Our roofing contractor put all the material for reshingling our roof, on our roof nearly 4 weeks ago. In that time the unprotected felt has been exposed to sun and rain. Can the felt be damaged?

As long as the felt is not torn by wind it should be fine.

Chuck

Yes it can. I am 57 years old and have spent a considerable part of my life in the roofing business.
First, if the heat wherever they are stored is high enough, the shingles will laminate to each other and when you tear them apart you will sometimes also tear of some much needed asphalt sealant which is a measured amount on each shingle. Not only does this damage the shingle but it may also have some warrantee implications. Tar paper should never be reused if it has been on the roof too long, after several days of hot and dry climate the moisture in the felt will equalize and it will not furnish the quality vapor barrier you expected.

Once it has gotten wet fis okay to leave uncovered overnightelt is no longer a vapor barrier and will probably buckle. It is okay to leave uncovered overnight but not much longer.

4 weeks! Wow!

I've been a tewksbury roofing contractor (http://www.mbmcarpentry.com/services/roofs) for almost 20 years and I, like others have said, wouldn't let it go one night, let alone 4 weeks. Now, if you had a synthetic felt, like deck armor, I would be saying something different.