Rotten Floor Joist - options?

[Mike Dodd]

Just been helping my sister who's "new" 140-year old house has many, many unique fixer-up opportunities etc.

This particular problem is related to the floor joists in the kitchen, by the back door.

There was a piece of floor-grade chipboard, approximately 3ft by 2ft on by the back door entrance. This was "springy" to step on, and she suspected foul play underneath. Prising the chip-board up revealed the following two joists (apologies - bad mobile-phone images) :-

joist, looking side-on)

slightly different angle)

joist, looking in from the back door)

out of focus, joist to the left of the previous)

better picture of the one to the left)

I've yet to get under the floor (I might need to lose a few pounds to fit under), but from what I can tell, the joist is good wood 2-3 foot in, and the problem would appear to be related to damp coming under the kitchen door over many, many years.

The joist is now dry - in fact there's a good amount of material that flakes off in your hand (sister stopped me before I removed all of the material with my thumb)

There is some evidence of creepy-crawly activity - there's obvious sign of wood worm at some stage, but the most obvious things are the occasional wood-louse (I saw 2).

My immediate thought was that, provided the joist timber is sound 2-3 foot in, I could get a, say 6ft length of similar timber, and bolt this alongside the joist (either 10mm coach bolts, or similar coach screws), sit this new timber on top of the same dwarf wall, with the end wrapped in damp-proof membrane. Maybe treat the original timber with some insecticide?

Is this sensible?, crazy?, is there any other suggestions from the people that know?

Any information gratefully received... then I can get back to DIYing on someone else's property :s

Regards

Mike

[visionset]

Yes you can, but do not underestimate how good that join has to be. A couple of bolts will not suffice. There is no real substitute for a complete new joist. But you can join if you do it properly. There are a host of timber joining fixings and you should bolt also with a good say 2ft overlap. And really bolt them up tight. I'd go for 6 to 8 bolts in pairs at centres 30mm from top and bottom. I'd also use some form of timber join fixing along the bottom. You might as well glue it while you're at it! Can you not just say to hell with it and take it as a renovation opportunity with nice new hardwood floor for example.

-- Mike W

[Roger Mills]

If the wood really is sound further back, what you suggest will work. But I suspect from some of your photos that the joists near the door are crumbly because of woodworm infestation rather than from rot. If this *is* the case, the same problem is likely to exist further back - and in the floorboards too - making a more drastic solution necessary.

I think you need to get down there and examine them thoroughly for woodworm, prod them for firmness, and see how much they deflect when someone jumps on the floor above.

[Roger Mills]

If the new joist is supported on dwarf walls *both* ends (which is what I

*think* is intended), the fixing doesn't need to be so exotic as it would if the joint were suspened in mid-air.

[dom]

Looks very much like dried-out wet-rot to me. If you cut back to good wood and keep it all dry, you should have no more problems. Repair sections in treated timber a good idea.

I agree very much with what MikeW says. Perhaps even a longer overlap and lots of bolts/screws. I did a very similar repair around my entrance, and it was convenient to add some extra masonry support under the joint. Also easy to double up parts of neighbouring joists at the same time. I was surprised how perceptually different it was to step through the door and feel rock sold floor rather than previous slight spring.

[visionset]

Yes if the old joist is sound over the soldier wall, then a new section that spans both walls needs very little fixing. More just to keep everything in check.

[Phil L]

joist end rot is almost always ventilation related, the fact that it is, or has been infested with woodworm is coincidental.

Remove and burn all affected timber, then treat remaining and new timbers with a good quality timber treatment, Cuprinol do a good one that prevents both wet and dry rot and also kills woodworm - it's fairly expensive but goes for miles, spraying is better than brushing.

You may need to affix a vent brick into the wall that carries the joist ends on this elevation, or uncover the existing one(s) which are possibly buried

[Jason]

Except that the floor is likely to need lifting just to get a new joist over two dwarf walls. If the floor is being lifted, then the old joist might as well come out.

-- JJ

[Cicero]

=============================== Just to add that these things are the recommended fixings for side-by-side timber fixing:

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