Getting Adequate Attic Insulation
By: Danny Lipford
No matter where you live in the U.S., homeowners are struggling more than ever before to find the balance between being comfortable inside their homes and keeping energy bills smaller than their mortgage payment.
Although adjusting your thermostat will help, the ultimate in energy savings is to keep the heat you’ve paid to produce within your walls as long as possible. That makes adding insulation one of the single most effective ways to save on heating costs.
In almost any climate, if you can see the tops of your attic floor joists when you venture up there, you’ll need to add more insulation. Depending on whether you live in a warm or cold climate, home in the U.S. should have between an R-38 and R-49 in the attic – that’s about 12″ to 15″ of insulation.
Go to the Dept. of Energy Zip Code R-Value Calculator to find insulation recommendations where you live. The DOE Website has a wealth of easy-to-access information about saving energy that is practical and accurate.
To determine if you need more insulation, use a ruler or tape measure to see how much insulation you have in your attic. When you do the measuring, make sure you have plenty of light to work because you will have to walk exclusively on the top edge of the joists—let your foot slip in between where the insulation is and you will end up breaking through the drywall or plaster ceiling in the room below.
Once you determine how much insulation you have and the amount you need, it’s easy enough to install additional amounts over existing insulation yourself. There are quite a number of insulation types including rigid foam, sprayed foam, mineral wool, and natural products like cottons and wools, but most attics in the U.S. are insulated with either fiberglass or cellulose.
Fiberglass insulation comes in rolls or batts and is formed at a particular width and thickness to fit between studs in walls or joists in attics. Each thickness represents an R-rating standard (for instance, R-19 is 5½” thick for use with 2×6 wall studs or attic/floor joists).
This is fiberglass in a loose form that can be blown into your attic by a professional installer through a hose to whatever level is desired.
You can also rent blowers and buy loose fill insulation at home center to blow in insulation yourself.
Cellulose is a paper-based insulation (much of it recycled newsprint) treated with fire retardant that can also be blown into attics or walls with blower.
Which material you use is less important than making sure you have enough insulation for your climate. All of the insulation types above do a good job, and you do not need to stay with the type that’s in your attic now when adding more.
Here are some tips for installing insulation:
- If you are installing fiberglass insulation in batt or roll form on top of existing attic insulation, make sure the insulation is unfaced and doesn’t have a paper or foil facing on either side.
- Wear a long-sleeve shirt, long pants, gloves, eye protection, and a dust mask when installing insulation.
- If you’re installing roll or batt insulation on top of existing attic insulation, lay it perpendicular to the joists so it doesn’t compress the existing insulation below it and creates a blanket with fewer areas where air can leak through from below.
- Don’t cover can (recessed) lights unless they are rated for contact with insulation. If using loose (blown) insulation, build a small enclosure with hardware cloth or plywood to keep the insulation away from lights and exhaust fans.
- Use cardboard or rigid-foam baffles to keep soffit vents from being blocked by insulation where the rafters rest on the outside walls. Encouraging this cold air circulation above the insulation will help exhaust moist warm air leaking from the living space below. If it can’t find a way out, it can condense and begin to rot the roof sheathing.
- Fill all cracks between the living area and the attic with caulk or expanding foam. This includes areas where plumbing vent pipes, flues, electrical wiring, and vent fans, and light fixtures poke through into the attic. Sealing these voids helps defeat the “chimney effect” that draws cold air in at the base of the house and exhausts warm air (that you’ve already paid to heat) out into the attic floor.
- If you are insulating walls or uninsulated joists, fill the cavity completely with insulation.
- Don’t overly compress the insulation—it’s most effective in a fluffy state.
- Split or cut insulation when you run into electrical wiring across the stud or joist bay.
- In walls and floors, staple faced batts every 8″ to 12″ with the facing toward the inside of the house.
- Insulation R-Value (article)
- How Much Insulation You Need (video)
- How to Install Fiberglass Attic Insulation (video)