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TOPIC: Underlayment

Metal boathouse roof

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My boathouse is now finally under construction, and I am debating with the contractor over types of roofing underlayment and structure to be used. I have settled on dark green metal R channel (?) panels fastened to treated 2"x4" perlins. He strongly suggested going with a plywood deck, but I am thinking the open metal roof on top of the perlins will be sufficient. I plan to use pre-engineered treated trusses set 4' O.C., with a 6" bottom chord. This roof will be exposed to extremely hot weather here in Texas. Is the plywood deck really necessary or will the perlins be just as good? Will it be necessary to place the trusses at 24" O.C. rather than 48"? Thanks for your help.
Guest User

11/20/2002
I forgot to mention that this boathouse will be open-sided.
Guest User

11/20/2002
Like you I have a boat house in my back yard however mine is timber frame and must go through the winter months in Canada. I have however completed a few "Boat Ports" as we call them. I am first questioning why you are using pressure treated purlins and are you intending to put a ceiling in it. We have the biggest problems with birds roosting in the rafters and messing up the boats and the next largest problem is spiders who love the water. So most have either metal ceilings which are easy to wash the spiders off and keep the birds out or they line the ceiling with chicken wire mesh that keeps the birds out. As to your construction, if you put a metal ceiling in I would suggest strongly that you provide some good ventilation which will deal away with most of your condensation problems. I would however recommend a good underlayment. I do not see the need for plywood except to brace the trusses which is very important on a boat port as you have limited walls to brace the roof but minimal wind load to deal with. next you should be concerned with the PT strapping as it has copper in the treatment and could react with Galvalume if it becomes wet. I would suggest the plywood sheathing (not OSB) with a 30 lb felt underlayment. If you then close the ceiling put in Gable ventilators. Good Luck.
Allan Reid
Dura-Loc Roofing Systems, Inc.

11/21/2002