Help my stairs are collapsing!

[champy]

Over xmas we discovered a lot of our suspended ground floor floorboards where rotten in our Victorian house, so we decided to replace them. We couldn't find the same depth of board so the whole floor is now 1cm lower than it was (there is a 1cm gap under the bottom stairs)

Our stairs have brick walls on either side.

This morning I ripped out the lath and plaster from the underside of the stairs and the bottom of the stairs has started to sink and pull away from the walls, I guess since xmas the only thing supporting the bottom part of the stairs was the lime plaster on its underside wedged between the stairs and the wall. I think the original floorboards where the support for the bottom of the stairs, i assumed it was the two brick walls.

How do I fix this?

Is it common to just have the bottom part of stairs supported directly by the floorboards?

 

[big-all]

are you sure you mean 1cm/10mm/1/2 inch [nearly ]
what size where the boards you took out ??
what size are they now ??
and yes normal to sit on floor

 

[Deleted member 174758]

Is it common to just have the bottom part of stairs supported directly by the floorboards?

It's not uncommon, especially in terraced properties, although there is often a joist or trimmer directly below the bottom of the stairs in my experience. The problem is that

...we discovered a lot of our suspended ground floor floorboards where rotten in our Victorian house, so we decided to replace them. We couldn't find the same depth of board so the whole floor is now 1cm lower than it was (there is a 1cm gap under the bottom stairs)

When you replaced the boards you should have got flooring which was nearer to the original thickness - 10mm is far too much of a difference. What did you do, replace 1-1/8in softwood boards with 3/4in (18mm) chipboard? When there is a discrepancy (normally only a few mm) the new boards are normally packed-up on top of the joists so that the surface of the floor is the same. TBH your doors and skirting must look a mess. What you now have is an unsupported staircase and a taller bottom step (uneven going). All I can see you being able to do is to pack-out beneath the stairs, assuming that the floor you've installed is strong enough to support the weight of the staircase (in the absence of a trimmer or joist directly beneath the bottom step). The bottom step may need angle brackets onto the floor as well. In immediate terms you need to get some thick softwood wedges beneath that bottom step ASAP

 

[champy]

Thanks for the info.

When you replaced the boards you should have got flooring which was nearer to the original thickness - 10mm is far too much of a difference. What did you do, replace 1-1/8in softwood boards with 3/4in (18mm) chipboard? When there is a discrepancy (normally only a few mm) the new boards are normally packed-up on top of the joists so that the surface of the floor is the same. TBH your doors and skirting must look a mess. What you now have is an unsupported staircase and a taller bottom step (uneven going). All I can see you being able to do is to pack-out beneath the stairs, assuming that the floor you've installed is strong enough to support the weight of the staircase (in the absence of a trimmer or joist directly beneath the bottom step). The bottom step may need angle brackets onto the floor as well. In immediate terms you need to get some thick softwood wedges beneath that bottom step ASAP

Yes that's exactly what I did, replaced it with 18mm pineboards, I couldn't find 1 -1/8 boards that weren't reclaimed and even then couldn't find 50m2 worth.

Will those board be strong enough?

The skirts have come off to relay at the the new height.

I'll do what you said and stick wedges in and then pack it out.

 

[champy]

Okay, the plan now is to wedge 2 2x4 u frames between the stringers and floor, then screw in place, as you can see in the below image (the blue lines) and then also screw the stringers in to the brick wall for added support which you can see in the below image (blue dots on stringers)

Would this be a good solution, and would I be better attaching the u frame directly on to the joists rather than the floorboards? There are 3 joists under the stairs.

 

[Deleted member 174758]

The floor boards run at right angles to the stairs which means that the joists run in the same direction as the stairs, so basically if you make up a 10mm plywood plate the same size as the "footprint" of the stairs (i.e so that the bottoms of both stringers are supported) then that should be enough. No need to make up frames, but you should ensure that the bottoms of the stringers are adequately fixed to the plate and that the plate in turn is fixed into the joists beneath. There is a possibility, however, that you may have b#gg#r#d some of the glue joints in the stairs - in which case it will start squeaking and creaking in due course. And BTW 18mm will be (just about) enough providing that your joists are solid and at 400mm centres, but I feel it won't take high loads without creaking

 

[champy]

The floor boards run at right angles to the stairs which means that the joists run in the same direction as the stairs, so basically if you make up a 10mm plywood plate the same size as the "footprint" of the stairs (i.e so that the bottoms of both stringers are supported) then that should be enough. No need to make up frames, but you should ensure that the bottoms of the stringers are adequately fixed to the plate and that the plate in turn is fixed into the joists beneath. There is a possibility, however, that you may have b#gg#r#d some of the glue joints in the stairs - in which case it will start squeaking and creaking in due course. And BTW 18mm will be (just about) enough providing that your joists are solid and at 400mm centres, but I feel it won't take high loads without creaking

Thanks so much for the info!

I thought 18mm was floor grade and was the standard nowadays?

 

[Deleted member 174758]

In a new build, yes, however it is the bare minimum. But in a new build you aren't permitted to use the floor to carry structural weight. In any case your biggest problem is that you didn't pack the floor up to the original level - something any competent chippy would do.