Of the new siding jobs Iíve been involved with, itís been a tossup as to the number of times the old siding was removed first, versus the number of times the new siding was simply put over the old. However, normally when simply putting new vinyl siding over old asbestos or cedar siding, usually furring strips are nailed vertically over the siding to provide a flat surface to nail the new siding to. Also, sometimes the client request that new insulation panels be placed between old and new siding.
The first step is to determine if there is any other siding under the vinyl. One way to possibly improve your guess without removing anything is to look at your windows. With only one layer of siding, the window frames usually stick out Ĺ" to 1" or more. When a second layer is added, and especially if firing strips and insulation are used, this raises the surface and the window frames become flush, or even a little indented. This is not an absolute, however. They may have been capped with aluminum, something people often do to both make the windows maintenance-free, and to build up the frames after re-siding.
If you have no old siding underneath, then thereís no problem. If you have, chances are you have firing strips, too. It is also possible that the old siding is not made with asbestos, and that is something your municipality may be able to tell you.
Now, the next step is largely dependent on what you plan to do. If you already have firing strips, and you simply want to put a different new siding over the house, you need only to remove the old "new" siding, leaving the firing strips in place, then use them (the furring strips) to attach a different siding. You see, the firing strips are nailed through the old asbestos siding, but the new siding is nailed only to the firing strips. The only snag here is that it may be difficult to go with a vertical siding since it would be going in the same direction as the furring strips.
The remaining issues are your addition, when you will need to cut through all siding materials, and, of course, what if you find you have old siding underneath, but no furring strips.
All still may not be lost. The house next to my beach house in NJ was rebuilt this summer. Many have asbestos siding. Mine does, and was covered with new siding, using firing strips. Next door they opted to remove everything, and local codes did not require special crews. I checked this since they were ripping away on the weekends while I and my family were around. The regular contractors did the work. They wore masks and gloves, and had to haul away the siding in plastic bags. I think even a special dumping permit was required, but thatís it. Apparently asbestos in shingles have a far lesser danger then in other applications. However, even though the township had no reason to worry, we stayed away from the work and kept our windows closed.
If you have asbestos siding, the bottom line is to check with your municipality to see what needs to be done. This is one of those situations I would heed their advice.