Wet rot or dry rot?

[Tim S]

Hi all,

Lots of work at the Bungalow today. All went well, until this, though:

if the phots are enough for someone to be able to cast an opinion on whether it's dry or wet rot?

These are the timbers underneath a lead flat roof, on the side of the building (which is otherwise hipped roofed).

Looks more like wet rot to me - but how can I be sure it's not dry rot?

If it's wet rot, then I can replace the visible section of wall plate and one flat roof rafter (which is separate to the main roof rafters) and one ceiling joist.

If it's dry rot, then I'm scared... Presumably that means new flat roof time, due to having to cut back 2-3 feet from the affected areas?

More background:

I didn't see any "cotton wool" nor fruiting bodies. Not sure what the white staining is, but it's not hairy.

The neighbour told me that the roof used to be felted, and was leaded 10-15 years back - presumably there could have been a serious leak then. It's generally dry now.

The rafter has rotted completely at the end, and is apparantly all right, otherwise *except* that the core has rotted for about another 8" (needed to jab a chisel in to discover that).

The wall plate is totally gone a foot either side, but neighbouring rafters seem fine. The wall plate has bottom half rot for all the visible parts, but on the far left, it's petered down to perhaps only 1/8" is dodgey.

Looks like the water got into the inner wall leaf, then rotted the wall plate from beneath.

The planks supporting the lead seem solid and as you can see, not problems at all at the other end, where the main hipped roof rafters sit.

Thanks *very* much in advance :(

Cheers

Tim

[RubberBiker]

AIUI the diamonding pattern in the timber is characteristic of wet rot and, as you say, the only remedial action required should be to cut out and replace the affected areas. So long as the source of dampness has been stopped, ther should be no more problems. Was that an enclosed roof void with no ventilation?

[Tim S]

RubberBiker coughed up some electrons that declared:

Yea! Then I won't worry if the odd millimeter or so of the base of the wall plate is rotton to the far left then - it would be a right PITA to replace that bit as it disappears behind various things.

Replacing the bit that disappears off the right side (over the end external

11" wall) will be bad enough, but I think I can wiggle/hack that out once I've acrow-propped the roof up and relieved the load. There's only one further rafter beyond the right side and it feels sound to my fingers, though I can't actually see it.

I'll stick some DPM under the new section of wall plate for good measure.

It has - probably 10+ years back.

Sort of. It is open to the roof voids in the main house via a 2" gap over the main wall plate on the inside wall, but not to the outside directly. This area is going to be a shower room, so I knew I needed to take the plasterboard off in order to insulate, vapour seal and re-panel with aqua-panel or similar - otherwise I'd get a ton of moisture going up into that space.

I'll be adding ventilators into the fascia too (no soffits in that part).

Is it worth sloshing some fungicide around too?

Thanks very much :)

Cheers

Tim

PS

I should be grateful - despite the house having had some abuse over the years, this is the first bit of serious rot I've come across, apart from the soffits - but they always go eventually. I'll be re-doing them in a couple of years.

[Rob G]

Tim AFAIK the characteristic of dry rot is that the mycellium will grow out from the initial place of infection to seek moisture. If there is a centre here - the rotted area - I would have expected dry rot in the intervening 10 years to have spread out from that seeking moisture and rotting the timbers in the process. The other factor is that dry rot requires a degree of warmth hence the problem with adding CH to old buildings - if this roof space is dry and 'cold' then any DR spores won't have had an opportunity to develop.

One of the best examples of DR I've seen was in an old building that had wooden warm air ducts for it's CH - it also had a cavity constructed wall with heather insulation. Sadly there was a water pipe leak and DR developed in the ducting where the fruiting bodies were large - was transmitted round the building and got into the cavity insulation. I think in the end the building was flattened.

Anyhow I would, as you suggest, slosh some suitable anti-fungal stuff around.

All the best and I well understand your worries. Rob

[Tim S]

Rob G coughed up some electrons that declared:

That's very interesting - didn't know about dry rot not liking cold. Regarding the 10 years - I would have expected serious devastation too, from dry rot in that time, which gave me hope.

The only time I've actually seen dry rot, was in a window frame and surrounding wall when I was a lad, so only vague memories...

Thanks :)

Tim

[John Rumm]

Yup I would agree - almost certainly not dry rot. None of the tell tales like (fruiting bodies etc), no filaments with dripping water, and none of the typical crazing/shrinkage visible where the wood shrinks and cracks like a dry river bed as the cellulose gets digested.

As long as you make sure no new water can get it, then that should fix it.

Its not as scary as people make out... The main requirement is to cut off the source of water. Ventilation helps as well. Cut away anything obviously rotten and a bit beyond (2 - 3 feet is probably excessive), spray everythign in the are with a decent dry rot treatment.

Quite possible.

Found something similar in the under stairs cupboard here. 9" solid wall with waterproof render over and no ventilation at the far end of the cupboard (about 12' deep!) resulted in condensation on the wall. Since the wall was impermeable, this just ran down behind the skirting and into the floor, when it then tracked along the under side of the floor boards until it hit the joist. It rotted a joist (which was also placed parallel and too close to the outside wall), plus the end of another couple that met it on sleeper walls.

My fix was to foam 50mm of celotex to the inside of the wall, replace the dodgy bits of joist, and fit another 9 air bricks to help ventilate the (substantial) under floor void - see if we can dry out the damp bits)

In the words of the HHGTTG, Don't Panic!

[John Rumm]

I thought they grew out from a wet place to seek new timber - conducting the moisture with them to otherwise dry timber (hence the name)?

[Andrew Mawson]

though:

plate and

leaded 10-15

dodgey.

That looks identical to the dry rot fungus I had in my last house before Rentokil replaced timbers and sprayed. Surpula lacrymans iirc but it was 25 years ago!

AWEM

[Tim S]

Andrew Mawson coughed up some electrons that declared:

Oh - the concensus is no longer 100%. :(

[The Natural Philosopher]

well it hardly matters which it is, since both need damp to flourish and both need entirely removing, and remedial action to remove the wetness applied, as well a replacement of structurally deficient timbers.

A good fungicide is also a good idea as well.

[Tim S]

The Natural Philosopher coughed up some electrons that declared:

So would it matter if a section of generally sound, but inaccessible timber with a trace of rot is left in place (the alternative being to strip the roof, which is lead)?

For wet rot, I would say yes.

For dry rot, I'm still a bit contaminated by the 70's notion that one hint of dry rot left will eat your house alive.

Where did that idea come from? Was it scaremongering by rot-killing firms?

Cheers Tim

[meow2222]

If theres no water getting to the wood, it isnt going to rot any more. That simple.

If you realy want to know which it is, this should clear it up:

[Tim S]

[e-mail] coughed up some electrons that declared:

OK - I'm happy to believe that now, but old habits die hard - hope you understand!

posted the start of this thread!

[Andrew Gabriel]

[Andy Burns]

[Tim S]

Andrew Gabriel coughed up some electrons that declared:

I took it to be, after the first couple of sentences. Sadly, it *is* an accurate reflection on the results of earnest research into the subject on google. There seems to be very little deliberate effort at parody and a great deal of bollocks on the web.

The problem with something like this is the FUD factor - *if* dry rot can consume your house, even after the initial water ingress is cured (by supposedly generating its own water as a by product of eating the wood), then you scare people into expensive work just to get a 10 year guarantee.

OTOH, if that were true, given my roof has been dry for 10+ years, then it should have continued to eat at least the entire rafter, not stopped after about 8".

My concern is that once this ceiling is put back, there's no easy way to monitor the situation, which amplifies the risk of getting it wrong.

But I'll go with the general opinion that the sodding mushrooms are dead/inactive, and I'll just replace structurally deficient timber as is practical, lob some fungicide in because it's cheap and why not, and reconstruct things so that damp can never form there again.

Sound reasonable?

Cheers

Tim

[meow2222]

Perfectly. I also note that on roofs like that, even if one joist fails completely the result isnt anything serious, just a little minor local sag, hence some folk wouldn't do anything about it.

Rot fungi are like any other fungal plant, they need water to survive. Without that, they're going nowhere.

NT

[Andrew Gabriel]

I've written a few articles about dry rot if you search on Google. I agreed with the comments others already made that this doesn't look like dry rot from what I can see in the pictures. However, it's perfectly possible to have dry rot with no fruiting bodies, and it's possible you can't see the mycellium, so it's impossible to completely rule it out. The pictures aren't easy to examine in detail. The location looks perfect for dry rot though.

It needs a source of moisture (doesn't need to be visible water, a damp wall will do). It will carry the water from one site to another, in order to infect timber which wouldn't otherwise be susceptable, hence its ability to infect dry timber, unlike wet rot. If the water source is cut off, it will stop growing. There could still be enough moisture leaking in from the house to stop it from completely dying though.

It's not true.

Keeping water out, and ventilation are the important things. Secondly, you can try protecting new timber against contact with walls. Nowadays, joist hangers are often used which are much better in this respect. The other technique is to wrap the joist ends which are in close contact with walls (although the wrapping could be bad if you end up with water streaming in, by keeping it in the timber).

I couldn't make out any mushrooms in the pics. Were there some?

You won't be able to get any fungicide nowadays which will protect against anything, and there never was one which was particularly effective against dry rot (it's one of the most resistant fungi). The only protection was to make the whole area toxic with heavy metals, but that's no longer allowed.

[The Natural Philosopher]

If you mange to halt the fungus growth and th wood is adequately sound, thats all that matters.

[Tim S]

The Natural Philosopher coughed up some electrons that declared:

Thanks for the re-assurance :)

I'll order the wood. As the room's a shower area, I'll make sure the ceiling is totally vapour proof (that's why I pulled the plasterboard off in the first place!).

Cheers

Tim