Roofing/sweating attic

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Question
here is my story my attic is sweating making the outside walls wet i have four roof vents,two end vents and 8 soften vents  i'm lost the roof is a 6/12 pitch tell me do i need more vents ?

Answer
Robert,
Without knowing the actual sizes of the opening for the vents, and the square footage of the attic space it is a difficult question to answer. Here is a link to a good deal of information regarding attic ventilation http://www.airvent.com/pdf/literature/PAVbooklet.pdf - this is from a ventilation manufacturer so there is a bit of salesmanship for their products, however the information is well written.
We are learning more and more that the combination of gable end vents, along with ridge and eave vents, actually cause airflow issues and we recommend that the gable end vents be removed from the equation - this can be as simple as installing something on the attic side of the vent to prevent airflow. This will force the eave and ridge vents to work with each other.
First calculate the attic space in square feet by taking the length and width of the footprint. This area is divided by 150 to give you the net-free-ventilation-area (NFVA) that is required for the space. This amount should be divided by 2 (one-half for the ridge and one-half for the eave).
Now you can calculate the amount of soffit venting (if they are traditional round "bird-block" type vents you can measure one and count the quantity), and the ridge vents (depending on the size - the vent may say on it what it is). The ridge vents are based on the size of the throat venting the space. Measure the diameter of the throat and calculate it based on 3.1415*(one-half of the diameter or the radius)*(one-half of the diameter or the radius) - this calculating the area of the circle. For example - if you measure the diameter of the throat of the RV is 8" you will take one-half of the diameter (4")* one-half of the diameter (4") for a total of 16"*pi (3.1415) for a total of 50 square inches of NFVA. Count the number of ridge vents and you now know the ridge ventilation, eave ventilation and how much total you need.
These numbers will let you know if there is enough ventilation.
Sorry for the long answer - and the math, however this is the only way to properly determine if the ventilation is adequate.
Thanks for asking - Aaron

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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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