wet rot query (after survey)

[seneca]

Hi folks,

Just moved into a house and the survey report into the flooring for a downstairs reception room said
"extensive decay of joists by wet rot species (coniophora puteana.) complete replacement of this floor is advised."

I've had a quick look at the floor and it looks ok to me. Now I'm no expert, and don't really know what this wet rot species is, but the floor and joists seem ok to me, no holes/cracks and they are dry.

My query is:
1) how common is this? (ie. do surveys often pick it up)
2) does it need to be acted on immediately, or can I leave it for a few years.
3) how can you tell? what are the signs? can it be done by visual inspection?
4) can it spread to other rooms
5) does the whole floor (boards and joists) need replacing, or is there some other treatment.

any help would be greatly appreciated.
thanks.

 

[^woody^]

If you have paid for a survey, then why not take the advice?

Wet rot is caused by the fungus, and the timber does not have to be wet. The spreading of the fungus and spores is the problem

The fungus will spread to adjacent timber, and the floor can fail suddenly and without notice. So its not just about treating the affected timber

A quick google on wet rot or the specific strain, will tell you a lot about it.

And you will also have to treat the cause as well - ventilation or damp proofing or it is likely to return

 

[seneca]

I fully intend to take the advice. I was just wondering whether it was an immediate problem or whether it could wait a couple of years. The joist seem to be pretty strong, can they really just give way and collapse?

If ventilation is the problem, will a few extra air bricks solve it?
Underneath the floorboards there is about a foot of space, and then rubble and soil/dirt. Is that normal? or should there be a plastic damp-proofing sheet or something over the rubble. There is a fair bit of airflow already down there.

 

[^woody^]

Wet rot typically occurs at the joist bearings where they are in the wall and get damp. And yes, they can fail suddenly

The issue may be persistant rising or penetrating dampness causing the timber joists to stay wet, and the fungus to take hold.

Your survey should have detailed the remedial works with regards to damp prevention, not just treating the resultant damage.

Dampness under floor is not the probelm, as long as there is adequate ventilation.

Putting the new joists on hangers or wrapping the bearings with polythene may help, along with increasing cross ventilation, not just more airbricks

 

[anobium]

The fungus will spread to adjacent timber, and the floor can fail suddenly and without notice. So its not just about treating the affected timber

Not strictly true, wet rot fungus will not spread to other timbers , it will be confined to the area where the cause of the moisture is located.
In this case from what you describe I suspect that the cause or the decay is condensation in the sub floor area, which in turn is caused by lack of adequate ventilation.
Solution check that air bricks are not blocked , if so clean out, if not fit extra air bricks.
As to wether or not the floor needs complete renewal check ends of joists and middle with a screwdriver, if there is no resistance and screwdriver goes right through , you need a new floor.
If it is just surface breakdown you should be ok as long as you rectify underfloor condensation problem.
Finally as wet rot requires a high moisture content, around 40%, it would be advisable if you retain the floor, to give it a spray on the underside with a fungicide to prevent other types of fungus, such as dry rot occurring during the drying out process.

 

[seneca]

thanks for the info woody.

I've had quite a few floorboards up and there is some rot at the ends of 4 joists only. The rotted area is about 20-25 cm long. Can the dry rot spread further down the joist? You were right about the rot being where the joist touches the wall. The joists just rest on bricks and then the floorboards run the opposite direction.

Should all of these joists be replaced, or should every joist be replaced regardless. Is there not a way of treating the rotten ends only. I recall reading somewhere that joists could be reinforced by attaching another joist to the rotted end, say half the length of the complete joist.

Your survey should have detailed the remedial works with regards to damp prevention, not just treating the resultant damage.

it just says add two airbricks at the front and back of the house.

increasing cross ventilation, not just more airbricks

how can this be done. the shape of the house is such that there are no other walls that can be accessed except the front and back wall.
There are currently 2 bricks and 2 more are recommended. These are shown on a drawing and are a few feet from the existing ones. What else can be done to increase"cross-flow" or ventilation?

thanks.[/quote]

 

[^woody^]

The fungus will spread to adjacent timber, and the floor can fail suddenly and without notice. So its not just about treating the affected timber

Not strictly true, wet rot fungus will not spread to other timbers , it will be confined to the area where the cause of the moisture is located.

Yes thats right. The fungus does need moisture, so it will only spread to timber of similar moisture content. But it is common for elevated moisture level to exist in adjacent timber so this need to be addressed, or the fungus will spread

With regards to cross flow ventilation, then I would assume that the surveyor has looked at this and made recomendations accordingly. It is not always necessary to have direct air movement routes, as the air will be moved if there is sufficient airbricks, reasonably spaced out. But any sleeper walls should allow air through them, and partition walls off the foundations should have gaps in them to so as not to impede air-flow

Yes you can bolt a new joist next to the existing and/or splice in a new end piece. Just make sure that all the rot plus 500mm extra is cut out.

 

[anobium]

If it is as you say only the ends which are affected then the cause is not condensation, but dampness within the wall, ie rising or penetrating damp.
I doubt it, but if you decide to renew just the ends of the joists make sure to encase the end of the new joists were it seats in the wall with a dpc .

 

[seneca]

Cheers guys, you've been very helpful.