Garage roof insulation

[Gliderman8]

Tom, I bought RadiantGUARD breathable Ultimate-Foil.
https://www.radiantguard.com/
I will be happy to take some pics but honestly it will be a while before I get to installing it as my “to-do” list is rather long.
Next up on my list is to buy/install a dishwasher; my 29 year old GE Monogram just quit. After 29 years it owes me nothing.

 

[NutmegCT]

No problem. I had thought you already installed it. Thanks for the Radiant Guard link.

And congrats on the GE Monogram longevity. I'm betting the next one you get will have all sorts of digital controls, and let you turn it on using your Smartphone while you're in Antarctica! Wow Golly!

 

[Gliderman8]

No problem. I had thought you already installed it. Thanks for the Radiant Guard link.

And congrats on the GE Monogram longevity. I'm betting the next one you get will have all sorts of digital controls, and let you turn it on using your Smartphone while you're in Antarctica! Wow Golly!

Exactly Tom. The LG model I looked at is “wi-fi enables”... Why? It’s only a dishwasher!

 

[NutmegCT]

Why fi?

 

[NutmegCT]

Rick - your comment about Camilla's hat immediately reminded me of Phyllis Diller. She once appeared on Johnny Carson's Tonight show with a similar headpiece. Her line: "It's not a hat. Those are bleached nerve ends."

She was a *hoot*.

 

[NutmegCT]

Friday update. Noon here in eastern Connecticut. Here's the garage enjoying the sunshine:



Here's the test patch area of generic kitchen aluminum foil: 1 - shiny side toward roof, 2- shiny side toward interior.



I used laser gun to measure surface temps.



Underside of roofing: 122F
Underside of "dull" foil on left: 85F
Underside of "shiny" foil on right: 92F

Looks like the foil idea works better with shiny surface toward roofing. Either way, seems a definite reduction of infrared radiation compared to the bare roofing underlayment.

 

[Popeye]

Good stuff. I'm late to the conversation, and far from knowledgeable on such matters.

But keep in mind ventilation and possible condensation during cold weather. I believe the garage is unheated, but still, sun shining on it during the day followed by a cold night ...not sure what would happen.

I am mainly saying this b/c of the many "dire warnings" that many people talk about when insulating a roof - again, I am far from an expert. Looking at the picture, it appears the ridge is not vented. Adding a ridge vent, or a few vents at the top, might be easier than insulation?

 

[NutmegCT]

Thanks Mike. Already have roof vents, so my main concern is the heat-up of the MG parked inside, due to the heat radiating from the underside of the south-side of the roof.

When I did the actual temp measurement, I had sprayed flat black paint on the foil, so reflectivity wouldn't be an issue on that laser beam.

So far, seems that the foil is a better choice than lots of insulating material. I don't heat the garage, or cool the garage. I just want to keep down the temp of the car.

Tom M.

 

[PC]

...When I did the actual temp measurement, I had sprayed flat black paint on the foil, so reflectivity wouldn't be an issue on that laser beam....

With apologies to Mick Jagger, painting it black defeats half the purpose of the foil.

They recommend the shiny side down because the emissivity (the material's tendency to give off heat) of the shiny side is lower and will re-radiate less heat. By painting the surfaces you make the emissivity the same, and very high, near 100%.

A better way to perform that experiment would be to leave the foil bare and place a black object underneath it (but not touching it), measuring the temperature of the object, not the foil.

 

[NutmegCT]

Thanks. So you'd suggest I put a black object below the bottom surface of the foil, then measure the temp of the *top* of that black object, right?

I sprayed a small area on the foil, as I know that laser (infrared) guns don't get a good reading from a shiny surface.

Tom M.

 

[PC]

.... So you'd suggest I put a black object below the bottom surface of the foil, then measure the temp of the *top* of that black object, right?....

Yes.

...I sprayed a small area on the foil, as I know that laser (infrared) guns don't get a good reading from a shiny surface...

That's correct (except technically, the laser is just a spotting guide. The actual measurement is made by a sensor that's looking at the surface. It can't see the laser but they're aligned together to make it easier for us to aim where the sensor is looking).

Most IR guns assume emissivity is fairly close to 100%, maybe 90ish%. The more expensive ones are adjustable. But some surfaces, especially metals, can be far off from that. And shiny metals can actually be so reflective that they act like a mirror and you end up measuring the temperature of a reflected image of some other object in the area.

 

[Gliderman8]

Tom, the radiant material I bought is perforated to prevent condensation.

 

[NutmegCT]

Thanks Elliot. I've heard about condensation issues so need to keep that in mind.

Yesterday's test: three panels of the roof. One with foil (shiny side up) across two rafters. Second, with foil (shiny side down) across two rafters. Third, "bubble wrap foil" (Reflectix) across two rafters.

I placed a flat black painted 2/4 below the panels. After 30 minutes, here are the IR gun temps:

Roof underside: 120F
Wood under foil with shiny side toward roof: 90F
Wood under foil with shiny side down: 90F
Wood under Reflectix: 89F

I'm not concerned by the minor variances, as just moving that IR gun an inch left or right can change the reading.

Seems to me the foil is all that's needed, altho' the Reflectix is much easier to staple in place. I'd leave 1/2 gaps between foil strips, so cut down on possible condensation.

If I can lower the temp of the MG 20 to 30 degrees from the radiated heat from the roof, that is Progress!

Tom M.

 

[NutmegCT]

Update. I put Reflectix on the underside of the roof rafters, only on the south (sun facing) side of the roof.

Yesterday at noon, cloudless day, outside temp 91.

Underside of bare roofing without Reflectix: 123 degrees
Underside of Reflectix: 85 degrees.

That is progress! MG doesn't get nearly so hot as before.

 

[TomMull]

Lots of stuff here but I'll add my 2p. In the old days they'd put a cupola on the barn to allow the heat to escape. I use a vent in both peaks. Easy to do with or without the radiant barrier.
Tom

 

[NutmegCT]

Thanks Tom. I've got roof vents in there, but they don't have any effect on the radiant heat from the roof itself. That's what was heating up my MG parked inside.

So I cut down the radiated heat. The convective heat is still there, but escapes through those roof vents without building up inside.

Learning the differences between conductive, convective, and radiant heat was quite an adventure!
Tom M.

 

[Bayless]

That's pretty impressive Tom. I did not expect it.

 

[Gliderman8]

You beat me Tom. I have yet to install my Radiantguard. Your numbers are impressive so I can’t wait to install mine.