Like sullen teens, these trees are throwing shade, and now there’s moss on the roof

Plus, tips for insulating an attic to boost the life of your roof and air-conditioning units.

Moss can grow under the shingles, shortening their life span. Adobe Stock

By Mark Philben -- Globe Correspondent

July 31, 2024

Q. Although we’ve lived in our house for 30 years, moss has been growing on the porch roof in recent years, and it’s visible from the street and upper-floor windows. Will it damage the shingles, and should we remove it?

G.C., Brookline

A. Gina, moss needs a shady area to grow, so I’m guessing that maybe the trees around your porch have grown and are throwing more shade. Whatever the cause, the moss can create problems and should be addressed. For one thing, it acts like a sponge and holds moisture, which is never good against the house. It can also grow up under the shingles, albeit slowly, so you want to take care of it in a timely manner. It’s not difficult to deal with, but you do not want to go at it aggressively or you can damage the shingles. The larger pieces can be broomed off. Then have the roof treated with an algicide solution, or, better yet, a vinegar-based solution, which is more eco-friendly. You want to be mindful of plantings under the roofline with either application: Hose them down before and after the treatment.

There is an old trick we have used without fail. At the top of the roofline, presumably against the house, install a strip of copper or zinc in such a way as to have 2-3 inches exposed to the rains. The chemicals in the metal will wash onto the roof, and these will keep at bay the fungi and algae that cause moss and lichens to form. Good luck!

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Q. Hi, Mark. My attic is very hot in the summer and cold with some frost on the rafters, particularly on the side that gets the sun last. I have AC and don’t like that it’s probably working harder. The insulation is scant on the floor of my attic, and my electrician will fill the gaps where the recessed lighting is. I don’t have soffits or a ridge vent, and the roof is only six years old. There are working, or hardly working, gable vents at the ends of the house, which is a ranch that dates to 1948. I have lived here for 50 years. Everyone I speak to wants to sell me something, anything, but I know it won’t take care of the problem. Some say leave it alone. They all say it’s condensation. The only thing I’ve had done in the past few years was repoint my chimney and waterproof. What should I do?

P.L., Lynn

A. Phil, I feel bad saying this, but the reason people are trying to sell you something is because, well, you probably should be buying some solution to the problem. It sounds as if you have the worst of all scenarios: A poorly vented attic with AC equipment up there is going to take years off the air handler. It is working extremely hard to overcome the heat in the attic. I am going to guess that the ducts are not sealed and insulated quite up to par, adding to your woes. The heat buildup in the attic will also take a toll on your new roof, shortening the life span of the shingles. In the winter, the scant insulation on the floor of the attic will allow a significant amount of moist heat to escape into the space, which will allow that condensation to form on the roof boards and rafters. It also won’t help your heating bills or carbon footprint.

It is not a cheap solution, but you would benefit greatly from having the attic roof and gable walls insulated with closed cell icynene, especially since you now have a newer roof. Done properly, this will change the thermal envelope of the house, keeping the attic at a steady temperature year round. This will add years onto your AC and roof shingles, getting you some payback.

At the very least, you should get the floor of the attic properly insulated so you have the winter side of things covered. It sounds as if you have the recessed light code under control. Be sure all of your vents are connected to an outside vent. You should also make sure your ducts are properly air sealed and insulated. This will help somewhat with the performance and quality of the cold air in the summer when the system is struggling against the heat.

Mark Philben is the project development manager at Charlie Allen Renovations in Cambridge. Send your questions to [email protected]. Questions are subject to editing.