Published 2026-07-19 · New Build Mortgage Guide · Written and reviewed by Phillip Wakeling-Smith (CeMAP)
Shared ownership on a new build: the part-buy route most buyers price wrong
Quick answer: Shared ownership lets you buy a share of a home — typically 10–75%, mortgage and deposit only on that share — while paying sub-market rent on the remainder to a housing provider. Most shared-ownership homes are new builds, so if you're browsing developments you'll meet it whether you planned to or not. It can genuinely beat a small-deposit full purchase on monthly cost and deposit size — but only if you price all three outgoings (mortgage + rent + service charge) and understand staircasing before you commit, not after.
How the numbers actually work
Say a new-build flat is £300,000 and you buy a 40% share (£120,000):
- Deposit: 5–10% of the share — £6,000–£12,000, not £15,000–£30,000. Compare that with the deposit routes on a full purchase.
- Mortgage: on £120,000 — smaller loan, easier affordability test.
- Rent: typically starting around 2.75% a year of the unsold £180,000 — roughly £412/month, usually rising annually by an inflation-linked formula.
- Service charge: payable on 100% of the property, not your share — the line item that most often breaks the "it's cheaper" assumption on flats.
Eligibility: household income under £80,000 (£90,000 in London), and you can't (with limited exceptions) already own another home.
The new-build-specific catches
- It's a leasehold, on a new development — so everything in our LTV caps houses-vs-flats guide about flats still applies, plus estate/service charges that are estimates at reservation and real numbers later.
- Builder incentives don't map across. The incentive machinery on open-market plots (how lenders treat them) mostly doesn't apply to shared-ownership units, which are sold by the housing provider at a fixed valuation.
- Down-valuations still happen — the share price is based on the full market value, and if the valuer disagrees with it, the same down-valuation dynamics apply to your share.
- Fewer lenders. Shared ownership is specialist lending: a meaningful subset of the market does it, at ordinary rates, but your lender pool is smaller — and smaller again if anything else about your case is non-standard.
- Timeline pressure is the same. Provider deadlines and mortgage-offer expiry interact exactly as on a full purchase.
Staircasing: buying more later
You can increase your share over time — newer-model leases allow purchases in 1% increments for the first 15 years (older leases typically 10% steps), each at the market value at the time, with valuation and legal costs per step. Staircase to 100% and the rent disappears and you own outright (on houses, usually with the freehold transferring).
Be realistic: each staircase is a mini-purchase. If your plan is "buy 25% now, own 100% within five years", price those steps — rising values make each one dearer — and compare the total against simply buying with a 95% or 100% product today. Run both versions of your numbers through the affordability check.
When shared ownership wins — and when it doesn't
Tends to win when: your deposit is the binding constraint; your income can't support the full-purchase mortgage; you're in a high-price area where even 95% LTV is out of reach.
Tends to lose when: you could scrape a 5% deposit on the full price and qualify — combined mortgage+rent+service charge on a share can exceed the mortgage on the whole home; or when service charges on the development are high and rising.
FAQ
Do I pay rent and a mortgage at the same time on shared ownership?
Yes — mortgage on your share, rent on the provider's share, plus the service charge on the whole property. Always compare the three-line total, not the mortgage alone, against a full-purchase alternative.
What deposit do I need for a shared-ownership new build?
Usually 5–10% of the share you're buying, not the full price — on a 25% share of a £300,000 home, that can be under £4,000. Deposit size is the scheme's biggest genuine advantage.
Can I buy more of the property later?
Yes — staircasing, in 1% steps on newer leases (10% on older ones), each at the market value at that time with its own valuation and legal costs. You can usually staircase to 100% and own outright.
Is stamp duty different on shared ownership?
You choose between paying SDLT on the full market value up front (one-off, protects you from tax on staircasing) or paying on the share now and potentially more as you staircase past 80%. The right choice depends on your staircasing intentions — take conveyancing advice on this one.
Do all mortgage lenders offer shared-ownership mortgages?
No — it's a subset of the market, though it includes major names and rates are generally ordinary. Your choice narrows further if your income or credit profile is also non-standard, so check the lender fit early.