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What is Rafter Insulation?

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  • Written By: Sheryl Butterfield
  • Edited By: Bronwyn Harris
  • Last Modified Date: 09 September 2016
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Rafter insulation is a material used to insulate a home's roof or attic. The heat in a home flows from the warmer rooms to the cooler areas. In cold weather, warm rooms often lose heat to uninsulated attics and garages. When temperatures soar, heat flows from the rafters or attic into a home's interior, causing the cooling system to work overtime.

Rafter insulation, also called attic insulation, is a simple way to provide heat flow resistance. Rafter insulation also serves as damage control against moisture. The better the insulation coverage, the lower the energy bills.

Many types of home insulation are available. Homeowners can choose from a vast array of materials to fit the area they want to insulate. Fiberglass is not the only option. Increased energy-efficiency can be gained from insulation constructed from wool and natural fibers, foam board, concrete and even straw. Some materials, such as foam board, provide a high thermal resistance.

Rafter insulation installation methods vary. Some types of insulation, such as blanket rolls or reflective foil-faced systems, can be easily installed by a homeowner. Other insulation materials required professional installation or equipment, including concrete block, structural insulated panels (SIPs) and rigid fibrous insulation.

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Insulation's effectiveness is measured by a number called an R-value. This number measures how efficient the insulation is at resisting heat. A higher number equals greater efficiency. Adding multiple layers of insulation means adding together the R-values of each layer. The more layers, the higher the number and the more heat flow resistance. Many factors are considered when calculating an R-value, including insulation material, installation location and the method of installation.

Rafter insulation is most energy-efficient when both the rafters and the entry to the attic are insulated. Air sealing the hatch, kneewall door, or pull-down attic stairs, as well as gaps between frames and insulation, stops more air leaking to the outdoors. Homeowners can gauge air leakage by having an infrared scan performed. Typically, older-style fiberglass insulation does not cover the colder areas of an attic, such as gable ends, or the perimeters of an attic. Blown-in insulation, using special equipment, can fill gaps in these cases.

Rafter vents should be installed in attics where insulation covers the floor out to the eaves. These vents provide a place through which air can move. Rafter vents remove hot air during warm-weather months and moisture from condensation during colder months. Usually, rafter vents are simply stapled to the roof decking between rafters and run from the attic ceiling to its floor.

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titans62
Post 4

@Emilski - Good point talking about the different savings that you might see by getting the different types of insulation. It could very easy work in the opposite direction, though.

I had a friend who was very economically savvy, and when he went to buy new insulation he looked at all the different options and the projected cost savings. The place he lived was a pretty consistent temperature all year round, so it was a little easier to figure out than in some places.

It turned out, though, that the thicker insulation that was recommended to him by a professional would have saved him money over the course of the year, but the extra cost compared to thinner insulation was greater, so he went with the thinner. His savings might change depending on how fuel prices change over the next several years, but it is at least worth thinking about when buying new insulation.

Emilski
Post 3

If you are ever looking into getting attic rafter insulation, I would highly suggest having someone do an infrared scan. It might cost a little bit more upfront, but we had it done in our house and found several places that were letting in cold air that would wouldn't have guessed.

If you are doing the infrared scan, you will probably have a specialist there who can help you pick the best type of insulation depending on what he or she discovers. In the end, the best option for us was blown in insulation.

We got the kind that is made from recycled denim and other plant fibers, and it works great. We had all this done about five years ago, and our heating and cooling bills decreased immediately. We just recently made up the cost for the extra insulation and inspection, and everything now is just pure savings.

JimmyT
Post 2

@TreeMan - Depending on who you talk to, different people will swear by different types of roof rafter insulation. Personally, I think it all just depends on the attic itself and how you plan to use it. You didn't mention any details, but if this is an unfinished attic that will be used for storage or something, I would just go with more of the rolled insulation or maybe even insulated fiberboard. They are both fairly inexpensive, durable, and easy to install.

If this is somewhere that you will be spending a lot of time, though, I would suggest going with something a little more high tech like foam or blown in insulation. If the area is already finished with

something like drywall, the foam would probably be the only route for the walls unless you were going to replace them.

I would just ask around a little and maybe talk to some of the other people in the neighborhood and see what they have and whether they like it or not.

TreeMan
Post 1

Does anyone here have any suggestion about the best type of attic insulation? We just moved into a new house, and it has the rolled fiberglass insulation. That looks like it is getting a little old, though, so we're wanting to start fresh. We live in the Midwest, so the winters can be pretty chilly, but not at bad as in some other parts of the US.

That being said, I am still concerned with being as energy efficient as possible. I know in our old house we used the blow-in stuff for our basement insulation, and it seemed to work pretty well. How is that for an attic?

If there is something that works just as well and we could install ourselves, though, that would be nice.

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