What R-value should my attic have?

The US Department of Energy recommends R-49 to R-60 for most US climates, which typically means 14 to 16 inches of loose-fill insulation. You don't have to reach the target in one project — topping up from a low existing R-value still delivers meaningful savings, and you can stage it over time.

Is blown-in or batt insulation better for an attic?

Both meet the energy goal. Blown-in loose-fill is the better choice for top-ups because it conforms around ceiling joists and any existing insulation. Batts work well if the joist spacing is standard and the attic is open. The choice is mostly about access, budget, and whether you are doing the work yourself.

How much does it cost to insulate an attic?

For a 1,500 sq ft attic top-up from R-15 to R-49, expect roughly $500–$900 for DIY blown-in (rental blower plus material), $1,200–$2,000 for contractor-installed loose-fill, and $2,000–$3,500 if you add professional air sealing. The air-sealing add-on usually has the highest return on investment of the upgrade.

Can I insulate over existing insulation?

Yes, as long as the existing material is dry, pest-free, and not compressed. Remove clutter, fix any roof leaks first, verify recessed lights are IC-rated, and install baffles at the soffits so ventilation is not blocked before adding new material on top.

How to Insulate Your Attic: A Plain-English Walkthrough

Q: Should I air seal before adding insulation?

Yes. Air sealing is the single most important step in an attic insulation project. Insulation slows heat movement through material — it does not stop air moving around it. A leaky attic with high R-value insulation will not perform to spec, and the air-sealing component usually has a higher return on investment than the marginal R-value from adding more insulation.

For most US homes, adding attic insulation is the most cost-effective home energy project available. It's accessible (you can usually reach it), it doesn't require opening up walls, and the savings are predictable. This is a plain-English walkthrough for someone considering the project for the first time.

Before you start: air sealing

The single biggest mistake in attic insulation projects is adding insulation without first sealing air leaks. The reason: insulation slows heat movement through material — it doesn't stop air moving around it. A leaky attic with high R-value insulation won't perform to spec because warm air bypasses the insulation through gaps.

Common attic air leaks:

Around recessed light fixtures (without insulation-contact-rated housings)
Plumbing vent pipes
Chimney / flue chases
Attic hatch or pull-down stairs
Wiring penetrations
Bathroom exhaust fan housings
Open web joist cavities that connect to wall cavities

Most leaks can be sealed with caulk (small gaps), spray foam (medium gaps), or fire-rated foam and metal flashing (around chimney and flue penetrations — code requirements apply).

Read our guide on common home air leaks and how to find them for the leak checklist.

Step 1: figure out what you have

Measure existing insulation thickness in a few places. Convert to R-value using the material's R-per-inch:

Fiberglass loose-fill: ~2.5 R/inch (older, lower density) or 2.8 to 3.0 (newer)
Fiberglass batt: ~3.0 to 3.5 R/inch
Cellulose loose-fill: ~3.5 R/inch
Mineral wool: ~3.5 to 4.0 R/inch

Multiply thickness by R-per-inch to get current R-value. If you have 6 inches of older fiberglass loose-fill, you're at roughly R-15.

The US Department of Energy recommends R-49 to R-60 for most US climates. The gap between current and target determines how much material you'll be adding.

Step 2: pick a material

Two main options for attic top-ups:

Fiberglass or cellulose loose-fill (blown-in)

Loose-fill is blown from a machine into the attic, leveling itself to a target depth. It's the most common approach for top-ups because it conforms around ceiling joists and any existing insulation. Fiberglass loose-fill costs roughly $0.50 to $1.00 per sq ft for an R-19 top-up. Cellulose (denser, more air-tight when dense-packed, but slightly heavier) costs similar.

Fiberglass or mineral wool batts

Batts are rolled out manually. They work well if the attic is open and the joist spacing is standard, but they don't conform around irregular framing as easily. Batt top-ups are usually a DIY-friendly choice where loose-fill is best done with a rental blower (or contractor).

Both materials meet the energy goal. The choice is mostly about access, DIY vs. hired, and personal preference.

Step 3: clear and prepare

Before adding anything:

Remove clutter, stored items, debris. You need clean ceiling surface to work on.
Inspect for water damage or roof leaks — adding insulation over an active leak traps moisture and ruins both the insulation and the ceiling below. Fix the leak first.
Verify recessed lights are insulation-contact (IC) rated. If they aren't, install covers or maintain the required clearance.
Verify exhaust fans vent through the roof, not into the attic (common mistake).
Create dams around any non-IC-rated lights, chimneys, and flue penetrations to maintain clearance.

Step 4: install

For loose-fill: rent a blower from a local hardware store (~$50 to $100/day). Two people work it — one feeds the machine, one in the attic with the hose. Depth targets are usually marked on the joists with chalk lines.

For batts: roll perpendicular to the ceiling joists so the second layer covers the joist and reduces thermal bridging. Butt-edges tight; no gaps.

Step 5: don't block ventilation

Attic ventilation (soffit vents, ridge vent, gable vents) lets humid air escape and prevents roof-deck moisture problems. Achieving R-49 generally needs about 14 to 16 inches of loose-fill; ensure baffles are installed at the soffits to prevent insulation from blocking the air path from soffit to ridge.

Step 6: address the attic hatch

The pull-down stairs or hatch is usually the biggest single leak in an insulated attic. Insulate the back of the hatch cover with rigid foam or a batt; weatherstrip the perimeter; add a latch to hold it closed tightly. A pre-built insulated hatch cover with weatherstripping costs about $40 to $100 and pays for itself in the first winter.

Scale and cost

A 1,500 sq ft attic top-up from R-15 to R-49 typically costs:

DIY loose-fill (rental blower + material): $500 to $900
Contractor-installed loose-fill: $1,200 to $2,000
Contractor-installed with air-sealing add-on: $2,000 to $3,500

The air-sealing add-on usually has the highest ROI of the upgrade, because the leak-sealing component contributes more to comfort and energy savings than the marginal R-value from R-15 to R-49. Use the insulation calculator on our home page to estimate the savings side.