Frequently Asked Questions
I am dedicating this post to frequently asked questions about how to insulate homes and save energy. This is really cool because I have always felt hamstrung by the limits of 15- and 30-second commercials. After all, how helpful can we be in such a short time period? If you have an insulation question that is not answered in the FAQs, please drop me a line and let me know. If I don't know the answer, I'll find someone who does and get back to you.
Attic
My attic currently has about six inches of loose-fill insulation (loose insulation pieces) and no vapor retarder. If I want to add another six inches of insulation, what type should I use?
Always use unfaced fiber glass insulation with no vapor retarder when adding another layer to existing blanket or loose-fill insulation. If your attic has existing insulation but no vapor retarder, you will need one square foot of free vent area for each 150 square feet of attic floor area. (To add ventilation, consider a combination of soffit and roof vents.)
My home has about six inches of fiber glass insulation in the attic, and I'm planning to add more. Should I use faced insulation?
No. Use only unfaced fiber glass insulation with no vapor retarder. A facing acts as a vapor retarder, which helps reduce the amount of moisture entering a wall, ceiling, or floor. In heating climates, your original layer of insulation should already have a vapor retarder facing the "warm-in-winter" side (living area) of your home.
If you add a second vapor retarder with another layer of faced insulation, any moisture that does get through the first layer may condense on the second. This might cause water stains on the ceiling and could lead to severe structural damage. Install the second layer of unfaced insulation perpendicular to the first, covering the wood ceiling joists to reduce heat loss through the wood. (NOTE: Apply the second layer of insulation perpendicular to the first layer only when the joist cavity is full. Otherwise, apply the second layer right on top of the first layer, between the joists.)
How do I add additional layers of attic insulation to a joist cavity that is only half full?
If joist cavity is only half full and the recommended insulation level in your area is R-38, fill the joist cavity flush with the top with the appropriate thickness of fiber glass insulation. Then lay a second layer of unfaced insulation perpendicular to the existing layer to give a total of 12" (or an R-value of 38) in the joist cavity. Covering the attic joists with the second layer will reduce heat loss through the wood.
What are radiant barriers? Are radiant barriers an effective way to upgrade my home's insulation performance?
Radiant barriers recognized by energy codes come in three basic types: single layer film material, multilayer or bubble film material, and single films applied directly to the underside of roof (plywood/OSB) sheathings. Radiant barriers are not insulation, and by definition, have no R-value. However, there are some radiant barrier products that have entrapped air spaces (bubble pack or multilayer films) where an R-value may be available for the product. In these situations, the product is operating as an insulation as well but the winter R-value (heat flow up) is very small. Often the manufacturer of these product types will list the summer R-value (heat flow down) because it's so much higher than the winter time (heat flow up) value.
Testing has shown that it is more cost effective to add insulation than a radiant barrier. Additionally, the actual reduction in heat flow achieved through properly installed radiant barriers is substantially less than that claimed by some manufacturers. In cold weather, radiant barriers may reduce beneficial heat gains from the sun; because of this, they are mainly sold in areas with warmer climates.
If I install a vapor retarder in my attic, do I still need ventilation?
Yes. Even with a good vapor retarder, proper ventilation is considered essential to prevent damaging condensation. Eave vents openings at the roof overhang combined with a ridge vent, roof vent, or gable vents, are effective ways to create a positive movement of air in and out of the attic. As a general rule, when a vapor barrier is used, 1 sq. ft. of free vent area per 300 sq. ft. above floor area is recommended. When no vapor retarder is used, 1 sq. ft. of free vent area for every 150 sq. ft. of attic floor is recommended.
In the winter, I notice a wet spot on my ceiling where it meets the inside of the exterior wall. My attic area above this room is insulated. What might be causing this moisture problem?
Check to see if your attic insulation completely covers your ceiling area. Attic insulation should extend out over the wall top plate, but not over the eave. You may have a cold spot caused by a lack of insulation over this area, or you may have a ventilation problem or "ice damming". Insulation should extend out over the exterior wall, right up to the roof line, but should not cover the eave vents. Install eave baffles wherever there are eave vents to assure air flow. For additional ventilation, install roof vents.
Crawlspace
If my crawlspace is ventilated, can I still insulate the walls of the crawlspace, or is it better to insulate the floor?
If you have a vented crawlspace with pipes and uninsulated ducts, it is better to insulate the crawlspace walls. If there are insulated ducts and no pipes, the best course of action is to insulate the floor above. The vents should be closed in the winter and open in the summer.
Noise Control
What is QuietZone® and how is it different from standard kraft-faced R-11 building insulation?
QuietZone® is a fiber glass acoustic batt designed to help control sound between interior walls and floors. It has a kraft facing (no vapor barrier) with flanges for easy installation.
What are the acoustical qualities of QuietZone® acoustic batts compared to R-11?
The acoustical performance of QuietZone® acoustic batts are similar to R-11.
Note - if QuietZone® acoustic batts are not available in your area, R-11 fiber glass insulation would be an acceptable substitute. Do not use QuietZone® on exterior walls as the facing is not a vapor retarder. R-13 or R-15 fiber glass batt insulation is recommended for exterior walls.
What are resilient sound channels?
Resilient channels are metal channels that are placed horizontally across the studs to space the dry wall off the studs. This minimizes the connection points between the drywall and the framing, making it harder for sound to vibrate through the wall.
Wall
Since fiber glass blankets compress so easily, can I increase the effectiveness of my insulation by squeezing a 5 1/2", R-21 blanket into a 2 x 4 wall instead of using 3 1/2", R-15 blankets?
No. Compressing fiber glass blanket insulation into a smaller wall space will not necessarily increase your insulation's efficiency. Fiber glass insulation works on the principle of trapped air pockets. By compressing fiber glass insulation, you decrease the amount of air trapped in the material. For example, compressing R-19 into a 2x4 wall will give you an R-13 value. It would be better to buy the product that best fits in the space. R-13 or R-15 batts are the best products for a 2x4 wall.
To see a general compression chart, click here.
Should I staple the facing to the front of the stud or to the inside?
Either is acceptable. Most drywall installers prefer to have the kraft paper stapled to the inside. Inset stapling allows them to glue the drywall and gives a smoother surface to attach to. The flanges are not part of the vapor retarder so faced stapling does not give you a better seal.
General
Do higher insulation levels create condensation problems?
No. Insulation is not a source of condensation problems. Ventilation and vapor barriers are the general solutions.
Do I staple the flanges on faced fiber glass insulation to the face of the stud or to the inside of the stud?
When stapling is necessary in cathedral ceiling projects, always staple insulation to the face of the rafter to maintain the necessary 1" ventilation space. If Raft-R-Mate baffles have been installed up the entire length of the cavity, then either way is acceptable. In other projects, such as walls, either way is also appropriate.
Does R-value refer to inches?
No. R-value refers to insulation's resistance to heat flow, not to its thickness. Tiny air pockets trapped in the insulating material resist the passage of heat -- heat gain in the warm summer months, and heat loss in the colder months. The higher the insulation's R-value, the greater its insulating power.
I know insulation helps keep heat in during the winter months, but is there any benefit to having it during summer months?
Yes. Traditionally, insulation has been perceived as a cold climate product that is effective in helping reduce winter heating bills. But the fact is, insulation can be just as effective in helping cut air-conditioning costs during the hot summer months.
Regardless of outside or inside temperatures, the main concern is heat. Whenever there is a temperature difference between outside and inside, there will be heat flow.
Insulation helps slow the transfer of summer heat entering the home, which helps keep the inside cool and lessens the need for continuous air-conditioning. Similarly, in winter, insulation helps keep the house warm by reducing the escape of interior heat.
I am in the middle of an insulation project, but I accidentally tore the vapor retarder. Is repair necessary?
Not usually. The edges should lie close enough together to block most of the water vapor. To fix a large tear, tape the two edges together with standard duct tape.
Does the vapor retarder on fiber glass insulation affect the R-value?
No. There is virtually no thermal performance difference between unfaced fiber glass insulation and kraft-faced or foil-faced fiber glass insulation when properly installed. Faced insulation contains a built-in vapor retarder.
What happens when I compress fiber glass insulation?
Fiber glass insulation works on the principle of trapped air pockets. By compressing fiber glass insulation, you decrease the amount of air trapped in the material, therefore reducing the overall R-value. So compressing a thick product into a small space won't necessarily give you a better R-value. Typically if you take a thicker product and compress it down to a smaller size you will end up with an R-value equal to one that is already available.
For example, compressing R-19 into a 2x4 wall cavity will give you an R-13. Owens Corning already make an R-13 batt, so it is best to just purchase the R-13.
