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Tim S

coughed up some electrons that declared:

Hi Chris,

The fungus is unquestionably a brown rot but as dry rot is also a
brown rot that does not help!
The photographs have most of the characteristics of wet rot and none
of dry rot. The white part looks to me like a sporophore of C. puteana
(one of the wet rots).

OK

The reasons for my opinion a
a superficial hard outer skin about 0.5 to 1.0 mm thick

Check. That was what I found for the next 8" or so beyond the totally gone
bit. Looked OK, but poking a chisel in showed the core to be rotted.

the absence of obvious hypal strands
the absence of visible mycelial strands
the confined location
the characteristics of the location (in a roof timber without the
necessary lime mortar for dry rot)
the history of past leaks

OK.

To answer and dispel some of the comments and assertions made by
others
Serpula (with an "e") lacrymans has no requirement for a high
temperature and most strains have their optimum at 26 C and are
controlled/killed only a few degrees above that - hence the lack of it
in the outside timbers of south facing windows

This is a north facing roof. Interestingly, I've measured 38C in the roof
voids on the southern facing side, during the height of summer.

Coniophora - cerebella/puteana actually has a higher optimum growth
temperature

You only have to remove unsound timber if the timber cannot fulfil its
structural role
I concur with the opinion that if there is a bit of rot and it is not
fulfilling any structural role it can be left in

Whew! As I said, the mostly good bit on the far left would be a sod to
remove as it goes behind a wall.

It is good sensible practice to isolate from timber with a dpc and
essential to instal ventiation and cross flow of air with cross
battening if you can

Yes - I was going to put the new section of plate on a DPC. I'll be sure to
put plenty of ventilation in the fascia - the wind will be able to blow up
into the main roof from this flat roof, and ultimately out some other
vents.

Use a thin long drill bit to check for hidden decay in any rafters
timbers about which you are concerned

Good idea.

Use only Tanalised replacements and dip treat overnight any cut end
grain
Put the tanalised end near the brick and the on-site treated end in
the room

OK

It is not worth "sloshing" any fungicide arouond - complete waste of
money and not reasonable in a coshh assessement. Immersion of cut ends
is the only effective use needed

Strands are for the purpose of conduction of nutrients from the hyphal
front not water to it. The strands are thought to have evolved to
reduce water loss in this process. Water at the hyphal front is
abstracted from the atmosphere not along strands
This was published in 1981 by DH Jennings at the University of
Liverpool using C 14 glucose to follow the nutrients - mostly in
trehalose. The conclusion was that one needed 95% RH for DR to
flourish.

Ah. So prior to then, a lot of misbelief was floating around.

Meow2 is correct but that does not fix your structural problem or
prevent recurrence if there is a new leak

Dry rot can only continue to "eat your house" (after the water source
has been fixed) if the interstices are at an RH of greater than 95%
and that only happens when the masonry is very wet and acts as a
reservoir. it also has to be alkaline as cement mortar does not suppor
the dry rot. This is not common so most dry rot dies when the water
source is fixed. That is most - not all!!!
If, however, you have active dehumidifiction you will cure it and
after a year at normal ~RT it will die

I do not agree with Andrew G that the location is perfect for dry rot
for the reasons cited above and specifically absence of lime mortar in
the roof where the sporophore/mycelium is and the absence mortar to
act as a reservoir

It does not carry water from one site to the other - read the Jennings
paper.

There are plenty of fungicides available - how about boron for a kick
off - but I agree that non is needed for sloshing. All on the market
have passed efficacy tests or they would not get the licence!

OK

I shall be interested to know which Parliamentary Act requires one to
cut out a metre beyond as I have served on various committees such as
the BWP(D)A / HSE consulation group prior to the introcuction of COSHH
in the late 70s and am familiar with COPR, BRE digest 299 and BRs and
have been working both academically (my thesis was at ICST on
hemicellulose degradation by fungi) and practically since the late 60s
and am unaware of such a law. Indeed I have spent most of the last 35
years promoting the complete opposite and opposing the con-men who
propose such rubbish

I've heard everything from a foot to 3 feet - mostly I assumed from
companies offering remedial work!

Many thanks indeed for such an informed reply.

This sure could form a good Wiki entry

Cheers

Tim