Building Construction Handbook, Eighth Edition

For domestic situations a spiral stair of 800 mm clear width can
provide an alternative compact, space saving means of access to
the upper floor of a private dwelling. With a clear width of only
600 mm this type of stair may also be used to access the space
available in a roof void. Approved Document K to the Building
Regulations refers the design and application of spiral stairs to
guidance in BS 5395-2, as summarised on pages 713 and 714.

Typical timber spiral stair components

upper newel post

steel tube or

solid timber

dowel central

column

tread

balusters

annular spacer

landing

helical

handrail

lower newel post

Assembly

tapered treads

floor

pattress

Note: Clear width is measured between handrails or between
central column and handrail. If strings are used, measurement is to
or between strings. Take greater value.

Timber Spiral Stairs