Enclosed Unheated Porch - Crawl Space Question - Vapor Barrier - Rotting Wood

This old house had a porch with storm windows that for years caused much agony. It leaked everytime it rained hard and required replacing wood and painting every few years.
A contractor was hired last year and replaced a lot of wood and installed replacement windows. The windows didn't have the extra piece like a new window, he did it like a replacement window. He felt the rotting wood was caused by a bad roof. The roofing, gutters and siding were replaced and the grading around the porch was changed. Today, the porch is air tight and covered with aluminum trim and there have been no leaks that I can see. But I noticed the caulking splitting here and there and the aluminum trim changed shape a bit. I've had to caulk after one year. I think there is a moisture problem.
I looked under the porch and found there was no insulation or vapor barrier. How much do you think the lack of a vapor barrier adds to this problem? If I were to add a barrier only, could I just attach it to bottom of the joists? Your prayers are always welcome.
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extra piece ? do you mean exterior casing? a 'new construction' window is not designed to be installed like a replacement window.

the
But
probably used "phenoseal" caulk (soon it will turn yellow) instead of exterior silicone. aluminum trim installed correctly requires NO caulking.

the aluminum trim has expanded and is starting to buckle (probably from NOT pre-drilling with an 1/8" bit before nailing the trim on).

barrier.
If
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and
installed
Yes, that's what I meant. I wonder about the installation. If it's faulty.

In fact, that's exactly the stuff he said he used!

That's interesting. On the vertical pieces there was expansion at the bottom or something so that the instead of being flat the piece is now concave when viewed from the side.

No comment here?
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Sorry if I'm being a pisher here, but it seems to me that you are suffering the consequences of cheap home repair work, not lack of a simple vapor barrier beneath the porch.
I think stuff like this is covered by the old adage: Pay me now or pay me later.
AJS
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problem?
the
With life comes experience. I wish I knew more about construction.
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