ONLINE VERSIONStairs and laddersK1 See paras 1.25–1.27Stair width less than 1m50mm minimum treadEqualEqualwidth at narrow endMeasure going at centre of tread;measure from curved stair line, even when treadis in rectangular closureGoing (not more Stair widththan maximum 1m or morefor stair category see para 1.3)WidthGoing (not less than minimum for stair category see para 1.3)Landing lengthmeasured oncentre line270mm 270mmDiagram 1.9 Measuring tapered treadsSpiral and helical stairs1.28 Design spiral stairs and helical stairs in accordance with BS 5395-2.Alternating tread stairs in dwellings1.29 You may use alternating tread stairs – in one or more straight flights – only in a loft conversion, and only when there is not enough space for a stair that satisfies paragraphs 1.2–1.24, and the stair is for access to only one habitable room and, if desired, a bathroom and/or a WC (although this must not be the only WC in the dwelling).12 t K, 2013 edition t K, 2013 edition t K, 2013 edition Approved Document K, 2013 edition Building Regulations 2010ONLINE VERSIONONLINE VERSIONONLINE VERSION