Radiant Barrier in Attic + Garage Door

Hi Folks,

My local HD is clearancing the Reflectix brand of radiant barrier (Reflectix 48 in. x 25 ft. Double Reflective Insulation Roll BP48025) and I have two use cases for this:
1) Attic. It's about 1500 sqft with a roof pitch about 1.3 and largest standing height in the attic must be around 4 - 4.5ft'. According to an online calculator (SQFT *1.2) I will need about 1800 SQFT - sound about right? Has anyone used this in their attic by stapling it against the joists? Good product to use here?

2) Garage door. It a two car metal garage door (overhead) with rivets on the back supporting structure (not screws). Even if I stuff the 1" cavity with foam boards, I was thinking I can hang this on top and take advantage of it. Thoughts?

Thanks!

 

Well I called Reflectix and since the bubble version is not perforated as they advised to staple directly to the roof decking since I am in the southern region. I also inquired on just stapling directly to the joists and with this product that is not advised since the air gap will now create a place for moisture to build up and not escape the attic.

 

1. As you found out. No, don't do it. There is a reason insulation is on the floor of the attic (ceiling below) and the attic space and roof is kept cool/hot.

2. I wouldn't bother. The insulation value you get will be minimal considering the difficulty in installing it (tape?). Rigid foam board would be money better spent. If you want you can use foil faced rigid foam to give you the radiant benefits.

 

I realized I mixed up joists for rafters in my original post. The intention here was to staple it between the rafters, against the roof decking.

 

I've never worked with this stuff but have always heard that it's not quite as effective as advertised. You might want to investigate more before going that route.

Also, you insulation doesn't look to be as robust as it should, that might be an easier first step!

 

Yes, re-insulating the attic is part of the plan and thought the radiant barrier would be a nice touch as well. It's currently 70% off at my local HD, hence my eagerness to understand if this is a wise decision.

 

​​​​​​​Might be a reason behind that!