Costings for this garage conversion?

[Grace Wright]

Sounds like it needs ripping out and started again to comply with building regulations 12k

[Brian Vasey]

For the floor insulation, most installers charge around £35-£40 per sqm depending on the insulation type and labour, so you’d probably be looking at roughly £400-£500 for insulating that size floor.

If you’re doing a full build-up with DPM, 100mm PIR and a screed finish, that usually comes out somewhere in the region of £1,200-£2,000 for a typical single garage depending on labour rates and screed type.

For soffit vents to improve roof ventilation, that’s normally more of a small roofing job. If the soffit already exists and you’re just adding vents you might be looking at a few hundred pounds, but if new soffit boards need installing it could be closer to £400-£800 depending on access and length.

Very rough ballpark for everything you mentioned would probably land somewhere around £1.5k-£3k depending on the contractor and spec.

If you’re buying a place with an older garage conversion that was passed by building control as compliant at the time it was converted then doing things like adding insulation means you don’t need to inform building control again. That’s something I cover step-by-step in my garage conversion guide if it helps you plan the work.”

Hope this helps

[Charles Bryden]

thanks for the breakdown, this is really helpful. Unfortunately there are no building regs for this existing garage conversion. It was done over ten years ago.

The walls are dry-lined and the garage door was bricked up and replaced with a window. Also I believe the outer wall of the house was knocked out to create an internal doorway into the garage.

Would this affect the cost or approach in doing this?

I’m keen to hear your thoughts

[Brian Vasey]

In terms of reducing your offer that’s really more of a negotiation question than a technical one but the lack of Building Regs paperwork can sometimes affect value slightly because there’s a bit of uncertainty around how the work was done. Some buyers do use that as leverage in negotiations especially if the seller originally suggested the paperwork existed and it now turns out it doesn’t.

That said, it’s also very common with garage conversions that were done 10-20 years ago. A lot of them were completed properly but the paperwork was lost or the work was never formally signed off. The fact your surveyor hasn’t seen any signs of structural movement is a good sign.

If it was me in this situation I think your options are to ask for a small reduction or request an indemnity policy through the solicitor, or simply factor in that you may want to upgrade certain things like insulation or electrics themselves over time. I guess it all depends how much you want the house and how good value it is at the current price

Regarding extending the space later on if you do any new work in the future that requires Building Control then that new work would just be assessed on its own merits. Building Control don’t usually go digging into historic work unless it’s directly related to the new alterations you’re proposing.

[Charles Bryden]

ah brill. Thank you. I agree. Its a bit of a minefield when you start looking into it! Appreciate you being generous with your knowledge

I think the Electrics have been daisy chained from an existing circuit.

In our particular circumstance. Do you think it’s worthwhile reducing our offer due to the lack of building regs? (Before making the offer, the seller said they believe they had the paperwork from the previous owner, and so far they have been unable to provide anything).

Currently without building regs, it feels like we can extend this space without the lack of Building Regs potentially being identified.

[Brian Vasey]

Thanks, I’m glad it’s helped. My area of expertise is garage conversions but the nature of conversions often means you have to become knowledgeable in quite a few areas as I’m sure you are finding out.

From what you’ve described so far the main things I’d usually keep an eye on with an older garage conversion are the structure of the openings, the level of insulation in the walls floor and roof and ventilation in the roof space. Those are the areas where older conversions often fall short compared to current standards but they’re usually things that can be improved fairly easily over time.

With the electrics the lack of an RCD in the consumer unit isn’t unusual for a house built in the 80s. RCD protection only became standard in later regulations so a lot of older fuse boards don’t have it. It doesn’t necessarily mean there’s something wrong with the wiring but it does mean the electrical protection isn’t at the level modern regulations would require today.

In practice many people take the opportunity to upgrade the consumer unit when they start renovating or improving a space like this. A modern consumer unit with RCD or RCBO protection gives much better safety especially for sockets in a habitable room. It’s usually a fairly straightforward job for a qualified electrician and not massively expensive compared to other renovation work.

[Charles Bryden]

thank you, you’ve been super helpful.

You sound like you’ve got a lot of experience in this area, appreciate you sharing your knowledge.

If there’s anything else you think we should look out for in this circumstance, please let me know.

I just remembered – the Electrics for the conversion don’t have their own RCD in the fuse box. The fuse box is quite old (1986 house). Not sure whether this is something to be concerned about or not?

[Brian Vasey]

The surveyor’s comments are fairly typical in these situations as they can only do a visual inspection but the fact there’s no cracking or movement around the opening is definitely a positive sign.

If you wanted someone to properly check whether a lintel has been installed the usual options would be a structural engineer or a local builder with experience in structural alterations. In most cases a structural engineer would make a small opening in the plasterboard above the doorway to see what’s actually there and confirm whether a lintel is present and adequate. It’s usually a fairly small inspection hole that can easily be patched afterwards.

Another option some buyers take is an indemnity insurance policy through their solicitor. This is quite common when there’s no building regs paperwork for older work and the structure appears to have been stable for many years.

Realistically, if the conversion has been there over 10 years with no cracking or movement, it’s often a good indication that the opening was supported properly, but getting a structural engineer to take a quick look would give you the most certainty.

[Charles Bryden]

thank you so much. The seller has no information about the lintel or the garage conversion itself. The work was done two owners previous to them.

Our surveyor did a non-invasive visual inspection and didn’t note any cracking near the internal doorway or anywhere else on the garage conversion. He did comment his inspection doesn’t allow him to open the fabric of the building. No structural concerns as far as he is concerned noted during his visual inspection.

Unfortunately, the seller has refused to provide regularisation or to fund an inspection themselves.

What professional could check whether a lintel has been installed?

Your help is really appreciated.

[Brian Vasey]

Oh ok that does change things slightly if there’s no Building Control approval especially if structural work was carried out.

The fact the garage door has been bricked up and an internal doorway knocked through the original external wall suggests a lintel or some form of structural support should have been installed, so that would be one of the first things worth checking. A lot of older conversions were actually done properly but just never went through the sign-off process.

From a cost point of view it doesn’t necessarily make the upgrades more expensive but it does mean it’s sensible to check a few things before putting money into improving it. I’d want to know whether there’s a lintel above the old garage door opening and whether the knock-through into the house has proper structural support. It’s also worth finding out what insulation, if any, is actually in the walls, floor and roof, and whether there’s a damp proof membrane in the floor.

If those things are all reasonably sound, then upgrading insulation such as adding a proper insulated floor build-up or improving ventilation in the roof would probably be very similar cost-wise to the rough figures I mentioned before.

Where costs can increase is if something structural wasn’t done properly and needs correcting, for example installing a lintel where one wasn’t fitted originally.

This situation is actually very common with garage conversions done 10-20 years ago. Some people apply for regularisation through Building Control, but others simply upgrade the insulation and improve the room without going through that process, especially if the structure has clearly been stable for years.

Hope this helps a bit more