Building Regulations Part M: Accessible and Adaptable Dwellings in London Extensions and New Builds

**Approved Document M Volume 1 — dwellings (the residential Part M)**:

• Building Regulations Approved Document M is split into two volumes:
• •Volume 1: Dwellings (residential)
• •Volume 2: Buildings other than dwellings (commercial, public, and other non-residential)

For London residential extensions and new builds, Volume 1 applies. Volume 1 defines three categories of accessible dwelling:

**Category 1 — Visitable dwellings**: The minimum standard that applies to all new dwellings in England. It is also the standard required for any new extension that creates a new habitable space (a new room within an existing dwelling).

• *What Category 1 requires (the key provisions)*:
• •A step-free accessible entrance to the dwelling
• •Level or gently ramped approach to the main entrance (max 1:20 gradient for a ramp)
• •A minimum threshold upstand of no more than 15mm at the main entrance
• •Doorsets on accessible routes: minimum 775mm clear opening width for doorsets forming part of the accessible approach
• •A WC on the entrance level (or within 1 storey of the main entrance level) that an ambulant disabled person can use — though the WC does not need to be wheelchair-accessible at Category 1

*When Category 1 applies in London*: Category 1 is the default standard for all new residential development in England unless the LPA requires a higher category. For London extensions, Category 1 is the standard applied by Building Control for any new habitable room created. Most London domestic extensions are assessed against Category 1 requirements at Building Regulations stage.

**Category 2 — Accessible and adaptable dwellings**: An enhanced standard that applies where the LPA has required it through a planning condition. The London Plan Policy D7 encourages London Boroughs to require 90% of new housing to meet Category 2 standard. Many London Boroughs now include a planning policy or condition requiring Category 2 on new residential development above certain thresholds (typically 10+ units; some Boroughs apply it from 1 unit).

*What Category 2 requires — the key additional requirements beyond Category 1*:

• *1. Wider door clear openings*:
• •Internal doors on the principal storey (the storey containing the principal entrance): minimum 850mm clear opening width
• •Internal doors elsewhere: minimum 775mm clear opening width

• *2. Step-free access through the dwelling*:
• •Step-free access from the entrance to at least one habitable room, the kitchen, and a WC on the entrance level
• •No internal steps or level changes on the principal storey accessible route

• *3. WC on the entrance level*:
• •A WC at entrance level capable of being adapted to a fully accessible WC — minimum floor space to allow a lateral transfer (disabled person transferring from wheelchair to WC): floor area of at least 1200mm × 900mm clear space to one side of the WC; plus a 1200mm × 900mm turning space within the WC compartment
• •The Category 2 WC is sometimes described as a 'cloakroom that can be converted' — the washbasin, fittings, and grab rails do not need to be installed at Category 2, but the room must be large enough to accommodate them later

• *4. Level 2 bedroom at entrance storey (or provision for a future lift)*:
• •At least one bedroom or room that can be used as a bedroom on the entrance level; OR the dwelling must include a suitable position for a through-the-floor lift to be installed in the future to provide access to a bedroom on a higher storey

• *5. Bathroom and shower provision*:
• •A bathroom or shower room on the principal storey (or at entrance level in a single-storey dwelling) capable of containing a level access shower — minimum 1500mm × 900mm shower space; shower tray not required but the space must accommodate one

**Category 3 — Wheelchair user dwellings**: The highest accessibility standard — designed so that a wheelchair user can independently use all rooms in the dwelling without any adaptations. Category 3 is required by planning condition on a percentage of units in larger residential developments — typically 10% of units where the LPA's Local Plan or the London Plan requires it.

• *What Category 3 requires — the key provisions*:
• •All doorsets minimum 850mm clear opening width (internal); 1000mm clear opening width (entrance level)
• •Hallway widths minimum 1200mm clear
• •Level access throughout the dwelling (no level changes)
• •Wetroom (level access shower) on the principal storey: 1500mm × 1500mm minimum internal dimensions for a Category 3 wetroom
• •Kitchen: minimum 1500mm turning circle; knee clearance under worktop; adjustable height worktops (or provision for adjustment)
• •Bedroom: minimum 1200mm clearance at foot and to one side of the double bed
• •All switches and sockets between 450–1200mm above floor level
• •Category 3 is designed for the specific user — a Category 3 dwelling is typically built or adapted for a wheelchair user who will occupy it

**Part M Category 1 for a London domestic rear extension — the practical implications**:

For most London homeowners extending their home (rear extension; loft conversion; side return), the Building Regulations requirement is Category 1. The practical implications are:

*1. Threshold at the new rear door*: The most common Part M issue in London rear extensions is the threshold between the internal floor level and the external patio or garden level. Part M Category 1 requires the threshold upstand at the main entrance to be no more than 15mm — but the main entrance for Part M purposes is the principal entrance, typically the front door. A rear door onto the garden in a Category 1 extension is not the main entrance and the 15mm threshold limit applies to the accessible approach to the principal entrance, not to every door.

However, Building Control inspectors in London vary in their interpretation — some apply the 15mm threshold to all new external doors including rear doors. Discussing the threshold detail with the Building Control inspector at the pre-application meeting avoids a costly argument at site inspection stage.

*2. Internal door widths*: For an extension that creates a new room accessible from existing circulation, the new internal doorsets serving the extension must meet minimum clear opening widths. Part M Category 1 requires 775mm clear opening width on accessible routes. A standard UK 762mm leaf door (sometimes called a 2'6" door) typically achieves 697–714mm clear opening width — NOT compliant with Category 1. A standard UK 826mm leaf door achieves approximately 750mm clear — borderline at Category 1. To reliably achieve 775mm clear opening width at Category 1, use an 838mm or 864mm (33" or 34") leaf doorset.

*Note*: clear opening width is measured from the face of the door leaf (when fully open at 90°) to the face of the door frame on the opposite side. It is NOT the same as the door leaf nominal width.

*3. WC provision*: For a Category 1 extension where the extension is adding habitable rooms to an existing dwelling, the WC provision applies at the dwelling level — if the dwelling already has a WC on the entrance level, no new WC is required in the extension. For an extension that creates a new entrance level accessible route to a new room, Building Control will check that the WC provision at Category 1 is met at the dwelling level.

**Part M Category 2 for a London extension — when it applies and what it means**:

If a London Borough has a planning policy requiring Category 2 standard for new residential development, and the planning permission for the extension includes a condition requiring Category 2, the extension must satisfy the Category 2 requirements. The most common impact on a London domestic extension at Category 2:

*1. Wider internal doors throughout the extension*: 850mm clear opening width on the principal storey (entrance level) — use an 900mm or 926mm leaf door to reliably achieve 850mm clear. 775mm clear elsewhere.

*2. Level or step-free access from entrance*: No level changes on the accessible route from the main entrance to the kitchen and principal living space. Where an existing house has a step at the rear into the garden or extension, the design must eliminate or address this step to provide a continuous step-free route.

*3. Cloakroom at entrance level*: If the extension design includes a new cloakroom or WC, it must comply with the Category 2 cloakroom dimensions: 1200mm × 1200mm minimum floor area if the WC is in the corner; 1700mm × 800mm if the WC is against a wall. These are larger than a standard UK cloakroom (typically 1100mm × 900mm in pre-2015 houses) — allowing for the Category 2 dimensions in the extension design can require more floor area than might otherwise be allocated.

**Practical Part M design checklist for London extensions**:

*Before design is finalised*: 1. Confirm with the London Borough's planning portal and the planning condition whether Category 1 or Category 2 applies 2. Check the existing main entrance threshold and door clear opening widths — to confirm the existing dwelling already meets Category 1 at the principal entrance before adding the extension 3. Design new internal doorsets at 838mm leaf minimum (for 775mm clear at Category 1) or 900mm leaf minimum (for 850mm clear at Category 2) 4. Design any new external thresholds for a maximum 15mm upstand where the accessible route applies 5. If a new cloakroom is included in the extension, check Category 2 floor area dimensions if a Category 2 condition applies 6. If the extension is single-storey and creates new entrance-level accommodation, confirm the existing WC at entrance level satisfies Part M

*At Building Regulations application stage*: 7. Submit floor plans and sections showing door clear opening widths, threshold upstands, and WC/cloakroom dimensions on the drawings 8. Include a Part M compliance note on the drawings referencing the Category level being achieved and the evidence

**The history of Lifetime Homes and Part M Category 2**:

Before the current three-category system was introduced in 2015, many London Boroughs required residential development to meet the Lifetime Homes standard — a set of 16 design criteria developed by the Joseph Rowntree Foundation in 1991 that were intended to make homes adaptable over a person's lifetime as their mobility needs change. The 2015 revision of Approved Document M replaced Lifetime Homes with the current Category 1/2/3 framework.

For planning purposes, some older London Borough planning policies may still reference Lifetime Homes — where this is the case, the London Borough will typically accept Category 2 compliance as equivalent to Lifetime Homes compliance.

**Why Part M matters beyond the minimum Building Regulations requirement**:

For London homeowners, Part M compliance has commercial as well as legal implications:

*1. Future-proofing*: a home that is designed to Category 2 standard is more adaptable for occupants as they age or if a member of the household acquires a mobility impairment — it is cheaper to build in wider doors and level access thresholds during construction than to retrofit them later

*2. Resale value and lettability*: a home with accessible features (step-free entrance; wider doors; level access shower) is marketable to a wider range of buyers and tenants, including older purchasers and those with disabilities. London's ageing population means accessible homes command a premium in certain price brackets

*3. Planning condition compliance*: failure to comply with a Part M planning condition can result in the planning condition being enforced — requiring works to be carried out to comply. Building Control will also require compliance to issue a completion certificate. Where the completion certificate is withheld, selling the property later is significantly complicated

**Part M and Building Regulations applications for London extensions**:

• For a domestic extension in London, Part M compliance must be demonstrated in the Building Regulations Full Plans application or Building Notice. Building Control inspectors will check Part M compliance at:
• •Commencement inspection: confirm foundation and slab levels will allow the specified floor-to-threshold relationship
• •Structural inspection: check door opening widths are as specified
• •Pre-completion/completion inspection: check final threshold upstands; door clear opening widths; cloakroom dimensions (if applicable)

The most common Part M enforcement issue at completion inspection is the threshold between the new extension floor and the existing house floor — where a step has been introduced during construction that was not shown on the planning or Building Regulations drawings. Plan the extension floor level at the design stage to ensure the finished level is continuous with the existing house floor level (or with a maximum 15mm threshold upstand at the critical accessible route).