is no wall in the middle currently as the area sticks out currently as a living space as part of the kitchen/diner already. I’m basically knocking the middle section down completely and rebuilding by knocking out the left and right parts of the wall that exist in order to open it out. Hope that makes sense, hopefully if you look at the original sketchup in the opening post (the left side drawing) you can see the current setup.

I'm referring to the rear wall of your house. If you left the middle section, the steels would bridge each span.

You wouldn't get a whole width opening but you may be surprised how much a few meters of opening either side actually opens up the space.

However, you would actually gain more usable space by extending further out from the house but not across the full width. Ie creating a room that's 4m-5m x 4m-5m.

This is all in the context of achieving a 20k-30k extension and not 40k+ which is where I am guessing you want to end up for the finished shell.

 

[Ripper]

Thank you for your help and advice so far.

Since my last post I’ve had a builder friend-of-the-family round to offer a bit more advice and have since asked the structural engineer to begin his work (after agreeing £800 cash after his initial £750+vat quote).

He’s taken a while but has come back to me today with a provisional drawing and some questions which I was hoping somebody on here could assist with, as I’ll be honest I’m not 100% on what he’s asking me.

He’s said:

Please find enclosed a preliminary copy of my construction drawing showing the sizes of the rafters, beams, columns and foundations on your proposed extension. I am sending this to you so you can approve the layout before I complete the construction details. The drawing shows the central column that you agreed to and I have managed to reduce the return piers to 450mm rather than the 600mm shown on the Architect's drawing.

A steel wind post is required in the pier between the bi-fold doors and the rear window because the length of the rear wall exceeds the allowable limit without an intermediate restraint. This wind post will be hidden in the inner leaf as shown on the drawing.

The lintel over the bi-fold door needs to be a minimum height of 180mm to minimise the deflection of the lintel due to the long length of the door opening. This will mean that the eaves detail will be 50mm deeper which may reduce the pitch of the new roof. The Architect's drawing shows the eaves height is 2100mm and the roof has a pitch of 22 degrees, but this only gives 130mm between the wallplate and the door head in which to fit the lintel in. The length of the door opening is 5000mm so a lintel depth of 130mm will give excessive deflection over this span and this deflection will prevent the doors from opening properly. The depth of the eaves therefore obviously needs to increase in order for the 180mm lintel to be installed or the width of the door opening will need to reduce.

and the drawing is below:

Two questions:

-Perhaps obvious, but is he saying the central pillar will be 152mm x 152mm wide? Not very big at all really then? (Was expecting bigger that’s all).

-The last paragraph confuses me, is what he’s suggesting a huge difference? If anyone is able to explain what he’s said in that paragraph in simple terms I’d appreciate it!

Anything else that I should be asking do you think?

 

[the_r_sole]

That's going to look very strange imo.
That's really something that needs to be designed in, the placement of the column works for an engineer but it really ruins the room.
I would ask if they could line the column up with the edge of the door and have an eccentric load - where it is would annoy me every time I saw it!
I take it the design had changed along the way somewhere? I'm not convinced the outlay on an extension this size will be worth it, doesn't seem to add much

 

[Derek W]

Two questions:

-Perhaps obvious, but is he saying the central pillar will be 152mm x 152mm wide? Not very big at all really then? (Was expecting bigger that’s all).

-The last paragraph confuses me, is what he’s suggesting a huge difference? If anyone is able to explain what he’s said in that paragraph in simple terms I’d appreciate it!

Anything else that I should be asking do you think?

1. Steel columns are surprisingly strong as they work better under load vertically rather than horizontally.

2. It can make a big difference. He's asking for an extra 50 mm to allow a suitable beam to support the roof and form the bi-fold door entrance where as your architect has only allowed 130 mm for said beam. This will mean that you either reduce the height of your bi-fold door to a non standard size which would mean they'd come in more expensive or your eaves height need to be raised which will mean that your roof pitch will become less than 22degrees and depending on how you're finishing it (presumably to match your existing tiles / slates) you'll have to check they can be laid to such a low pitch. Reducing the size of the opening would mean that the size of the lintel won't have to be as deep to span the reduced size.
2a. If you're meaning what does he mean when he mentions deflection etc then it means under load your beam might sag in the middle (probably not noticable but enough to stop the doors from operating as they'll stick and potentially shatter if the deflection is great enough.)

 

[Ripper]

Here’s a couple of actual pics of the area to hopefully help visualise. The column would sit roughly in middle of the rug in line with the purple chair. Having it there would create a larger living space one side, and a much larger kitchen the other.

The section with the dining table is essentially the bit being knocked down, and it all would be opened up and extended along the back.

 

[Ripper]

2. It can make a big difference. He's asking for an extra 50 mm to allow a suitable beam to support the roof and form the bi-fold door entrance where as your architect has only allowed 130 mm for said beam. This will mean that you either reduce the height of your bi-fold door to a non standard size which would mean they'd come in more expensive or your eaves height need to be raised which will mean that your roof pitch will become less than 22degrees and depending on how you're finishing it (presumably to match your existing tiles / slates) you'll have to check they can be laid to such a low pitch. Reducing the size of the opening would mean that the size of the lintel won't have to be as deep to span the reduced size.

Thanks for this. So technically it could be a case of increasing the eaves height and having the pitch lower than 22degrees. This would be ok right? Quick Google suggests tiles are available that can be laid down to 12.5 potentially?

 

[jellybeard999]

-Perhaps obvious, but is he saying the central pillar will be 152mm x 152mm wide? Not very big at all really then? (Was expecting bigger that’s all).

To my uneducated eyes, I'm reading the drawing that the steel within the pillar would be dimensions, but the presumably brick pillar surrounding it is much larger?

 

[fatbatman]

Looks like you're going to keep running into these issues when trying to skimp on a few hundred quid here and there.