The design of domestic staircases causes a number of problems – here are just some of them
Over the next few months, I’ll be looking at some of the most common problems that I see week in, week out as a building inspector.
The first of these is the design of domestic staircases, where guarding, headroom and design problems are commonplace.
It seems that the technical requirements for timber stairs are poorly understood by the marketplace, and as a result are often largely ignored, and stairs are ‘knocked up’ on site by a well-meaning chippy. The fact that BS 585 Parts 1 and 2 have been superseded by BS EN 15644, but are still referred to in Approved Document K doesn’t help.
There is also no straightforward method for building control officers to verify that a stair has been manufactured correctly, and that it complies with the relevant safety standards and building regulations. It is not a requirement, for example, to CE mark stairs, though stairs can be CE marked if assessed under ETAG 008.
In response to this, the British Woodworking Federation has developed an accreditation and certification scheme – the BWF Stair Scheme badge – that launches this month as a new industry standard. A few of the most common problems follow.
Acoustic performance – sound attenuation
A staircase separates different compartments in a building, and as such may be required to provide a specified level of sound attenuation. In areas where the reverberation of sound can be a problem, such as in common stair enclosures, sound-deadening and sound-absorbing construction are often missed out.
Protection from falling
When Part K was last revised, the rules on guarding changed. It is now no longer necessary to comply with the 100mm gap where children are not expected to be left unattended. This has lead to homeowners wanting to replicate the funky guardings that architects have designed for commercial buildings. However, the 100mm rule still applies in domestic situations, and must be adhered to. Another problem is marrying the handrail height (typically 900mm above pitch) with the height of guarding to a landing (typically 900 – 1100mm). This means the handrail and guarding do not always aline, resulting in a ‘swan neck’ that needs to be re-designed and fixed.
One of the most common problems, particularly for loft conversions. It usually results from poor measurement at the start of the project, and failure to plot an accurate section through the stairs. Contractors rarely set out the stair before they install the structural engineer’s beams and trimmers and, as a result, last-minute changes are often required.
Landings should be clear of any door swing or other obstruction, though a door may open on to a landing if, at any angle of swing, a clear space at least 400mm deep is maintained across the full width of the landing.
Tapered treads or kites
The going of the tapered treads should be uniform and should not be less than the going of the straight treads measured at the centre line of the flight. This means that on a typical 860mm-wide staircase with a standard 90mm newel post in the corner, the area for a three-tread winder corner increases by around 52mm2, so 890 x 890mm. On narrower staircases there is a requirement to increase the winder box size by even more than 52mm2 – for example, a 600mm wide staircase would typically need a winder box size of 750 x 750mm.
Geoff Wilkinson is managing director of approved inspectors Wilkinson Construction Consultants