New build buying process

[Newbuildbuyerconfused]

We went and looked round a new build site a few days ago and really liked a property. We came home to consider our options and make sure we can afford it, the sales advisor says we have to exchange in 6 weeks but the house won’t be built until May!
I don’t understand why exchange has to be so quick (and also how is it so quick when it took 14 weeks when we bought our current house).
Also she said most people just move in with family whilst waiting for the build, that isn’t an option for us so do we have to sell our house and move into an air /rental in the meanwhile? That’s going to be very costly for us.
The site is very big and building will be going on into 2027 they think.
I’m worried that we sell our house to become homeless when it took us so long to get on the property ladder.

As this appears to be at an early state of estate development, unfortunately for you the developer holds the cards and early exchange will be their norm. Only if they are sitting on completed but unsold properties will the balance switch to the buyer in terms of being able to negotiate with the developer over timetables

So unless you have cash up front to pay the deposit on exchange, the "expectation" is you will need temporary accommodation for yourselves between selling your own to raise the deposit and moving into the completed new build. That is the way of the world, the developer needs early exchange to lock you into the purchase, make their sales figures look promising, and also get a bit of cash from the deposit to help fund the rest of their work.

if unwilling to play that game, then don't buy new build.

If you are willing, then make sure the contract has a clear timetable for completion date, and penalties that favour you if the developer fails to meet it. "you exchange contracts within a set timeframe after reserving the plot, which legally commits you to buy the property. The contract includes a "completion on notice" clause and a "long-stop date", allowing you to walk away and get your deposit back if construction isn't finished by that date. You then arrange your mortgage and other finances during the lengthy period before the developer serves you notice that construction is complete, at which point you have a short window, often 5-10 working days, to finalize the purchase."

That obviously is very risky as short term rentals are rare and very difficult to perfectly time it so that you don't end up paying rent and mortgage at the same time.

You might find this useful for more background:
New Build Conveyancing Explained 2025 - HomeOwners Alliance

Most builders have a similar stipulation, but they aren’t all rigid. A lot depends on how well the development is selling. Usually, you have to have an offer on your property before they will reserve a plot.

We’ve bought several new builds and they’ve all been a bit different. The one before last we reserved early December when our house went under offer. We completed on our sale in March, moved into rented for six months and completed the purchase at the end of August. That will be what the sales person is suggesting. Yes, you have to factor in the cost of renting and/or storage, but you know that the purchase is more straightforward because you aren’t in a chain.

We moved last November and reserved the house in May. They said a short exchange time, but the market is flat, so they didn't resell the plot. In fact, there are still three houses here that have been reserved since we arrived.

So the answer is, yes, you have to sell your property and factor in the cost of renting, if you want that house. It also depends on what stage the development is at. In the early stages, they’re less flexible, but when most of the houses are sold and they want to finish up the site, they’re usually more accommodating.

Thanks for explaining @Bluevelvetsofa @Wot23 .
So does that mean we don’t need a mortgage in principle before reserving the plot? Only once we are closer to completion?

Was completely out of the loop when buying our new build as the last time I moved was 30yrs previously.
Was completely taken back and even contacted the developers regional office to make sure we hadn't misunderstood what the sales team were telling us (we hadn't and it was all true😲).

We were only allowed to reserve when we were SSTC, exchange then had to be within 6-weeks with completion 12-months later.
As it happened the 6-week window extended beyond 10-weeks and although the sales team were making unhappy noises, our solicitor told us not to worry as we were now so close they would not bin us and start again with another buyer.
We exchanged and set a completion date (on our sale) of 5-months later which gave us time to prepare another property we already owned. After completion (on the sale) we moved into our other house until our NB was ready some 7-months later.

Speaking to our new neighbours, all had done something similar (rented, moved in with family etc) apart from a couple who had bought outright with no need to sell their previous houses until after they were in the NB.

If there was a downside it was the double moving fees and having to change address twice in 12-months.
The good thing about buying off-plan was that there was lots of time to sort out extras, many of which would not be available when buying a NB which was ready or v.nearly ready. We also got to see our house being built and photographed the various stages (for posterity and also for reference when carrying out changes in the future).

Some developers will offer part exchange on your house too, so they will buy your house - which can make it a bit simpler logistics wise.

indeed, one I know of achieved this: