Metal Roofing With No Decking Or Underlayment

Gentlemen, I have recently purchased a home that has exactly the metal roof installed exactly as pictured above (with blown in insulation on the ceiling below). Aside from discussion about weather it is a proper way to build a home; I ask you this: If you owned a home with the metal roof installed this way, how would you address it? What insulation would add? I’m going to complete an extensive remodel on the property, how could we address it best? I do not want to remove the roofing and reinstall with decking because of the cost. Thanks in advance for your ideas.

Get a technician to do a blower door test and determine how well the attic is air sealed from the rest of the home. Make sure to run a probe in to the attic to test for any attic depressurization. You don’t want leakage from the conditioned area of the home to get into the attic. Do a search “air sealing attic” as to what air sealing entails.

Make sure there is enough attic insulation, after air sealing the attic.

Make sure there is adequate attic ventilation, calculate the square inches of venting against the square footage of the ceiling. Usually the 1/300 rule applies. Make sure the ventilation in the attic is balanced between the soffit and ridge.

If you’re in a cold climate, you should consulat with an energy audit technician or a ventilation specialist.

Thanks Michael.
I should have included that I’m in Central Texas (Austin).

Your comments are really appreciated and make perfect sense. Follow up question: Is there any case for adding insulation to the back of the metal roof? Spray foam or otherwise?

Roof sheathing has several important purposes. It adds structural rigidity to the rafters to prevent racking or spreading. With an impermeable underlayment applied over the decking, it provides a drainage plane to carry off the condensation that otherwise collects on, and drips from, the underbelly of your metal roof covering onto your sensitive building materials below.

IMO, closed cell spray foam on the attic side of the panels is prudent to prevent condensation when the attic is filled with warm and relatively moist air, and the colder outside air is cooling the steel roof panels.

I have no direct experience with applying spray foam to steel roofing, so consult with an installer. In your climate the foam will be directly exposed to the hot temperature of the steel in the summer heat, maybe or maybe not an issue of concern.

Thanks so much for that. Really appreciate it. Thanks David, I purchased the house as is, so unfortunately I didn’t have the option of adding roof sheathing. The home was built in 1994 and the attic, blown insulation and even the rafters and Purlins show now sign of any water. I’m guessing because the house has huge amounts of ventilation (soffits, ridge line and very large areas of venting on the sides at top of gables it must keep the air in the attic the same as the outside most of the time. I do want to improve the rigidity, insulation performance and seal up the envelope of the conditioned space below during the remodel. I need to make lemonaid out of lemons here, aside from this issue the house is in great shape for its age and will make a nice remodel if I can figure out this one large issue.

I’ll inquire about spray foam direct to the metal roofing from the attic side with installers, curious if anyone here has any experience with that? I also plan to add a dehumidifier to my HVAC system as well.

Bingo!! !!

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Most common underlayment i see for metal roofs is skip plank sheathing. The OPs picture shows they skipped quite a few planks!

Obviously even the “skipped plank” sheathing with no vapor barrier underlayment will expose pockets of lower-dewpoint metal roofing, allowing the rising humidity-laden warmer air escaping from the heated space below to become entrapped and condense on the cool metal underbelly of the metal.