John

Agree wholeheartedly that lichen will cause deterioration of the surface
on which it is growing.  The very fine fungal tendrils have to go
somewhere, and they work their way through the pore structure of the
material.  Similarly, there are without doubt organic acids released.
The timescale is relatively slow, and in our part of the world, the
deterioration of membrane roofing due to ultraviolet radiation and other
environmental factors is much faster than the rate of decay due to
lichen could ever be.

Another complicating factor would be if the membrane roof also happens
to contain asbestos fibres.  In that case, if the lichen has already
developed, then removal could lead to disturbance of loose fibres,
whereas leaving it alone means that it is still nicely bound in place. 

David West
Executive Director
internationalconservationservices
T:     +61 (2) 9417 3311
M:    +61 (411) 692 696
sustaining your heritage

-----Original Message-----
From: The listserv where the buildings do the talking
[mailto:[log in to unmask]] On Behalf Of John Leeke
Sent: Friday, 28 August 2009 9:46 PM
To: [log in to unmask]
Subject: [BP] mold on membrane roofing

 >>If it bothers you then there is a product you can get called moss off
or
some such that also works on lichen. At Home Depot it is too damned
expensive, but our local landscape shop has a product<<

Why support the petro-chemical corporations with your dollars? On sloped

roofs we have had good success keeping the mold, lichen and moss from 
growing by flashing the ridge with copper or lead. Even running a single

line of bare copper wire along just under the edge of the upper coarse 
of shingles can work. On one project we reused the old worn out copper 
screening from the windows, tacking a 3" wide strips along the ridge.

On a flat roof you might just put out a few scraps of copper or copper 
screening.

I have seen clear cut evidence that lichen and moss do consume and 
deteriorate the structure of asphalt shingles. It is well known that a 
thick moss does damage wood shingles, but that when it is wet and rainy 
the moss expands and can keep the shingles from leaking.

The strategy of homeowner insurance companies is to limit their coverage

and create excuses to drop policies on older houses. This is how the 
industry scrapes money out of poor homeowners to pay out on the big 
claims like the one on the World Trade Center. The insurance payout on 
that tragic fiasco shook the foundation of the entire insurance industry

world-wide, which figures it will take 40 years of bilking howmowners to

get their money back. I can't wait to see what they do when the 
crackerbox cardboard and plastic MacMansions start falling apart in 
about 10 years.

Then we will be growing moss on our cardboard roofs and harvesting it to

feed our kids. (those of us lucky enough to have a piece of cardboard to

live under.)

John (eating moss for breakfast, just to get in practice) Leeke

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