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I am building a commercial building with a SIP's roof. I would like to use a metal roof. What would the recommended installation be for a screw down type? Should there be ventilation under the metal? Should I use 30lb felt? What type of screws would be best?
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Knowing your location and building use helps however I am assuming you are in a cold weather climate.
A proper roof assembly starting from the inside requires 1) an air barrier with a low perm rating, 2)Insulation, 3) Sheeting, 4) vented air space, 5)Moisture barrier and 6) Roof Covering.
The new IBC calls for a minimum of 1" vented air space under the roof covering on sloped roofs (unless assemblies are tested and approved otherwise).
Looking at your proposed assembly the SIPS provide a reasonable air barrier provided the joints are tight and sealed properly. I would advise a 6 mil poly air barrier over before the interior finish and caulk seal the laps and protrusions. Alternately if you were to leave it exposed prime it and apply two coats of a good quality oil base paint.
The SIPS provises good insulation so you are covered there. Minimum I would use as a moisture barrier is 30lb felt and I would use Ice and water shield up from the eaves and in any valleys.
Last is to choose a metal roof system that can be applied over strapping and provides for vertical air movement. Last then is to provide ventilation at the eaves and ridge. Depending on the style of roofing there are a number of options including vented closure strips if you are using vertical rib steel. If colour is not an issue remember that the whiter or lighter the colour the cooler the roof will be and help kepp the interior more comfortable and energy efficient.
Sounds like you have choosen a through fastened panel. Remember to make sure the base steel is G90 or AZ50 to provide protection and choose a good paint system. Once you have completed that then investigate fasteners. They all look close to the same but if you are putting on a long life roof then don't make the screws a weak point. There are a couple available at a reasonable cost that have zinc shafts and stainless heads with good quality rubber washers that come with long term warrannties. If you need names contact me directly. Hope this helps.
3/25/2003
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3/26/2003
Or copy this URL: https://www.metalroofing.com/spirit/comment/1741/find/