What are the Building Regulations requirements for basement stairs?

Approved Document K requires: maximum riser height 220mm, minimum going 220mm, maximum pitch angle 42 degrees, minimum headroom 2000mm (reduced from 2100mm for loft conversions but not basements), minimum width 800mm for a private staircase. The 2R+G formula (twice the riser plus the going) should be between 550mm and 700mm for comfortable use.

What is the minimum headroom for basement stairs?

The minimum headroom for a private staircase is 2000mm, measured vertically from the pitch line. In basements with restricted headroom, achieving this can be challenging. Solutions include adjusting the stairwell opening position, using winders or a spiral staircase to change direction, or extending the stairwell opening. The reduced headroom allowance (1900mm) only applies to loft conversions, not basements.

How wide should a basement staircase be?

The minimum width for a private staircase under Part K is 800mm between walls or strings. However, 850-900mm is recommended for comfort, especially for furniture moving. The width between handrails must be at least 600mm. If the basement is intended as a self-contained dwelling, the minimum width increases to 900mm.

Can I use a spiral staircase for a basement?

Yes, spiral staircases are permitted for basements serving as secondary stairs. They must comply with Part K — minimum clear width of 800mm (measured from the centre column), adequate headroom (2000mm), and consistent riser/going dimensions. However, spiral stairs are difficult to move furniture up and down and may not meet fire escape requirements for habitable basements.

What is the 2R+G rule?

The 2R+G rule states that twice the riser height plus the going should equal between 550mm and 700mm for a comfortable staircase. For example, a 190mm riser with a 250mm going gives 2(190) + 250 = 630mm — well within the comfortable range. This formula has been used by architects for centuries and is referenced in Approved Document K.

TradeCalculator

Basement Staircase Calculator

Calculate staircase going from floor-to-floor height, check Part K compliance for reduced headroom basements, and determine flight width and stairwell dimensions.

Floor-to-Floor Height

Vertical distance between finished floor levels

Staircase Type

Affects stairwell dimensions

Flight Width

Minimum 800mm for private stairs

Target Riser Height

Part K maximum: 220mm

How We Calculate This

This calculator determines the number of risers, treads, and overall staircase dimensions for a basement installation. It checks compliance with Approved Document K of the Building Regulations (England).

Calculation method

Risers: Floor-to-floor height ÷ target riser height gives the number of risers. The actual riser height is adjusted to divide evenly into the floor height.

Treads: Number of treads = risers - 1 (the top floor acts as the final tread). Total going = treads × going depth.

Pitch: Calculated as arctan(riser / going). Must not exceed 42° for Part K compliance.

Stairwell: Length based on total going plus clearance. Half-turn stairs approximately halve the required length but double the width.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.