One of the most common questions we are asked is where the line falls between a commercial mortgage and a residential one, and whether a property can cross from one side to the other. The answer runs in both directions. Some residential assets are financed with commercial-style lending, and some commercial premises can never be bought with a residential mortgage at all. Getting this right matters, because applying for the wrong type of finance wastes time and can breach the terms of the loan.
In this guide we cover both directions. First, when a residential asset is treated as commercial: large HMOs, multi-unit blocks, holiday-let portfolios, and limited company landlords. Second, the reverse: why you cannot buy commercial premises with a residential mortgage, what happens with mixed-use property, and where the regulated boundary sits. That boundary is important, because some cases fall inside the FCA's regulated mortgage perimeter and we refer those to a regulated firm.
For a broader comparison of the two products, read alongside our guide on [commercial versus residential mortgages](/knowledge-hub/commercial-vs-residential-mortgages).
When residential property is financed as commercial
Not every residential asset is bought with a residential mortgage. Once a residential property is held or operated as a business, lenders often treat it as commercial or use commercial-style underwriting. Several situations trigger this.
Large HMOs
A house in multiple occupation let room by room is a business, not a home. Small HMOs can sometimes be financed on specialist buy-to-let terms, but larger HMOs, typically those above a certain number of lettable rooms or licensable size, are usually assessed as commercial or semi-commercial. The lender looks at the rental income the property produces as a business, rather than a simple loan-to-value against a family home. Our [HMO commercial mortgage guide](/knowledge-hub/hmo-commercial-mortgage-guide) covers the thresholds and lender appetite in detail.
Multi-unit freehold blocks
A single freehold title containing several self-contained flats is another case that often sits outside standard residential lending. Because you are financing an income-producing block rather than one dwelling, many lenders underwrite it on commercial or portfolio terms, assessing the aggregate rent and the quality of the units. The freehold structure, rather than the residential use, is what pushes it toward commercial treatment. A standard residential mortgage is designed for one dwelling on one title, so a block of several units on a single freehold does not fit its model, which is why these cases are placed with lenders that understand multi-unit blocks.
Holiday-let portfolios
An individual holiday let can sometimes be financed on specialist residential terms, but a portfolio operated as a trading business, with turnover, seasonality and management, is frequently treated as commercial. The lender is effectively assessing a hospitality operation, and the income assessment reflects that. The more the property functions as a business rather than a let dwelling, the more likely commercial-style lending applies, particularly where several units are run together under one brand or booking system and the income depends on active management rather than a single long tenancy.
Limited company portfolio landlords
Many landlords now hold residential property inside a limited company or special purpose vehicle. Larger portfolios held this way are often financed on a portfolio or commercial basis, with the lender assessing the company, the aggregate rental income, and the overall gearing rather than looking at each property in isolation. The corporate structure and the scale of the portfolio move the lending into commercial territory even though the underlying units are homes.
When lenders treat residential as commercial
The common thread across all of these is purpose and scale. A single home you or a tenant lives in is residential. Once residential property is held as a business, a block, a portfolio, an HMO run for room income, or a trading holiday-let operation, lenders assess it on the income it generates and the structure that holds it, which is the essence of commercial underwriting. Rates for this kind of lending typically sit in the 6.5-8.5% band for investment cases.
The reverse: buying commercial with a residential mortgage
Going the other way is far more restricted, and the short answer is that you cannot use a residential mortgage to buy genuine commercial premises.
Why a residential mortgage will not fund commercial premises
A residential mortgage is designed and priced for a dwelling that is lived in. Lenders assess it against residential criteria, residential valuations and, where it is a home, consumer protections. Commercial premises, a shop, a warehouse, an office, an industrial unit, do not fit any of that. The valuation basis is different, the risk is different, and the lender's funding and permissions are different. Attempting to buy commercial premises on a residential mortgage would breach the mortgage terms even if it could somehow be arranged. Commercial premises need a commercial mortgage, which is what our [commercial mortgages](/services/commercial-mortgages) service arranges.
Mixed-use and semi-commercial property
The interesting middle ground is mixed-use property, such as a shop with a flat above. These are neither purely residential nor purely commercial, and they are usually financed with a semi-commercial mortgage that reflects both elements. The residential portion is often weighted favourably in the valuation, which can improve the loan-to-value available. Semi-commercial rates generally fall in the 6.5-8.5% band. Our [semi-commercial mortgage guide](/knowledge-hub/semi-commercial-mortgage-guide) explains how these are assessed and who lends on them.
The regulated boundary
There is an important regulatory line to understand. Most commercial mortgages are unregulated lending and fall outside the FCA's regulated mortgage perimeter. However, certain cases can fall inside it. A common example is a sole trader buying a shop with a flat above where they will live in that flat: because it becomes their home, the loan can be a regulated mortgage contract. We are not authorised for regulated mortgage business, so where a case falls inside the regulated perimeter we refer it to a regulated firm rather than trying to place it ourselves. Being clear about this boundary protects you and keeps the transaction properly advised.
How lenders assess income on these properties
The reason these residential-but-commercial cases are underwritten differently comes down to how the income is assessed. On a standard residential mortgage, the lender looks at your personal income and affordability. On the properties above, the lender looks at what the asset itself produces.
For a large HMO, that means the aggregate room rent, adjusted for realistic voids and management costs, tested against the mortgage cost through a debt service or interest cover calculation. For a multi-unit block, it is the combined rent from all the flats assessed as a single income stream. For a holiday-let portfolio, the lender takes a view on seasonal turnover rather than a single annual rent, which is why it looks more like lending against a trading business. And for a company-held portfolio, the lender assesses the company's overall rental income and gearing across the whole book. In each case the property is being treated as an income-producing investment, which is the defining feature of commercial underwriting and the reason the pricing sits in the 6.5-8.5% investment band rather than at residential levels. Our guide to the [commercial buy-to-let](/knowledge-hub/commercial-buy-to-let-guide) route explains how this income assessment works for investors.
Refinancing across the residential and commercial boundary
The boundary matters at refinance as well as purchase. Landlords sometimes buy a property on residential or standard buy-to-let terms, then convert or extend it into an HMO or multi-unit block. Once the use changes, the appropriate finance often changes too, and a refinance onto commercial or semi-commercial terms may be needed to reflect how the property now operates. The reverse can also happen: a former commercial building converted into flats may move onto residential or portfolio lending once the conversion is complete and the units are let. Timing these refinances around the change of use, and around any planning or building work, is part of getting the structure right. If you are planning a conversion, it is worth understanding the likely finance route before you start, not after.
Worked examples of each direction
Examples make the boundary clearer than any rule. Consider three common cases we see.
A landlord buys a six-bedroom house and lets it room by room to young professionals under a licence. Although the building is residential, it is being run as an income business, so it is financed as a large HMO on commercial-style terms, assessed against the room rent. A standard residential mortgage would not fit, and using one would breach its terms.
A business owner buys a shop and warehouse to trade from. This is genuine commercial premises, so it needs a commercial mortgage assessed against the business and the property. No residential mortgage exists that could fund it, regardless of the price or the borrower's income.
A couple buy a high-street unit with a two-bedroom flat above, intending to run the shop and live in the flat. Because it is mixed-use and they will live there, the case is likely semi-commercial and may fall inside the regulated mortgage perimeter. We would assess the structure and, if it is regulated, refer them to a regulated firm to arrange it properly.
What lenders want to see
Whichever direction your case runs, being ready with the right information speeds things up. For residential assets financed as commercial, lenders typically want the tenancy or licence agreements, a schedule of rents, evidence of any HMO licence, and, for portfolios, a full schedule of properties with values and mortgages. For genuine commercial premises, expect to provide business accounts, details of how the property will be used, and your deposit evidence. For semi-commercial cases, the split between the residential and commercial parts, in floor area and value, matters, because it influences both the loan-to-value and whether the loan is regulated. Preparing these before you approach a lender avoids the stop-start that frustrates so many applications, and it lets a broker place your case with confidence.
How to know which route you need
The practical test is to ask what the property is and how it will be used. A single dwelling that is a home or a straightforward let is residential. Genuine commercial premises need a commercial mortgage. A property held as a business at scale, an HMO, a block, a portfolio, a holiday-let operation, is generally financed commercially even though it is residential in nature. And a mixed-use building sits in the semi-commercial middle, with the added check of whether anyone will live in it in a way that makes the loan regulated.
If you are not sure which side of the line your property falls, that is exactly the kind of question we answer every day. [Contact us](/contact) and we will tell you which type of finance fits, and if your case is regulated we will point you to the right regulated firm. You can also compare lenders on our [lenders](/lenders) page.
*Written by Matt Lenzie, Founder of Commercial Mortgages Broker. Ex-Lloyds Bank & Bank of Scotland.*