How to Insulate an Attic with Fiberglass | This Old House

General contractor Tom Silva shows affordable ways to create an energy-efficient attic. (See below for a shopping list and tools.)

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Kevin and Tom insulated an attic using a combination of loose-fill (blown-in) fiberglass insulation and fiberglass batts. They cut the batts to size and installed them in-between the floor joists close to the eaves, taking care not to block the flow of fresh air coming into the attic through the soffit vents. For the floor joist bays that were inaccessible due to a subfloor, they installed loose fill fiberglass insulation using a blowing machine, which allowed them to dense pack the material inside each of the joist bays.

Cost: About $300 to $600
Time: 2 to 4 hours
Difficulty: Easy. Kneeling isn't fun, but the work itself is relatively easy

Shopping List for How to Insulate an Attic with Fiberglass:
- Fiberglass insulation (faced and unfaced)
- Loose fill insulation, for insulating under attic floor

Tools for How to Insulate an Attic with Fiberglass:
- Utility knife
- Blower pump, for pumping loose-fill insulation
- Dust mask and eye goggles
- Work gloves
- Kneepads

Steps:
1. Cut fiberglass batts to fit tightly between floor joists.
2. Lay the fiberglass batt between the joists with the paper vapor barrier facing down toward the heated space. Lightly press the batt down between the joists.
3. When installing insulation along the eaves, be careful not to cover the soffit vents.
4. Use unfaced fiberglass batts to insulate over existing insulation.
5. Add a second layer of insulation by lying unfaced fiberglass batts perpendicular to the floor joists. Butt the batts tightly together for maximum efficiency.
6. To insulate under attic floor, use a pump to blow in fiberglass loose-fill insulation.
7. Insert the hose under the floor and turn on the blower.
8. As the loose-fill insulation packs tightly into the space beneath the floor, it will slowly push out the hose. Turn off the blower when the void is completely filled.

Both the batts and loose-fill fiberglass insulation were manufactured by:
Johns Manville [jm.com/]

Insulation blowing machines are available for rent at many home and rental centers.

The insulation blowing machine that Tom used was manufactured by:
AccuOne Industries, Inc. (model#9218)

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How to Insulate an Attic with Fiberglass | This Old House
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