Clueless on next steps for extension

[Alasitsme]

We got planning permission for a small extension a few years ago from a design & build. They messed us around and kept increasing the quote so we didn't proceed. We want to find out now how much it would be to go ahead before the permission lapses. But we don't know who to ask! Can we go straight to a builder, or do we need to pay a quantity surveyor first so the builders can quote?
Money is tight so looking for the most budget friendly option. Realistically not sure if we can afford the extension anyway so don't want to throw too much money at the project before we know how much it would cost to complete!

Do you have building regs drawings and specification for builders? If so, you can go straight to local builders as they can accurately quote based on these.

To give some context, we had a couple of ballpark quotes before the building regs drawings for our single storey extension. These were about £50k. Once we had the building regs drawings with the foundations and steelwork and materials, this ranged from £80k to £120k for shell build only (no plaster, no glass, no flooring).

Make sure you look at any builders financials on companies house - one we were about to use we discovered had huge debts he couldn't pay. Luckily we got another builder

Make sure you look at any builders financials on companies house - one we were about to use we discovered had huge debts he couldn't pay. Luckily we got another builder

great advice and I’d add that you should ask to see the liability insurance certificate for the builder you do choose, particularly the expiry date.

Thank you, really useful advice!
We don't have building regs plans, just the ones for planning permission. Who do we need to approach for those?

An architectural technician should be able to do them for a simple extension. I think ours cost about £1k. They're the same ones you submit to building control and get approvals and inspections based on. A good builder can maybe point you in the right direction also.

Thank you!

Yes @A1b2c3d4e5f6g7 is right. You need building regs drawings. They have a lot more detail and specifications than the planning drawings. That's why they are the ones you use to get quotes from your builder. You might also needs calculations for steels or lintels if you are removing load bearing walls.

One thing though, I have always wondered how much of starting the project would deem the planning permissionnot expired? Is it when you inform the building regs people and they acknowledge receipt or when you start to dig your foundations? Hmmm...

@Notyetthere I'm not sure as we started soon after planning. But I reckon I'd get the building regs notice in, and then dig a very small hole myself so it's started 🤣

Another question to add to your list, what are the current wall/roof insulation specifications, would the interior space now be less than your original plans show?
Two years ago we had a 4x4m extension to half of our kitchen, from memory I think that at the time, the insulation requirement was 30cm between the exterior and interior walls.
We were told at the time by the planning inspector that this was due to change, and future extensions would require more insulation, and therefore, decrease in the internal measurements. If you need a specifically sized interior space, you may find you will not have as much as you thought. Would this affect your required space adversely?
It would depend on whether you were fitting it out, (e.g. kitchen units) or had specifically sized furniture in mind.

This is correct. Using standard wall fill insulation (glass or mineral wool blocks), the cavity must now be 150mm to accommodate (increase from 100mm). However, if it bothers you, use a more expensive insulation that is thinner. Or just build what is meant to be 4m to 4.05m. It's not like building regs measure on site visits unless it's material and obvious.