There are actually specs. within the Building Regs as well as the relevant BS specs for components of straight flights in domestic dwellings which were BS.585
art 1:1989 and BS.5395
art 1:1977. The Building Regs are much more concerned with the minimum width, going, etc., than with the materials - for recommended component sizes you need to look at BS.1186
art 1:1986 which lists minimum finished thicknesses of members for stairs
with closed risers and states that open riser stairs will need to have thicker components.
The relevant data is:-
1. For stairs up to and including 990mm over strings
Tread thickness = 20mm
Riser thickness = 14mm (wood), 9mm plywood
String thickness = 27mm
2. For stairs exceeding 990mm but less than 1220mm over strings
Tread thickness = 27mm
Riser thickness = 14mm (wood), 9mm plywood
String thickness = 27mm
The problem is that a lot of people (including builders
) seem to be unaware of the BS standards, and although I thought that the BCO should be enforcing them, I'm unsure of whether installing to non-BS spec. is an offence or not. I'm just the poor b***** joiner who makes them at times. .
Your staircase seems well under spec. and as for securing it the main place a staircase is secured is through the top riser into a floor joist and I'd agree through the wall-side stringer at a couple of points, although this is not necessary if it has been secured at lower floor level in some way.
I trust that answet satisfies you're needs. And with stairs like yours it's still no wonder I keep getting undercut at times.
Scrit