So you have a mossy roof?

While it’s surely beautiful, as your home inspector I’m tasked with the job of informing you to remove the moss from your roof. Now why is that you ask? Well, moss holds a lot of moisture, and won’t allow your roof to dry out in these areas, reducing the lifespan of your roof. Although there should be adequate protection at your primary roofing substrate (asphalt shingles, tile, steel, etc.), sustained, elevated levels of moisture may work beneath this substrate, reaching your underlayment. Overtime, this too can fail, leading to roof leaks, decking failure, and potential microbial growth.

Moss will most often take hold in the most shaded areas of your roof that remain the most damp. This might be under the cover of a large Oak, or the north facing roof, either way it should be removed. Depending on the pitch of your roof, most home owners prefer to hire this job out, but if you’re like me, and enjoy walking roofs, you may want to tackle this job yourself. Of course, it should go without saying, you should use adequate fall protection when working on any roof.

First, I recommend removing the largest portions of moss off your roof, light sweeping can usually tackle this job, for more difficult areas, you can use your hands.

Next, most roofing manufacturers recommend spraying down the roof with a bleach and water mixture and allowing to sit for a few minutes. I recommend roughly 1 part bleach to 3-4 parts water. Once adequate time has passed you can lightly rinse the roof with a hose, making sure not to direct water up under the shingles.

This should kill off the moss shortly. For more problematic reoccurring areas I recommend installing a zinc, lead, or copper strip at the ridge. This will prevent the further growth of moss, lichen, and mildew.

As usual, Tom Silva from This Old House has a great video on accomplishing all of this as well which I’ve included.