AIBU about not paying for work that is 90% done but not finished?

[shovetheholly]

As I may have mentioned a few hundred times we're having building work done soon.

Background is that for a while I was a project manager on a specialist kind of construction in London. We had it drilled into us that you never pay an invoice until the job is finished and snagged to satisfaction (apart from agreed advance payment deposits). Financial trails were all managed very carefully and precisely.

I now living in a much more laidback city, and obviously the work I'm doing is domestic not business. But I'm a bit surprised that I'm repeatedly being asked to pay for services before the work is entirely finished. The architect asked me to pay when the drawings were 90% done, but items were outstanding (e.g. the design of a green roof, which is dependent on loadings). Now the structural engineer (commissioned by the architect) is also asking for payment when the job isn't finished - because roof details are outstanding.

In both cases, these are NOT deposits for building materials, which is totally normal, but comparatively small sums for regulation prep work and drawings/SE (e.g. £500).

Is this normal? Am I being ridiculously uptight to want to pay only when the job is really finished? I do trust the architects but I feel like I have no comeback on the final details if cash has changed hands? I am quite willing to be told I'm being totally unreasonable if I am importing a load of expectations from larger builds inappropriately to smaller ones!

No. It is not normal. DH is a Consulting Engineer and whilst they do stage payments on very big jobs, just calcs for a house would be payment on completion. It is hardly a mega job it is? We paid an architect when everything went into planning. Then extra for detail when that was ready. Is this how the invoice is bring split up? There are two different stages for architects. Cannot think why there would be for structures.
What good is 90% done to anyone? However, I think it is reasonable to split the design for the green roof away from the rest as it is detail and not required for planning. The structural calcs are pretty basic really any may well be required for planning.

Yes, it makes no sense to me and seems unprofessional, but I wondered if I was overreacting. To be clear: we've already secured planning - these are the detailed building drawings and structural engineering calculations for the building regs/builder himself.

I have paid the architects promptly by the stage, but payment is demanding before each stage is finished, IYSWIM. So we almost have the final building drawings, but the final payment has been demanded while items are outstanding. Similarly, we almost have the structural engineering calculations, but payment has been demanded while these are not quite finished. I have only ever paid when a job is complete before.