Shared ownership mortgages: how they really work

Shared ownership lets you buy a share of a home, typically between 10% and 75%, from a housing association, and pay a subsidised rent on the share you do not own. You need a deposit and a mortgage only on your share, which is why it opens up areas otherwise out of reach. Most schemes are leasehold, you pay rent and a service charge on top of the mortgage, and both usually rise each year. You can buy more of the property later, which is called staircasing.

You buy a leasehold interest in a percentage of the property. The housing association owns the rest and is your landlord for that portion.

You have the full right to live in the whole home. You are responsible for the whole home, not just your share, when it comes to the parts you maintain. That asymmetry is the thing people find least intuitive: you own 40% but you are usually responsible for repairs inside the property as though you owned all of it.

Newer leases have improved on this. Many now include a repairs period, often the first ten years, during which the landlord contributes towards essential repairs to specified elements. They also commonly allow staircasing in increments as small as 1%, where older leases typically required 10% at a time. Check which version of the lease applies to the specific home, because it makes a genuine financial difference.

Take a home valued at 250,000 pounds and a 40% share.

• Share price: 100,000 pounds.
• Deposit at 10% of the share: 10,000 pounds.
• Mortgage: 90,000 pounds.
• Rent on the remaining 60%, which is 150,000 pounds of value, charged at a subsidised annual rate. Schemes commonly set this in the region of 2.75% of the unsold value a year, which would be 4,125 pounds a year, or roughly 344 pounds a month. The exact percentage varies by scheme and by lease.
• Service charge on a flat: often somewhere between 90 and 250 pounds a month, and higher in blocks with lifts, communal grounds or concierge.

So your total monthly outgoing is the mortgage payment, plus around 344 pounds of rent, plus the service charge. On a 90,000 pound repayment mortgage over 30 years, the payment might be somewhere around 450 to 550 pounds a month depending on the rate, giving a total in the region of 900 to 1,100 pounds.

Compare that with buying the same home outright. A 225,000 pound mortgage on a 25,000 pound deposit would cost far more each month, and the deposit alone is two and a half times higher. That is the trade shared ownership makes.

Two costs escalate and you should plan for both.

The rent is reviewed annually under the terms of the lease, usually linked to an inflation measure plus a fixed percentage. Over ten years that compounds noticeably, so model it rather than assuming today's figure.

The service charge is not capped by the lease in the same way. It reflects actual costs of maintaining the building, and it can jump sharply when major works are needed. Ask for the last three years of service charge accounts and any planned major works before you commit. A building facing a roof replacement or cladding remediation can produce a bill running into thousands.

Staircasing means buying a further share. The price is based on the property's market value at the time you buy, not what you originally paid.

If the home rises from 250,000 pounds to 300,000 pounds, staircasing from 40% to 60% costs 20% of 300,000 pounds, which is 60,000 pounds, rather than 20% of 250,000 pounds, which would have been 50,000. Rising prices help the equity in your existing share and hurt the cost of buying more. Falling prices do the reverse.

Each staircasing transaction has costs: a valuation fee, legal fees, sometimes an administration fee to the housing association, and a mortgage arrangement fee if you are borrowing more. Budget 1,500 to 2,500 pounds per step. That is why the 1% incremental staircasing in newer leases is useful only if the associated fees are also low, so ask.

Reaching 100% is called staircasing out. On houses that usually means you own the freehold outright. On flats you normally still hold a lease, but you stop paying rent. Some leases, particularly in designated rural protected areas, cap staircasing below 100%.

This is the least understood part and the one that catches people.

When you sell, the housing association typically has a nomination period, often somewhere between four and twelve weeks depending on the lease, during which it has the exclusive right to find a buyer from its own waiting list. Only if it fails can you market the property openly.

You will also usually need a valuation from a RICS surveyor to set the price, rather than choosing it yourself, and that valuation has a limited validity period, often three months.

The practical effect is that shared ownership resales are often slower than open market sales. If there is any chance you will need to move within two or three years, factor that in seriously.

It suits you if your income is the binding constraint, you plan to stay put for at least five years, you want to live in an area where full ownership is unrealistic, and you are comfortable with a leasehold arrangement and a landlord.

It suits you less if you might need to move quickly, if you dislike the idea of ongoing rent and service charges alongside a mortgage, if you are buying in an area where prices are static (which makes staircasing painful without growth in your own equity), or if you could reach a 90% mortgage on a smaller home instead.

• Ask for the full lease and read the rent review clause and the staircasing clause.
• Ask for three years of service charge accounts and the reserve fund balance.
• Ask whether the lease includes an initial repairs period and what it actually covers.
• Ask what the minimum staircasing increment is and what fees apply per step.
• Ask how long recent resales on the development took.
• Check the ground rent and the lease term remaining, because a short lease affects mortgageability.
• Confirm which lenders will lend on that specific scheme, because not all do.

You have a choice on how to pay. You can pay tax on the market value of the whole property up front, or pay only on the share you buy now and pay more later if you staircase past a threshold. Which is better depends on whether you expect to staircase and on prices. The rules and thresholds differ between England and Northern Ireland (Stamp Duty Land Tax), Scotland (Land and Buildings Transaction Tax) and Wales (Land Transaction Tax), and they change with policy, so check GOV.UK, Revenue Scotland or the Welsh Revenue Authority and ask your conveyancer to run both options.

Not every mortgage broker handles shared ownership regularly, and lender panels for these schemes are narrower than for ordinary purchases. The MortgageMatch directory lets you find an FCA-authorised broker who does this kind of case routinely.