Fitting timber treads and risers to a concrete staircase.
Project overview.
Stair design. Stair layout.
Project status: The stage we are at.
The project is to supply and fit timber treads, risers, landing nosings, spindles and handrail to fit onto a precast concrete staircase.
The staircase had already been designed by the concrete fabricators, with no consideration to the setting out of the tread covers or the balustrading. The concrete structure is fairly constant but needed some dressing to get a smooth flow to the stringers and landing fascias in order for the treads and nosings to have a smooth and constant flow, ready to accept the spindles and handrail.
As no stringers are being added and the project had progressed before we wher called in, the soffits to the staircase followed the cast staircase lines. this left angular transitions rather than curved. That said, cast stairs do not lend themselves to getting flowing soffits. Due to the way the molds are constructed.
Project Stages.
Design intent.
What the cliant would like to have.
Component design.
The ffl’s had already been set by the cast stairs, the clearance left over the top of the concrete sub structure is only 20mm, Therefore the treads will either have to be rebated over the concrete or a finished thickness of 20mm used, Oak is not ideal at this thickness; as it is more than likely to crack or have shakes, that will open once exposed to interior heating or summer heat. Adding a return nosing rather than the nosing being profiled onto the endgrain of the tread will help restrict any shakes from opening.
The treads and risers are to have an Oak scotia molding. The spindles chosen are square with a 90º twist. the handrail profile was our profile 10.
The feature “D” tread at the start of the ground floor flight is to have a Monkey’s tail set over each side.
The monkey’s tail is to be set on a bird’s cage of spindles.
Survey of sub structure.
With the design in place, the survey data can be collected if not already obtained. dependant on programme timing etc. the data is not genrally required until this stage, this allows for the design to be confirmed before spending time surveying.
It however worth doing a few checks early on to confirm that the stairs are level both along the flight and left to right.
Dependant on the client you can work from generic visuals to get the design concept, others will like to see it as their stairs will be. in many cases working from the drawings is good enough for thr visuals other times it is of benefit to survey first and then work with the correct data to save drawing everything twice, this will also depend on the amount of detail that is created for the visuals.
When just an idea, not so bad.
When drawing in the details maybe not such a good idea, as these can take considerable time to draw.
Check list, before drawing the cladding system.
I have listed up some of the details that will need to be checked, I have added options that to the purist should not even exist but in this modern day of jobs being carried out in unusual ways, I have included them to show how to overcome design flaws, created in the earlier stages of a project.
Design details.
Intent.
An idea of the clients expectations.
With detailed section drawings signed off.
Stringer style.
Riser/stringer junction.
Mitred.
face mounted with shadow gap
Treads
Nosing projection.
Nosing profile.
Scotia molding.
Return nosing.
Profiled end.
Stringer/plaster soffit
finishing at same level.
plastered into bead.
Shadow gap between.
Inset soffit – distance inset by.
Design to bottom of stringer for inset soffit.
SFL/FFL
Distance from structural floor level to sub structure top of first tread.
Distance from finished floor level to sub structure top of first tread.
Distance from top of last sub structure going to structural floor level.
Distance from top of last sub structure going to finished floor level.
Check any structure being clad.
Using spirit levels, plumb lines, tape measures and any other device you may have at hand, carry out a quick check to see if treads and risers are level and vertical.
Edges of different flights that are meant to sit over each other, do so.
Parallel flights, are so.
Stair structure thickness.
Confirm from tread surface the amount of structure set under the stairs, both on any landing spaces and through the pitches.
Required to know where to set the bottom of the stringer, especially through drums.
Floor thickness.
The distance between ffl and skim coat to the ceiling beneath.
Required to know where to set the bottom of the stringer.
Working drawings.
Once you have the survey data and design intent the nitty gritty bit starts, Producing the working drawings.
This is the technical stage where you have to draw all the components, often produced by different manufacturers, that must work together when delivered to site, with the possibility that there will be another company involved in the installation stage.