I have a double wide and want to put a metal roof over existing shingles, I have had two different bids, one with vapor lock and one without, is the vapor lock just an added expense that is not really needed to still have a good roof when we are finished

I had a very large double wide mobile home in South Florida years ago that I had a metal roof over put on it. I had the thick white rigid insulating foam put on first and then the metal roof. That house became instantly cooler in the summer and warmer in the winter and of course the roof never leaked again (the original reason for the roof over). The white metal roofover was coated with special white material that was literally cool to the touch regardless how how the summer sun got.

For the extra money involved, why wouldn't you want more insulation when most of the heat gain and heat loss is in the roof anyway? I'd go for it and have it added.

And yes, my roof over was so well insulated I couldn't hear the rain unless it was coming down in torrents as the insulation really made a difference.

Also, be sure to get free gutters and downspouts thrown into the deal while you're at it. I had them added for free when I got my roof over. The gutters are good to keep water from intruding around the tops of your windows and doors. This can cause wall damage and ultimately floor damage.

clevins, another reason for the vapor barrier is so the shingle roof system and the substrate don't deteriorate and cause your metal roof to become unstable. It is well worth the price.