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Roofing/exessive mosture in ttic

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Question
I have a steel roof 4" to the foot,installed over strapped trusses.
In winter when it gets really cold (5 degrees F), frost builds on the underside of the steel. Then when the temperature reaches above freezing, the frost melts.  The water runs thru the fiberglass insulation and stains the ceiling interior.
To my knowledge the are NO vents-any where in the attic.
Except the ridges in the steel that go the length of each panel
and possibly the ridge cap.
The area consists of 600 sq. ft.
I am considering a fan with humidity control (and temp. also).
Probably a 14", with louvers to keep blowing snow out.
To bring outside air into the attic.
Maybe no controls---just a switch at eye level to turn on the fan when temp. reaches 32F in winter (for about 4 hours in winter)---And on hot summer afternoons.
WHADAYA THINK?   john sims  hope you can help

Answer
John,
The fan will likely help the moisture issue - this sounds like a typical condensation issue. The lack of intakes is an issue. Ideally you would like to have a chimney effect where there are intakes at the eaves, with exhaust at the ridge. Is this in your residence, or is this a shop or warehouse that has been converted to occupied space? The fan should be utilized to draw the moisture laden air from the attic space to the exterior to exhaust.
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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