Dry Rot: replacement flooring options?

[David1905]

Good morning,

This is my first post on this forum, I’m seeking advice as there seem to be some very knowledgeable folk on here. Unfortunately, my house has a dry rot infestation which has caused no end of stress and bother.

Background:

1905 build Edwardian terraced house, two stories, purchased 1996. When we moved in the two ground floor reception rooms had been knocked through into one, flooring was thick fitted carpet on underlay sitting on floorboards on a suspended joist floor, the joists are 3”x2”.

We have spent the intervening 28 years opening fireplaces and restoring the house to its original configuration. This included rebuilding the dividing wall between reception rooms 1 (front) and middle (2). The work was carried out in 2006, and I used a builder who had come highly recommended (of more anon, sadly): as the floorboards were in poor condition, I decided to have a laminate floor installed in both rooms over the boards. The laminate is 10mm thick with 3mm oak veneer on top. In retrospect, I know that I should have opted for replacement floorboards alone …. hindsight, and all that.

All was well until January of this year (18 years having elapsed) when I was horrified to discover fruiting bodies of dry rot emerging around the hearth in room (2). I immediately took advice from another builder friend who referred me on to a Property Care Association registered company, in the hope that they could provide an insurance-backed guarantee for subsequent works.

A survey has been conducted which confirms extensive dry rot in the wooden subfloor which extends out into the middle of the room. The surveyor thinks this has been present for 18 months to two years. Thankfully it has not entered room 1. The dry rot is present in the party wall and the neighbour (since 2021) admits that he has rotten floorboards in the hearth area directly opposite our outbreak. The surveyor and I were invited in, and one floorboard has fallen through completely, with cuboid cracking on the underside. The surveyor popped his camera into the void and confirms the presence of what appears to be dead dry rot remains on the joists.

To cap it all, the one and only underfloor vent to outside in our room is blocked, seemingly by the builder who carried out the work in 2006. So, the theory (and that's all it is, cannot be confirmed) is that the dry rot started in next door, when the neighbour improved ventilation in his room (due to a ‘musty smell’) the mycelium migrated through the party wall and found a more agreeable place to live in my house.

The exposure schedule has commenced, and it seems that I now have two options:

1. Replace the original woodwork with a new suspended timber floor after the eradication process has been completed.
2. Opt for a concrete floor option, which will entail removal of the wooden floor in room 1 due to the ventilation issues this will cause if only room 2 is so-treated.

The complication is that the neighbour has seen how drastic and destructive the eradication work is on my side and won’t (yet) entertain similar works on his side (I suspect that all this will change once the dry rot manifests itself on his side). For this reason, my contractor will not issue a guarantee for his work, as there’s every chance that the dry rot may reappear elsewhere in my property if left unchecked in the neighbours - I can see his point, in fairness.

So, the key question: I wonder which flooring option I should go for?

Budget is not an issue, I am more concerned that the eradication is completed successfully in room 2, rather than how much it costs.

The other factor is that I intend to sell-up and move on in the spring of 2027 when I retire! My final "forever home" will be a detached house, after this palaver

Apologies for the somewhat wordy summary, I’d be grateful for advice on my options from those more qualified to speak than I.

Some photos:

Dry rot just before exposure woks commenced last week:



The room before exposure: the single under floor vent (blocked) is directly under the patio door:



Exposure works ongoing. The fireplace was safely and skillfully removed by my contractors without damage. The blue DPC plastic has caused a lot of issues, with mycelium spreading beneath it. I would take issue with my original builder about this (apparently) shoddy work, but he died in 2014 ....

 

[malcolm]

Don't fall for the story about a magical fungus that needs to be killed. Next door doesn't matter. The dry rot fungus will die off anyway once the wood gets down to a sensible moisture level. For that to happen you want a good amount of under-floor ventilation and I don't see any air bricks in the pictures. Ideally you would have a cross flow of air and have it nice and breezy under there.

Plastic against wood is a bad plan. It traps moisture in the wood. Laminate flooring is also plastic and will need spacing from the joists to allow air flow.

And of course it is hateful to see the plaster removed from the walls ready for tanking. Tanking keeps any excess water in the walls rather than letting it get out. Hides the problem for a while but your walls will get wet if there was a problem in the first place.

 

[David1905]

Hi Malcolm,

Thanks for that. Obviously this is at odds with what the company concerned are telling me, it looks like I may have fallen for a horror story scenario here.

The brick walls appear bone dry, but there was a high moisture content reading to the right of the chimney breast, and there are three points identified where mycelium have (apparently) entered:



There is damp in the earth underneath the blue DPC with mycelium spreading out into the middle of the room. Otherwise, the room appears dry.

The surveyor has concluded that this is all down to insufficient sub-floor ventilation. There is one airbrick under the patio door, this is completely blocked from the inside by the piece of wood you can see in the above photo, and a strange accumulation of small stones which are jammed in the cavity beyond the airbrick louvres. This may have happened when the patio door was installed in 2013?

The airbrick from the outside:



At the front of the house there are three airbricks in the bay, all these appear clear and there is an obvious airflow in and out. No dry rot apparent in room 1!



Thanks for your comments about the neighbour. I was in a state of anxiety about their reluctance to engage at this point, but from what you are saying it would appear that they may have already solved the problem on their side by improving ventilation and drying out the floor (although they will need to replace all their rotten woodwork).

There is a suggestion from my contractors that a concrete pour would cure all this but I've already decided that this is not going to happen, having taken advice from my usual trades who all shouted at me not to do it!

The surveyor mentioned that clearing the airbrick and (perhaps) adding another alongside it would do the job. So I will go with this.

Thanks once again for your valued comments which I read with a great sense of relief!

 

[malcolm]

It would make a lot of sense to re-introduce the vent, and given the panic even consider another vent further along the wall.. What's on the other side of that breeze block wall? If it's a ventilated suspended floor on the other side the breeze block should have been built with gaps between the blocks and I would introduce some holes in the bottom of the wall to let the air through. Breeze blocks are soft so it's DIYable with a 240V hammer drill with a chisel on the end.

It's a shame they removed the plaster. What the plaster is made from probably not too important as the under-floor ventilation would dry the wall before any damp made it's way above floor level. It would have been better left as lime as it presumably was before especially on the fireplace and on the exterior walls which won't dry to the outside due to the cement pointing.

 

[David1905]

The breeze block wall is the dividing wall between the front and middle rooms. When we purchased the property it was a through room with a hideous 1970s semi-circular arch which my builder blocked up during the work in 2006, returning the house to the original configuration. Underneath this wall there is indeed a sequence of air gaps in place.

There is a further room (down a step) to the left of the patio door as you look at it from within room 2, this would have originally been the kitchen but is now our dining room (so room 3). So I don't imagine there's any point installing an airbrick between room 2 and room 3 as it is internal? Although room 3 also has an open fireplace/chimney, so there is a good flow of air there.

At the same time as he reinstated the dividing wall, my builder opened up the fireplace / chimney in room 2 and installed the reclaimed fireplace in post #1. He replastered the breeze block wall, right alcove and chimney breast with ordinary plaster. So the only original lime plaster lost recently was to the left of the chimney breast as you look at it.

Hope this makes sense!

 

[alexander]

clear out all the junk between the floor joists and add a couple of extra vents under the floor to allow better air flow, renew the joist & floorboard's problem solved

 

[David1905]

clear out all the junk between the floor joists and add a couple of extra vents under the floor to allow better air flow, renew the joist & floorboard's problem solved

Yes that's now the plan, they are coming later this week to clear away all the garbage and joists.

It will all need a drying out period (a week or two?) before the new joists and floor goes in. Floorboads this time with a large rug, as nature intended. No laminate!!

 

[Matt Green]

"high moisture content reading to the right of the chimney breast"

Nooo.... there was a low electrical conductivity reading taken to the right of the chimney breast where all the salts from fossil fuel burning have been deposited are that electrically conductive.

There is a suggestion from my contractors that a concrete pour would cure all this but I've already decided that this is not going to happen, having taken advice from my usual trades who all shouted at me not to do it!

Absolutely do not do this under any circumstances.

 

[David1905]

Nooo.... there was a low electrical conductivity reading taken to the right of the chimney breast where all the salts from fossil fuel burning have been deposited are that electrically conductive.



Absolutely do not do this under any circumstances.

Thank you, Matt. Duly noted, very interesting re: the damp reading. As for the concrete pour: that is not happening.

 

[David1905]

I've spent the morning clearing the airbrick. I tapped in a bolster from the outside, it was a perfect width size for each of the four slots. An absolute ton of rubble came out of the void and I can now see daylight from the inside. No wonder it failed to do its job of ventilation, and I suspect that this is the cause of all my dry rot woes.

I will be instructing my contractor to install another airbrick alongside this one as a precaution. Maybe even a bank of the things!!

 

[alexander]

I would suggest an other couple approx. 1.5mts apart to allow for cross air circulation

 

[David1905]

I would suggest an other couple approx. 1.5mts apart to allow for cross air circulation

Unfortunately not possible, there is only 45" width to play with (see photo, airbrick circled). That's my dining room wall (room 3 mentioned above) behind the ladder.

The surveyor has returned, have advised that a concrete pour is off the cards. Re: the airbrick, he has suggested a vent on either side of it with internal pipe/ducting carrying air into the room positioned to allow cross-ventilation. Makes sense to me?