Dry rot in ground floor lounge joists

[billm]

Having seen the red dust around the edge of the ground floor carpet, I suspected dry rot was the culprit so pulled up the carpet to see rotten floor boards in the corner of the room. Pulled up a load of floor boards and yep, the ends of several joists are all rotten and the ground below the joists is coverd in a creeping pale coloured mushroom like substance.

So my plan is to cut back all the joists 500mm beyond the worst bits and replace with new timber. Then shovel out all the cr*p from under the joists and scrape it off the walls around there and then spray the walls and ground with a dry rot treatment.

Does this sound right ? What treatment/product would you advise ? Cuprinol Dry Rot ? Do I have to inject it into the bricks around the joists where the mushroom stuff was attached also or just spray them ?

Thanks
I had thought of wrapping the ends of the new joists with DPM before fitting them into the walls or is it easier / better to use metal joist hangers ?

There is a small wall across the middle of the room to support the joists and the only air brick is on the side of the wall that has no rotten timber and only a small amount of reddish dust. on the ground. So I am thinking of adding a 2nd air brick on the side of the wall where all the mushroom stuff was on the basis that that side of the floor is lacking air movement and maybe that's why I have got the dry rot ?

Would you also spray the treatment stuff on the floor/wall area on the side of the supporting wall which is not as affected ? or is that a waste of time ?

 

[anobium]

You have by and large got it right , but I would add treat the remaining sound floor timbers and remove and treat/renew the adjacent skirtings and door casings.
Just bear in mind that you are trying to isolate the fungus from its food source, as without food it will die.
Apart from the obvious in replacing the affected timbers, it is equally important that you identify the cause of the outbreak and rectify that.
It may well be that you have already pinpointed the cause as insufficient underfloor ventilation, but I would strongly recommend that you carefully check for other contributory factors such as leaking pipes rising damp, penetrating damp etc.
Failure to find the cause could well result in the dry rot coming back.
Good luck.

 

[billm]

Hi thanks for the reply. I can't see any damp problems, gutters etc, so maybe the old dampcourse has given up. This would be rising damp ??How do I check it ?

Come to think of it .. there is a slight damp patch on the wall in the other lounge just over the skirting board .. so maybe the dampcourse is on the way out.

If so, whats the easiest way to replace a dampcourse .. I've never done one before. Can you inject stuff into the bricks or do you remove bricks and add a new DPM ?

Whats penetrating damp ?

thanks again

 

[noseall]

ventilation.

 

[anobium]

Impossible to diagnose cause of dampness without carrying out on site inspection.
However if the decay seems to be emanating from where they go in the wall, by that I mean that the ends of the joists are more greatly affected, then the chances are that the moisture is coming from within the wall, which could be rising damp, penetrating damp, blocked cavities etc
If however the joists are decayed on the underside in the middle of the room, then the problem is due generally to inadequate underfloor ventilation. You can check this by probing the undersides of the joists with say a large screwdriver, and if it goes in easily then that is a probable cause
You should however also bear in mind that you could well have more than one cause of attack.
For further info on damp just click on the the search on this forum, and you should get all the info you require, some good , some not so good.
Photo's of the affected area would help!

 

[billm]

Hi, OK I've just taken these photos, it isn't pretty. Lets see if I can explain them:

This is the corner of the room with the outside wall at the top and the joists going into the kitchen wall to the right. Kitchen has a solid floor. Note ends of joists rotten and also all the dry rot (coloured stuff on the ground) "flowing" from the corner/outside wall towards the camera into the room.

A closeup of the same corner. Notice a strut holding up the joists, so obviously this has been going on for many years so someone has made a botched repair previously ie more than 5 years ago I guess. I doubt the dry rot has been there for years as the red dust only started appearing about a month ago

Even closer. The worst joist is the one nearest the wall. This is covered in the fungus.

Moving further along the outside wall/joist, this is what the fungus looks like. The only air brick is to the left of the stubby wall supporting the joists and the extent of the fungus there is alot less .. just a sort of slight dusting. This is why I thought of adding another air brick in the corner of room (1st photo) to help ventilation incase the stubby wall is restricting it.

Finally, this is the left side of the room, to the left of the stubby wall. This is dampness on the side of the chimney breast. The joists all around here are perfect and only slight amount of dampness on the floor below but its obviously affecting this chimney breast wall/corner somehow (chimney/fire never used)

I was thinking of removing the skirting, knocking off all the plaster in this area and replastering with sand/cement but the bricks could be damp behind it ??

Hope this helps.

PS There is nothing on the outside wall I can see that can cause damp, no leaking downspouts etc although the bricks below the airbrick / dampcourse level could do with pointing

 

[anobium]

Great photos Billm, bit tied up tonight visitors etc , but I will get back to you tomorrow with my detailed response

 

[anobium]

OK billm here goes.
Based on your photo's I suspect that you have 2 probable causes of the outbreak, these being dampness in the wall and insufficient underfloor ventilation.
The lack of underfloor ventilation is simply rectified by installing additional airbricks.
As a rule of thumb allow 1 for each external 2.4 metres run.
With regard to the dampness in the wall this is a process of elimination.
Check the external ground level to ensure that it is below the internal floor level.
Check that if it is a cavity wall that it is not blocked.
And if all these are ok check for the possibility of failure of the dpc, ie rising damp.
I should at this stage point out the importance of locating the cause of the outbreak.
Contrary to what a lot of people think dry rot needs a certain moisture content in the timbers for the spores to germinate.
The spores are the red dust you are seeing on the oversite.
With regard to the dampness on the side of the chimney breast this may well be condensation with in.
If the chimney breast been sealed up a vent should have been installed , if not put one in.
If it already has one check that it is not blocked , if ok follow procedure as previously outlined to identify cause of damp in wall.
With regard to the eradication of the dry rot I would remove the skirting to the rear and right walls, and cut back all the affected joists to the sleeper wall.
To be on the safe side remove the joist which runs parallel with the rear wall for the full length.
Remove all the timber debris and any other organic material from the subfloor and subfloor walls.
Now apply a fungicide to all these areas and to the exposed pockets where the joists went into the wall.
Renew all the joists boards and skirtings thoroughly treating either in situ or before with a fungicide paying particular attention to the ends of the joists where they go in the wall and to the reverse side of the skirtings.
As an additional precaution encase the built in ends of the new joists in a damp proof membrane.
You shouldn't really need to remove the plaster unless there are some timbers in or on the wall within a 1 metre range.
On a final point I am assuming that the rear wall is an external wall and not a party wall?
You should also check the condition of the skirting on the reverse of the right wall which I understand is the kitchen as it is more than likely that this is affected.
Good luck

 

[billm]

Thank you for your very detailed reply. That gives me the direction to work from now. I'll be working on it over this next week (from Wed) so I'll update this post with any findings towards the end of the week.

 

[billm]

We've just had a heavy downpour .. so out came the camera again ..

As you can see this is the outside wall. The DPC I think would be ontop of the 2nd brick course and below the airbrick ? It looks OK to me. But I think there are maybe 3 problems here :

1. the lower course needs pointing
2. the lower coursework are laid side-on and could be transmitting dampness directly from outside to inside .. below the cavity
3. the concrete surface outside could be allowing heavy rainfall to bounce up

So I think, in addition to putting an extra air brick in here, I need to point the bottom course and then maybe spray some waterproofing solution on the lower 4 courses.

Could this be the cause of the dampness .. the inside area directly behind this spot would seem to have the heaviest area of fungus, as can be seen on the first photo above

Does this sound right ?

thanks again

 

[anobium]

billm wrote

1. the lower course needs pointing

Agreed , but I don't think it has any bearing on the cause of the dry rot.

2. the lower coursework are laid side-on and could be transmitting dampness directly from outside to inside .. below the cavity

Unlikely if the cavity is not blocked.
I can't understand why there is a course of headers at that level, maybe somebody else has the answer.
In any event they should not transmit moisture to the internal course as they project externally.

3. the concrete surface outside could be allowing heavy rainfall to bounce up

Correct, but if the cavities are not blocked it has no relevance to the internal course.
Think of all the heavy rain directly on the face of the bricks higher up the wall

So I think, in addition to putting an extra air brick in here, I need to point the bottom course and then maybe spray some waterproofing solution on the lower 4 courses

Extra air bricks yes, pointing yes , but waterproof solution in my opinion a waste of time and money.

Could this be the cause of the dampness .. the inside area directly behind this spot would seem to have the heaviest area of fungus, as can be seen on the first photo above

It may have had some effect, but, from your photos I am more inclined to think that the main cause was inadequate underfloor ventilation.
I say this because if you look carefully, the underside of some of the joists have been affected by wet rot fungus.
In any event just to be on the safe side, when you replace the affected joists, even though you are covering the ends with a dpc, make sure the when they go back in the wall that they only sit on the internal course.
In other words they only need to go in the wall for approx 100mm.

 

[noseall]

has the external ground level been lowered at some point?

 

[billm]

The outside floor I think used to be part of some external lean-to building, maybe an outside store or coal shed or something. I've been here 5 years and its always been like the photo so it's not been messed with in that period.

I will point the bottom bricks in anycase, just in case. I'm not sure about the water run-off around this area, it might be running back to the house but I'd hope that when that original concrete was laid that they did ensure a run-off away from the house. I could check tho by dumping a bucket of water on it and see where it runs.

Because of the previous repairs, and the strut holding up some of the joists, clearly this has been a problem for a number of years.

So if I do the airbrick and pointing outside, then follow Anobiums advice and remove all the old timber that is affected, apply preservative to the new timbers, scrape the brickwork inside, dig out 75mm of the ground soil beneath the joists then spray fungicidal treatment to brickwork, woodwork and ground soil and then wrap the new joist ends in DPC I guess that (hopefully) will sort it.

 

[masona]

I can't understand why there is a course of headers at that level, maybe somebody else has the answer.

The only thing I can think of is the bricklayer went too high from the footing(?) or the ground was lowered as suggested from noseall. As it is now, rainwater cannot run of it.

 

[anobium]

billm, I forgot to mention that in addition to treating all the new timbers, you must also treat the underside of the remaining floor joists and boards, as these will be contaminated with the dry rot spores.