Floor joists damp, how's it getting in?

[tbear]

Hi All

Recently noticed that that the front room floor feels a little springy in the right hand corner of the bay, it's a 30s semi. Lifted a couple of boards and was quite shocked to see that two main joists are rotten from damp back from the wall to a couple of feet along their length and a couple of smaller joists that go between the chimney breast and the bay have also suffered but not to as bad an extent.

i've figured out where the slate DPC is, bit tricky as its been pointed over but the soil level outside was maybe half to one brick below the DPC

Ive now removed soil to about three courses below the DPC but I can see a few tiny droplets on the inside bricks just below the DPC, not sure if this hitting the joists or if the DPC is doing its job and preventing the damp. Maybe this is normal and clearing the soil will fix the issue?

If not whats the best course of action, do chemical damp courses actually work?

 

[gregers]

chemical dpc's do work if done properly.
and everything else has been checked to make sure it is rising damp and nothing else.

but i think in your situation is that there is no dpc membrane under the wall plates hence why the damp is tracking onto your joists,have you stuck a screwdriver into any joists/wall plates??
if you have and it disappears into the wall plate then i would say you need to do a bit of lifting cutting out and replacing rotten flooring that you come across.
if its not to bad IT might dry out once you have eliminated the damp source.
hth.

 

[tbear]

Difficult to tell without lifting more boards to get a better look but the joists appear to just sit directly on the top of the slate DPC, poking the joists with a screwdriver would most likely go almost straight through.

The joists will be repaired or replaced as required but I need to get the damp problem sorted out before this step...

There is a slight damp smell under the floor but the bricks all feel dry, it's almost as if the joists are wicking the water in from their ends.

Are these types of properties prone to this sort of problem I wonder..

 

[Static]

There is a slight damp smell under the floor but the bricks all feel dry, it's almost as if the joists are wicking the water in from their ends.

well urm yes it was once a tree
Chances are your cavity is full of rubble or some fool has put cavity wall insulation in.. As the joists are built into the wall there is little you can do except when you replace them put them on joist hangers instead.

But lowering the ground level so its 150mm below the DPC allowing a splash zone will also assist.

 

[ajrobb]

My structural surveyor suggested wrapping the ends of the repaired joists in 1000 gauge polythene. Hopefully, just dropping the ground level will eliminate the damp for you. I'm not sure the DPC should have been pointed over - sounds like a damp bridge to me.

 

[stuart45]

Have you got cavity or solid walls?
Also have you checked whether it's wet or dry rot?

 

[Static]

Have you got cavity or solid walls?
Also have you checked whether it's wet or dry rot?

Good point,, you should also check what sub floor ventilation you have.. ie airbricks if any..

 

[noseall]

Good point,, you should also check what sub floor ventilation you have.. ie airbricks if any..

Nice to see you paying attention Stats as i'm still p1$$ing mesel at the "it was once a tree" comment.

 

[tbear]

There is a slight damp smell under the floor but the bricks all feel dry, it's almost as if the joists are wicking the water in from their ends.

well urm yes it was once a tree
Chances are your cavity is full of rubble or some fool has put cavity wall insulation in.. As the joists are built into the wall there is little you can do except when you replace them put them on joist hangers instead.

But lowering the ground level so its 150mm below the DPC allowing a splash zone will also assist.

A tree, arn't they waterproof? lol

Carried out some more investigation work, it's defintely wet rot by the feel of it. The end of one of the joists is rotten and fell apart in my hand, usesful as it allowed me to look at the wall construction better.

Its a cavity wall with a gap that just allows me to get my hand in, the joists actually sit on the slate bed and there is also an upright slate that the end of the joist touches, slates are in very good nick, there are three airbricks and all are clear. The gap looks to be blocked/bridged with what feels like mortar altghough I cant be sure until I get more of the boards up this weekend. The outside lowest three courses look newer than the rest so maybe some remedial work has been done. The house has been in the missus family since the early 60s, we have it as part of an inheritance, she cant recall any type of building work being carried out so maybe the rot has been ongoning for the last 50 years.....

Its all starting to look a lot less serious than thought although one thing is worrrying me, what is the best method of repairing the joists? dont fancy replacing the whole joint, are these metal splicing kits any good?


http://www.joist-repair.co.uk/Joist...halfway along its lenght so look feasible..

 

[ajrobb]

The outside lowest three courses look newer than the rest

From your first post, it sounds like they have been protected underground.