Insulation — where to add it what type and what you'll save

This article is for educational purposes only and is not a substitute for professional advice. Local codes, regulations, and best practices vary by region.

Insulation keeps your home warm in winter and cool in summer. Most homeowners don’t think about it until they realize their energy bills are too high. But adding insulation is one of the most straightforward energy upgrades you can make, and the science behind it is simple.

How Insulation Works

Insulation works by trapping air in tiny pockets. Stagnant air doesn’t conduct heat well, so trapped air provides resistance to heat flow. This resistance is measured as R-value. A higher R-value means better insulation. R-30 insulation provides twice the resistance as R-15 insulation.

Your climate determines appropriate R-values. Cold climates need more insulation. Warm climates need less. Typical attics in cold climates should have R-38 to R-60. Walls typically have R-13 to R-21 depending on cavity width. Basements vary from R-10 on walls to R-30 where foundation meets house.

Most homes are under-insulated relative to current energy codes. Going from R-19 to R-38 provides dramatic savings. Going from R-38 to R-60 provides incremental improvements. An energy audit shows your climate’s cost-effective target.

Types of Insulation

Fiberglass batts are cheapest at R-3.5 per inch. They’re common in existing homes but irritating to handle. Blown-in fiberglass works well in attics, filling irregular spaces. It settles over time, so you need to add extra initially.

Cellulose is a recycled paper product at R-3.6 per inch. It has excellent sound dampening and fire retardant properties. Spray foam achieves R-6 per inch (closed-cell) and provides excellent air sealing plus insulation, but it’s the most expensive at $1 to $2 per square foot. Rigid foam achieves R-5 to R-7 per inch and works well on exteriors and basements.

The choice depends on application, budget, and climate.

Where to Add Insulation

The attic is the first priority. It provides the biggest energy savings and is the easiest DIY improvement. Basement rim joists come next, as they’re major air leakage points where foundation meets house. If finishing a basement, insulating walls is natural to include. In crawl spaces, rim joist insulation is similarly critical.

If you’re opening walls during renovation, adding insulation while walls are apart is cost-effective. Exterior insulation on the building envelope is very effective but expensive. Small improvements like pipe insulation on hot water lines have good payback.

Attic Insulation: The Easiest Upgrade

If your attic is accessible, adding blown-in insulation is relatively simple. Check what’s already there. Measure the depth. Calculate what you need to reach your climate’s recommended R-value.

A blown-in machine rental costs $50 to $100 per day with a refundable deposit. Material costs $0.50 to $1.50 per square foot. A 500 square foot attic takes 4 to 6 hours of DIY work. Rental plus materials typically costs $300 to $600, compared to $800 to $1,500 professional installation.

Ensure soffit and ridge vents aren’t blocked by insulation. Ventilation is critical for attic health.

Basement Insulation Challenges

Basements have moisture risk. Below-grade walls need moisture control before insulation. Above-grade walls can use standard insulation. Interior insulation using fiberglass batts is cheapest but uses interior space. Exterior insulation with rigid foam is most effective but requires excavation.

Rim joist insulation is critical and often overlooked. Address air sealing and insulation together in basements.

Expected Savings

Attic insulation typically provides 10 to 15 percent heating and cooling bill reduction. Basement insulation provides 5 to 8 percent. Real dollar savings range from $100 to $300 annually depending on climate and existing insulation.

A $2,000 attic insulation job saving $150 per year has a payback of about 13 years. In cold climates, payback is faster. In warm climates, slower.

Non-energy benefits include improved comfort, reduced drafts, and noise dampening.

Federal Tax Credits and Rebates

A 30 percent federal tax credit applies to insulation added to existing homes through 2032. Many utilities offer $0.50 to $1.00 per square foot rebates. Some programs allow stacking, combining federal credit plus utility rebate.

Keep receipts and installer certification for claiming credits.

The Bottom Line

Insulation is straightforward science and among the best energy investments. Adding insulation to under-insulated homes is one of the highest-ROI efficiency upgrades available. Start with the attic, which provides the fastest payback and easiest DIY implementation.

© The Whole Home Guide