Dry Rot and Rising Damp

[daiking]

I have a friend with a problem house, he’s had for about 2 years. They had a damp survey done before they bought it which flagged some things but despite repeated attempts to fix things its getting worse. The house is a typical semi but the problems are compounded by the fact that the groundwater level is very high and the attached neighbour house is in a very poor state of repair, full of junk and not lived in.

 

Around the time they moved in they had parts of the floor lifted (<0.5m void), there was evidence of dry rot – the webs and the brown dust – on the party wall, front and back room chimneys and  toward the front of the house, ground floor. The wood was treated and the bottom 1m or so of plaster on these walls removed and re-done as the plaster was apparently conveying the growth of whatever it was.

 

Well 2 years in and the problem has far got worse. Someone has come in, put a hole in the floor to survey and it seems to be dry rot and rising damp partly attributable to a failed damp course although I suppose its possible that there was no damp course originally.

 

He’s been quoted £7000 to fix including treatments, replacing the joists and floor boards or half the 2 rooms adjoining this party wall and the plaster, clearing the blocked up chimneys as well. Apparently the masonry is saturated. The added problem is that next door has an absentee owner. AIUI, he inherited it and it is in a terrible state, full of junk unheated, inhabited etc and this guy is incredibly slow at sorting it. Unless this house is also fixed my mate has no chance of success in fixing his own and progress in getting the absent owner to do stuff is slow. My mate has a new born and a toddler so want to get this sorted asap.

 

What would be your plan of action if you were in his boots?

[Jeremy Harris]

I think the first thing is to find out, for certain, where the damp is coming from.  "Rising damp" isn't at all common, as very few building materials are  porous enough to sustain capillary action for more than a few tens of mm at most, and as long as the vertical surfaces of the lower walls are ventilated any tiny amount of moisture that does wick up though something like soft Victorian bricks will usually evaporate away from the surface before reaching floor level.

 

The two most common sources of damp are external penetration from the ground outside the building being higher than the floor level, allowing moisture to penetrate sideways, and leakage from defective gutters, downpipes or other drains that allows water to run down or into walls. 

 

Checking that the ground all around the house is at least 150mm below the internal floor level would be quick and easy, as should checking that all the gutters and rainwater goods are in good condition, and not leaking or overflowing.  Making sure all underfloor vents (airbricks I suspect) are clear would also make sense.

 

Rot only grows when the conditions are right, and that means damp, usually.  "dry rot" is really a misnomer, as the fungus needs moisture to survive - dry the area out and it will die.

 

There are other things to look at, but right now I'd hold off from suggesting any form of damp proof course injections or wall treatment, as the best fix will be to find a way to keep the lower walls dry (I'm assuming from the description that there is a suspended timber ground floor).

 

One other thing to check might be the height of the local water table, as there is a suggestion it may be high.  A test pit fairly near the house, covered with a board for safety, and to prevent rain and evaporation from affecting things, might indicate just how high the water table is.  Knowing this will help in coming up with schemes to try to keep the lower walls of the house dry.

Edited September 20, 2017 by JSHarris

[MikeSharp01]

The Chimney sounds like it might be the key source of the problems because if it is blocked, and the capping is not watertight then water is building up in the blockage and this may be the whole source of the problem as its a big hole and ends up delivering water quite a way up the walls from which it can run a long away along lintels and the like - we had a defective hood on our chimney and we had dark stains about 6 feet from the chimney, once we fixed it the whole lot dried out. If next door have theirs blocked then this won't be helping your side of the wall either.

[daiking]

55 minutes ago, JSHarris said:

I think the first thing is to find out, for certain, where the damp is coming from.  "Rising damp" isn't at all common, as very few building materials are  porous enough to sustain capillary action for more than a few tens of mm at most, and as long as the vertical surfaces of the lower walls are ventilated any tiny amount of moisture that does wick up though something like soft Victorian bricks will usually evaporate away from the surface before reaching floor level.

 

The two most common sources of damp are external penetration from the ground outside the building being higher than the floor level, allowing moisture to penetrate sideways, and leakage from defective gutters, downpipes or other drains that allows water to run down or into walls. 

 

Checking that the ground all around the house is at least 150mm below the internal floor level would be quick and easy, as should checking that all the gutters and rainwater goods are in good condition, and not leaking or overflowing.  Making sure all underfloor vents (airbricks I suspect) are clear would also make sense.

 

Rot only grows when the conditions are right, and that means damp, usually.  "dry rot" is really a misnomer, as the fungus needs moisture to survive - dry the area out and it will die.

 

There are other things to look at, but right now I'd hold off from suggesting any form of damp proof course injections or wall treatment, as the best fix will be to find a way to keep the lower walls dry (I'm assuming from the description that there is a suspended timber ground floor).

 

One other thing to check might be the height of the local water table, as there is a suggestion it may be high.  A test pit fairly near the house, covered with a board for safety, and to prevent rain and evaporation from affecting things, might indicate just how high the water table is.  Knowing this will help in coming up with schemes to try to keep the lower walls of the house dry.

 

Yes it is a suspended floor but not a void you can work in without lifting the floor unfortunately. The groundwater level is high locally. The gardens are all boggy but not every house on the street has this problem.

 

It was thought the original plaster was bridging the 'damp into the house so this was replaced specifically with a break however the 'damp' is rising up the plaster again. I've seen your previous posts about damp and how material are not porous enough. All I can say is I don't know. Whatever the problem is that is causing damp focused on this party wall needs to be resolved.

 

The house has a side and rear extension and conservatory. It predates the online planning system and with what I know about the house, its fair to assume its done to dodgy standard. I expect that the under floor ventilation is now less than adequate due to those previous changes - but he has previously told me its ok. I wonder if the rear conservatory may also be contributing to these woes. IIRC its lower than the house so could possibly be causing part of the damp bridge.

 

The dry rot is a recurring problem so replacement of the worst timber and treatment of the remaining timber seems inevitable.  My friend, like my wife, is a Scorpion so does not believe in extended investigation. So if someone says its damp and rot, that's what will get fixed and if the actual problem gets fixed in the process then that's good fortune.

[daiking]

56 minutes ago, MikeSharp01 said:

The Chimney sounds like it might be the key source of the problems because if it is blocked, and the capping is not watertight then water is building up in the blockage and this may be the whole source of the problem as its a big hole and ends up delivering water quite a way up the walls from which it can run a long away along lintels and the like - we had a defective hood on our chimney and we had dark stains about 6 feet from the chimney, once we fixed it the whole lot dried out. If next door have theirs blocked then this won't be helping your side of the wall either.

 

It does and they did something (not very intrusive) with the chimneys original but that hasn't been enough if they are the problem. It is suggested they clear the chimneys properly this time so if this is the cause it should get resolved in the overall blitz.

[Onoff]

There's not a bfo water main nearby that's been leaking for years is there?

 

[Triassic]

Also worth checking the gutters are working and not overflowing and constantly  wetting the exterior wall in the damp area. A neighbour had a damp patch and this was traced to a leaking leaf flashing, this allowed water to trickle down inside the cavity wall. So worth checking the roof for loose flashing and defective tiles.

[Ian]

1 hour ago, daiking said:

 

The house has a side and rear extension and conservatory. It predates the online planning system and with what I know about the house, its fair to assume its done to dodgy standard. I expect that the under floor ventilation is now less than adequate due to those previous changes - but he has previously told me its ok. I wonder if the rear conservatory may also be contributing to these woes. IIRC its lower than the house so could possibly be causing part of the damp bridge.

 

Rear extensions are a common cause of dry rot in cases like the one you describe. The problem occurs when the continuity of the under floor ventilation system of the original house from front to back is broken by the extension. The original house will have had air bricks front and back and continuity between the two needs maintaining - this requirement for ventilation continuity is often ignored when a modern extension is added - they often have concrete slab floors rather than suspended timber.

[daiking]

1 hour ago, Onoff said:

There's not a bfo water main nearby that's been leaking for years is there?

 

 

No idea, think its just the area unfortunately

 

1 hour ago, Triassic said:

Also worth checking the gutters are working and not overflowing and constantly  wetting the exterior wall in the damp area. A neighbour had a damp patch and this was traced to a leaking leaf flashing, this allowed water to trickle down inside the cavity wall. So worth checking the roof for loose flashing and defective tiles.

 

There have also been issues with the upstairs bay window roof bit that has been fixed since he's been in there. But unlikely to be still causing problems with the party wall.

 

45 minutes ago, Ian said:

Rear extensions are a common cause of dry rot in cases like the one you describe. The problem occurs when the continuity of the under floor ventilation system of the original house from front to back is broken by the extension. The original house will have had air bricks front and back and continuity between the two needs maintaining - this requirement for ventilation continuity is often ignored when a modern extension is added - they often have concrete slab floors rather than suspended timber.

 

I have said it in the past but don't think I got listened to. As I said this extension has been there for 20+ years we think. plenty of time to cause problems when the ground is never particularly dry

[Jeremy Harris]

99% of the time damp in houses comes as a consequence of either penetration or condensation, in my view, so the fix is to find where the moisture is coming from. 

 

Given there is a rear extension, then, as above, the chances are that the underfloor ventilation in the older part of the house may have been degraded by the blocking of air bricks, leading to condensation in and around the floor timbers, which is then causing the dry rot.

 

There's a high probability of the cause being penetrating moisture, though, from gutters, flashing or even leaks coming through from next door.  My experience of living in and doing up old places years ago was that damp was always from penetration in every place we lived that had a problem.  We had one place where the building society insisted on the house having a silicone injection "damp proof course" to fix damp in plaster at the lower edge of one wall.  We had no choice but to do it, but it didn't fix the problem.  Not surprising, as the walls were solid granite, a stone that's as near as dammit  impermeable.  The problem was that, like a lot of old cottages, the ceilings were too low, so instead of raising them the floor had been dug out and a concrete floor laid a fair bit lower.  The result was that the ground level at the front of the house, where the damp problem was, was around 100mm above the floor level.  The fix was easy; dig a narrow trench all along that wall on the outside, to a depth that was a few hundred mm below the internal floor level and fill it with gravel, to create a French drain.  This worked a treat, and the problem went away, to the point that when we sold the house a couple of years later, the surveyor for the purchasers expressed surprise that the walls were all dry according to his meter (I'm convinced some surveyors get a back-hander from the damp course injection people.........).

 

I've seen water coming in from bad flashing over poor render, running down inside the pitched roof of an extension and filling the extension cavity wall with over a foot of water inside.  It was only when we took a window out and shone a torch down the cavity that we saw all the water and we ended up ripping all the ceilings down in order to find where it was tracking in, as there was nothing obvious outside.  Once we found the source indoors, climbing up on the roof revealed flash band flashing stuck to render that was all loose.  A leaking gutter on the house roof above was letting water in behind the render, where it was running down behind the dodgy flashing until it hit the wall plate for the new extension, where it then ran down the rafters and dripped into the cavity wall on the outer side of the extension.  There were no weep vents, so the cavity just filled up with water.

Edited September 20, 2017 by JSHarris

[Simplysimon]

7 hours ago, JSHarris said:

"dry rot" is really a misnomer, as the fungus needs moisture to survive - dry the area out and it will die.

 

 

unfortunately not, there is sufficient moisture in the timber, even the cellulose is sufficient to allow dry rot to continue. it will grow through brick walls and everything 1m past the last visible signs of the mycllium needs to be removed (carefully) and burnt. upon replacing the timbers, they need to be treated, new dpc and kept well away from brickwork. as stated outside ground level needs to be 150mm below inside floor level.

[Jeremy Harris]

On 9/20/2017 at 20:04, Simplysimon said:

unfortunately not, there is sufficient moisture in the timber, even the cellulose is sufficient to allow dry rot to continue. it will grow through brick walls and everything 1m past the last visible signs of the mycllium needs to be removed (carefully) and burnt. upon replacing the timbers, they need to be treated, new dpc and kept well away from brickwork. as stated outside ground level needs to be 150mm below inside floor level.

 

If the timber is dry (specifically, a moisture content of under about 20%) then dry rot cannot grow.  20% is quite moist, the sort of moisture level that timbers in a poorly ventilated underfloor void might sit at, or above.  However, keep the moisture level of the timber down below the sort of moisture content of typical, as-supplied, kiln-dried timber (around 8% to 10%) and dry rot can neither establish nor survive. 

 

When the timber dries out to about 15% moisture content dry rot can remain dormant, but not grow, so there is a marginal condition where timber can remain infected, but not grow or develop.  Once the moisture level in the timber creeps up to about 19%, the dormant fungus starts to grow again, but doesn't really start to spread and produce fruiting bodies until the moisture content has crept up above 20%.

[Ferdinand]

@Daiking, as a strategic thing they need also to deal with next door being empty. This is a huge issue now.

 

Write to the Council Empty Homes team, or report it here:

https://www.gov.uk/report-derelict-abandoned-building

 

Or to You Spot Property:

http://youspotproperty.com/

 

Or make an offer to buy it, even.

 

Ferdinand

Edited September 21, 2017 by Ferdinand

[Jeremy Harris]

Once all the obvious causes of moisture penetration in the house have been looked at and ruled out, I wonder if the problem could be coming from the empty place next door?

 

Might be worth asking the current owner of the empty place if they will allow a surveyor in to see if there is a problem.  If they won't, then I wonder if it's possible, legally, to gain access to an empty attached property in order to inspect for things like water leakage that could be causing problems to the adjacent property?

[Simplysimon]

On 9/20/2017 at 21:18, JSHarris said:

 

If the timber is dry (specifically, a moisture content of under about 20%) then dry rot cannot grow.  20% is quite moist, the sort of moisture level that timbers in a poorly ventilated underfloor void might sit at, or above.  However, keep the moisture level of the timber down below the sort of moisture content of typical, as-supplied, kiln-dried timber (around 8% to 10%) and dry rot can neither establish nor survive. 

 

When the timber dries out to about 15% moisture content dry rot can remain dormant, but not grow, so there is a marginal condition where timber can remain infected, but not grow or develop.  Once the moisture level in the timber creeps up to about 19%, the dormant fungus starts to grow again, but doesn't really start to spread and produce fruiting bodies until the moisture content has crept up above 20%.

 

Having done a few dry rot repairs, i certainly wouldn't trust it not to spread if the source of moisture was found and rectified and the mc of the timber to be reduced. i've seen dry rot in timber and brickwork where there was no damp but had spread from a damp area which had been removed and repaired.

[Brickie]

I have no experience of dealing with it so all I can offer is what I was taught at college-the absolute key to prevention is ventilation. 

The spores are present in the air,lack of airflow is what allows them to settle & thrive (so we were taught.)

[Jeremy Harris]

7 hours ago, Simplysimon said:

having done a few dry rot repairs, i certainly wouldn't trust it not to spread if the source of moisture was found and rectified and the mc of the timber to be reduced. i've seen dry rot in timber and brickwork where there was no damp but had spread from a damp area which had been removed and repaired.

 

 

For once, the Wikipedia entry is reasonably spot on with regard to the physiology of "dry rot" and gives a pretty accurate account of the moisture levels needed for survival and growth.  These match up reasonably well with those in the reference book I bought years ago, when we were doing up old cottages, that I quoted in the previous post : https://en.wikipedia.org/wiki/Dry_rot

 

I agree that the key is getting the moisture content of the timber down below the ~15% needed for the fungus to lie dormant, but with no source of moisture available and good ventilation it's usually possible to get covered timber down below about 12% or so.  At that moisture level it's unlikely the fungus could survive, even in a dormant state.

 

Having said that, although "dry rot" spores are pretty much everywhere, from natural decay of timber in woodlands, hedges etc, there is likely to be a greater concentration of spores in areas where there has been an outbreak, so removing and burning all affected timber and treating the surrounding area with a fungicide before fitting replacements would seem a sensible precaution.

 

The bottom line here is that as long as moisture is present then there is a risk of rot, so the key to resolving the problem is getting rid of the source of the moisture.  If it's condensation, then ventilation needs to be improved, if it's seepage leaking in from a defect than the source needs to be found and eliminated.

[SteamyTea]

To reduce condensation by ventilation quickly and, initially, cheaply, could you not stick a fan in the underfloor void?

 

[Ferdinand]

1 hour ago, SteamyTea said:

To reduce condensation by ventilation quickly and, initially, cheaply, could you not stick a fan in the underfloor void?

 

 

Yes.

 

Chatting with the professional disaster recovery chappie who sold me those dehumidifiers last week, he said this was a standard technique to provide a short term fix underfloor.

 

It also makes it easier to see where the water is coming from, of course.

 

If is is inaccessible then a length of flexible duct can be used to channel the air from the heater.

 

F

[SteamyTea]

Seems a good thing to try out first.

 

Someone, and I think it may have been @joe90, fitted some pipes with a venturi on the top of them to draw out damp.

That seemed to be a good idea.

 

[joe90]

2 minutes ago, SteamyTea said:

Seems a good thing to try out first.

 

Someone, and I think it may have been @joe90, fitted some pipes with a venturi on the top of them to draw out damp.

That seemed to be a good idea.

 

#

Not me Nick. I had rot in a corner of our current house and found a shared rainwater drain between us and next door was blocked (it was in their garden), cleared it relaced the wood and all sorted.