Which Roof Type Holds the Most Heat? Shingles vs. Metal vs. Roof-Over

Which roofing assemblies heat up the quickest and which assemblies release heat efficiently?

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All roofs hold and transfer a certain amount of heat to a home or building's interior, but some assemblies perform better than others. Today on The Metal Roofing Channel, Thad and the entire crew build four sample roofing assemblies to test which one stays the coolest throughout the course of a week.

The assemblies are:
1. Metal
2. Asphalt shingles
3. Metal over asphalt shingles
4. Metal over fanfold insulation over asphalt shingles

Topics Covered:
►Intro 00:00
►Experiment setup 0:53
►Temperature readings and analysis 4:47

Check out these pieces of content for more information:

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[tylermanley]

I like the options. Some of the high performance builders I have seen use an underlayment then insulation. On top of the insulation then 1x4 furring strips then metal roofing. This air gap allows less heat transfer from the metal roof to the assembly and the space allows for moisture to run out of there was ever a leak or condensation. It also allows for that airflow to cool the decking at night.

[acoustic]

I would like to see you add one more to the test group. Do exactly the same thing using your best reflective metal color which probably is Arctic White.

[johnquattrone]

WOW, WHAT A GREAT VIDEO!!!
Back when I was getting my master’s in mechanical engineering, I did a research paper on heat transfer through a small 1 room house using computational fluid dynamics (CFD). I was amazed at how much heat transfer was through the roof. It was over 20yrs ago, but I seem to remember it was almost 75% of the heat transfer, followed by windows and a distant third was the walls. When I used to do heat transfer analyses of gas turbines, I would simulate thermal break between the parts. So, the affects you are seeing in your test with the asphalt/foam/metal combo being best during the day is not surprising. There is a good amount of thermal resistance for the heat to get to the attic air space when moving across these roofing components. Also not surprised the asphalt/foam/metal combo was the worst during the night. I bet it’s the thermal capacitance of the asphalt, it’s retaining heat and the foam is restricting the nighttime cooling. Still, I would use the foam under the metal. I bet if you added an “attic fan” you would see some big temperature drops.

Now some real-world experiences, 10 years ago I lived in the NE and I needed to replace my a 20yr roof on a 40yr old house. The old roof was white asphalt shingles, and they were replaced with black shingles. It was early April with a daytime temp of around 55F. Using an infrared laser thermometer, the temperature was about 110F-120F with the white and then 130F-140F with the black. The original builder installed vinyl soffit vents, but it was over solid plywood. There was absolutely no attic ventilation. All the plywood had to be replaced. There was no bathroom vent in the 2nd floor bathroom. The roof plywood over the bathroom was covered in mold and one rafter was dry rotted. Even though the black shingles made the roof hotter the corrected ventilation cooled the house down better at night (also added ridge vents). In July, our 2nd floor bedrooms were HOT until about midnight. After the new roof, the bedrooms cooled down sooner.

[HoosierBoy]

I was under the impression that you needed to have an air gap between the radiant fan fold and the roof, in order to achieve a true radiant barrier. Would be interesting to see you test a system with the proper air gap.

[maytons]

A peer into the difference between radiant heat vs ambient heat may help with this experiment. If we are looking critically at efficiency then shade must come into play to block the sun's radiant heat while concurrently allowing heat dissipation. A white mesh shade canopy mounted to the roof with 4"-6" offsets would reflect back some of the radiant heat from the sun, providing shade while still allowing rain and wind to pass through for ventilating the ambient heat at the surface.

[josephwhatley]

Cars with tinted windows and no venting get just as hot as those without.
The venting would make the closer to real results id think.

[barbaramaganadominguez]

First and foremost WE LOVE YOUR CHANNEL THANK YOU SO MUCH FOR CREATING IT! Great job speaking, explaining, asking questions, and communicating in a way we understand! I’m glad you did the experiment! We live out in Ventura, Ca. While it is a beach city unfortunately it has gotten hotter! We accidentally started looking at metal roofs because of fires but also have learned about it helping with cooling the home. We don’t have an ac so I have been looking for information of what degrees difference could it make? Enough that we don’t need ac? We just have a few weeks in the summer that get 90s-100s. I get that ventilation and Sri value will make a difference. Maybe lil models of homes? To find out the data? Or at least another experiment like this one with different metal Sri values to see that difference? Then maybe a something about ventilation? We wish you guys were close to do our roof!

[dennisgarber]

I have been digging up forum post after post, with testimonials of people who get condensation on inside of the panel which drips down the screw and into the roof. The perilins shift and rot too. This is caused by the insulation under the metal and open air flow design by the roofers. In Southern climates, the night temperature does not swing 50 degrees as it does out West and in the North, like Cleveland.... This means to avoid the Drip failure, go directly over shingles with the metal. However, something soft, synthetic, and thermally conductive must go under the metal to avoid rock scraping during thermal changes.... The other solution would be to spray foam the backside of the panel. If I could think of how to glue a some insulation to back of the panel, I might try it.... Unfortunately, I do live near Cleveland and have no attic or way to insulate other than putting insulation between my metal and roof. I did testing on stove and oven with affordable bubble wrap on stove top and pans heated to 190F. White side touching pan quickly melted air bubbles. Silver side touching pan softened the bubble plastic enough that I could pop the bubbles more easily. Putting white nylon weed fabric between shiny side and pan, I was able to keep the bubbles plastic from softening up, and the ir meter read 114F, a 50 to 75F degree drop, just with bubble wrap, reflective silver, and thin weed fabric. Unfortunately, even if I close off top and bottom of the panel so it stays a tiny bit more temperature stable, I might run into condensation problems. Maybe going over the old asphalt roof, it might melt around screws and seal the screws and prevent the condensation Drip from entering the roof... I am on the fence about attempting any installation under the metal between shingles (foam board or bubble wrap). Foam board is out of my price range anyway. I guess I need to figure out the expiration date of bubble wrap in storage to figure out if it is even worth it.

[marilynmatthews]

I hope you do additional tests with the variable insulation between the shingles and metal roofing to ascertain which offers the best results.

[doyola]

Exposed fastener high rib metal over 1×4 or even better 2x4 lathe is my favorite. Use wide ridge, bend up the flats, and don't use closures. The ribs vent under the lathe in an amazing way.

[trntbls]

I'm guessing there's a wintertime version of this to get at least 2 of the extreme seasons worth of data as a general overall best juice for squeeze

[daviddesilva]

I believe letting your attic breathe properly is the best method. Pleated soffit. Rafter venting every 2nd space. Relief vents installed near the pitch of the roof. Minimum R40 attic insulation hot or cold climate. Stay away from dark colours for roof finish. Attic fan would be beneficial. Let the attic breathe. Less chances of mold or condensation. Enough said...thxs for the vids!

[johnowens]

I love the fact you’re trying to quantify this. Can you cover what an installation would like with insulation and air gap underneath the standing seam? It’s Something I want to do with my new build in AZ.

[williambates]

How about doing one with inch strapping under the metal with the same three treatments as the metal without strapping.

[tinkermouse-scottrussell]

Like to see a built-up roof of a peel and stick ice guard, fan type insulation, 2lb mass loaded vinyl to help reduce the sound, and a galvalume standing seam roof silver no color.
Play Safe From Elliot Lake Ontario Canada.

[KevinCGleason]

You are welcome to run those tests at my home in Hollywood, Florida. HOT HOT HOT! Thanks to what I've learned from your videos, I am under contract for a standing seam metal roof to be installed in January, 2021.

[nwirentals]

Would like to see how a metal roof over a membrane with a radiant barrier (with a air gap) and vented out the top!

[blh]

Curious to see how a Energy Start rated shingles would compare with your metal rood and against a generic 3 tab(3 tab is banned for new work in our area, only repairs are allowed). One energy star roof is Owens Corning Dura Max Cool Roof. Im not trying to drop names, but it's one I know of and is currently on our old home and it's a premium shingle that has a rated 30-50 year, depending on model/install. That makes it more comparable to metal in lifespan whereas 20 year, 3-tab is low end and users wanting that are only looking for cheapest. I'm seriously considering metal and will need to install myself because in my area, residential metal roofs are expensive(treated more as a commercial install). This is not the same in other parts of the US. Thanks, Brian

[bradZXS]

We have a metal roof and our attic gets super hot in the summer. Our house used to have a shingle roof and I don't know if they took the shingles up or if they left them and out insulation down. I would like to put in an attic fan to alleviate the heat in the daytime.

[GuentherJohnny]

Applying a rough 1x4 strapping prior to installing metal could effect different products in varying degrees..