Adding extra floor joists

[slingshotx]

Hi, can't find an answer for this so thought I'd ask if anyone has a best practice.

We are renovating a 1930's council house and recently had an extension built. The builder knocked a small hole in the back of the house to find the joist level for the extension. When he did this he found the end joist had what looked like dry rot and was very soft. i.e. he could push his finger into the joist, this didn't affect the extension, and the upstairs floor doesn't bow, creek or deflect, even when I get the other half to jump up and down (well I wasn't going to test it myself just in case was I?)

So with the extension complete we are now doing the room below this joist and with the ceiling down, though it would be a good idea to add an extra joist just in case.

First I'm going to treat the existing joists with dry rot treatment, looks like the problem itself was caused by an old leak that the previous owners couldn't be bothered to fix.

So rather than replace the joist I'm going to install another 10' 2x8 joist by the side. The joist rests in a hole in a brick wall on the external wall and a hole in a breeze block wall the other. There are no pipe, wires etc in the way.

So my question is how to put in another joist, 2 ways I can see.

1 - Make a couple of small ledgers (11" between existing joists) with offcut of 2x8, bolt to wall with a couple of M10 bolts and stick joist on hanger.
2 - Cut extra slots in existing brick and breeze block and rest on wall as per existing joists.

Or are there any other options, didn't really want to remove the existing joist and replace because it's seems happy enough.

Regards

Kevin

 

[kbdiy]

Firstly you need to distinguish the difference between dry rot and wet rot. From your description it sounds more like wet rot which is relatively easy to deal with but if it's dry rot then much more treatment will be required as this can and will spread to adjacent timbers.

Just google dry rot and you will see what I mean.

 

[slingshotx]

Sorry typo, meant to type wet rot. We have a local damp shop that were very helpful and he suggested we treat this (and outside loo that has beetles) with Wykabor, so hopefully a couple of coats of that on all joists will stop it spreading.

I've attached a really bad photo below the joist to the left is the problem one, although problem only really visible at end of joist.

View media item 65050

 

[dann09]

Difficult to figure out what exactly is your situation.

However, you dont seem to be going about it with best practice - forget, for instance, a salesperson in a "damp shop" who wants to sell you chemicals.

Its your house & your rot, and if you are serious about remedial work, then perhaps research your issues on here and esp in the building forum.

Then come back with, hopefully, better pics & a more informed sense of whats happening, and why, in your house.

 

[slingshotx]

Thanks for the reply.

Think I said it was an old leak that has now been fixed, I've done plenty of research, thought I'd written a decent description of the issue, but maybe not:-

1 - Joist end has some wet rot.
2 - While ceiling below is down thought I would treat it (no, not take it out for a nice meal).
3 - Stick another joist by the side of it.

And talking to nice bloke in shop simply gave me more options, in addition to those on the web!

 

[slingshotx]

OK here's a couple of better photo's. The main bathroom is directly above above this section. When the ceiling was taken down there was some evidence of water damage and the floor boards seem to have some water marks, but seem pretty solid.

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• slingshotx
• 14 Aug 2013
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• slingshotx
• 14 Aug 2013
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The joist on the left is the joist that had a soft end when viewed from outside, via hole knocked in outer skin.

None of the joists seem in bad condition, the left one seems to have a few beetle holes, but doesn't seem active since there was no obvious frass on the plasterboard ceiling that was taken down.

 

[dann09]

Probe the joist tails as they enter the brickwork pockets - use a thin screwdriver.
Probe the wood plate that the joists are sitting on.

Come further back, say, 300mm - 400mm and probe again.

If both tails are rotted then research cutting joists, propping and bolting-on.

The plate both tails are sitting on could be a built-in wall plate ( if its built-in its suspect), or the top plate of studwork? Either way, it req's further examination. Go along that wall probing everything wood, as above.

Have you spotted any strands of white or discoloured "spiders web" like material?

 

[slingshotx]

Thanks for the help.

The whole joist is pretty solid, the only exception is the bit about 100mm from the end, which some has broken away and there is some evidence of wood worm, this is a little soft about 5mm pentration witch small screw driver.

The plate is built-in and there is a DPM (and slate in a couple of places) between the wooden plate and the joist.

All the web like stuff seems to be normal spiders web, no fungal growths that I can see.

Wonder if the issue on end of joists is due to lack of air since the cavity has been filled after the house was built.

I was thinking adding a new joist next to it just in case would be a good idea while there was no ceiling, but I'm tempted to leave it for now and then simply replace the whole joist (and some of the damaged floor boards) when we do the bathroom upstairs next year.

Thanks

Kevin