Foam roof a 2-for-1 deal?

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

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