Q: We would appreciate your advice regarding our San Francisco home’s roof.

We have a 1915 Edwardian with a flat tar-and-gravel roof in one of the "sunny" San Francisco neighborhoods. We’ve had the home for a dozen years, and while we don’t know the date of the last roofing job, my husband thinks it’s time to reroof.

I would like some insulation on our top floor — insulation seems an afterthought in the house as a whole — and my husband is thinking of installing tubular skylights called Solar Tubes to bring light into the two north rooms of the house. There is some blown-in insulation — not sure how extensive because the access to the attic is via a small space I can barely poke my head into.

Last, we’ll add a solar-energy system, although we are not sure when. We’ve gotten several roofing-only quotes, most for typical tar and gravel, and find it hard to differentiate how the work is different from one to the next, except for a quote from a company that will do a "foam" roof, claiming it is superior and adds an R insulation factor, negating the need for insulation above the ceiling.

Here are my concerns:

1. We’ve not heard you mention foam roofs and are wondering if there are downsides we should be aware of.

2. What questions should we ask to determine whether one roofer is using a better method or materials than another? Are there warranties or items we should insist on?

3. While I agree more natural light would be nice, I’m not sold on the Solar Tubes. They don’t appear to have a way to shut them, and while we use the rooms for offices, they’re meant to be bedrooms. Once they’re installed I imagine they are difficult to remove.

4. What are your suggestions on how to add insulation? Can we keep what’s there now, even though we can’t tell how much is there or what it is? Can a roofer add more blown-in insulation from the roof, or is this a separate job for a different contractor?

A: We don’t have any experience with foam roofs. But we have done some research, and they look inviting. The only downside we’ve come across is that application is specialized and the number of applicators is somewhat limited.

Closed-cell sprayed polyurethane foam (SPF) is composed of two liquid components — isocyanate and a resin (or polyol) — that are pumped from separate containers and mixed in the nozzle of a spray gun at a 1-to-1 ratio. Upon combining them, a chemical reaction takes place and the mixture expands 20 or 30 times to form a solid, lightweight, monolithic closed-cell mass. When sprayed on a roof deck, it provides a roofing membrane with excellent water resistance and thermal insulation. …CONTINUED

You could be killing two birds with one stone if you go with a foam roof. You may not need added insulation in your attic area. A foam roof is dense. This density provides thermal resistance, also known as R-value. Foam roofing can be rated with an R-value of 6.25 per inch. Said another way, a roof requiring R19 insulation will receive about 3 inches of polyurethane foam.

Your tar-and-gravel roof is a good candidate for a foam roof system. The new roof can be applied over the old. Before the foam roof system is applied, all loose dirt and gravel must be removed and hauled away. The tar membrane must be secured to the roof deck. Deteriorated edge flashing and vent caps must be replaced. And low areas must be identified so they can be built up.

SPF spray is applied in a series of passes. Each pass is a single application of foam that can vary from 1/2 to 1 inch thick. Multiple passes are made to build up SPF roofs to the desired thickness.

Foam roofs are strong and durable. They can handle foot and construction traffic as well as other roofs. But SPF decomposes in the sunlight and dents easily, so it needs a protective elastomeric top coat. Elastomeric means that the coating must be able to stretch and return to its original shape.

Top coatings are sprayed on and can be acrylic, silicone, butyl rubber or various urethanes. Coatings are usually installed in three stages: a base coat, a middle coat and a final coat. Granules can be embedded into the mid- and top coat or only the top coat for added protection against ultraviolet radiation and mechanical damage, and to increase the system’s fire resistance.

If properly maintained, foam roofs are long-lasting. There is some maintenance, though. Every 10 or 15 years, depending on the type and amount of coating installed, the roof will need to be cleaned, primed and recoated. If this is done, then a good-quality SPF roof could last 50 years or longer.

Remember that when choosing a roofing contractor, longevity and experience count. Ask for a warranty and by all means compare them. But a warranty is only as good as the company giving it. Check its license with the Contractor’s License Board, check the bond, and get proof of worker’s comp and liability insurance.

Your final job is to ask for and check out references. That means go look at the job and talk to the owners. Foam roofing requires quality control by the mechanics doing the work. If the gun gets dirty or a hose gets clogged or any one of a hundred things goes wrong, the mechanics must be able to recognize the problem and be willing to shut down operations until the problems can be taken care of.

Pride in workmanship is an extremely important factor in a quality foam roof. If you go the foam route, choose a company that has been in business for a long time and look at jobs it’s done similar to yours.

We have no experience with roof-mounted solar panel energy systems but can tell you that the technology is always changing — monthly, it seems. We suggest that when you’re ready to install a solar-heating system, that’s the time to do your homework.

As far as Solar Tubes go, we like them. We suppose the determining factor will be the use of the room and if you have a day sleeper. If you opt for the Solar Tubes, install them when the new roof goes on.


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