When to replace 90 year old wooden floor joists?

[Adsibob]

Getting prices back on a tender for a full refurb of a 1930s semi, together with double storey rear extension and loft conversion.

Big variation in price for upgrading the the existing subfloor of the first and second floors (the second floor being the floor of the loft). As much as £10k +VAT difference.

I had specified that first and loft floor joists should be inspected and only replaced if necessary, and that the joists should be reinforced with noggins and additional joists in one of the bathrooms (because heavy stone bath tub in that bathroom). Although those joists will be 90 years old, there is no damp/rot (as far as I'm aware), and so I don't see why we should necessarily replace them. One builder has said that in his experience joists this old always need replacing and given the amount of changes I'm making to the floor layout (I'm moving the stair case, for example), it's going to be easier to rip everything out and start again with new joists. He therefore thinks I should budget for this at the outset, rather than work off provisional sums depending on what is revealed when we expose the subfloor. A separate point is that the "subfloor" is already exposed in the loft, so if he wasn't being lazy he could just go up there and show me why he thinks the existing joists aren't good enough.

Thoughts anyone?

[Gone West]

1 hour ago, Adsibob said:

Although those joists will be 90 years old, there is no damp/rot (as far as I'm aware), and so I don't see why we should necessarily replace them.

The timber used 90 years ago would be a lot better quality than what would replace them.

[Russell griffiths]

You will probably find that in the last 50 years the house had central heating installed as well as numerous bathroom changes, every plumber that did a job would have hacked a chunk out of the joists to get their pipes in, sometimes leaving very little meat holding it all together. 

The loft joists will be in a better condition as pipes and cables would have been run on top instead of through the joist.

 

If you you are going full out loft conversion you will probably be better off ripping all the ceiling joists out and replacing the whole roof, will work out quicker to start with all new or even loft trusses and a crane, will be all installed in a couple of days.