Homeowners upgrading their attic usually choose between rolling out fiberglass batts or blowing in loose-fill cellulose. The main types of attic insulation are fiberglass batts, loose-fill (fiberglass or cellulose), spray foam, and rigid foam boards. The best type depends on your budget, climate, and attic structure, though blown-in cellulose or fiberglass are generally the most cost-effective for unfinished attic floors.
Quick answer
Blown-in loose-fill insulation (cellulose or fiberglass) is the most cost-effective choice for unfinished attic floors, offering great coverage around joists. Spray foam is the top premium choice for sealing the roof deck in unvented attics.
- Best for DIY budgets: Fiberglass batts
- Best for filling irregular floor gaps: Blown-in cellulose
- Best for maximum R-value and sealing: Closed-cell spray foam
- The US Department of Energy recommends R-30 attic insulation in warm climates up to R-60 in cold climates.
- Always air seal the attic floor before laying down fibrous insulation to stop warm air from escaping into the cold attic.
- Blown-in cellulose settles by up to 20% over time, so you must overfill it to maintain your target R-value.
- Homes built before 1990 may contain vermiculite insulation, which carries a high risk of containing asbestos.
- What types of attic insulation are there?
- Is it better to use batts or blown-in insulation for an attic floor?
- Which type of attic insulation gives the highest R-value per inch?
- What type of attic insulation is best for a DIY project?
- What types of older attic insulation contain asbestos?
- How do different types of loft insulation compare in cost?
- Do I need to remove my old attic insulation before adding a new type?
- What do owners say?
- Frequently Asked Questions
What types of attic insulation are there?
You have four main options when insulating an attic space. Each material behaves differently and fits specific areas of your roof or floor.
Fiberglass Batts and Rolls
Fiberglass batts are large, pre-cut blankets of spun glass fibers. They come in widths designed to fit perfectly between standard attic floor joists or wall studs. Fiberglass batts typically offer an R-value of R-3.1 to R-3.5 per inch of thickness. They are inexpensive and easy to find at any hardware store.
Blown-In / Loose-Fill Insulation
Blown-in insulation consists of loose particles blown into the attic using a special machine. You can buy blown-in insulation as either fiberglass or cellulose (recycled paper treated for fire resistance). Blown-in cellulose provides an R-value of about R-3.2 to R-3.8 per inch. It creates a seamless blanket over the attic floor, wrapping around wires, pipes, and awkward joist framing.
Spray Foam Insulation
Spray foam is a liquid chemical mix that expands into a thick foam on contact. Professionals usually spray it directly onto the underside of the roof deck. It comes in two forms:
- Open-cell spray foam: Lighter and cheaper. It offers a lower R-value of roughly R-3.7 per inch and allows moisture vapor to pass through.
- Closed-cell spray foam: Dense and rigid. It provides a highly efficient R-value of up to R-6.0 to R-7.0 per inch and acts as both an air and vapor barrier.
Rigid Foam Board Insulation
Rigid foam boards are solid panels of foam (like polyisocyanurate or extruded polystyrene). They are not commonly used on attic floors but work well for insulating attic access hatches, knee walls in finished attics, or under roof rafters where space is extremely tight.
| Insulation Type | R-Value Per Inch | DIY Friendly? | Best Application |
|---|---|---|---|
| Fiberglass Batts | R-3.1 – R-3.5 | Yes | Standard joists with no obstructions |
| Blown-In Cellulose | R-3.2 – R-3.8 | Yes (with rented machine) | Irregular joists, filling gaps, upgrading old insulation |
| Open-Cell Spray Foam | ~R-3.7 | No | Roof deck (requires vapor breathability) |
| Closed-Cell Spray Foam | R-6.0 – R-7.0 | No | Roof deck (requires max R-value and moisture barrier) |
Is it better to use batts or blown-in insulation for an attic floor?
For an attic floor, blown-in insulation generally beats batts. Attic floors are rarely empty. They have wiring, pipes, cross-bracing, and uneven joist heights. If you try to lay fiberglass batts over these obstacles, the batts bunch up. When batts compress, they lose their R-value. They also leave gaps around the edges where cold drafts slip through.
Blown-in insulation flows like a liquid before settling. It fills every crack, covers the joists completely, and leaves no gaps. However, if your attic is perfectly square, completely empty, and has standard joist spacing, batts are much faster and less messy to install.
Which type of attic insulation gives the highest R-value per inch?
Closed-cell spray foam gives the highest R-value per inch, offering up to R-7.0. However, spray foam is usually applied to the roof deck, not the attic floor. For the attic floor, blown-in cellulose provides the highest R-value (R-3.2 to R-3.8 per inch).
The US Department of Energy recommends total attic insulation levels ranging from R-30 in warm climates to R-60 in cold climates. To reach those numbers on an attic floor, you simply add more depth.
Calculating Cellulose for a Standard Attic
Let us look at a real-world calculation. Assume you live in a moderate climate and want to hit R-38 in a 1,000 square foot attic using blown-in cellulose.
- Cellulose offers about R-3.5 per inch.
- To reach R-38, you need roughly 11 inches of depth (38 ÷ 3.5).
- Because blown-in cellulose can settle by up to 20% over time, you must overfill it. You will need to blow about 13 to 14 inches initially.
- A standard 25-pound bag of cellulose covers about 40 square feet at an R-38 depth.
- For 1,000 square feet, you will need 25 bags (1000 ÷ 40).
At an average price of $15 to $18 per bag at a US hardware store, the materials cost roughly $375 to $450 to reach R-38.
What type of attic insulation is best for a DIY project?
Fiberglass batts and blown-in cellulose are both excellent DIY projects. Fiberglass batts require very few tools. You just need a utility knife, a tape measure, long sleeves, gloves, a mask, and goggles. You unroll the batts and press them into place.
Blown-in insulation requires renting a blower machine from the hardware store. It is slightly more complex because you need a two-person team: one person in the driveway feeding bags into the hopper, and one person in the attic pointing the hose. However, many homeowners find blowing cellulose easier on their knees than crawling around cutting batts to fit.
What types of older attic insulation contain asbestos?
Vermiculite insulation installed in North American homes built before 1990 has a high probability of containing asbestos. This material largely originated from a mine in Libby, Montana, which was contaminated with natural asbestos deposits.
Vermiculite looks very distinct. Unlike the fluffy pink fiberglass or shredded gray paper of cellulose, vermiculite looks like pebble-like, grayish-brown, or silvery chunks. It resembles coarse gravel or the potting soil additives used in gardening.
From the Shop
We frequently see homeowners discover vermiculite by accident. A common scenario is pulling up old fiberglass batts to run a new bathroom vent fan, only to find an inch of silvery, pebble-like chunks hiding at the bottom of the joist bays. If you see this, stop immediately. Do not sweep it, do not vacuum it, and do not disturb it. You must call a certified asbestos abatement professional to test and safely remove it.
How do different types of loft insulation compare in cost?
Costs vary widely based on materials and labor. Fiberglass batts and loose-fill cellulose are the cheapest materials, especially if you install them yourself. Spray foam is highly expensive because it requires specialized chemical rigs and professional installation.
- If you want the lowest cost and will do it yourself: Choose fiberglass batts or blown-in cellulose.
- If you have a very leaky roof deck or want to convert the attic to living space: Choose open-cell spray foam.
- If you live in a hurricane zone or need maximum moisture blocking on the roof deck: Choose closed-cell spray foam.
As a rough estimate for professional installation in the US, blown-in insulation typically costs $1.50 to $3.00 per square foot. Spray foam on the roof deck can easily run $3.00 to $7.00 per square foot.
Do I need to remove my old attic insulation before adding a new type?
Usually, no. You can lay new insulation directly over old insulation to increase your total R-value. For example, you can blow a thick layer of loose-fill cellulose right over the top of old, squished fiberglass batts.
There are only a few times you must remove old insulation. Remove it if it is wet, moldy, heavily infested with rodent droppings, or if it contains asbestos (vermiculite). Also, if you are changing your attic from a vented space to an unvented space (spraying the roof deck), you should remove the old floor insulation so the attic space matches the temperature of the house below.
What do owners say?
Owners like
- Fiberglass batts are very easy and straightforward for DIYers to handle and lay out.
- Blown-in cellulose fills irregular gaps and completely covers joists, stopping drafts effectively.
- Spray foam on the roof deck dramatically reduced HVAC bills and kept the attic within a few degrees of the home’s temperature.
Common complaints
- Blown-in cellulose creates an incredible amount of dust during the blowing process.
- Fiberglass causes severe skin and respiratory irritation if full protective gear is not worn during handling.
- Spray foam off-gassing smell lingered for several days after professional installation.
- Cellulose settled much more than expected after 3-5 years, lowering the effective depth.
Summarised from owner reviews and long-term user reports; individual experiences vary.
Frequently Asked Questions
what types of attic insulation are there?
The four main types are fiberglass batts, blown-in loose-fill (cellulose or fiberglass), spray foam (open-cell and closed-cell), and rigid foam boards. Each serves a different purpose, with batts and blown-in being standard for attic floors, while spray foam is typically applied to the roof deck.
what types of attic insulation contain asbestos?
Vermiculite insulation installed in homes built before 1990 has a high chance of containing asbestos. It does not look like modern fluffy fiberglass or shredded cellulose; instead, it looks like small, pebble-like, grayish-brown, or silvery chunks. If you see this, leave it undisturbed and call a professional for testing.
which type of attic insulation is best?
The best type depends on your goal. For an unfinished attic floor on a budget, blown-in cellulose is the best choice because it fills irregular gaps effectively. For maximum energy efficiency in an unvented attic space, closed-cell spray foam on the roof deck is the premium choice.
what type of attic insulation is best for a DIY project?
Fiberglass batts are the simplest for a DIY project because you only need basic cutting tools and protective gear. However, many DIYers successfully use blown-in cellulose by renting a blowing machine from a local hardware store, which provides better gap coverage over uneven attic floors.
different types loft insulation?
The terms loft and attic insulation mean the same thing. The types available are blanket rolls (fiberglass batts), loose-fill material (blown-in cellulose or fiberglass), spray foam, and rigid foam boards. Blanket rolls are the most common choice for simple, empty loft floors.
