A Rightmove listing won't tell you ceiling heights, loft head height, or which neighbours are already HMOs. So this is the tool you run once you've booked the viewing — take the measurements below while you're at the property, then work through it to answer one question properly:
"Can this property actually become a viable, profitable HMO?"
📏 Measure these at the viewing
Floor-to-ceiling heights — ground floor, first floor, and loft floor-to-ridge
Room sizes and total floor area (pace it out, or ask for the floorplan)
House width & depth, the outrigger width, and the rear garden
Any existing extension, the roof type, and signs of damp or movement
Walk the street — how many neighbours are already HMOs (then cross-check the council register)
Your answers save automatically on this device — start it before the viewing, fill the gaps while you're there, and hit Start again up top to clear it for the next property.
Every council is different — HMO rules are not standardised across the country. Tell the checker about your council and what you're aiming for, and it adapts everything below to your situation. Enter these once; they flow through every tool in the kit.
Property address / area
Local authority (council)?The council that handles planning and HMO licensing for this property. Not sure which one covers a postcode? Search "[postcode] which council" on gov.uk.
Is this area under an Article 4 direction?
?Article 4 removes the automatic right to convert a normal home (C3) into a small HMO (C4) without planning permission. If it's in force, you need full planning permission even for a small HMO. Common in university towns, big cities and London boroughs.
How to check in 2 minutes: Google "[your council] Article 4 HMO direction". Open the council's own page. Look for whether it's borough-wide or limited to named wards, and the date it came into force. If your street isn't in a named ward, you're likely outside it — but confirm on the council's map.
Target number of lettable bedrooms
?This drives everything. Up to 6 = small HMO (C4). 7 or more = large HMO (Sui Generis), which always needs planning permission, Article 4 or not.Enter a target to see your planning use class.
Current storeys (as it stands today)?The property now, before works. Most BRRR conversions add a floor — a 2-storey terrace becomes a 3-storey HMO once the loft's in. It's the finished height that drives your fire spec, so this is a heads-up for budgeting, not a pass/fail.
Which HMO licensing applies here??Mandatory licensing always applies at 5+ tenants from 2+ households (national law). On top of that, many councils run additional licensing (catching 3–4 bed HMOs) and/or selective licensing (all rentals in an area). Over 70 councils run extra schemes. Licensing is a separate regime from planning — a property can have one without the other.
How to check: Google "[your council] HMO licensing" and open the council page. Note the scheme type, the fee (typically £500–£1,500 for 5 years, more in London), and any room-size or amenity conditions they publish — budget these in.
2 Planning Route —
Can this property legally become an HMO, and what planning route does it need? This updates live from your answers above.
Complete Section 1 to see your planning route
Tell the checker your Article 4 status and target bedroom count above.
Use class?C3 = normal home. C4 = small HMO (3–6 sharers). Sui Generis = large HMO (7+) — its own category that always needs planning.—
Planning permission?Permitted development means you can convert without a planning application. An Article 4 direction removes that right; a 7+ bed HMO never had it.—
Is it already operating as an HMO??Buying a running HMO is different from converting a house. First check whether it has formal planning consent; only if it doesn't are you relying on grandfather rights (lawful use).
Don't confuse a licence with planning — three traps when buying a "licensed HMO":
• A licence is not planning. Councils grant HMO licences without checking planning — a licensed HMO can still have no planning permission or lawful use.
• Planning is not a licence. Even with the right planning or lawful use, the property still has to meet licensing standards separately to actually get a licence.
• Licences don't transfer. An HMO licence belongs to the licence holder, not the property (s68 Housing Act 2004) — when you buy, the old one becomes invalid and you must apply for your own. It can still serve as useful evidence of past HMO use for a CLEUD.
Does it have HMO planning consent (or a lawful-use certificate)??Check the council's planning portal for the address. A small C4 HMO outside an Article 4 area never needed planning (it was permitted development); inside Article 4, or for a 7+ Sui Generis HMO, formal consent (or a CLEUD) is required. A C4 consent does not cover a 7+ use.
No formal permission — check whether the use is already lawful through grandfather rights (continuous use):
For how long, continuously??HMOs follow the 10-year rule (the 4-year rule never applied to them, and the 2024 reforms didn't change that). Either 10+ years of continuous use, or use that began before the Article 4 date here and has run since.
Ever reverted to a family home (C3)??The key gotcha: the use must be continuous. If it ever went back to a single family home, the clock resets and the lawful HMO use is lost — you'd be treated as a fresh conversion.
Can the HMO use be evidenced??A CLEUD is proved on the balance of probability: tenancy agreements showing multiple unrelated tenants over time, council tax records, bank statements of rent, utility bills and HMO licence history — plus statutory declarations from the previous owner or tenants where documents are missing.
3 HMO Density & Concentration —
Will the council accept another HMO here? This only matters where a planning application is actually required — and how the council measures concentration varies, so set that first.
Not applicable to your scenario. Concentration and "sandwiching" rules are planning-application refusal criteria — they only bite when you have to apply. So you can skip this section.
Worth a sense-check anyway: even where it's not a planning issue, an area already saturated with HMOs can mean softer room demand and longer voids. Keep that in mind when you reach the Market Scorecard.
How does your council measure concentration??There's no national rule — every council sets its own geography. Common bases: a radius around the property (Portsmouth: 10% of dwellings within 50m; others use 100m+), the street frontage (both sides of the road), a fixed number of adjacent properties, or a ward / census output area. It's in the council's HMO policy (Article 4 SPD or local plan), and it changes which properties you count below.
Radius the council uses?Use the exact figure from the policy. Common values: 50m (e.g. Portsmouth), 100m, sometimes 200m+. The bigger the radius, the more streets fall inside it.
m
Dwellings in the assessment area
Existing HMOs in that same area?Count HMOs within the same area you used for the total. Most councils publish a public HMO register / licence list — search "[council] HMO register". Cross-check the planning portal for consented HMOs that may not be licensed.
Estimated HMO concentration—
Council's concentration threshold?Councils refuse new HMOs where more than a set % of dwellings in the assessment area are already HMOs — commonly 10% or 20% (Portsmouth: 10% within 50m). Find yours in the council's HMO policy.
%
Two adjacency rules catch deals even when the percentage is fine. Walk the row (or check the council's HMO register) and answer honestly:
Would converting this leave a family home sandwiched between two HMOs??The sandwiching rule: councils protect a C3 family home from having an HMO on both sides. Look at a run of three houses — if turning yours into an HMO leaves a neighbouring family home flanked by HMOs, it's usually refused. Some councils also count opposite and rear neighbours.
Would it create three or more HMOs in a row??Continuous frontage rule: councils refuse a run of three (sometimes two) HMOs immediately next to each other. So if the two adjoining houses — or your neighbour and the property beyond it — are already HMOs, converting yours tips it over. Widespread: Brighton, Cambridge, Southampton, Hull and others all apply it.
Set the measurement basis above
Tell the checker how your council measures concentration, then add the figures — it'll compare against the threshold and check the adjacency rules.
4 Physical Space & Room Viability —
Does the property physically have the floor space to hold your target rooms at lettable sizes? Rule of thumb: ~100m² of current floor area is the sweet spot — big enough to reach 6–8 ensuite rooms once you add a rear extension and loft. Much under that and the maths rarely works, however clever the layout.
Current floor area?Internal floor area as it is today, excluding the loft — Rightmove floorplans usually state it. Our sweet spot is ~100m²+: enough to build out to 6–8 rooms. Around 70m² rarely works — you can't add enough via loft and extension to make the room count.
m²
Current bedrooms?Just context — you'll change this completely. A 3-bed is the classic BRRR HMO starting point.
Target rooms (HMO)?How many lettable bedrooms you're designing for. Shared with Section 1 — adjust here to test layouts. This drives the space build-up below.
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Target bedroom size?The sleeping area only (ensuites are added on top). Legal minimum is 6.51m² (10.22m² for a double). Aim for 10m²+ — smaller rooms let for less and are exposed to rule changes. Many councils now apply the Nationally Described Space Standard (7.5m² single).
m²
Ensuites??An ensuite adds roughly 3m² to each room's footprint — so a 10m² sleeping area becomes ~13m² with its own shower room. Ensuites also push the property toward a commercial valuation and satisfy the bathroom ratio automatically.
Circulation allowance (dead space)?Halls, stairs and landings you can't let. Added on top of rooms + communal. A tight, efficient layout runs ~15%; a typical converted house ~18%; tall (loft) or awkward layouts ~20%+. Adjust if you know the property.
%
Communal space your council requires?The shared kitchen/diner/lounge area your council demands. There's no national figure and no safe average — every council sets its own, often on a sliding scale by room size. Look yours up and enter it. Until you do, the total below is illustrative only.
m²
How to find it: search "[your council] HMO space and amenity standards" or "[your council] HMO SPD" and find the communal/living-space table — it usually scales with occupancy and room size. For a sense of the spread: Portsmouth, one of the strictest, wants ~28–34m² of open-plan communal living depending on room size; many councils ask far less. There's no shortcut — yours could be anywhere in that range, so confirm it and enter the real number.
Floor area needed?Built up properly: bedrooms + ensuites + your council's communal requirement + circulation (halls, stairs, landings). See the breakdown below.—
Space you'd have (incl. extension & loft from Section 5)—
Component
Area
Status
Before you rely on this: you've modelled the space — now confirm the layout actually meets your council's HMO standards: minimum room sizes, the communal figure you entered above, bathroom/kitchen ratios and amenity rules. They differ by council and override these defaults. Search "[your council] HMO space and amenity standards" and check your numbers clear theirs.
5 Space, Extensions & Permitted Development —
Most 3-bed-to-6-bed conversions only work because of space won from a rear extension and loft — and most of those works are done under permitted development. Two separate questions decide whether you need planning.
Two different things — don't confuse them
1. The building works (rear extension + loft) — usually permitted development, as long as they stay within the size limits below. 2. The change of use to an HMO — that's the planning question from Section 2: permitted development for a small C4 HMO unless Article 4 applies, but always full planning for a 7+ Sui Generis HMO.
In a conservation area or listed??Conservation areas and listed buildings are "designated land", where permitted development is heavily cut back: side extensions aren't PD, the larger 6m/8m rear-extension route is removed, and roof dormers/mansards need consent. Many HMO hotspots (especially Victorian terraces) sit in conservation areas — check the council's online map. If listed, almost any change needs listed-building consent.
House style?Plan-view footprint. A flat-back terrace is a plain rectangle; an L-shaped (Victorian) terrace has a rear outrigger with a side-return gap alongside — the classic infill opportunity. Style sets your PD limits, the side-return options, and how the plan below is drawn.
House width
m
House depth?Front-to-back footprint of the ground floor (from the floorplan). For an L-shaped terrace, measure to the back of the main body — the outrigger is drawn on top.
m
Rear garden depth?Keep at least ~half the original garden after extending, or you'll struggle with planning and lending.
m
Outrigger width?Width of the rear outrigger (the back wing) on an L-shaped terrace. A rear extension off the outrigger is this wide — not the full house width — so entering it keeps the area and the 3D model accurate. The side-return gap is the rest of the width.
m
Is there an existing rear extension??Permitted-development limits are measured from the original rear wall (as built, or as at 1948) and the allowance is cumulative — an existing extension uses part of it up, and you generally can't add a PD extension off a later extension. Add one here so it's built into the shape and the remaining PD allowance.
Existing extension depth?How far the existing rear extension already projects from the original rear wall. This counts toward the cumulative PD limit.
m
Existing extension width?How wide it is. Leave blank to assume the full house width.
m
Ground-floor extension?Rear projects into the garden. Infill fills the side-return gap beside an L-shaped terrace's outrigger. Side is a proper side extension (needs side land — end/semi/detached). The combinations stack them; a wraparound squares off the whole back corner and usually needs full planning.
Rear projection depth?How far the extension projects from the rear wall into the garden.
m
Side / infill width?Width of the side strip you'd build on — for an infill this is the side-return gap beside the outrigger; for a side extension it's how far out you'd go (PD limit: ≤ half the original house width).
m
Side / infill length?How far it runs front-to-back. On an L-shaped terrace the infill is the length of the outrigger return; on an end/semi/detached a side extension can run most of the house depth.
m
Floor area gained from extension—
3D model — your house, extension & roof
Loft conversion type?Different conversions gain different usable space and sit differently with PD. Rooflight (Velux) = least space, almost always PD. Dormer / hip-to-gable = more space, PD if rear-facing and within the 40/50m³ volume cap. Mansard = most space but usually needs planning. A loft also adds a floor — turning a 2-storey house into a 3-storey HMO.
A usable loft needs to clear your council's minimum room height once the new floor and insulation are in. If it's short, you gain height with a floor drop — lowering the loft floor into the room below (and, if needed, lowering that floor too). Enter the heights and the checker works out whether it's a single or double drop. You can't raise the roof under permitted development.
Council minimum room height?This is not building regs — it's set by each council's private-sector housing / HMO standard, and it varies: e.g. Portsmouth 2.3m, Chichester 2.14m, with the building-regs default around 2.1m. Find your council's HMO room-height standard and enter it — every viability and floor-drop check below uses this figure.
m
Roof structure?A traditional cut roof (rafters over an open void, usually pre-1970s) converts easily. A modern trussed roof needs steel beams and structural redesign first — viable, but more expensive.
Ground-floor ceiling height?Floor-to-ceiling height of the ground floor. A double floor drop borrows height from here, so it decides whether a deep drop is possible.
m
First-floor ceiling height?Floor-to-ceiling height of the first floor. A single floor drop lowers this ceiling to gain loft height — it works only if there's height to spare here.
m
Measured loft height — floor to ridge?On the viewing, put the tape on top of the existing ceiling joists (the loft floor) and measure straight up to the underside of the ridge at the highest point. The single most useful number for judging a conversion.
m
Section view — loft head height
Size the roof addition so we can check it against your permitted-development volume cap:
Width
m
Depth
m
Height
m
Added roof volume vs PD cap?Additional roof volume must stay under 40m³ (terraced) or 50m³ (semi/detached) for PD — including any earlier dormers. Over the cap, on the front roof slope, or on designated land → planning.—
Usable floor area gained from loft?Estimated from your floor footprint and the conversion type — a rooflight keeps least usable area under the slopes, a mansard the most.—
Total additional space (extension + loft)—
Does this make your target rooms fit??A live copy of the Section 4 space check, repeated here so you can see straight away whether the extension and loft you've chosen give you enough floor area — without scrolling back up. Change anything above and this updates.
Floor area needed—
Space you'd have (current + extension + loft)—
6 Construction & Structural Risk —
Some issues don't just add cost — they make a property unmortgageable or unlettable. Flag them before you fall in love with it.
Construction type?Standard brick/stone is fine. Timber frame, concrete panel, prefab and steel frame can restrict which lenders will touch it — critical for a BRRR refinance.
Tenure
Any structural / legal red flags? (tick all that apply)?Conservation-area / listed status is asked in Section 5 (it drives your permitted-development position).
7 Amenity & Operational Requirements —
Councils judge more than rooms. These are common conditions — and common refusal points — even when the concentration maths is fine. All council-variable, so confirm the specifics in your council's HMO standards.
Space for bin & cycle storage??More occupants means more refuse and recycling, and councils routinely require dedicated bin and cycle storage — usually at the front or side without harming the street scene. A frequent planning condition and a common hold-up.
Usable outdoor amenity space retained??Many councils require some private or shared outdoor space for tenants to remain after the works — another reason not to extend over the whole garden. Check your council's minimum.
8 Commercial Valuation Potential —
This is the bit that makes BRRR work at scale — whether a lender will value the finished HMO on its income rather than on what the house next door sold for.
Strong room demand confirmed??Confirmed via the Market Viability Scorecard and SpareRoom research — rooms in this area letting quickly at your target rent.
Ensuite spec (set in Section 4)?Ensuites (plus fire doors and interlinked alarms throughout) are what take a property "far removed from a family home" — the trigger for a commercial valuation. Set this in Section 4 where it also sizes the rooms.
Ensuites—
Commercial valuation likely?—
How a commercial valuation works: the surveyor takes the gross annual room rent, deducts running costs (typically 20–45%), then divides by the local investment yield. Lower yield = higher value, and yields vary hugely by region (roughly 7% in London, up to ~13% in the North East). It's usually reserved for 6+ bed HMOs that can't be sold as an ordinary home. Below that, expect a standard "bricks & mortar" valuation — and the BRRR numbers rarely stack. Not every lender offers it, so confirm with your broker before you commit.
✓ Before you offer: confirm with your council
This checker runs on the figures and assumptions you entered — it can't know your council's exact standards. Every item below is council-specific. Verify each one on the council's own pages (or with a local planning consultant) before you commit:
Planning route — confirm the Article 4 status and whether your conversion is permitted development or needs an application (and check recent decisions on the planning portal).
Concentration & adjacency — the council's exact threshold and radius, plus the sandwiching and three-in-a-row rules for your street.
Room & communal standards — the minimum bedroom sizes and the communal-space requirement actually published in the council's HMO SPD.
Amenity requirements — bin/cycle storage, outdoor amenity space and bathroom ratios to their standard.
Licensing — which scheme applies, the fee, and remember it's separate from planning — you'll need to apply for your own licence; the seller's doesn't transfer.
If it's an existing HMO — confirm the lawful-use evidence stacks up for a CLEUD; don't rely on the existing licence as proof of planning.
The Verdict
Complete the sections to get your verdict
Work down from Section 1. The checker only asks what's relevant to your council and your target — and tells you, with reasons, whether this property can become a viable HMO.
2026 watch: factor these into your plan. From 1 May 2026 the Renters' Rights Act made all tenancies periodic and abolished Section 21 — HMO rooms are affected. And from October 2030 every let property, assessed as a whole-building EPC for HMOs, must reach EPC C — older solid-wall stock may need insulation budget to get there.
HMO BlueprintFast Track Toolkit
HMO Potential Report
Property assessment
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At a glance
The key facts
Space, extension & permitted development
The detail
Before you offer — confirm with the council
Pull the property up on the council's planning portal for any existing permissions, refusals or enforcement history.
Check the Article 4 direction map and whether C4 change of use is withdrawn from permitted development here.
Confirm the council's HMO concentration / saturation policy and the exact threshold percentage and radius.
Verify the licensing scheme (mandatory / additional / selective) and the standards you'll have to meet.
Check conservation-area or listed status before relying on any permitted-development works.
Get pre-application advice in writing if planning is borderline — it's cheap insurance before you offer.
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