You might wonder why with all the snow and ice covering roofs around the state of Minnesota that we're talking about moss.  That's a very good question. As roofing contractors, we're always thinking about what is coming up in the next season so that we can help homeowners be prepared.  And for those who live here in the Twin Cities, you know that means spring rains.  Wet roofs that don't get a lot of full sunlight can develop moss, algae, and scum.

Sometimes as we drive around the Minneapolis and St. Paul area we see roofs that have greenish or gray patches, and we realize it's often because the owners don't know about the importance of maintaining their asphalt roofs.  But issues like this can't be ignored because it is more than just ugly.  Moss, algae, or other gunky build-up on a roof can actually cut its useful life - up to as much as a third.  And considering that asphalt roofs in our area rarely last more than 20 years, that's a pretty significant impact.

Moss, mold, and the like send out tiny little fibers called rhizomes.  These are miniscule threads that burrow down into the roofing substrate, eventually loosening the roofing granules that protect the shingles from cracking and drying out.  And what's worse, moss absorbs as much as 20 times its weight in moisture, so you're getting a lot of water held in place on a compromised roof.  That could lead to damage to not just the asphalt shingles but the underlayment and roofing structure.  Wet insulation in the attic and ceiling leaks may also occur.

This may cause problems with your insurance company, by the way.  Homeowners insurance companies may send someone out from time to time to inspect the condition of the homes they insure.  It may also happen if you're refinancing.  A dirty roof may result in you getting a notice to get it cleaned or get your policy cancelled.

So, now that you know it's a problem, what do you do to take care of it?  First off, we don't recommend that homeowners tackle roof cleaning themselves.  Without proper fall protection equipment, the right tools, and expertise, it's a very unsafe project even for the most experienced DIYer.

Yet we see people up on their roofs on the weekends, either with pressure washers or brooms and scrapers, attempting to get rid of the mess.  DO NOT USE ANY OF THESE ON AN ASPHALT ROOF.  And if you are consulting with a roof cleaner who says they will use any of these methods, drop them like a hot potato and look for another company. All you'll get is more roof damage, more roofing granules going down your downspouts, and a roof that is now in worse shape than it was before.

The best answer is to hire a professional roof cleaning company that will apply a commercial spray designed specifically for this purpose. And keep in mind you will need to do this every couple of years - anywhere from every other year to 5 or 6, depending on your situation.  Each roof is different.  Another plus of having this done is you've got a roofing professional with sharp eyes on your roof that can catch problems when they are easy to repair.

Finally, we'd like to recommend that if your roof is prone to developing moss or algae that you consider replacing it with a steel or other metal roof.  A steel roof is impervious to those damaging little rhizomes; there's nothing for them to cling to, and debris washes right off.  So if your roof's days are numbered, why not call us today for a free estimate on having a new metal roof installed before those spring rains bring more problems?

Quarve Contracting, Inc./Metal Roofing & Siding of Minnesota is a licensed Minnesota roofing and siding company specializing in steel roofs and siding.  We serve the entire Minneapolis and St. Paul metro area as well as outlying communities.