Fixing spongy stairs from beneath - will this work?

Hi all

We have a staircase and the three bottom steps are larger than the others because they turn a corner (see photo). As such, they have become very spongy/springy over the years and need repairing.



For the first time, we will soon be able to access these easily from behind/beneath (because we are having an understairs cupboard built and so the area will be behind closed doors). I have some unused 100mmx100mm fence posts and planned to cut them to the right height and then just put them in vertically to support the steps. Perhaps three or four posts per step.

Does that sound like a good plan? If so, should I JUST use these posts (from the floor to the bottom side of the step), or should I also use a plank of wood horizontally to distribute the support. Like the red part in this picture:



And one other thing.... My partner says that the steps need to have a certain amount of spring and so we need to make sure we do not support them too "tightly". I'm not sure about that and cannot find anything on the net suggesting it is the case. Is she right or should I do my normal trick of ignoring her?!?!

Cheers

Max

That's a fairly typical set of winders, Max......are they creaking?
Personally, I'd wait until you can see how they are fixed - maybe a wedge or two has fallen out or something.
Failing that, there's nothing wrong with your proposal, and I would put a timber board above any posts - two would be quite enough.
John

ignore the misses too, just don't over wedge them though

Stairs shouldn't have a 'spring' in them!
Without actually seeing the stairs underneath, difficult to say what would work.
Your idea of 3 100x100 posts per step is potty if you don't mind my saying; - it will be a mass of timber.

Indeed, a single bit of 50x100 would likely be sufficient. examine how the step springs.. Stairs get most of their rigidity with regards to tread flex from the riser, so check your risers are still well attached to the treads?