Metal Roofing With No Decking Or Underlayment

Is it generally permissible (or even acceptable under Best Practices) to construct a SFR dwelling’s roof with no sheathing? I have seen it done this way on plenty of storage sheds and metal buildings. And I have seen plenty of metal roof coverings on SFR homes; but they have mostly been re-roofs over existing roofs with plywood decking, or new roofs with plywood decking. This particular roof has very lightweight metal covering. The gable endwall has plywood sheathing and vinyl cla

dding.

Solid sheathing is only required for shingles. From there, you will have to follow manufacturer guidelines. In my opinion, looks like a fine install from here in GA.

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I bet it’s gonna get real noisy in a hail storm!

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…not to mention the potential for sweating/condensation.

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Shouldn’t your metal roof have underlayment installed, per IBC 1507.4 ? And how about flashing, such as drip edge? I do not think this roof meets residential roof standards.

Like Larry said, that roof is going to have a big condensation problem, I’ve seen it.
I would let the buyer know that this roof is not built right, and is likely to have problems that would have been prevented with proper construction.

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Material and procedures that are meant for equipment or storage sheds were never right for a home when it comes to metal. Plywood sheathing has a purpose.

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My interpretation it is per manufacturer’s instructions. But, as a HI, we can provide further guidance or opinion. based on our experience. My experience has been no issues with proper ventilation, however it is not something I come across regularly.

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That is what I see Brian. Underlayments are required for that type of roof covering, which is metal. Hard to do if you don’t have a roof sheathing.

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Why do you think underlayment is required?
Sheathing may not be required either depending on design.

The second line of defense for any leakage.

Underlayments are designed to lay under metal roofs and provide thermal protection as well as waterproofing solutions for your home. Without them, metal roofs tend to be loud when it rains, cold during the winter, and hot during the summer with the raging sun and high temperatures. There’s no question that you should have one under your roof, but the question you should be asking is: Which roofing underlayment should you choose?

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Not only IBC, But IRC as well.

The Importance of Following IRC and Manufacturer Instructions

The IRC is a prescriptive code and there are many specific requirements for underlayment and metal panels. But because of the wide variety of styles, the IRC appropriately requires installation according to manufacturer’s instructions. It’s important to specify a new roof using both manufacturers’ instructions and IRC’s specific requirements. And, remember, a metal roof will have a long service life, so the underlayment’s service life should equal that of the metal roof. Don’t be shortsighted when designing for longevity.

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@bhull1 @mcyr

I think we are confusing requirement vs recommendation. High wind areas may require it. Manufacturer may require it. If the previous do not apply or not verified, inspector may recommend it.

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My two cents:

As HI’s, we shouldn’t be doing anything other than 1) reporting what we see, 2) recommending repairs for material defects, or 3) referring a component for further evaluation. Recommending an upgrade to a component is beyond the scope of a HI, imho.

As for this home’s metal roof, I would have advised the buyer that some metal roofs require underlayment, and some don’t, but there’s no way to tell without knowing the specific product and manufacturer. I also dislike professional risk, so I would have referred the client to a roofing contractor to evaluate whether the roof meets the code that was in place at the time of construction.

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“As for this home’s metal roof, I would have advised the buyer that some metal roofs require underlayment, and some don’t, but there’s no way to tell without knowing the specific product and manufacturer. I also dislike professional risk, so I would have referred the client to a roofing contractor to evaluate whether the roof meets the code that was in place at the time of construction.”

Yes, Darren. But we aren’t code inspectors. As NACHI home inspectors, we are guided by the concept of Best Practices. In this particular case , I found an almost unnoticeable area in the ceiling over the master bedroom door (corresponding to the ridge vent) where nail pops and buckled drywall joints are starting. And yes, I recommended conulting a qualified roofer for recommendations.

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So if I state: the metal roofing was installed without sheathing, directly over rafters/trusses. Without second layer of protection provided by an underlayment, typically installed over a roof’s sheathing, the metal roof may leak prematurely and under adverse rain/snow conditions. The lack of sheathing also may contribute to lack of sound dampening, resulting in increased noise during rain events.

What does that imply? component upgrade or not?

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The metal roof manufacturer may not require underlayment or sheathing. Recommending either could be an upgrade that’s not warranted. I wouldn’t want to put my opinion for an upgrade between the roof and the buyer. I would explain to them what’s there, that some metal roofs need sheathing and underlayment depending on the product, and some don’t, and that it’s a good idea to have a metal roofing contractor look at it if they’re uncomfortable with not knowing whether sheathing or underlayment should have been installed.

I view a home inspection as not being technically exhaustive, and the inspector as not being a product specialist. There’s a lot of risk when you wander off the fairway into the tall grass.

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You did not answer my question.

I don’t care if the manufacturer recommends it or not. If installed on a house where there is conditioned space below I will state exactly what I put above. Your lengthy explanation of not what I asked implies that you disagree with what I stated. That’s fine. You could have just stated so :joy: It’s not a matter of what should have been done, it’s a question of what now, what is the possible and likely consequence of metal roof installed the way pictured in OP’s pic. Apparently you have zero issue with the way it is installed, that is fine. It is home inspector’s job to know and understand construction methods and consequence of improper methods. Deferring is last resort. The client does not pay inspector to defer. But as PE/SE, you guys love when clueless inspectors defer to you so you could make $200/hour or more :smiley:

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It would be zero value to the homebuyer if, after I surrrender my common sense, construction experience, and Best Practices; I tell him or her that the flawed roof construction is OK because it is grandfathered by the code standards of 5 to 10 years ago. The homebuyer would find out firsthand that there is a real problem during the hot and humid Dog Days of Summer, when condensation from a dripping metal roof starts appearing as black mold spots on the bedroom ceiling.

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Any roof may leak prematurely. Though, I agree underlayment is a nice layer of protection, but metal roofs without underlayment are very common in commercial applications and some residential applications. I have installed many with no underlayment and no leaks. Screws with neoprene washers when installed correctly on a proper slope roof are very reliable.

Then it is likely an insulation or ventilation problem. That is why you see most metal roofs insulated on the underside vs the ceiling. In my opinion, you are boxing yourself in.