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Attic insulation options  - There are several good options for installing additional insulation to an attic. Unless wet from roof leaks or excess moisture from the building below, there is no need to remove existing insulation. Your choices include:

  • Batts or blankets. Fiberglass is available in a variety of thicknesses and widths, and can be laid on top of existing insulation. If the top of the existing insulation is below the top of the ceiling joists, fill the spaces between the joists first. Then lay batts or blankets perpendicular to the joists to provide the best coverage. Carefully cut around pipes and truss pieces, and don't bunch or fold the fiberglass.
  • Blown-in. Genrally composed of a cellulose (made from recycled newspaper) or fiberglass fibers, blow-in insulation does a much better job of filling around framing and providing a consistent layer of insulation. Blown-in insulation can be applied directly over existing insulation. Proper application requires a special machine and moderate skill.
Regardless of which insulation material is selected, plastic baffles must be inserted between rafters extending past the wall plate to keep insulation form falling into soffits and to provide ventilation. And every attic insulation project must also include sealing of air leaks!

Start in the attic

Your home can lose a significant amount of heat through the roof, so the best place to start insulating is the attic. Compared to walls, access to the attic is relatively easy, therefore the cost of attic insulation projects are considerably lower; it is also the easiest place for “do-it-yourselfers” to begin. You can install loose-fill, batt or blanket insulation over existing insulation. If you choose to use a blown-in insulation (such as fiberglass or cellulose ) or a sprayed-on insulation (such as polyurethane or polyicynene), you’ll probably need to have it professionally installed. 

Most home attics in Minnesota have some insulation; many homes can benefit by adding more attic insulation. Increasing attic insulation to an R-50 can provide a good barrier to heat loss. To determine the present R-value of your attic insulation, have an energy assessment; you can also measure the height of the insulation and multiply times the R-value per inch of the material that is in place (2.5 to 4.0 per inch, on average). Roughly 12 to 20 inches (depending on the material used) will provide an R-50 rating. Although it generally won’t hurt to add more, the return on the investment decreases as the R-value increases above R-50.

Things to look for if you do it yourself

If you are insulating your own attic there are several things to check out to ensure the best possible results:

  • Check for attic air leaks around pipes, wires, and chimneys and seal them up!
  • Make sure baffles are installed at eaves to allow ventilation and prevent “wind-wash” of insulation.
  • Inspect wires and fixture boxes before covering with insulation. 

Insulate the top plate to reduce ice dams - In most homes, the top of the exterior wall (the "top plate") is very close to the roof deck because of the slant of the roof. This means there is much less space for insulation, especially when baffles for ventilation are installed. Less insulation means more heat loss, and it is right at the location prone to ice dam foundation.

The solution is to apply an insulating material with a higher R-value, such as a spray foam (left), to increase the effectiveness of the insulation at that critical location. There are challenges, however, in gaining access to the space. Here are three options:


  • An insulating contractor can often access hard-to-reach top plates from inside the attic with the use of an extended "wand" as part of their spray equipment.
  • Soffit pieces can be removed and access gained from underneath and outside of the attic.
  • If a re-roofing is planned, roof boards or plywood can be removed to gain access from the top and outside of the attic.