£323,568 Difference: Why Great HMO Design Isn't a Cost, It's a Return
( 3 Min Read )
£323,568.
That's the difference, over ten years, between a well-designed HMO portfolio and a poorly designed one and it comes down to a single variable most investors underestimate: void periods.
Here's the Maths:
1 / Starting With the Ceiling
Take a standard 6-bed HMO. At the UK average room rent of £749/month, that's £4,494/month across all six rooms — or £53,928 gross annual rent at 100% occupancy.
That number is your ceiling. You will never earn more than that from this property.
The only question is how much of it you actually keep.
A Well-Designed HMO: 5% Voids or less
A well-designed, well-run HMO with a good layout, good spec, strong marketing, tenants who actually want to stay typically runs at around 5% voids. That's roughly three weeks of empty room-time per room per year, which is achievable and, frankly, expected of a property that's doing its job.
At 5% voids, that same HMO brings in £51,232 gross annual rent.
A Poorly Designed HMO: 20%+ Voids
Now picture the alternative: awkward room layouts that don’t feel quite right, a dated spec, weak marketing, or a location that doesn't quite land. Tenants churn faster, rooms sit empty for longer between lets, and voids creep up to 20%+ which is around ten weeks of empty room-time per room, every single year.
That property brings in just £43,142 gross annual rent.
The Gap: £8,090 a Year
The difference between 5% and 20% voids is £8,090 per year — and here's the part that stings: your costs don't drop to match.
Council tax, utilities, insurance — these stay roughly the same whether you're running at 5% voids or 20%.
So that £8,090 doesn't get absorbed anywhere.
It comes straight off your profit, every year, for as long as the property underperforms.
Ten Years, One HMO: £80,900 Lost
Run that gap forward over a 10 year hold and a single underperforming HMO has quietly cost you £80,900 — money that never shows up on a spreadsheet as a "loss," because nothing dramatic happened.
No tenant trashed the place, no boiler blew up. It just sat empty a bit more than it should have, month after month, year after year.
Scale It Across a Whole Portfolio: That’s £323,568 Gone
Now scale that across a portfolio of just 4 x 6-bed HMOs running at 20% voids instead of 5%.
£323,568 gone. From voids alone on only 4No HMOs.
Not from a bad tenant. Not from a market crash. Not from rising interest rates. Just from the compounding cost of design and management decisions made or skipped right at the start.
Now Do you Agree that Great Design Isn't a Cost — It's a Return?
This is exactly why it's baffling to see investors skimp on working with HMO specialist Architect from day one. The difference between a well-designed HMO and a poorly designed one was never just aesthetic. It was never about whether the communal space looks nice in photos.
It's about void rates. It's about how quickly a room re-lets. It's about whether tenants stay twelve months or three. And multiplied across a portfolio and a decade, it's the difference between six figures in your pocket and six figures gone.
Great design costs money upfront. Bad design costs far more, quietly, for years.
Great design isn't a cost. It's should be viewed as a financial return.
If you're planning an HMO project and want to make sure it's designed to minimise voids from day one, please get in touch as we'd love to help you get it right the first time.