Joist issues (w/pics)

[Matt Green]

It looks like you'll either have to replace the joist back from the nearest beam/supporting wall or run additional sections either side of the effected joists and knock out some bricks to enlarge the bearing pockets. Either method will do- one might be easier than the other though.


Matt

 

[markwm]

Here's a plan of the underground of the entire house. I've put on all the locations of air bricks currently.




The problem is it's difficult to get a flow of air through the house because of the vaulted cellar. There's only 1 place where the cellar isn't valuted living room side (behind the cellar stairs) and that already has an air brick in it. It just doesn't seem to be doing much good as it is situated underneath the stairs.

When it rain the cellar does hold water also. We have a problem with condensation down there. The other two air bricks in the cellar on the external wall are located where the coal shoots are.

 

[Matt Green]

I wouldn't worry too much about the air bricks, it seems that you are not going to get much more airflow under the floors without quite abit of invasive work. Remember that a lack of airflow did not cause your dry rot problem: that was caused by the timber props put on a wet floor beneath a previous outbreak.

Try not to get the mindset that increasing the ventilation is critical, a lack of it is seldom a root cause but often makes a bad situation worse. Deal with the problem at hand and see what happens.


Matt

 

[Nemesis]

Another way to get some ventilation in, don't know how appropriate it may be here, is to put a grille or two in the floor itself. On a suspended floor walsking across creates some amount of a 'bellows' effect and can keep some airflow?

We always try to have a couple of floorboards screwed rather than nailed, so access to the underfloor is more simple.

 

[Raylea]

Have you got radiator pipes under the floor, without adequate airflow condensation could be building up as well. This happened to us, ok when there was no floor covering above, but as soon as we layed a floor covering and turned the heating on after a while in a corner there was a damp spot that was getting bigger. Realised what was happening put in an airbrick sorted . This could be contributing to your problem.

Raylea

 

[markwm]

There are plastic radiator pipes under the floor, loose not even fixed to the joists. They aren't leaking and I can't see any condensation either.

 

[markwm]

It looks like you'll either have to replace the joist back from the nearest beam/supporting wall or run additional sections either side of the effected joists and knock out some bricks to enlarge the bearing pockets. Either method will do- one might be easier than the other though.


Matt

Assuming I kill all the rot as you guys have advised....how does this sound for the structural repair of the joists:

a) http://img169.imageshack.us/my.php?image=r2os9.jpg
Cutting back the rotten joists, a metre or so back from the rot. The I bolt on new timber on one side and sit them in a widened hole in the wall. New timber will be treated of course. If this method is sound just how far alongside the existing joist do I need to run the new timber?

b) http://img405.imageshack.us/my.php?image=r3za1.jpg
Again cutting back the same amount, this time fixing a new piece into the original wall hole and sandwiching it to the old timber.

I also thought about wrapping the new joist ends in membrane and using plastic wedges/packers if needed in the damp wall.

c) Here's the masonry wall fix, or something similar:

http://img228.imageshack.us/my.php?image=r4ja7.jpg

There's also enough room in the cavity to leave acro props permanently in place if I wanted.

 

[Ian Bond]

Just a thought, and I've never done this myself, but would a timber resin splice let you replace just enough of the joist to give a sound repair?

e.g.
http://www.rotafix.co.uk/timberrepair.htm

Or would the bower beam still work if you also used a short length of new, treated joist, supported on a new plinth and isolated with dpc from the damp wall/plinth?

 

[Matt Green]

b) http://img405.imageshack.us/my.php?image=r3za1.jpg
Again cutting back the same amount, this time fixing a new piece into the original wall hole and sandwiching it to the old timber.

I also thought about wrapping the new joist ends in membrane and using plastic wedges/packers if needed in the damp wall.

This has to be the best option if possible as it does the least lasting damage to the building. There is no need to cut back a metre past the last sign of decay. None at all. That whole concept was cooked up by the remedial industry to generate more work and larger bills. The decay in the joist bearings doesn't even look active.

Just remove the timber that has decayed past the point it can support a bolt or itself. Remember that the timber you are using for the repairs is much lower quality than that you are replacing. Try to keep as much as you can as it is far more durable, treatmnet or not.

You need to go about a metre past for bolting I would think, but do check with a structural engineer. Agony Uncle might be able to help you directly or indirectly.

And, yes, wrapping the replacement joist ends is a prudent measure.


Matt

 

[markwm]

Thanks guys