Is this dry rot?

[Roger Mills]

At the end of my pond I have a small roughly semi-circular brick enclosure about 3' across and 2' high which houses a filter and air pump. It has a flat 'roof' consisting of a piece of WPB, covered with roofing felt which is wrapped round the edges and stapled on the underside. This just sits on the brickwork, and supports a few pot plants for decoration.

This 'roof' has been in poor condition for a while, and the WPB has started to go a bit soggy due either to water penetrating the felt or condensation on the underside - not sure which. [I mentioned this a while ago in a thread about cement board].

When I removed the 'roof' yesterday, it was in a much worse state than when last lifted. There was a thick layer (probably 40mm) of what looked very much like orange rockwool over much of the underside. Some of this had also started to attach itself to the brickwork. Growing in this 'rockwool' (mainly on the brickwork) were a number of white objects which looked similar to button mushrooms.

I've scraped this stuff off the roof but the WPB is seriously disintegrating. I've tried to remove it from the brickwork but that is clinging on quite tightly.

Obviously, I need to replace the roof and I need to kill the remnants of the stuff still inside the chamber. A few questions . . .

1. Does this description sound like dry rot? If not, what?

1. How do I kill it in order to prevent it spreading to the new roof?

2. What material should I use for the new roof? Anything involving timber seems likely to suffer a similar fate. Cement board seems like a possibility - but it needs to survive being mounted horizontally with pot plants on it, and I need to be able to cut it to the right shape - roughly semi-circular but probably better described as an unsymmetrical shield shape.

[Dave Liquorice]

Pictures are very useful for IDing things. tinypic and post the direct link to the image(s).

Rots need the right dampness to survive make it too dry or too wet and they die (though may go dormant rather than actually die). Plenty of rot killers out there once you've reasonably well identified what you have choose the appropriate killer.

Proper WBP ply is almost indestructible. From your description I suspect the failure of the current bit is due to insufficient ventilation to the chamber and/or water running round the folded under and stapled felt into the chamber or top of walls. Allowing the underside to get into right dampness comfort zone for your rot.

This time put slim spacers between the wall and roof board, say around 3/8" and don't fold the felt under. Instead leave the felt hanging down an 1" or so from the bottom side of the board and fix with galvanised clouts into the edge. Boars about 1/2 to 3/4" overside all round, this allows air to flow freely but will stop all but the worst driven rain getting into the chamber.

A batten around the edge with the inner recess oversize as above with the felt covering it would avoid the vulnerability of the unsupported felt. The curved shape may present a challenge ...

[Mike Tomlinson]

En el artículo , Roger Mills escribió:

I'd scrape off what you can (be wary of tracking it into the house), and spray the remnants with neat bleach, then if you can leave it open for a few days to ventilate.

Pass

Whatever you use, it might be worth knocking out a couple of bricks and putting air vents in.

[meow2222]

Copper wire creates leachates that kill mould long term. Copper sulphate, ZnSO4, or short lived bleach kill short term.

New roof: plastic, cement/fibreglass board, fibre/bitumen board etc.

NT

[Tim Streater]

Did you mean CuSO4 ?

[Brian Gaff]

Or simply use plastic bits of that cellular stuff they use for conservatories. I'm sure on could join then together somehow. Brian

[Brian Gaff]

Yes keep the spores out of the house at all costs. If it finds a home it will eat the stuff its growing on, that is what fungi are for after all, waste not want not and all that.

Brian

[meow2222]

CuSO4 is copper sulphate

NT

[Tim Streater]

So you didn't mean CuSO4, you meant ZnSO4 which is Zinc Sulphate, yes?

[Dave Liquorice]

Probably not up to supporting the flower pots placed on top used to disguise the pump/filter house.

[meow2222]

CuSo4 is copper sulphate, and means copper sulphate ZnSO4 is zinc sulphate, and means zinc sulphate

[Tim Streater]

So when you wrote: "Copper sulphate, ZnSO4, or short lived bleach kill short term." then you were saying that either copper sulphate *or* zinc sulphate would do. As opposed to you making a typo, which is what I'm getting at.

[Nick Odell]

This suddenly brought to mind the warning from our school chemistry teacher.

An epitaph:

Little Johnny Dimwit Lies here for evermore For what he thought was H2O Was H2SO4

... which has absolutely nothing to do with the subject.

Carry on. As you were. Nick

[Roger Mills]

Yes, sorry - should have taken a photo before I destroyed the evidence!

The best I can do is this photo - taken after rescuing some of the offending material from the bin.

It clearly shows what the 'rockwool' type stuff looks like, plus one of the mushroom-type things.

I hope that helps to ID it!

[Tim Watts]

No - classic dry rot is when timber breaks up in a cubic fashion.

This does not mean it *isn;t* dry rot, but it sounds more like wet rot to me.

Dry it out and keep it that way.

There was a lot of panic about dry rot being able to eat your entire house, even the good bits. It can grow in damp masonry which allows it to spread further than you think.

However, I think a lot of the panic was unjustified.

Dry our and ventilate and maintain ventilation.

Soak it on some chemicals if you feel like it - won't do any harm.

Get rid of the rock wool. It's holding water and preventing air flow. This and the probably lack of exterior vents is almost certainly the cause of your problem.

Insulate with celotex, leaving a 2" air space betwene the top of the celotex and the bottom of the new OSB deck that you install.

Then ensure that you have *lots* of ventilation under the eaves directly into this space. 25mm effective continuous is a typical working figure.

If the roof section is short, you'll probably be OK if the air space is "blind". Ideally the ventilated space should lead on somewhere the air can blow into, eg cold loft space, or the ventilated part of a hipped roof.

I have 4 flat roofs. They are all done like this and I have seen inside them and they have no problems. Mine do ventilate though into the main roof though.

If you'd care to post some pictures of your roof edge outside I can probably recommnd some vents that will work - it can be fiddly sometimes to install vents that vent without letting in rain.

Essentially, your main choices are:

1) If you have an overhang of >100mm or so (ie a soffit), then install circular or strip soffit vents. I did this on my front bays.

2) My rear "bay" had about 2" overhang. I replaced the gutterboard 9red cedar) and installed a special strip vent on top of the gutterboard.

BCO approved - if fact it was his suggestion - I had not seen them before.

[Dave Liquorice]

Given the right conditions dry rot will travel through out a building. "Damp masonary" isn't particulary damp either, 20% once established and it will survive down to 15% which is "dry timber for burning" level...

Read the post and see the recent piccy the "rock wool" is the fungus and pretty impressive as well. Unless I'm way out with scale that fruiting body is an inch across. Can't help with ID though.

The roof isn't a flat roof to a building it's a cover over pond pump/filter kit.

[Roger Mills]

I would say that the head of the "mushroom" is about 15mm across. [The "rock wool" was lying on a pea gravel path when I photographed it].

Thanks for putting him straight!

[Tim Watts]

Bugger me...

Here's my bill of 0p for random thoughts - sue me! ;->

Seriously, clearly got to ventilate better - or use materials that cannot rot like metal, plastic or GRP.

[harryagain]

I would get rid of the wood and use a concrete paving slab. Problem solved.

Cast one yourself if neccessary, even in situ if awkward.

[Roger Mills]

Just to put a bit more meat on the bones, I've dug out some old photos taken at and just after installation time.

The top left photo shows the chamber with the lid off, with the filter and air pump inside. [From a ventilation point of view, the blue brick between the two pipes is no longer there - so there's plenty!]

The top right shows the back of the chamber - this time with the original lid on. You can judge the size from the bricks. [The lid which has just failed is the second one (in 12 years) and has a single piece of felt rather then the 2 over-lapping bits in the photo].

The bottom left shows an aerial (from a bedroom window) view of the whole thing before the water feature was added.

The bottom right shows the water feature - a fibreglass gunnera leaf which hides most of the chamber from the house and which acts as a mini fountain and waterfall - and a bird-bath. BTW, the heron is *real* - the bastard was after my fish! (The dove behind its beak isn't).

I totally agree with the need to make a new lid out of something which won't rot - but I'm still not sure what.

The polycarbonate stuff used for conservatory roofs which someone suggested wouldn't be strong enough, even though additional support is provided by two lengths of angle running side to side (but not shown in any of the photos).

Someone has suggested paving slabs - but they wouldn't be quite big enough, even if I butted two 900x600 slabs against each other before cutting them to shape (assuming I could!). Casting a slab in situ isn't on either, 'cos it needs to be able to be lifted off to get at the gubbins.

If I started with a rectangle of whatever material, it would need to be about 1500 x 1000.

In the old days, a large sheet of thickish asbestos would probably have done - but that's now taboo! What's the nearest equivalent?