P Lyons wrote:Dale,
Thanks for that tip, I would have assumed the opposite.
I did assume that clearing moss would help a roof that was really too flat for 3 in 1 three tab shingles. I cleaned it off. Bad idea. Not only was there moss, that moss had trapped fine dust. When wet, it created a pretty good seal. There was sleight evidence of moisture before I cleaned the roof. After cleaning, we got some snow. Melting snow creates little dams which backed the
water up to the now clear sides. It leaked like a sieve. I tarped it and replaced it during good weather. Just to be sure of causation, I tried this on a few small sections of homes slated for demolition. I got the same result. Moss can destroy asphalt shingles. It must be dealt with regularly and early in the life of the roof. If a roof has already been badly neglected, it's best to leave it pretty much alone. It's OK to remove thick balls of moss from the lower edges of shingles if they are causing water back up. The stuff on the edges is best left alone on older asphalt.
This
thread shows how moss can preserve roofs that have a covering of
pea gravel.
Dale's 53 year old green roof. ---
https://permies.com/t/29729/green-building/Dale-year-green-roof --- Same plant --- totally different result.
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Here's a copy of my reply to your questions in that thread. --- Sorry for the delay P Lyons. I just now saw this. The only thing I would change about this plan is that I would use recycled, tight weave carpet as the protective layer beneath the membrane. Sometimes as
wood ages, sharp splinters can separate and poke upwards. Foot traffic on the roof can force the membrane against hazards. Don't use carpet that has been stapled. You will miss one. Use stuff that used carpet stripping along the edge. This is a free product, so cut out any questionable areas.
If the roof can handle the weight, a very thin layer of pea gravel could be added. Battens 3/4 inch thick, run horizontally across the roof would create little dams that could hold the gravel in place. They won't hold much gravel or water, just
enough to prevent the liner from blowing up and to work as needle dams. Hopefully moss will take hold and spread from these moist lines. Dust, bird
poop and sticks will accumulate. Don't try to cover the whole roof with gravel if weight is an issue. The 3/4 strip will easily back up a strip of gravel of that thickness at it's bottom edge and becoming progressively thinner going up. The roof will appear to have a dozen little terraces. Walk only on the clear areas immediately below battens where gravel does not gather. Use only nice round pea gravel. A misstep could cause sharp crushed gravel to puncture the membrane.
Don't try to stretch the membrane out. We don't want the weight of the organic layer to hold the membrane in perpetual tension.
I wouldn't glue it except possibly along the edge. weight alone should hold it in place.
Sun is the enemy of rubber. I would rake up plenty of needles and apply them before a rain and during a period of little wind. Moss can be gathered from the woods or from other areas. Try seeding a little. A small amount of grass clippings might help things to get started.
Once it is established, stay off of it. Pop up for inspections regularly, but mostly it should be admired from the ground or from the ladder.
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