What is reflective foil insulation (RFI)?
Insulation is a material that is placed on the side of a wall that is internal to space being insulated. RFI is a reflective insulation that has the explicit objective of insulating the inside space from heat generated specifically by light-ie sunlight. You'll likely find reflective insulation at the closest point of contact in which the sun hits the so called membrane of the inside room. This location is key, because the insulation is reflective, ie it bounces light and heat in, generally, the opposite direction. So, if you place RFI at the bottom of your insulation stack, your this will likely produce a sort of greenhouse effect, where whatever heat does get through the initial layers of insulation, will be reflect by the outer reflective insulation but will likely be false enough to be trapped at a rate of 98% back inside the room.
RFI is cost effective; it's a light material, and builders like it because it's amiable in terms of shaping in hard or difficult contorted positions on more intricate roofing and insulation projects. RFI is typically made of aluminum, and is reliably light weight and physically easy to manage.
Again, the location within the stack of insulating materials should be at the top or closest to the point of contact, ie closest to the sun. RFI is known to reduce the amount of heat that lower lying insulating materials have to absorb by a rate of 15 to 65%, depending on the quality, the thickness, the engineering of the aluminum.
RFI is reliably cheaper in the Atlanta, Phoenix, Miami, and Los Angeles metros due to those locations' overbearing sun exposures during the summer, or even year round. Some fireproofing insulation comes built in with RFI; these products though are only found in roofing insulations, and less so with room to room insulating materials and products. Foam board insulation does not typically carry any RFI features, while mineral wool insulation never carries any RFI features.
Where can RFI be installed?
RFI is typically installed in and during roofing projects. Again, the objective is to place your RFI where the building will be seeing the most sun-or any sun for that matter. If you're on a tight budget, you really should not skimp on RFI, though. It's difficult to undo or redo, and when you get insured, you incorporated such features as RFI into your risk profile-ie your insurance agent will ask you if you have RFI installed, and where you have it installed. Same goes for tax credits related to energy savings, so called green initiatives, and sustainability programs in your area.
RFI is usually installed toward the top of your house, but your sun exposure is unique to your building, and should be analyzed and respected on a case by case basis. Your foundation, as unusual as it might be, could be a point of high sun exposure. You might have a sun or moonlight feature that is an opening at mid ground to your basement. You'll want to check this point for abnormally high sun exposure, especially if it's on the side of the property that bears the brunt of the morning or setting, or worse, lunch time sunlight.
When can RFI be installed?
RFI is installed when the property project is completed; it's typically installed soon after the frame of the project and building is completed, when there's a roof to speak of, and an insulating room to protect the exposed insulation material from the elements. The timing of RFI installation is key, since it's very difficult to go back and correct poorly timed RFI pieces-especially if the roofing project is one that's intricate, detailed, or unconventional.
RFI is a great tool to use, if you're missing in space, or if you're in an industrial space that does not allow for very many of the conventional insulating materials that aim to absorb. They're also great for outdoor use, where humidity and rains can spoil absorption based insulating materials, such as wool insulation. The general rule is that if your property and building project is over 1,000 square feet, you'll not want to do this project on your own, but rather have a professional contractor do this for you.