[Gerry Zagorski]

Installing a roof over an existing roof is pretty standard practice. The only thing you need to make sure of is you have no leaks to begin with. If you do have leaks you may need to tear the old roof off, replace repair and seal any flashing around vents and chimneys to stop the leaks and replace any rotted wood.

If your current roof does not have them, you also want to make sure you have either a ridge vent or roof fans and vents installed which will add to the life of your roof. That is pretty standard practice now and most companies will not warranty the roof with out them.

A few other reccomendations.
- Labor is probably the most expensive part of the job so it might make sense to spend a few more bucks on better shingles, 30 instead of 25 year, especially if you intend to stay in the house for a while.
- A lot of fly by night roofing companies out there. Make sure and choose one that has been around for a while and has a good standing with the Better Business Bureau. Personal reccomendations from people in your neihborhood is always a good source to find a reputable, local roofer.