Metal Roofing With No Decking Or Underlayment

I agree and:

I recommend the manufacturer’s installation instructions and refer to a qualified metal roofing specialist.

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Case in point, you can walk into a million flex space warehouses today and look up. You will see metal roofing attached directly to metal purlins with jacket insulation attached to the underside of the metal panels.

There is nothing wrong with that roof other than the insulation technique which may produce condensation. Some people love the sound of rain on a metal roof. Other people love the low maintenance. Others love the look. I do not know how old this home is, but if that roof is performing with no evidence of condensation and not leaking, what is the fuss?

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Great point, Brian!

However, I believe it will condensate and drip without the insulation in the place you describe above, unless it is highly insulated and sealed extremely well on the ceiling, which is very uncommon to be sufficient.

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Yes, agreed. Then, why all the underlayment/sheathing questions? Should we not be discussing insulation? LOL

This would be my narrative:
Metal roofs are known for condensation problems if not properly insulated. Condensation may cause moisture issues and damage if not mitigated. Recommend evaluation for correction by a qualified insulation contractor.

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As a second layer of protection with ice and water shield, or such, on top of the sheathing.

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So I think this quote from Darren is interesting in general. I think any of us can go down a rabbit hole over any issue you can think of. I can see arguments for both ways of thinking about things like this. Maybe it’s not our responsibility to look up the installation instructions for every product we come across? But how will you know if the installer made a mistake in some cases if you don’t read them? It’s a double edged sword. Where do you guys draw the line on this kind of thing?

There is no line… you must know proper construction methods. You’re hired to consult the client on any deficiencies. This topic is not a mere manufacturer compliance. The way this roof is installed is redneck’ish at best. Now, if the client is okay with it, there is no issue. But the job of a HI is to advise the client on any potential, and likely, pitfalls of poorly and or improperly installed systems and or components of a dwelling being inspected. Comparing a commercial metal roof with layers of foam insulation is silly. The roof in OP’s is built, like mentioned above, using a method that even, often – depending on climate, does not work well for a shed/garage, let a lone a dwelling.


Yeah I don’t care about this roof post. I’m talking big picture. When we talk about a home inspection not being technically exhaustive, what does that mean exactly? And there is always a line that you draw during every inspection otherwise you would still be there doing your first inspection now… and as we can see from this forum there are tons of opinions about every issue.
What I’m trying to get clarification on is where everyone draws their line. How much time do you spend looking up product manuals? What is the realistic responsibility of this for us? If we look something up for one customer do we then have to do it for every customer? For every appliance or furnace or roofing material we have ever seen? Isn’t doing that technically exhaustive like Darren said?

Like I said, I can see arguments for both, just trying to understand what everyone else is doing in terms of these things.

Technically exhaustive implies, for example, you won’t measure/calculate to see how many gallons of waste a drainage system can handle a minute or how many gallons of hot water a water heater can sustain. It implies, when inspecting a roof, you won’t be checking every nail or corner of an attic. However, you must have a solid and broad understanding of these systems to spot anomalies and point them out and or defer them. If you’re not capable of doing this or even understand what I’m referring to then you either have much to study or you will simply never become a good home inspector. For example… I walk into a 10,000sqft and the boiler’s manifold is 1/2" Right away, I know, that won’t handle the heat load required to heat the space. While I won’t perform the calculations, I will call it out and have a plumber do it. Now, if it “looks” right, but may be a little bit off… since I’m not performing the calculation, I’m not being technically exhaustive. That is the best I can explain it at the moment :slight_smile:


Rolled jacket insulation or SPF are reasonable and acceptable forms of insulation for metal roofs to control condensation and energy efficiency. To say the roof will leak is a falsehood.

I see you are in NY, climate zones make a big difference in building styles and materials. Both the OP and myself are in GA. R-30 is the minimum value in most of our state. Metal roofs are popular for aesthetics, cost and durability.

Are you trying or telling me the OP’s roof is insulated?

No, I am saying the metal roof is fine. The insulation is what we should be discussing.

The original posts was about the installation of the panels. Was sheathing or underlayment required. The answer is maybe depending on the manufacturer, IBC and IRC both defer to the manufacturer.

In my experience, metal panel roofs without underlayment or sheathing is very common and generally acceptable.

@lkage mentions condensation, rightfully so.

Therefore, my conclusion is: The metal roof install is fine, but condensation may be an issue. Therefore, we are back to insulation.


LOL you’re spinning it, my friend. I prefer, direct, honest answer. Thanks, though. You “know” there could EASILY be issues, you’re just too afraid to state so. Don’t be afraid, it’s bad for your soul, but good for the agent’s.

Not spinning anything.

Once we got past the sheathing and underlayment question which I directly referenced in both IBC and IRC, I went here.

Not in this area Brian. Any metal roof, whether corrugated or standing seam will have sheathing and a vapor barrier or slip sheet as they call it. Especially if installed over an abrasive substrate.


Let’s try to keep the discussion professional.

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Everyone is doing what works for them. Opinions on what inspectors should know and report is a daily debate. HI’s live in a large, nebulous gray area. ‘Standards of Practice’ are guidelines, but any time there aren’t specifics (which codes are, that we don’t follow/quote); one can’t say “this is how it should/has to be”, because the response back would be “says who… show me where it’s written”. Often inspectors quote “generally accepted construction practices”, but that is referring to another loosely defined gray area. Granted there are some things that are written/defined, but there are far more that aren’t. If everything was clearly defined, there wouldn’t be so much debate around a single issue.


Same in this area, Marcel


I know of only one good way to settle the argument: contact all the different metal roofing manufacturers and ask them whether they would recommend installing their product on a single-family residence without using a roof decking and water-repellent underlayment. I’ll do that when I have the time.