Joint building work with a neighbour - any pitfalls to be aware of?

[Glittertrauma]

Hi All

I'm after some advice or different perspectives, from anyone who has ever done building work jointly with a neighbour.

We have been planning a rear extension to our semi to create a family room and larger kitchen, and would like to start the build in the coming spring. We have met with an architect once, and set a date in a couple of weeks for him to come and measure up to produce plans.

I had coffee with my attached NDN the other week, and she mentioned that they are also planning a rear extension on a similar timescale. Her suggestion was that she'd spoken with a builder, who had told her that there were savings to be made if we did the project together.

On the surface I can see the plus points - a harmonious design, savings on costs and only one lot of disruption during construction. A lot of positives.

But I am also concerned that there may be downsides I have not thought of. We get on very well as neighbours but there is a lot we would all have to agree on to get this project off the ground, isn't there?

She has sent me details of the builder they met with and the architect their builder recommended. Should I postpone our own architect coming around to measure (we don't want to pay for one set of plans if we now need another that covers us both?)

Has anyone ever done joint building work with a neighbour and what pitfalls could there be?

We did it.
Architecturally, it made sense.
The extension is good.

Absolutely got railroaded into neighbours timetable. They refused to consider any architect or builder other than the ones they planned to use. Builder was great, architect was a waste of space, nearly derailed whole project, I declined to pay him.

Communication.
Insist it gets treated as a joint project, not just tacking you onto theirs.

I wouldn’t. If you have the money to do it then do it by yourself.

Not sure I would do this.
Do you know and trust this builder?
I wouldn't want to ditch an architect in favour of someone I hadn't vetted/chosen myself.
How would you safeguard against being liable for costs from NDN?
It may also mean the job takes longer. Eg. They want a plasterer but have to make you wait until next door is also ready to plaster.

@DancingLedge oh my goodness, that sounds like a terrible experience, I'm so sorry to hear that! I have agreed to meet with the builder they have been speaking to, not sure what would happen if we didn't think he was any good. This has given me food for thought, thank you! I'm mainly worried my husband will lump me with doing all the communication/negotiation. I'm about to give birth any day so I definitely don't want to be project leader. Also concerned things will take far too long to agree on with four people involved.... but the upsides are very real. Half think it may be pie in the sky as NDNs seem the type to constantly have builders out quoting and house being valued etc with no intention of action...

@Wolfiefan Some good points to consider- I certainly wouldn't agree to their builder/architect without meeting them myself and going through my own process with them. If we don't like them, suspect it may fall apart. The architect we were proceeding with has previously met with my neighbours but nothing came of it (not sure why). They seem to have found this builder they like and he uses his own recommended architect.
I'm not sure why plastering etc would hold anything up - it's only the shell we would be building together, everything else would be up to each of us individually. We'd probably source our own plasterer etc from people who have worked on our house before as we know them and what the work is like. Additionally my husband is very good practically and is likely to want to do a fair amount himself whereas next door wouldn't be doing anything themselves.

I have no experience of any of this except watching grand designs 😂 but could you appoint an independent project manager to manage your side and negotiate with your neighbours once building work starts?

If you get your own contract and payment terms with the builder and architect you'll have more weight.

We had joint planning permission with our neighbour. We each had our own contract. The builders first finished the neighbours then did ours. The discount was minimal though and only on materials which they were able to buy in a larger quantity.