TOPIC: I Have An Existing Metal Roof and Have A Question
Return to I Have An Existing Metal Roof and Have A Question
Return to Forum
I am considering putting on a 24ga standing seam roof. I only have gable vents on either end of the main house. A third gable vent is on the end of the house above the garage. so three gables and two exhaust fans in the main house close to the ridge that come on when the attic gets hot. The shakes have lasted almost 30 years. We are in a humid area in north east ohio. I am worried about condensation since I believe the shakes breathe more than the metal roof will. There is no evidence in the attic of any wet condition. I have blown in insulation that really holds the heat in the house. Do I have any cause for concern?
I do think that what you're describing will not meet code requirements. Keep in mind that code requirements are generally the bare minimum that is required, in this case, to avoid condensation or other not good situations. I do think that getting the ventilation up to code would be very wise. I assume that your standing seam will be on solid decking, not spaced sheathing. Spaced sheathing beneath a metal roof is a pretty big concern even with good ventilation. Here's an article that is a great resource in regards to ventilation: https://iibec.org/attic-ventilation-101/
Todd Thanks for the article. The standing seam will be on solid decking. The 3 gables are probably a total of 6 square feet of ventilation. How do I consider the electric fans (2 of them)? I believe you are suggesting that I get to work on putting in soffit vents
Think of ventilation as creating rivers of airflow. You really want a situation that creates airflow through the entire attic and does not leave any "dead zones" where moisture and heat will accumulate. Think also about always bathing the entire underside of your roof deck with fresh air. The best way to do this is usually with soffit vents for intake and a ridge vent for exhaust.
In looking closer at the soffits, I believe that I can get the minimum amount of airflow by adding them. One concern however is that there are a couple of sections at the eaves that are blocked by bay windows. This occurs in two areas with blocked footage representing about 12% of one side of eaves footage. If I put soffits everywhere but there, will this still remedy the situation? I would block off the gable vents and add ridge venting.
What can be done about that dead spot?
One other thing please. Would a bubblewrap reflective vapor barrier under the metal help insulate the wood in the attic from condensation. You commented to someone with an unvented attic space that a rigid foam underlayment would separate the metal roof from the wood below
I think you'd be fine even with the small areas blocked by the bay windows. Anything that creates a thermal break between the metal and the roof deck ultimately is helpful. The thermal break helps to reduce the transfer of cold from the roof surface to the roof deck. the bubble wrap type products do act as a thermal break. There are also entangled meshes available that serve a similar purpose but do not have the reflective material attached.
IS the bubble wrap enough using the current setup with gable vents and exhaust fans? one gable on the north and two on the south. I am getting about 60% of the minimum ventilation. I don't have alot of heat loss into the attic. The roof is always the last in the area to have snow on it
Unfortunately, on such things, the answer depends a lot upon habits inside the house and how much ambient moisture is inside the living space. I though would prefer to not try to make a thermal break substitute for ventilation.
We tend to keep our house on the cool side. The moisture level never really exceeds 50% in the summer and is 40% is in the winter. We have new a/c and furnace that we keep the fan running all the time. 73degrees summer daytime and 68 winter. 66 at night for both.
40% in the winter is certainly on the high end. My opinion is unchanged but there is a chance you'd be fine without ventilation.
If you would like to reply to this thread, please
If you do not have an Ask the Experts forum user account,