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Roofing/Metal roofing condensation prevention

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Question
I am building a 40x40 barn style cabin with vaulted ceilings that is heated and cooled. I am planning on using galvalume roofing and would like to know the details of the proper roof installation procedure to minimize condensation issues. It will be built in central Mississippi very hot and humid--very few cold days.

Answer
Todd,
The short answer is that it all depends. If you are installing all of the insulation above the substrate, then you should not have an issue with condensation. If the insulation is below the substrate, then you should leave a 1" airspace between the substrate and the top of the insulation. Each enclosed attic space must have 1:150 venting - 1square foot for each 150 square foot of attic space - this may be the space between the rafters/substrate/drywall - any closed space. Make sure that you don't have any "dead air spaces" where ventilation is not provided. Use a 50/50 ratio of intake and exhaust (eave and ridge). I am a proponent of continuous eave and ridge vents. You should verify the correct amount of insulation based on the local codes, and verify that the dew point in winter and summer conditions all fall within the insulation and you should be fine.
The rule of thumb - insulate above the substrate, if below the substrate, insure proper ventilation and your condensation issues should be mitigated.
Good luck!
Aaron

Roofing

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Aaron Nelson

Expertise

All types of questions with regard to roofing, waterproofing and sheet metal. This includes commercial and residential buildings, along with the various aspects of the construction means and methods, ventilation, steep-slope or low-slope, code requirements, installation errors and other such problems

Experience

I started in roofing fabricating and installing sheet metal flashings out of high school for a large commercial contractor. I worked for the same contractor in the office estimating and project managing commercial project for 10 years. I left the construction side of roofing and now work as a roof consultant, which I have been doing for 8-years.

Organizations
RCI, Inc.

Education/Credentials
I am a Registered Roof Consultant (RRC) and a Registered Roof Observer (RRO) through RCI, Inc. RCI is a international group of building envelope professionals. I am an approved instructor for RCI educational programs.

Past/Present Clients
We have worked with many local school districts, insurance companies, HOA's, building management companies, and we have a national client with buildings located throughout the US.

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