How to remove moss/mold/mildew from roof

Q. We have moss/mold/mildew growing on shaded parts of the roof and would like to have it removed professionally. The shingled roof is 11 years old on our cape-style house with two dormers. We have done some research and are finding conflicting suggestions as to removing it. What can you recommend?

A. An extensive exposure to the sun is a good deterrent to the formation of algae and the growth of moss or lichen on any surface. But on surfaces receiving little or moderate sun exposure, the sun is not likely to prevent the growth of moss, lichen and algae.

The Asphalt Roofing Contractors Association simply recommends a gentle spray of equal parts water and bleach, followed with a gentle rinse. Some precautions are essential.

But since you plan on having your roof cleaned professionally, there are a few cautionary steps of which to be mindful. Most importantly, do not hire a contractor who uses pressure-washing, as it is most likely to damage the shingles and void any warranty left, even though these warranties usually pay little and are difficult to collect.

Check that the contractors you interview have liability insurance. Once you have selected one, ask for a certificate of insurance to make sure. Insurers can send you a copy upon the contractor's request. Ask for references and check them out.

The length of time a contractor has been cleaning roofs, and the more experience he or she has, is a good guide.

An experienced contractor is likely to insist on doing the entire roof and not just the stained areas, as the contrast between the untreated areas, having been affected by years of exposure to the elements, and the treated areas, now looking like new shingles, will be startling. This is a good sign of professionalism. But the ultimate choice is yours, and the contractor may ask you to sign a letter releasing him/her of any responsibility if you are unhappy with the contrast between the cleaned areas and the rest of the roof.

Some contractors get on the roof while others spray from the ground.

There are a number of cleaning solutions on the market that are quite effective and each contractor has his/her favorite. One of the most effective is Wet & Forget Outdoor (www.wetandforget.com.) It is ideal for DIYs and for use on decks and pavement to remove mold and mildew.

Q. We have a Pella Sun Room (no longer made) that has one ceiling window, and it has been compromised with a break in the seal. The other windows appear to be intact. We have had the Pella company look at replacing the panel or just the glass, but they do not seem interested.

In addition, we have had other glass dealers in the Burlington, Vermont, area who do not want to tackle this as well. We have seen windows in new construction that appear to have the same look as our windows. Is there a solution to this? Or do we need to replace the ceiling glass with another option?

A. Pella's response to your problem seems unprofessional and very poor business if they didn't explain why. Is it that replacements are no longer available?

Over the years, I have heard of similar stories, which is why I no longer recommend Pella products. It's a pity as we used to consider them top quality in the 1950s and '60s and installed many of them.

I am also surprised that glass specialty shops have not been responsive and not offered a reason for it.

I know that glass replacements on skylights have been installed by remodeling contractors; you may want to contact some of them until you find one willing and experienced in this work.

Q. My enclosed screened porch floor is made up of tightly joined Trex boards. There currently is no provision in the floor for removal of water or melted snow. The contractor that built the porch cautioned against putting an opening in the floor as it might be an invitation for bugs to get in. Is there some optimal way to put a hole or opening, incorporating a cover seal, into the floor to prevent bugs entering the porch? Thank you for your quick reply.

A. Is rain or snow such a problem that you need to have provisions for drainage in your covered porch? Many porches built over decades were built with a very slight slope and floored with tongue-and-grooved boards while others had no slope at all.

If this is a serious problem for you, an experienced contractor can cut a space with a saw and ease the rough edges with a router.

If bugs become a problem, which may not happen, fly screening can be stapled under the cuts between the joists - quite a chore - or off-the-shelf soffit venting used instead, which should be a lot easier to install.

Q. I just read your answer to a question in today's paper and I am concerned about my flower beds near my foundation. Is this really bad? I have no shrubs but do have a lot of perennials as you can see by the picture.

The foundation is installed properly for drainage and I have not had any experience with water in the basement in this 8-year-old house.

A. The reason I urge people not to have flower beds or bushes close to the foundation is that these beds are often humped and form a barrier to the proper drainage of rain and melting snow. The trapped water drains down against the foundation and, unless the foundation was backfilled with coarse material over a properly filtered and effective footing drainage system, it can build enough pressure and find its way into the basement or crawl space.

Moreover, these beds and shrubs are often heavily mulched, which holds moisture.

Since you have had no problems, it seems that all is well and I would not worry about it.

My recommendation to have a gently sloping grade with a healthy grass cover, and to keep flower beds a few feet away, is made for new construction or any work done to repair a leakage problem.

It is not always possible or practical to achieve this if the plantings are plentiful and valuable, and it may be possible to handle roof water in other ways.

Another advantage of putting flower beds and shrubs a few feet away from the foundation is that you can enjoy them from inside.

• Henri de Marne, a former remodeling contractor turned columnist and consultant, is the author of "About the House with Henri de Marne" (Upper Access Publishing). He continues to take questions from readers for this column and his website, www.henridemarne.com. Email questions to aboutthehouse@gmavt.net.