Metal Roof on an RV Shop

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August 1, 2023 at 12:00 a.m.

alextolle

Charles, a homeowner in Salem, Oregon, asked the following:

I am going to put on a metal roof on a RV-Shop building soon. I have a few questions. 
1. I've been told if I have installed a metal roof that will be screwed down, the gaskets will rot within 15 to 20 years and have to be replaced. Is this true? 
2. One installer want to use 15 to 30 lbs. felt paper. Is this a bad Idea? What is a good quality underlayment for metal roof? Synthetic? 
3. Should the installer use OSB sheeting or 1/2" to 5/8' plywood? 
4. Does the roof need to be vented. Told the best is a vent all along the roof line.

August 1, 2023 at 12:00 a.m.

alextolle
Below is what our roofing expert Bobby from Bliss Roofing had to say in response to your question:

  1. The type of panel you are referring to, is an agricultural panel which is an “exposed fastener” application. I would recommend a standing seam snap lock type of panel where the fasteners are concealed. An example would a Taylor Metal Product’s “Easy Lock” panel.
  2. Our practice is to use a “high temp” Ice & Water self-adhered underlayment for better protection however, 30lb felt is specified by the manufacturers.
  3. I would recommend ½” CDX plywood.
  4. The ridge should be continuously vented to create exhaust if there is an attic and make sure there is Intake created at the overhangs to max the exhaust.
 
Let me know if you have any more questions and thank you for reaching out.
August 1, 2023 at 12:01 a.m.

alextolle
Hello Charles,  
 
Below is what our roofing expert Chris from Simply Affordable Roofing had to say in response to your question:
I am going to put on a metal roof on a RV-Shop building soon. I have a few questions.
1. I've been told if I have installed a metal roof that will be screwed down, the gaskets will rot within 15 to 20 years and have to be replaced. Is this true?
There are 2 main types of metal roofs, standing seam and exposed fastener. Exposed fastener is typical for barns, shops and carports due to its lower cost. The drawback is the exposed fasteners are prone to failure before the roof itself wears out. This is due to movement in the panel, and UV exposure. A common maintenance item for these types of roof is to seal or replace fasteners after 10-20 years depending on conditions.
 
2. One installer want to use 15 to 30 lbs. felt paper. Is this a bad Idea? What is a good quality underlayment for metal roof? Synthetic? 
Asphalt based products should not be used under metal due to the extreme heat that the metal creates. It  will cause the asphalt in the felt to stick to the panel and tear. A quality synthetic underlayment or high temp ice and water shield is recommended.

3. Should the installer use OSB sheeting or 1/2" to 5/8' plywood?
This really depends on the intended use, location, and design of the roof. Does it need to support a high load like snow? If it is a simple shed roof with adequate pitch then OSB or ½ CDX plywood should suffice. Certain metal panels are designed to span across purlins eliminating the need for sheeting al together, but this depends on the application.

4. Does the roof need to be vented. Told the best is a vent all along the roof line.

Again, this depends. Is their going to be an attic space, or a sealed area? Generally, it is not a good idea to create a sealed off area where air cannot flow. Another important consideration is insulation and climate control. If the space is heated without proper insulation, you can create a condensation issue in the roof. This is something that should be professionally reviewed and designed to avoid costly issues.

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