Expert: Bruce E. Johnson - 8/2/2009

Question
QUESTION: I want to put a 1x2'skylight in a new shed roof I am working on. Rather than frame the opening and put on a skylight with the framing raised above the shingles, how bad an idea is it to put a sheet of 1/2" plexiglass OVER an opening in the plywood (extending about 4" opening - not sure if before or after paper is best), then flashing and shingling over the plexiglass?

Any help is appreciated. Thanks.

MEC

ANSWER: Hi MEC, I suppose it will work okay.  Try to layer the plexiglass with the shed of the shingles.  In other words lap over the plexiglass at the top and have the plexiglass lap over the shingles at the bottom.   Seal the edges of the plexiglass well with mastic and you should be okay.  I hope this information helps, feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Sounds like a plan, and thanks. I want to use flexible flashing around the plexiglass. I was thinking of screwing the plexiglass to the sheathing. How should I do the shingles on either side of the plexiglass? Should I continue the lapping down each side? Since the plexiglass will be a bit higher, will water try to run horizontally and under the shingles.

Thanks again!

MEC

Answer
Hi again MEC, I would run the shingles as normal down the edges of the plexiglass making sure to caulk between the shingle and the plexiglass with blackjack or some other roof flashing mastic. I hope this information helps, feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com