Not every buy-to-let investment is straightforward, and some large lenders will not provide loans for complex investments. Fortunately, there are many smaller lenders who specialise in more complex investments.

The standard buy-to-let investment is for a house that will be rented by one household. Most large lenders can provide a commercial mortgage to finance investments of this nature.

There are several types of complex deals, including the likes of student houses, multiple occupancy property, semi-commercial property and nonstandard constructed buildings.

Landlords may find it difficult to get a loan from a large lender for houses of multiple occupancy (HMO). Some smaller lenders, however, see that there is less risk from an HMO investment. If a family rents a house then leaves, the landlord will receive no rent until he or she finds another tenant, but will still have to keep up with the commercial mortgage repayments. If a tenant of an HMO leaves, then the landlords will continue to receive rent from the other tenants.

Semi-commercial properties that have both residential and a commercial areas often means that there are two tenants: a commercial one and a residential one. Specialist lenders provide commercial mortgages for semi-commercial properties.

Some large lenders will not provide loans for nonstandard constructed properties. These include ex-local authority high-rise buildings constructed from concrete or steel frames.

A commercial mortgage broker has access to many lenders, and can find a commercial mortgage deal for complex buy-to-let investments that suits their clients needs.