Tiny Victorian Floor Joists

[njwilson]

I'm replacing the suspended floor throughout the downstairs of my early-/mid-Victorian terrace (extensive rot and beetle activity), and the joists are a teeny-tiny 3.5" x 2.5". They're at ~40cm centres and the longest unsupported span between sleeper walls is ~130cm.

I can't lower the sleeper walls without re-routing the gas and CH pipework, and I can't raise the floor without causing height issues with the front and kitchen steps as well as the original Victorian skirting in the hallway, so simply replacing them with taller joists would be... problematic.

Where the floor hasn't rotted or been eaten away, there's no obvious sign of fatigue to the joists, so I assume it'd be fine to replace like-for-like?

 

[Tigercubrider]

Use wider?

 

[njwilson]

I wasn't able to find any structural 3.5" x 2.5", only 3.5" x 1.5" - so I was going to just sister them to make 3" wide. Again, not sure if that's sensible.

A spot where the floor had been repaired previously had just used 100mm tall and cut notches to fit over the wall plates on the sleepers at the correct height.

 

[John D v2.0]

spot where the floor had been repaired previously had just used 100mm tall and cut notches to fit over the wall plates on the sleepers at the correct height.

That would be less deflection if you do it accurately, and would be my recommendation

Also the absolute deflection will be low due to short spans. And with no plasterboard underneath the are no finishes to crack. So your 3.5 inch joists would be fine anyway, although they can't be far off. 4 inch can go up to almost 2m span if they're c24 grading.