Funding an Office to Resi Scheme: Where the Valuation Basis Changes
A vacant office is worth what somebody will pay for the income it might produce. The same building as four flats is worth what four flats sell for. Those are two entirely different sums, and the gap between them is the whole reason anybody converts commercial property to residential use, and converting commercial property is the only reliable way to capture it.
Nothing about the bricks changes. What changes is the arithmetic a valuer uses: an income capitalisation on one side of the transaction, comparable sold prices on the other. Understanding that shift is the difference between a scheme that funds easily and one that a lender declines in ten minutes, because every ceiling in the bridging loan is a ratio of a valuation, and the property valuation basis is the thing you are actually buying.
What actually changes when commercial property becomes residential?
Four things change, and only one of them is the commercial property itself. The other three are all financial.
The valuation basis. A commercial building is valued by capitalising its rent at a yield. Empty, with no rent, that arithmetic produces a poor number, which is why vacant commercial property is often cheap. Residential property is valued against comparable sold prices, which do not care whether anybody currently lives there. Converting commercial property therefore moves the commercial property from a basis that punishes vacancy to one that ignores it.
The planning use. The building moves from a commercial use class to residential use, either through a full planning application or through the prior approval route under permitted development rights. That change is a legal event, evidenced by a decision notice, and it is what a lender funds against.
The regulatory standards. Residential conversions must meet residential building regulations: insulation, sound separation between flats, fire escape, ventilation, daylight and minimum space standards. Office buildings frequently fail several of those, and fixing them is the bulk of the development cost.
The lending. Commercial security supports a day one advance of 65 to 70 percent of current value across our lender panel. Finished residential units support up to 75 percent, and exit onto ordinary buy to let mortgages rather than commercial mortgages. The scheme therefore starts on one set of lending rules and ends on another.
The important consequence is timing. The valuation shift does not happen when the planning consent arrives, and it does not happen when the builders start. It happens when the residential units are physically complete, certified and capable of being sold or let, which is why the bridging finance has to cover the entire journey rather than stopping halfway.
Do you need planning permission to convert a commercial building?
Sometimes, and where you do not, you still need the council to say so in writing.
Two routes exist. A full planning application, which is required for most substantial residential conversions, anything involving significant external alteration, and any building where permitted development rights have been removed. And the prior approval route, under which certain commercial, business and service premises may change to dwellinghouses without a full application, subject to the council approving specified matters such as flooding, contamination, transport, noise and the provision of adequate natural light.
The prior approval route carries conditions that catch people out. There are qualifying periods, typically requiring the commercial property to have been in the relevant commercial use for a minimum period and vacant for a shorter period before the application. Size limits apply. And the permitted development rights are switched off in conservation areas, on listed buildings, and anywhere the council has made an article 4 direction, which many authorities have done specifically to control office to residential conversions in their town centres.
Two practical points. Prior approval is not a rubber stamp; councils refuse applications on natural light and noise regularly, and the specified matters are real tests. And the rules in this area change more often than any other part of planning, so confirm the current position on the planning register for the specific address rather than relying on a guide, including this one.
Whichever route applies, and no guide is a substitute for the planning register, the document a lender wants is the decision notice. Terms may be issued on a pending application, but almost nobody will release a works tranche against a consent that does not yet exist.
Which types of commercial property convert well?
Five property types convert readily and three convert badly, and the difference is almost always the commercial property’s depth and its services.
Small office buildings and upper floors above shops. The classic candidates. Shallow floor plates, existing windows on two or more elevations, and services that can be split. Most successful commercial to residential conversion schemes are this shape.
Former banks and professional premises. Generous ceiling heights, good frontages, and usually a decent structure.
Public houses and small hotels. Already configured with bedrooms, bathrooms and drainage in roughly the right places, which saves a great deal of first fix cost.
Light industrial units in residential streets. Where the surrounding area is already residential, both the planning case and the sales evidence are straightforward.
Redundant retail with upper floors. Often the upper floors alone convert, leaving a commercial unit below, which produces a mixed use building and an exit that needs care.
The three that convert badly: deep plan office floors, where the centre of the commercial property has no natural light and cannot meet daylight standards; buildings with no realistic way to provide separate access to the residential element; and property in genuinely commercial surroundings, where flats will be difficult to sell whatever the planning permission says.
Test the sales evidence before the planning question. A conversion with permission in a location where nobody wants to live is a scheme with consent and no exit.
How does the property valuation shift actually work in numbers?
Take a vacant two storey office building bought for £420,000.
As commercial property. Empty, with no lease and no covenant, a valuer capitalises a hypothetical rent at a yield that reflects the risk of it staying empty. The result is a modest figure, and it is why the commercial property is available at that price at all. Lending against it is 65 to 70 percent of that number.
As residential. Converted into five flats, the property valuation becomes a comparison exercise against recent sold prices of similar flats nearby. Five flats at £185,000 each is £925,000, subject to a discount if they are to be sold as a single investment lot rather than individually.
The gap between £420,000 plus the development cost of the conversion work, and £925,000, is the commercial conversion scheme. That is the arithmetic behind every commercial to residential conversion finance enquiry we see, and everything else in the transaction is about protecting it.
Three things erode the gap in practice. A bulk discount if the residential units are sold or valued as a portfolio rather than individually, which typically applies where more than a few units are involved. Sales periods, because five flats rarely sell simultaneously and every month is another month of monthly priced finance. And the cost of the residential standards, which is the item most often underestimated.
The valuation risk is concentrated in one place: the comparable evidence for the finished flats. Before buying anything, look up recent sold prices for similar flats within a few streets, using Land Registry price paid data, and be honest about whether a converted office flat sits at the top or the bottom of that range. It usually sits at the bottom.
What finance funds a commercial to residential conversion?
One product for the conversion work and a different one for the hold, and choosing between two versions of the first is the real decision.
Heavy refurbishment bridging finance. Where the structure is retained and the conversion work is internal reconfiguration plus services, this is heavy refurbishment bridging: a day one advance against the commercial value, plus a works tranche released in stages against a monitoring surveyor’s certificates, from about 0.75 percent a month across our lender panel over a 6 to 18 month term. Quoted as a margin over the Bank of England base rate of 3.75 percent, held since December 2025.
Development finance. Where the commercial conversion scheme creates several new titles, involves substantial new build, or takes the commercial property back to a frame, it is usually written as development finance instead, from 6.5 percent a year at 65 to 70 percent of gross development value. Longer terms, heavier appraisal machinery, and often better value on larger conversions.
The exit. Either sale of the completed flats, or a refinance. Where the residential units are held and let individually, buy to let mortgages take over. Where the commercial property is held as a single investment or retains a commercial element, commercial mortgages from 5.5 percent a year at up to 75 percent loan to value apply, with rental income covering 125 to 150 percent of the payment.
Most schemes of five units or fewer sit comfortably in the first category. Above that, get both quoted, because the pricing crosses over and the loan term available on development finance is frequently what the commercial conversion scheme actually needs.
How much will lenders advance on converting commercial property?
Less than on residential security at the start, and more at the end, which is precisely the problem to plan around.
The day one advance is measured against the commercial property as commercial property in its current state: 65 to 70 percent of that value across our lender panel, against the 75 percent available on residential security. On a £420,000 purchase with a £430,000 commercial valuation, that is roughly £280,000 to £300,000, so the cash requirement on day one is £120,000 to £140,000 plus stamp duty and fees.
The works tranche is added on top, released in stages, with the total drawn capped against the finished figure, commonly at 70 percent of the value on completion or at a percentage of total cost. Ask which test applies before accepting terms, because the same scheme can pass one and fail the other.
Three factors lift the bridging advance. A granted planning consent or prior approval, rather than a pending one. A borrower with comparable completed residential conversions behind them. And vacant possession, because a building with sitting tenants restricts what can be done and complicates the loan security.
Two factors reduce it. Deep plan floors or any doubt about daylight compliance, which is a valuation risk the bridging loan lender prices for. And thin comparable evidence for the finished flats, which caps the end value that every ratio depends on.
What does the conversion cost beyond the commercial property work?
Nine lines of cost, and the building work is only the largest of them. Three of the nine are finance items and the other six are the ones people forget.
Interest. From about 0.75 percent a month on the drawn balance, retained or rolled rather than paid monthly.
Arrangement fee. 1 to 2 percent of the bridging loan, charged on the whole facility rather than the drawn part.
Valuation. Two figures and often two bases, commercial today and residential on completion, so it costs more than a standard report.
Monitoring. An initial appraisal plus a fee per site visit for the life of the build.
Legal costs. Yours and the bridging loan lender’s, higher than on a simple refurbishment because new titles are being created and leases drafted.
Professional team. Architect, structural engineer, planning consultant, party wall surveyor, and a quantity surveyor’s cost plan.
Planning and building control. Application fees, prior approval fees, building control charges, and any community infrastructure levy the authority applies.
Statutory services. New water, drainage, gas and electricity connections and meter splits for each residential unit, which on a five flat conversion is a five figure sum on its own and is routinely forgotten.
Running costs. Business rates or council tax on an empty building, insurance on the correct basis, and security.
On the £420,000 office above, converting to five flats at a build cost of £310,000, expect finance costs near £45,000 over 12 months plus roughly £55,000 of professional, statutory and holding costs. Total outlay approaches £830,000 against a £925,000 gross residential value, before any sales costs. That is a working scheme with a thin margin, and it demonstrates why the £185,000 comparable figure has to be right.
Which mortgage takes out the conversion bridging loan?
One of three, and the mortgage decision should be made before the bridging loan completes rather than after the builders leave.
Individual buy to let mortgages, one per flat. The most common outcome on a conversion producing self contained residential units. Each unit needs its own registered title, usually a long lease with the freehold retained, its own EPC, its own utility supply and its own building control sign off. A mortgage lender will decline a flat that shares a meter with the flat next door, however good the conversion work is.
A single commercial mortgage over the whole building. Where the property is retained as one investment, or where a commercial element remains at ground floor, one of the commercial mortgages products from 5.5 percent a year at up to 75 percent loan to value is the exit, subject to rental income covering 125 to 150 percent of the mortgage payment. Simpler legally than five separate titles, and usually a lower advance.
A portfolio mortgage across several properties. Where the borrower already holds other property, some lenders will take the converted building into an existing portfolio mortgage facility. Convenient, and it ties the new asset to the old ones in a way worth thinking about before you sign.
Four things decide whether the mortgage exit is available at all. Whether the residential units meet the bridging loan lender’s minimum size, because many decline flats below a stated floor area. Whether any commercial use remaining in the building is acceptable, since a flat directly above certain commercial uses is unmortgageable with a large part of the market. Whether the planning permission and building control paperwork is complete. And whether the rental evidence supports the cover test at the mortgage rate available on the day.
The sequence that works is to obtain a mortgage decision in principle on the finished specification before the conversion starts. It costs nothing, it tells you whether the unit mix you have designed is fundable, and it converts the riskiest assumption in the development appraisal into a documented one. Borrowers who skip it discover the problem at month ten, with a bridging loan running and no mortgage available, which is the most expensive position in this entire market.
Where no mortgage will follow, the exit is a sale, and the finance should be arranged with a term long enough to sell into rather than a term that assumes a refinance nobody has tested.
Do the works themselves need planning permission as well?
Two separate questions, and people conflate them constantly.
The change of use needs either planning permission or a prior approval decision, as described above. That is a question about what the building is used for.
The physical work may need its own permission on top. New window openings, changes to the elevations, external staircases, roof alterations, balconies and refuse stores are all operational development, and permitted development rights for a change of use do not automatically cover them. So a scheme can hold a prior approval for the conversion and still need planning permission for the fenestration changes that make the residential units habitable.
Three moves avoid the trap. Submit the elevational changes at the same time as the change of use application rather than afterwards. Ask the planning officer directly whether the proposed works fall within the prior approval or need a separate consent. And where you need planning permission for the physical work, get it granted before drawing the development works tranche, because a lender’s condition will usually require every consent the scheme depends on to be in place.
What building regulations catch office conversions?
Five, and they are the reason conversion costs surprise people who have only done residential refurbishment before.
Sound. Separating walls and floors between flats must meet acoustic standards, tested on completion in many cases. Office floors almost never do, so new floating floors and independent linings are usually needed throughout.
Fire. Protected escape routes, compartmentation between units, fire doors, alarm systems and often sprinklers depending on the building’s height and layout. This is the single biggest cost item in most residential conversions.
Thermal performance. Insulation and glazing to residential standards, plus an EPC for each residential unit, which the property will need before it can be let or sold.
Ventilation and daylight. Habitable rooms need adequate natural light and ventilation. This is where deep plan buildings fail, and it cannot be fixed with a better specification.
Space standards. Nationally described space standards apply in many authorities, setting minimum floor areas per unit. A scheme designed around eight small flats can come back as six compliant ones, which changes the whole appraisal.
The order of operations matters. Establish daylight and space compliance at the design stage, before you buy, because those two decide how many units the building will actually produce and every number in the conversion scheme flows from the unit count.
What is the mortgage exit, and when should it be agreed?
Two types of exit, and the one you plan for should be tested before the first drawdown of the finance.
Sale of the completed units. The cleanest, and what most bridging loan lenders prefer on a first conversion. Its weakness is time: five flats sold individually take months, and a 12 month facility with a 4 month build has 8 months of selling in it, which is tighter than it sounds.
Refinance and hold. Individual buy to let mortgages on each flat, or a single commercial mortgage over the building where a commercial element remains, at up to 75 percent loan to value with rent covering 125 to 150 percent of the payment. This exit needs each unit to have its own title, its own EPC, its own certificates and, in many cases, its own utility supply.
Three conditions have to be true before either exit works, and they should all be confirmed before you buy. Each unit must be separately saleable or mortgageable, which is a title and services question rather than a building one. The comparable evidence must support the values in the development appraisal. And any remaining commercial element must not make the residential units unmortgageable, which is a live problem where a flat sits directly above certain uses.
A third path exists and it is worth naming: development exit finance, from 0.55 percent a month at up to 75 percent loan to value, which replaces the bridging loan once the residential units are complete and buys a 6 to 18 month sales window at a lower rate. On a conversion producing several units for sale, planning that step in from the start is usually cheaper than extending the original facility under pressure.
What should you have ready before asking for terms?
Seven items, and the first three decide whether the scheme exists at all. Every finance provider in this market asks for the same set.
The planning position: a granted consent or prior approval decision notice, not an application. A unit schedule showing the number of flats, their floor areas and their compliance with space standards. Comparable sold prices for the finished units, from the last six months and the same area. A quantity surveyor’s cost plan including fire, sound, services and a contingency of at least 15 percent. Drawings from an architect who has done residential conversions before. Your track record, written down. And the mortgage exit, named, with either an agent’s marketing appraisal or a decision in principle from a mortgage lender.
Assemble those and a conversion places with the finance houses that run development books, at sensible pricing. Arrive with a purchase price and an idea, and the case goes to the expensive end of the market or nowhere at all.
If you have a building and a consent, we arrange conversion finance across a panel of over 100 lenders and will tell you whether the scheme prices better as heavy refurbishment bridging or as staged development finance before anybody instructs a valuation. Where the finished building is held and let rather than sold, the mortgage exit is commercial mortgages or individual buy to let facilities.
Construction Capital is a trading name of Lenzie Consulting Ltd, registered in England and Wales, company number 08174104. We are a commercial finance broker and introducer, not a lender, and we are not authorised by the FCA. Where a case is a regulated activity we arrange it through lenders who hold the relevant FCA permissions. Rates, fees and terms are indicative, vary by lender and deal, and are never an offer of finance. Written by Matt Lenzie.