TheSamba.com :: View topic - Anyone using "bubble wrap type " insulation between roofrafter ?

Mon Aug 16, 2021 7:49 am

The last couple of years it is for sale all over the place. Anyone using it? It is the " bubble wrap type" reflective insulation with the silver lining on it. Comes usually in narrow rolls made to fit between the rafters.
Like to get some input from people who installed it and can tell how much the temperature dropped . Maybe a good way to drop temp in separate garages with no ceiling?
Like to get information especially from people living in the hot desert area with a daily summer temp above 100* and have first hand experience . Thanks

Tue Aug 17, 2021 4:29 am

Mmy 24 x24 garage has a ridge beam and 6" rafters and a "5-V" tin roof on pulling. Hot as hell on that metal in the summer sun. I covered the entire ceiling leaving the gaps between rafters able to vent to ridge area and gable vents on each side,. I had planned to put a fan in to draw circulation from the soffit up and out the gables. Never got to fan install,now I just avoid those too hot days,
The stuff I used, well some looked like mylar over bubblewrap; some was mylar over a 1/4" thick white foam sheet. Rolls were 4 ft iirc,and maybe 60 ft. Do it you will definitely reduce heat.. venting is best. I think at least a 10 degree drop.

Tue Aug 17, 2021 7:02 am

I installed it in my shed/shop because I was getting condensation inside on the metal roof at night that was dripping onto everything and causing problems with my tools and anything else I stored in there. I never did measure temperatures because the shed is otherwise uninsulated but it does feel like it takes longer to get hot inside the shed. You don't feel the heat from the metal roof radiating down on your head any more. And yes, it did help with the condensation problem.

I installed it to the bottom of the 6" roof rafters.

Tue Aug 17, 2021 1:04 pm

It is called Reflectix, and it is a great product. We mostly use it to wrap large HVAC ductwork, but it makes an excellent radiant barrier on the underside of roof sheeting.

https://www.reflectixinc.com/products/double-reflective-insulation/

Tue Aug 17, 2021 2:42 pm

We use it under radiant floor heating.

Tue Aug 17, 2021 5:23 pm

cdennisg wrote: It is called Reflectix, and it is a great product. We mostly use it to wrap large HVAC ductwork, but it makes an excellent radiant barrier on the underside of roof sheeting.

https://www.reflectixinc.com/products/double-reflective-insulation/

Yep,that is the stuff. I just like to get feedback from people who have it installed at home and can provide data. I do not like to spend $ 1000 + and lots of work just to find out that it creates other problems like mold on rafter or roof plywood sheets or that condensation runs down on it, just like it does on metal roofs.

Tue Aug 17, 2021 6:24 pm

Tvättbjörn wrote: cdennisg wrote: It is called Reflectix, and it is a great product. We mostly use it to wrap large HVAC ductwork, but it makes an excellent radiant barrier on the underside of roof sheeting.

https://www.reflectixinc.com/products/double-reflective-insulation/

Yep,that is the stuff. I just like to get feedback from people who have it installed at home and can provide data. I do not like to spend $ 1000 + and lots of work just to find out that it creates other problems like mold on rafter or roof plywood sheets or that condensation runs down on it, just like it does on metal roofs.

OK, here goes. Mold isn't caused by insulation, it is caused by moisture intrusion and a lack of ventilation. The condensation on the underside of the metal roofing is a natural occurrence. Most often, if metal roofing is installed on top of skip sheeting (instead of full sheeting like plywood or OSB) a layer of tar paper is put down first, to catch the condensation and make it run off the slope.

In many modern pole barn style buildings, there is a layer of fiberglass insulation, sandwiched by white plastic sheeting, that is installed before the metal roofing. It is not designed to actually insulate the building, it is to stop condensation.

All of this means, depending on your specific situation, adding that layer of reflectix to the underside of the roof will help reduce solar heat gain. If the building is basically open, and has good airflow, you should not have any moisture issues.

Make sure the foil layer has a nice snug fit between the rafters, and is up tight to the underside of the roof sheeting.

Tue Aug 17, 2021 6:24 pm

I used this https://www.amazon.com/gp/product/B07K35S6R3/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 in our attic. Stapled it to the rafters to form a "blanket" under the uninsulated roof. WE have ridge vents, so I didn't close those off, and left a few inches open at the eave end for air flow between the rafters. Did this a couple years ago and it seems to make a dent in the overall heat reduction of the house. By how much I can't say for sure - there really isn't a quantitative way to measure except "this feels cooler" during the 90 degree days.

Tue Aug 17, 2021 9:55 pm

Tvättbjörn wrote: The last couple of years it is for sale all over the place. Anyone using it?
Yes, I put Reflectix on the underside of my roof decking, and it WORKS! One way of knowing this with certainty is, on brisk mornings when frost is formed on the rooftops, there were distinct patterns on my roof: everywhere where I had installed Reflectix, there was heavy frost...but in the areas where I had not put it, there was no frost, because the warm surfaces in the attic (underside of the roof) did not let frost form (this heat results from warmth escaping through the insulation/ceilings of the living space).

Although not very scientific, I also shot it with the IR temp gun: exposed timbers midday during summer were ~125°F, but the Reflectix surfaces measured in the low 100's, much of which resulted from ambient attic temps. In an effort to minimize the emissivity discrepancy of the reflective surfaces, I laid down blue 3M painter's masking tape and only shot those surfaces for comparison (I can't remember what the reflective surfaces had measured...I have data somewhere).

Tue Aug 17, 2021 10:24 pm

I used it to cover the tent end roof on our hybrid Aero Cub travel trailer. Made a huge different in heat. It does get pretty beat up though when we'd roll it and store in the cubbies. Now for regualr tent camping we just use an emergency blanket (trailer is gone) to reflect the solar rays - pretty effective, but the bubble wrap is a little better, just doesn't fold down as nicely.

Wed Aug 18, 2021 3:30 am

Yup, that's the stuff. Regarding condensation, my barn/stalls front faces direct east. When the sun rises and hits the rear west-facing roof (and warms the air below, the inside drips condensate. The front half of the metal roof top surface is all rusty, while the back looks almost new, on top... So be aware that building orientation has a lot of effect on heat gain and resulting condensation. The shop/garage is oriented front facing north, never had any condensation occur.

Wed Aug 18, 2021 4:02 am

Be aware that reflectix provides greatest R-value with an air space around it. Yes, it does reflect some heat, but if you mount it against a warm surface heat will be transferred into the reflectix which kind of defeats the purpose. With a proper air space heat would have to first warm the air in the space before it would heat up the reflectix.
https://www.reflectixinc.com/tutorials-and-videos/attic/

Wed Aug 18, 2021 5:42 am

Great lesson guys, I never would have known about the gap for air flow. I love how much I learn from all of you.

I bought some for my bus as a replacement of the old fiberglass insulation. Would I need any gaps for air flow or is a bus application totally different?

Excellent videos from their site I'm archiving for when I can tackle my garage in the future:

Wed Aug 18, 2021 6:15 pm

Yes, to Q-Dog's point, you must follow Reflectix installation instructions.

Here is a video I really like which clarifies the thermal transfer physics...

https://youtu.be/E1IwS0_lpBc

Wed Aug 18, 2021 9:14 pm

Q-Dog wrote: Be aware that reflectix provides greatest R-value with an air space around it. Yes, it does reflect some heat, but if you mount it against a warm surface heat will be transferred into the reflectix which kind of defeats the purpose. With a proper air space heat would have to first warm the air in the space before it would heat up the reflectix.
https://www.reflectixinc.com/tutorials-and-videos/attic/

Only if that air space is completely sealed up tight. That is the tough part on a retrofit.

Wed Aug 18, 2021 10:15 pm

The Reflectix installation instructions video does make a difference on the installation depending in what climate you are in. Most of the time there is an air space needed between the panels / wall and the insulation. Which should be sealed off all the way. Some companies say it should be open on the lower and upper part for air flow. Possibly a good point when the roof has ridge venting. That way the hot air will get out quick, but on the other side you will not able to heat the space in the winter unless it has a ceiling.

I have also seen some similar stuff which is made to be used under tar roofing shingles. Some roofing wholesale places carry it. It will take place of the felt. However, I have not seen any independent test data on it, You will always here one side .....

Sat Aug 21, 2021 10:23 am

I was aware of the air space requirement for Reflectex.
I decided to use on my recent install of the Westy Luggage Rack
Obviously it it glued right to the surface so it was not going to work as designed.
With that in mind when I started I made the outer edge of the luggage rack into a sealed air chamber by covering the open area with it.

So what I'm seeing in temp difference before mounting it is that the roof temp measured on the inside was 120-125°F. After mounting the rack I'm seeing 99-102°
Now having done all this the rest of my roof rack is just a sheet of 3/4" marine ply.
The difference between the sun on the bare roof and in the shade under it is about 15-20°F.
So yes it did make a difference, but not a fantastic difference then just putting a sheet of plywood up there!

I still feel god about doing it because I now have one less thing taking up space in the workshop! 😁