Your Home’s R Value – Attic Insulation Do-it-Yourself Guide

Why Should You Care About R Value?

R value (resistance to heat flow) may not seem that crucial, but it could be costing you money! Insulation is a material you probably spend precious little time thinking about. Until sub zero (or sweltering) weather, a three-digit utility bill or chilly drafts start to come, and you start thinking about R value a lot!

At home, you ponder whether it’s worth the time and expense to optimize the r value of your ceilings, walls and basement. At the store, you ponder which type, thickness, width and density to buy. And when you install it, you wonder just how good is “good enough.” The typical R value of attic insulation in American homes can range anywhere from about R30 (not insulated, warm climate) to R60 (well insulated, cold climate).

Attic Insulation

How Much Attic Insulation Is Enough?

Careful installation increases the insulation’s R Value by over 20 Percent. Leaving 5 percent of a wall uninsulated will reduce the entire wall’s R value by 20 percent. It doesn’t take much more time to install fiberglass insulation properly. Install wall insulation so it completely fills each cavity side to side and top to bottom. But remember, packing and compressing insulation reduces its effectiveness.

Insulation is rated according to its R value, or resistance to heat loss: the higher the R-value, the higher the insulating value. Standard fiberglass insulation has an R-value of about 3.5 per inch of thickness; this provides an insulating value of R-11 for 2×4 walls and R-19 for 2×6 walls.

But if you’re serious about energy savings, you can buy better-performing products. High-density types of fiber-glass insulation, with more fibers and air spaces per square inch, offer R-values of up to 4.25 per inch. Some provide R-15 for 2×4 walls and R-21 for 2×6 walls.

There’s also high-density insulation for ceilings and attics. You’ll wind up paying more and in many cases you’ll need to special-order it, but high-density insulation delivers up to 35 percent more insulating value per inch.

The first 3 in. of insulation you add to a bare ceiling or wall will yield huge savings. Adding another 3 in. will increase energy savings, but not to as great a degree. Visit the Energystar.gov Website for more information on the Recommended Level of Insulation for your home. Their recommendations are based on climate, fuel costs and other factors. Adding more insulation in your attic than you need will give you a diminishing return on your investment.

The payback period for retro-fitting insulation varies greatly, but studies show that added insulation usually pays for itself in saved energy costs within 5 to 10 years. One typical two-story Minnesota home was fitted with blown-in wall insulation, additional ceiling insulation and rim joist insulation at a cost of $1,890. The result was a $325 savings in yearly heating costs, which represents a payback period of slightly less than six years.

Pay back in more temperate areas takes longer, but remember that insulation reduces air conditioning costs too.

When You Insulate Attics and Crawlspaces You’ve Got to Vent Them Too!

Since insulation changes the way attics and crawl spaces “breathe,” it’s critical that you maintain or install proper ventilation.

At first, it seems odd to add insulation for warmth and then purposely create ventilation “holes” for cold air to enter. But if you don’t do this, you’re setting yourself up for moisture problems.

Installing Attic Insulation

Make sure to follow these steps in installing your attic insulation:

  • Lay plywood across the joists and hang a temporary work light. You should leave insulation in its wrapper until you’re ready to use it. Insulation is packaged in a compressed state and expands greatly when the wrapper is opened.
  • Begin laying batts or blankets at the outer edge of the attic space and work towards the center (this will allow more headroom in the center of the attic for whatever cutting and fitting there is to be done). Lay in long runs first and use the leftovers for shorter spaces. Insulation should be installed around wiring taking care not to disturb it. Be sure to butt insulation tightly at joints for a complete barrier to heat flow.
  • Insulation should extend far enough out to cover the top plate of the walls but should not block the flow or air from the eave vents. For best results, install ventilation baffles at the inside of the eaves.
  • Insulation must be kept three inches away from recessed light fixtures unless the fixture is marked ‘I.C.’ (insulated ceiling) – a fixture designed for direct insulation contact. Insulation placed over an unrated fixture, like a recessed light, may cause it to overheat and start a fire. Fill the space between a masonry chimney and wood framing with noncombustible material such as unfaced Fiberglas insulation. If you are insulating around a metal flue, do not place the insulation flush to the flue. Always leave at least a three-inch space.
  • Ends of batts should be cut to fit snugly around cross bracing. If a second layer of insulation is needed and the cavity has been completely filled, the additional layer should be placed at right angles to the joists.
  • When adding to existing insulation, unfaced Fiberglass blanket is recommended. If the unfaced type is not available, use the faced type but remove the vapor barrier or slash it freely with a knife (then install the insulation with the slashed facing down). Do not leave faced insulation exposed. The facings on standard kraft- and foil-faced insulations will burn.

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