How to Insulate an Attic: A DIY Guide

Heat rises, so an underinsulated attic is one of the biggest sources of heat loss in winter and heat gain in summer. Topping up attic insulation is a project many homeowners can do themselves in a weekend, and it often pays back within a few years.

How much insulation do you need?

Insulation is rated by R-value — resistance to heat flow. The US Department of Energy recommends roughly R-30 in the warmest parts of the South and R-49 to R-60 in cold northern climates for uninsulated attics; most of the country falls in the R-38 to R-60 range.

Step by step

1. Measure what you have

   Push a ruler down into the existing insulation in several places. Multiply the depth by the R-value per inch of the material to estimate your current R-value.

2. Seal air leaks first

   Air leaks around light fixtures, plumbing stacks, wiring holes and the attic hatch carry heat directly into the attic. Seal small gaps with caulk and larger ones with expanding foam. Use fire-rated sealant around chimneys and flues.

3. Check recessed lights

   Older recessed lights that are not IC-rated must not be covered with insulation. Build a protective box around them or replace them with IC-rated airtight fixtures.

4. Install baffles at the eaves

   Staple rafter vents (baffles) between the rafters above the exterior walls so insulation does not block the soffit vents. Attic ventilation prevents moisture problems.

5. Add the new insulation

   Lay unfaced batts perpendicular to the existing layer, or blow loose fill evenly across the attic floor to the target depth. Use depth markers stapled to joists to keep it even.

6. Insulate and weatherstrip the hatch

   Glue rigid foam board to the top of the attic hatch and add weatherstripping around its edge.

Batts or blown-in?

Batts are easy to handle in attics with regular joist spacing and few obstructions. Blown-in insulation fills gaps around wires and odd shapes better and is usually faster for large areas. Many home improvement stores lend the blowing machine free with a minimum purchase of insulation bags.

What it saves

Adding insulation to an underinsulated attic can cut heating and cooling costs noticeably — often 10% or more of the total. Estimate your annual heating cost to see what that is worth: