Replace a rotten joist from underneath?

[d000hg]

At the end of sanding a floor and replacing boards, we noticed the joist right at the end of the room is rotted at one end - dodgy repairs included which have not helped at all (they cut out a rotted bit and added bracings, then it just rotted more!)

We don't really want to pull up the whole floor BUT underneath is a cellar which I plan to renovate. So we wondered when we do that, we could pull the ceiling down and get unrestricted access to all the joists and boards from underneath, to inspect how far the rot extends and treat the wood, etc.

We wondered if we could even replace the joist this way, carefully prising it away from the boards above... then put a new one in, pack it to the right height and nail the boards back.

 

[John D v2.0]

Sounds doable, but the number one for me is stopping the source of water. Is the ground level too high or if there water penetration from outside?

 

[d000hg]

There is no sign of damp at all. Wood is dry, wall is dry where the joist rests, plaster on that wall shows no signs of damp.

The floor boards are distorted at that end of the room as if they've been flooded but it's hard to see how... water would just run into the cellar (also has no damp issues). We're perplexed if a radiator burst when someone was on holiday or something. The joists appear to be original ~1860 and in great condition apart from this one rotten one, which then seems to have infected one or two boards - it was a single crumbling board which was our clue.

So signs of rot fungus outside the joist either... could it be an isolated dry rot outbreak?

 

[noseall]

We were asked to do a job under insurance claim supervision., which involved a pair of supporting water damaged joists. The assessor suggested removing the bathroom and the partition wall sat upon it (separating the bathroom from a bedroom) and replace the double joists with new ones.
I said I would do the lot from below. Leave the exiting joists in place, sister up a new pair each side and bolt right through the lot.
Much more fun from below.......

Below4

• noseall
• 24 Jan 2018

Below3

• noseall
• 24 Jan 2018

Below2

• noseall
• 24 Jan 2018

much more........

Below1

• noseall
• 24 Jan 2018

 

[d000hg]

I never knew bono moonlights as a builder

Many thanks for this, most helpful. The idea of sandwiching the joist is interesting too... Assuming the other end is sound... But with it being the end joist parallel to the exterior wall there's only a 6-9" gap. My guy had thought about shortening the existing one and splicing a new length with metal plates, but couldn't see how to get access to the far side, is there a clever way?

Assuming I treat the wood, is there any harm leaving it in place if this makes things easier?

 

[Doggit]

You can do it from below, but you can guarantee to asses the problem and damage completely. If there's no sign of water damage, then it may well be dry rot now, and that means spraying everything for up to a metre around the damage including the wall. Best to cut back the joist till you get to clean wood rather than just leave it in place. If the joist is by the wall, access is going to be restricted, but the loading isn't so great, so just 1 new joist should be sufficient, overlapping the old one by at least a meter and a half, and using 3 bolts.

 

[cdbe]

Did you charge £10,000 to do that job? When I worked for a large public sector housing provider that's what we paid our Prime Contractor (plus VAT) for a virtually identical job, but their approach was to replace the supported masonry dividing wall with stud and then the joist, despite the SE saying the sistering method was acceptable and the wall could stay. I was so disgusted I actually offered to do it myself at the weekend but wasn't allowed for insurance/commercial reasons. I honestly don't know how the company in question (which has been in the news a lot recently) managed to bankrupt itself.

 

[Doggit]

The word backhanders springs to mind to get the job speced like that.

 

[Nige F]

And all the Direct Labour Organisation guys ( like I was for a HA ) That were "Maggied" back in the day, they're all laughing We'd have done it just like Nose.