closd string stairs with no underneath access

[jonnyb]

I need to replace a few treads and risers in a closed string staircase, but there is no access to the underside of them.
Am I right in thinking the only way to do it is to remove the risers (by breaking them) and knocking the treads out and replacing them one at a time. Do you think I'll get the wedges back in doing it this way?

Also the treads are 20mm thick - is it ok to use MDF is this case?

thanks

Jonny

 

[Symptoms]

Jonny - why no access to underside? Boarded or in another dwelling? If boarded, remove it, repair the staircae, re-board. You really do need access to the wedges & glue blocks to make a satisfactory (& long term) repair - expect squeaks & creaks otherwise.

I'd avoid MDF and go for ply, unless the treads will be seen.

 

[jonnyb]

Yeah, in another dwelling. And the residence has been decorated. It's not feasible at all.

You don't think I could get to it from above, though the steps?

 

[jonnyb]

I'll take that as a 'no' then!

 

[freddiemercurystwin]

Yes.

 

[Symptoms]

Jonny - sorry for no earlier reply. Back to basics ... why do you need to replace these bits? Are they just squeaking or are they split/broken? The danger of breaking into the stair components from above is you don't quite know how the 'ceiling' below is fixed to the underside. Can't you fashion repairs to the broken elements in situ by easing apart, introducing glue & screws or are they too far gone? If not, then proceed as follows:

on one tread at a time ...
bore a 15mm - 20mm inspection hole through the tread to discover how far the ceiling is below
about 80mm in from each stringer make saw cut through the tread from front to back using a flooring saw (or jig saw if you have blade clearance below), cut across the back edge (maybe about 50mm from the riser), lift the damaged tread clear
introduce some 25mm x 50mm battens, or bigger (try to make these as close to the distance between the stringers as possible) into the void, glue & screw these into position below the tread position
fashion replacement tread from ply (same thickness as damaged tread) using old tread as template, glue & screw into the supporting battens

Warning - often cables can be run up in the void below the treads.