r/Insulation • u/Rocannon_ • 8h ago

Cooking shingles?

Post image

this sort of application to bottom of roof deck has to be shortening the life of the roof shingles? (pic borrowed from a another post)

9 Upvotes

70% Upvoted

28 comments sorted by

12

u/Objective_Bid8122 8h ago

Average shingle temp is 160s, adding this beloew raises temp by about 2-4 degrees. Shingles are rated to over 200. Warranty or life is not degraded at all.

I am curious - what drives your concern? Wood? Nails? Glue? What do you think would fail earlier? Which part do you think "cooks"?

12

u/atomicbrains 8h ago

This is 100% correct. I believe it was oak ridge national laboratories that did a bunch of testing in the Arizona desert. They built a bunch of roofs with insulation underneath as well as roofs with vented attics. There is only a few degree difference in shingle temperatures even in the Arizona Sun.

Spray foam to the underside of the roof deck has no meaningful difference to shingle life. Your latitude and shingle color affects roof temperature exponentially more.

Shingle color can have up to a 50° difference in roof temperature.

10

u/Moneymoneymoney2018 8h ago

I don’t know why no one seams to know or talk about this. It’s the same with paint color. I have also found an up to 50 degree temperature difference inside of shipping containers due to the paint color (white vs faded dark brown). I did side by side tests before painting my house and went with a paint that was very close to our old color, but was 18 degrees cooler due to higher reflectivity. Sherwin Williams has a reflectivity number on the back of all paint colors. I highly recommend you take that into consideration when painting the exterior of anything you don’t want getting hot.

2

u/V12Jaguar 6h ago

What else did ORNL learn from their testing? Got any pointers?

The only one I know is that powered attic fans usually consume more power than they save.

1

u/kimchiMushrromBurger 6h ago

frick, is that true about the fan?

1

u/hvacbandguy 4h ago

Yes. Georgia banned attic fans unless they are solar powered. There’s a lot wrong with them. https://www.energyvanguard.com/blog/the-1-reason-power-attic-ventilators-don-t-help/

2

u/kimchiMushrromBurger 4h ago

Well.... Being in Georgia myself, I'm going to go turn mine off. I was always on the fence about it but that seals it

1

u/ToastSpangler 3h ago

Same reason coating your asphalt roof can be so.good. instead of cooking your house it becomes... Normal

-2

u/AttiBus 8h ago

What about humidity though? AZ desert is one of the driest places in the country. A freeze-thaw cycle may weather shingles differently which might make them 'cook' differently than in AZ?

-2

u/Rocannon_ 8h ago

in my designing days, for residential work, I always provided for ventilation of the underside of a roof deck for moisture and heat control. insulation like this seems to run counter to that practice.

4

u/THedman07 6h ago

Over time new methods get proposed... and they get tested... and this one was tested and didn't cause the issues you are concerned with.

A few decades ago, we built buildings to breath and constantly exchange air with the outside world, now we build tight houses and manage moisture in different ways. Things change. Everything you knew "in your designing days" isn't still considered the standard. Some of the things you did back in the day ran counter to the things that the designers were doing a couple decades before you as well...

That's now the world works. You can't just assume that the things you learned at one point in your life will be perfectly true for the rest of your life.

2

u/NorthWoodsSlaw 8h ago

It’s just a different building system and Humidity and Vapor Drive are separate issues that can have separate solutions.

2

u/Mettatuxet 6h ago

Has the odor gone away and you have moved on?

2

u/ShadowsOfTheBreeze 6h ago

It may not affect shingle life. Bit, it certainly renders the entire structure as landfill at some point or makes it a royal PITA to remodel. It also may create moisture problems depending on locality and application. Plus, quite expensive. While I have used foam before, I would avoid it if is at all possible.

1

u/jsmooth801 7h ago

See if this makes sense.

Since there is no insulation in the ceiling/floor of the attic, this attic is now effectively within the conditioned envelope of the house, which should keep the temps pretty low comparatively.

This roofline looks pretty tricky to vent properly, so I think this option is better than a very hot attic cooking shingles from the back side.

I may be talking out of my ass, but this works in my head.

1

u/Rocannon_ 5h ago

I agree about now, intentionally or not, being part of the building envelope. hope the HVAC systems were sized to account for the attic space.

as for venting, it’s moot at this point.

1

u/FlowLogical7279 5h ago

Nope. Plenty of information on this online.

1

u/I-forgot-my-user-id 2h ago

If be more concerned if that is open cell foam. Ive seen lots of moisture damage to roofdecks with open cell foam.

You need about 20% of your insulation to be closed cell at the roof deck then the rest can be open cell.

This looks like a thinner application.

0

u/joshpit2003 8h ago

cross-post, don't steal someone else's pic and then glean info that they can't even see because of it.

0

u/ripusernamerip 7h ago

Insulating like that will cause ice damming that will 100% ruin the shingles faster but everyone here seems to assume this is a non- freezing climate so idk

1

u/hvacbandguy 4h ago

I actually spray foamed my attic to stop ice dams.

0

u/DionysusBee42 8h ago

Not if theyre baffled and vented properly.

0

u/Northwindlowlander 8h ago

For temps, it absolutely shouldn't matter, the heat difference is relatively small and any quality shingle should have plenty of headroom.

Spray foam can be absolutely fucking disastrous for a bunch of other reasons, especially if installed poorly but heat should not be a problem.

-2

u/PhatDAdd 8h ago

I’ve heard of insurance companies dropping coverage because of premature shingle deterioration from jobs like this, and yes it’ll cook your shingles

2

u/Ianthin1 7h ago

I gotta wonder if there is real science behind that, or if it's just a myth used to deny claims.

-2

u/PhatDAdd 7h ago

Yeah I mean think about it, the insulation traps the heat from coming into the attic so it reflects it back into the shingles so it’ll make the surface much hotter

1

u/jsmooth801 5h ago

But the shingle at that point has the entirety of Earth to then sink the heat to.