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TOPIC: Ventilation

Ventilation

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I have soffit and ridge venting with an 1 1/2" air space between my batt insulation and Reflectix radiant barrier.On top of that 1 1/2" thick purlins wich I'll externaly fasten galvinized roofing.The bottom of the panels will be sealed with closure strips and the tops sealed with a mesh "cobra vent". There is a crawl space in this roof.So,below the radiant barrier,my attic is vented by soffit and ridge,my question is,above the radiant barrier should I completely seal the air space or share the soffit and ridge vent.My thought is,keep the warm moist air escaping the living space away from the metal roof but also have outside air circulating under the metal by way of soffit to ridge.Someone told me that I should seal off the air space under the metal.My goal is to stop condensation leaking into the house.Today is 9/17,I plan on laying panels tomorrow,Please respond. Thanks Shawn
Guest User

9/17/2002
If you have built the house right then there should no warm air escapinging into the attic and causing condensation. You should have installed an air barrier to the inside of 6 mil poly with all joints and penetration sealed with caulk. I am not familiar with the Reflextix product but am assuming it is a foil faced foam core type product. The primary purpose of the underlayment is as a moisture barrier and unless you have a properly vented attic assembly it must allow air to pass through. Make sure you tape around any penetrations with a house wrap tape. I am assuming that you are using the vent mesh under your ridge cap as your ridge ventilation. The air space under the metal is better if it is vented. Make sure your underlayment as a 1" gap at the ridge and if possible add a vented closure at the eaves to help vent the 1 1/2" air space. Hope this helps.
Allan Reid
Dura-Loc Roofing Systems, Inc.

9/18/2002
DIY'ers installed a metal roof 2 years ago on a two story with attic crawlspace, 60 year old house. The old asphalt shingles were removed downe to the wood roof and the metal roof (dark brown) was installed over this. There are passive 12" by 12" vents in each end of the attice but in the summer the upper level of the house is extremly hot (100 to 120 degrees) even with 2 box fans blowing out through the east and west sides of the house. The upper story was warm in the summer but not to the point that you couldn't be up there. Did they goof or is this a common problem? Thanks
Guest User

1/23/2003
You need to somehow achieve airflow through the attic. This means that you have vents for intake and vents for outflow. One way to achieve this is to remove one of the box fans. Try to create airflow in the same direction as predominant winds, depending upon which direction the home is situated. Ideally, though, it would be nice to see soffit vents put in the eave overhangs and a ridge vent put into the roof. Yes, this will take some real effort and probably won't be easy. However, this create a situation where the soffit vents are the intakes and the ridge vent is the outflow. It is prett much proven to be the best way to achieve air movement in the attic. I would start by removing one of the box fans. Also, I would replace the other box fan with a temperature-controlled power attic fan intended for that purpose. Todd Miller
Todd Miller
Isaiah Industries, Inc.

1/24/2003