Every UK landlord has a private spreadsheet of pain. Mine has one column nobody talks about: vacant days. Not "rented" or "advertised" — actually empty between tenants. The mortgage is still due, the Council Tax flips back to you the moment the last tenant moves out, the utilities standing-charge keeps ticking, and the buildings insurance demands the property be reachable. On a £1,000/month flat, an average UK void runs 23 days and costs roughly £1,400 once you total the lost rent + the carry costs. Multiply across a five-flat portfolio with 1.4 voids per year and you're staring at a £10,000 hole that nobody at the agency emails you about.
Most landlords absorb it. A growing minority list the empty unit (or the garage, or the side return, or the loft) on Packhood as storage for the in-between weeks. Not a person living in it — boxes. Identity-checked renter, fixed monthly fee, four-month commitment, no tenancy created. The property earns £400–£800 between tenants instead of bleeding £1,400.
This post walks through the maths in plain English: what a void actually costs, how storage-between-tenants compares to leaving the unit empty, the legal angle (storage is a licence, not a tenancy — important), and the operational reality of running this on a 5-property portfolio without it eating your weekends.
What a void actually costs you (most landlords undercount)
Walk down the cost line by line on a typical £1,000/mo BTL flat in a UK city, 23 days vacant.
Lost rent: 23 days × (£1,000 / 30) = £767.
Council Tax: the moment the tenant moves out, liability flips back to you. Most councils give a 0–28-day exemption (postcode lottery — Manchester offers 14 days, Birmingham 28, Leeds 0, Westminster 0). Worst case at £180/month you owe roughly £140 for the void. Scotland and Northern Ireland figures sit similar.
Utilities standing charges: ~£20/month gas + ~£15/month electricity + ~£15 broadband if you keep it for showings = ~£40 for 23 days.
Buildings + landlord insurance: most policies have a 30- or 60-day "unoccupied" clause. Notify the insurer or risk the cover lapsing on a burst pipe — you don't lose money on the void itself, but the day you don't notify is the day the boiler dies.
Mortgage interest still ticks: on a £150,000 outstanding interest-only mortgage at 5.5%, that's roughly £440 over 23 days.
Re-let admin: agency fee 1 week's rent (~£250) plus a deep clean (~£150) plus EPC if it lapsed, plus referencing.
Total: £1,387 for 23 days. Round to £1,400. On a five-property portfolio with 1.4 voids per property per year, you're looking at £9,800/year of straight loss that doesn't show up on any line item — it's just the air leaking out of the rental return.
Why storage hosting is structurally different from short-term lets
Most landlords' first instinct when they see "rent it during the void" is Airbnb. That's the wrong framework, and your insurer will side-eye you for it.
An Airbnb stay is a short-term let. It triggers business-rate questions in some councils (especially London Article 4 areas), changes the insurance category, voids most BTL mortgage covenants (Lloyds, Santander, NatWest BTL all explicitly prohibit short-term letting), and generates Cleaning + linen + key-handover labour every 2–3 days.
A storage booking is a licence to occupy a defined space for stated items. No tenancy created. No accommodation provided. No nightly turnover. The renter's belongings sit in the unit for 4 months on average. There's a single check-in and a single check-out, both of which can be remote (smart-lock or coded keysafe).
On the BTL mortgage: most lenders accept short-term storage between tenancies because there's no occupancy. On insurance: most insurers prefer it to "fully unoccupied" because there's a regular check-in cadence (the storage renter visits ~once a fortnight on average) and the property reads as occupied to passers-by. Always ring your specific insurer and your specific lender — covenants vary — but the conversation is dramatically easier than "I want to put it on Airbnb."
The portfolio play: a 5-property landlord's real numbers
Take a London-zone-3 landlord — five flats, average rent £1,400/mo each, average void 26 days/year per property.
Without storage hosting: 5 × 26 × (1,400 ÷ 30) = ~£6,070 lost rent + ~£3,500 carry costs = ~£9,500 of voids absorbed across the portfolio annually.
With storage hosting between tenants: a void of 26 days is enough to host a 1-month storage booking on Packhood. Average unit hosts at £450–£700/mo as full-flat short-term storage (lower per square metre than dedicated single-room storage because of the longer lease, but high in absolute terms). Five voids × £550 = ~£2,750 of recouped income.
Net swing: from -£9,500 to -£6,750. £2,750 a year recovered for what is essentially listing the unit twice — once for the next tenant search, once for the storage booking — and one extra Stripe Identity check on each renter.
For landlords with garage parking the maths gets nicer. The garage is rentable independent of the void: even when the flat itself has a tenant, the garage often doesn't. Lease that out for £100–£180/mo permanently, separately from the BTL — that's another £1,200–£2,160/year per property with a garage, no void window required.
The legal + tax bit, in 90 seconds
Tenancy vs licence. A storage booking creates a licence agreement — the renter has a right to use the space for storing the agreed items, not to "occupy" it. They can't sleep there, run a business from it, or collect post. There's no AST. No s.21, no s.8, no Housing Act protections, no deposit-protection scheme. Packhood's standard contract handles this.
HMRC tax classification. Storage income on a BTL is ordinary rental income — the property is generating it. It rolls onto your self-assessment alongside the rental side. You can't double-claim the Trading Allowance against it (the £1,000 allowance is for non-property miscellaneous trading). You can deduct the legitimate property costs as usual (interest restriction rules on residential BTL still apply for higher-rate taxpayers).
The structure that gets the best of both: if the property is held in a limited company (which is increasingly common for portfolio landlords post-2017 Section 24), the storage income flows through corporation-tax-only and avoids the residential-BTL interest restriction altogether. Talk to your accountant before relying on this — the company structure has its own costs — but it's why pro landlords increasingly run storage income through the SPV.
Operational reality on a 5-property portfolio
Time cost per void: roughly 25 minutes. List from your phone, set the price, the renter applies, you approve, they collect via smart-lock. Packhood emails you a YTD summary every January for tax.
Time cost per garage: 20 minutes once. List, leave it. Renters change every 4–6 months on average; the platform handles all of that.
The professionalising landlord typically does this: (1) every garage on every property is listed permanently as storage — passive income, no overlap with the main let; (2) every void over 14 days gets the unit listed as short-term storage for the gap; (3) a smart-lock or keysafe is fitted on every property so you don't have to drive across town for handovers.
One landlord we work with in Glasgow scaled this to 11 properties. Total annual storage income across the portfolio (garages + voids): £14,200. That's roughly equivalent to a sixth flat's net rent — minus the mortgage, the wear, the agency, the EPC, the void itself.
The take
Voids are the most predictable loss in BTL portfolios and the least-discussed one. Storage hosting between tenants doesn't fix voids — nothing does — but it turns the worst case from "23 days of lost rent and bleeding carry" into "23 days of partial coverage."
For garages and parking spaces specifically, storage hosting isn't a void-mitigation play at all — it's net-new income. Most BTL garages sit unused 95% of the year because the tenant doesn't need a second car space. List it; that's £1,200–£2,160 annually on every garage in the portfolio without affecting anything else.
List the first one. Twenty minutes. The platform handles the rest. By month three the cheque is automatic and your spreadsheet's vacant-days column gets a lot less painful.