Moss: problem?

[david shapiro]

When I see anything growing on or in part of a building, be it only ivy, I get uneasy. The images shown are on a single-layer roof, normal pitch, about 7 years old, over an unconditioned attic with a ridge vent. http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=35088&stc=1http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=35089&stc=1http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=35090&stc=1http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=35091&stc=1

Why the moss?

Is it likely putting the roof at risk?

If so, what remedy do you see?

Thanks

[tkaiser1]

1. Is this on the north side?
2. Shaded by trees?
3. How many inches of rain/year?

I lived in the Willamette Valley of western Oregon for 30-ish years where moss on the north side, especially with conditions 1 & 2, mentioned above, is very common. An additional condition we had was long periods of overcast in the fall-winter-spring so that sun exposure to damp rooves was a very seasonal thing. We had an average 30+ inches of rain /year. The building's ventilation wasn't relevant, as far as I could see.

For treatments, in the short term, there are chemical compounds that can be sprinkled to kill the moss. Then it needs to be removed (gentle brooming off works) and go on to prevention. Zinc strips are available in 25' rolls and according to the manufacturer's info, are good for about 15' below the strip. They come with neoprene gasketed nails for installation. I placed the strip just below the ridge shingles and found them to be quite effective.

In short, I haven't seen it to be anything to be worried about; it's a product of conditions.



When I see anything growing on or in part of a building, be it only ivy, I get uneasy. The images shown are on a single-layer roof, normal pitch, about 7 years old, over an unconditioned attic with a ridge vent. http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=35088&stc=1http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=35089&stc=1http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=35090&stc=1http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=35091&stc=1

Why the moss?

Is it likely putting the roof at risk?

If so, what remedy do you see?

Thanks

[david shapiro]

Thanks, Tim.

The darker photos are E-SE, the light the opposite side of the house.
Annual rainfall about 43 in, wettest in May, 4.5 in.
Definitely some tree shading.

But bottom line, if it's not doing any harm, I'm fine with the aesthetic. If you don't zinc there's a reason for treatment, I won't fuss.

And HNY, Tim and all.

[tkaiser1]

David, HNY to you & yours!

In the long term, moss does decrease the overall life of a roof, I don't have any data to support that, but it's *common knowledge* in the rainy Pacific NorthWET. (the proper descriptor for the west side of the Cascades)

Overall, I'd say it's not an immediate problem.

Best!


Thanks, Tim.

The darker photos are E-SE, the light the opposite side of the house.
Annual rainfall about 43 in, wettest in May, 4.5 in.
Definitely some tree shading.

But bottom line, if it's not doing any harm, I'm fine with the aesthetic. If you don't zinc there's a reason for treatment, I won't fuss.

And HNY, Tim and all.

[Jerry Peck]

But bottom line, if it's not doing any harm, ...

I've always heard, and been told (by roofers and manufacturers) that the moss degrades the shingles. It keeps excess moisture in the shingles (that's why it even grows there) and as it grows in the slots and along the bottom edges, it also lifts shingles, allowing even more wind and moisture in.

[david shapiro]

Thank you, Jerry and Tim

I see there were earlier posts on related subject, but the links don't work for me. When I hit them, I get messages such as this:
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Warning: Cannot modify header information - headers already sent by (output started at [path]/includes/class_core.php:5615) in [path]/includes/functions.php on line 4513

I had wondered about the darker look of the shingles near the bottom courses, where the moss is most abundant.

What I'm understanding is that moss grows best where there's excess moisture, and it in turn holds moisture at those locations.

It sounds as though unless we have the trees removed, or the house and occupants relocated, (neither being part of our game plan) we have the option of tacking Zn strips up high to poison the moss. Anything additional, besides the mechanical removal?

[Jerry Peck]

... we have the option of tacking Zn strips up high to poison the moss. Anything additional, besides the mechanical removal?

You can install the zinc strips (which are basically just strips of metal flashing material) up under the edges of the shingles without the nails (using plastic roofing cement to hold them in place), sure, nails are mechanically attaching the strips to stay in place better, but each nail (even with a gasketed nail) is a new potential leak location - just a thought.

If the moss is mostly near the lower courses of shingles, why not just install a few strips 5 feet or so above the worst moss areas and periodically check it to see how it works before goin all out and installing more strips (why push the 15' spacing?).

I've also heard that lead works will too (the reason roof areas below lead VTR flashings are typically the cleanest looking on roofs), but with lead being more expensive, and with the lead poisonings potential on the plants rain runoff and at downspout discharges, why go with lead?

[david shapiro]

I'm agreed, Jerry.

I've had excellent success in the past with "rubber-collared" ring-shank nails. However, I see a rather low likelihood that these strips will either slide down or get ripped off by a windstorm. And if they were exposed to wind that might do so, I'd surely want to inspect nailed strips afterwards, too. So I probably will use construction adhesive, with a couple of nails at the overhangs where they won't be penetrating the house.

The odds are that I will look for an outfit that will sell me a few hundred feet of the stuff. The cleaning and installation will be the hassle, not the materials expense, and I can afford slight overkill in the hope that they'll do the job till my wife and I are both dead.

[Jerry Peck]

So I probably will use construction adhesive,

I wouldn't count on construction adhesive to bond adequately to asphalt shingles, especially damp/wet asphalt shingles.

If you find construction adhesive which is made to glue asphalt shingles to the roof instead of being nailed down, then use it ... but I'd wonder why roofers didn't use that instead of nails if that exists.

Even for gluing concrete tile to concrete tile, a special adhesive was developed 0 Ohio Sealants made some roof tile adhesive years ago ... (checking to see if they still do) ... yep: https://www.ositough.com/en/products/view-all-products/rt600.html and its Technical Data Sheet: https://dm.henkel-dam.com/is/content/henkel/tds-us-osi-construction-adhesive-rt600-voc-adhesive-2014-07-31

I don't see anything about using it for asphalt shingles, I would call them first.

[BARRY ADAIR]

when applying narrow zinc strips
dry fit under shingle tabs
apply occasional dabs of polyurethane sealant on the shingle tabs underside
press in to assure good contact
better brands cure in damp/wet conditions. no nails required & come in clear
working with shorter sections at a time is much better than trying to get an entire roll under the tabs
assure to leave loose fit at slots to allow for runoff

[david shapiro]

I wouldn't count on construction adhesive to bond adequately to asphalt shingles, especially damp/wet asphalt shingles.

I don't see anything about using it for asphalt shingles, I would call them first.

I've emailed them. OSI's "Quad" construction adhesive calls itself "synthetic rubber"; their "gutter micro," I can't tell. I don't see any product on their web site that is identified for this use. It could be that they have none, or it could be that the market's small enough they don't see the use as worth mentioning.

However, following Barry's suggestions, I looked and readily found polyurethane roof and flashing sealant than claims UV resistance, mold resistance, permanent flexibility, and 20 year lifespan--possibly even when exposed. Thanks, Barry, for that suggestion, and for the tip about not interfering with flow.

[david shapiro]

Both OSI and Loctite (as well as lepage) are owned by Henkel, which replied " Unfortunately, Henkel does not have a product to secure zinc strips to asphalt shingles. Please check with the manufacture of the of the zinc strips for recommendation."

That rules out Loctite's PLS30 polyurethane roofing/gutter sealant.

[Jerry Peck]

Contact the shingle manufacturer and ask them what would be the best adhesive to use.

[Joe Reilly]

Just tossing my 2 cents worth in, how many layers of shingles are on, as typical anything over 2-3 can cause a weight issue as the trusses are not built for the weight, could the moss and the excess water they hold create an issue for weight , hence structural issues ?

[david shapiro]

Thanks, Joe. Nah, it's a single-layer, no pullet roof. Jerry, I might contact the shingle manufacturer. however, Tremco responded to me recommending one of their silicone adhesives as doing well both with zinc and with asphalt--but recommending an initial-adhesion test, and using their primer if he silicone is unreliable.

Barry, what do you think of this? I was quite surprised that the manufacturer of OSI snd Loctite recommended against polyurethane. (I haven't heard back yet from 3M about theirs.)

[BARRY ADAIR]

dap mfr/warehouse is literally 5.5 miles from me

their polyurethane & ultra clear has been and is performing well on our props after 20+ yrs & other past const projects for much longer

ymmv

[david shapiro]

Thank you, Barry. They seem worth trying.

David