Property development means creating new value through planning permission and construction — building new units from scratch, converting a single property into several, or extending significantly enough to create genuinely new saleable or lettable space — rather than refurbishing what already exists. This guide covers the basics: how a development appraisal works, the planning risk that sits at the centre of every development decision, how development finance is actually structured, and the build process itself. It's a natural next step for investors who've built genuine experience with BRRR or flipping and want to take on projects that create value through construction rather than renovation alone.
1. Types of small-scale development
Building one or more new properties on a plot — the highest capital requirement and longest timeline, but the greatest control over the end product.
Converting a large house into flats, or a commercial building into residential units — typically lower capital and timeline than new build, using an existing structure.
Certain extensions, conversions, and changes of use qualify under permitted development rights, avoiding the full planning application process — but the rules are specific and easy to get wrong without proper advice.
A large extension or loft conversion that creates genuinely new bedrooms or floor area, increasing value beyond what a cosmetic refurbishment achieves.
2. Planning permission — the central risk
Almost everything about a development project's viability depends on planning permission being achievable on terms that support the appraisal — and this is fundamentally less certain than refurbishing an existing property, since planning is a discretionary decision by the local authority, not a guaranteed right. Pre-application advice from the local planning department, before committing significant money, is standard practice for a reason: it gives an early, non-binding indication of likely planning sentiment for a specific site and proposal, considerably reducing (though never eliminating) the risk of a costly refused application.
Buying a site or property subject to planning permission already being granted (rather than buying first and hoping to obtain permission afterwards) removes much of this risk, at the cost of typically paying a higher price that reflects the value the planning permission itself has already created. Buying without permission already in place can secure a lower price, but transfers the planning risk entirely onto the buyer.
Permitted development rights allow certain works without a full planning application, but the qualifying conditions are specific — size limits, location restrictions (including Article 4 Directions removing permitted development rights in some areas), and prior approval requirements for many categories. Always get a specific planning consultant's assessment for your exact proposal and site rather than assuming a general permitted development right applies, since an incorrect assumption here can mean unauthorised development requiring retrospective permission or, in the worst case, enforcement action.
3. The development appraisal
A development appraisal works backwards from the Gross Development Value (GDV) — the total value of the completed units once sold or let — subtracting every cost to arrive at the residual profit, which is then checked against the developer's required margin to determine whether the numbers actually work.
| Line item | Example (3-unit conversion) |
|---|---|
| Gross Development Value (3 units, sold) | £630,000 |
| Site/property purchase price | £220,000 |
| Build costs | £180,000 |
| Professional fees (architect, planning, structural engineer) | £25,000 |
| Finance costs | £22,000 |
| Contingency (10% of build cost) | £18,000 |
| Selling costs (agent + legal) | £15,000 |
| Residual profit | £150,000 (~24% of GDV) |
Developers typically target a minimum profit margin around 20–25% of GDV (or a comparable margin on cost) to compensate for the time, risk, and capital tied up over the project — a deal that only clears 10–12% on paper leaves very little buffer if costs overrun or the eventual sale value comes in below projection, both of which are common enough that the margin needs genuine headroom, not a best-case assumption.
4. Development finance
Development finance is a distinct product from a standard mortgage or even a simple bridging loan — it's drawn down in stages against build progress (rather than as a single lump sum at the outset), with a monitoring surveyor appointed by the lender inspecting progress at each stage before releasing the next tranche of funds. This protects the lender against funding work that doesn't actually get completed, but means the developer needs to fund early-stage costs from their own resources before the first drawdown becomes available.
Lenders typically fund a percentage of both the purchase/land cost and the build cost (rather than GDV directly), commonly leaving the developer needing 30–40% of the total project cost as their own capital contribution — development finance reduces but does not eliminate the capital requirement, and first-time developers in particular should expect to need genuine capital of their own, not just a strong appraisal.
5. The build process
Move from concept to detailed drawings and a genuine, quoted build cost — not an estimate — before committing to finance or planning submission where possible.
Submit the full application (or confirm permitted development compliance) and allow realistic time for a decision — including the possibility of a resubmission if initially refused or conditions are attached.
A fixed-price contract with a reputable, properly vetted contractor, ideally with a formal building contract (such as a JCT form) rather than an informal agreement, protects both parties and clarifies what happens if costs or timeline shift.
Regular site visits, a clear variation process for any changes to the original specification, and (where development finance is used) the lender's monitoring surveyor inspections at each drawdown stage.
Building control sign-off, any required certificates, and then sale or letting depending on the exit strategy decided at the outset.
6. Risks
Development carries a different, generally higher risk profile than refurbishment-based strategies, concentrated in a few specific areas: planning risk (covered above), build cost overrun (construction projects routinely exceed initial budgets, which is why a genuine contingency is essential rather than optional), contractor risk (poor workmanship, delay, or contractor insolvency mid-project), and market risk (the GDV assumed at the start of the project is based on current market conditions, which can move during a build period that may run a year or more).
Every month a development project runs over schedule extends finance costs, delays the exit, and increases exposure to market movement — in a way directly comparable to the bridging finance time-cost relationship covered in the Bridging Finance Guide, but typically over a longer base timeline and larger absolute cost. Realistic scheduling, with contingency built in from the outset, is one of the highest-leverage things a first-time developer can get right.
7. Exit strategy
Decide the exit strategy — sell on completion, let and hold, or a mix across multiple units — before starting, since it affects design decisions, finance structure, and the appraisal itself. A sale exit needs the GDV assumption to hold at the point of completion; a hold-to-let exit shifts the question toward whether the completed units, refinanced onto standard BTL or HMO mortgages, produce a viable long-term return — closer to the BRRR calculation covered in the BRRR Calculator, but applied to newly-created rather than refurbished units.
8. Common mistakes
Pre-application advice or buying subject to planning already granted significantly reduces this risk compared to buying and hoping.
Construction projects routinely exceed initial budgets — a genuine 10%+ contingency is essential, not a box-ticking exercise.
The qualifying conditions are specific and easy to misjudge — get a planning consultant's assessment for your exact proposal.
An informal arrangement with a contractor leaves both parties exposed if costs, quality, or timeline disputes arise.
A development that only works at the exact projected GDV and exact projected cost has no room for the realistic variance that affects most projects.
9. Frequently asked questions
How is property development different from BRRR?
BRRR refurbishes an existing property to increase its value and refinance — the underlying unit count and structure typically stay the same. Development creates genuinely new value through planning and construction — new units, a change of use, or significant new floor area — with a correspondingly different risk profile centred on planning and build risk rather than refurbishment cost estimation alone.
How much capital do I need to start a small development project?
This varies hugely by project size, but since development finance typically covers only a percentage of purchase and build costs, expect to need a genuinely substantial capital contribution of your own — commonly 30–40% of total project cost — alongside the development finance facility. First-time developers should generally start with a smaller, simpler project than their available capital might tempt them toward, to build genuine experience before scaling up.
Do I need to use an architect and planning consultant, or can I do this myself?
For anything beyond the simplest permitted development project, professional input from an architect and, where planning risk is genuine, a planning consultant, is strongly worth the cost relative to the capital at stake in the overall project. Professional design can also itself improve the GDV achieved, partially offsetting the fee.
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