Best Insulation Types for San Antonio Homes

No single insulation type is best for every San Antonio home. What works depends on where it goes. For most houses here, attic insulation is the place to start: begin with attic air sealing, then add blown-in fiberglass or cellulose until the attic reaches about R-38 to R-49.

Spray foam insulation is worth its higher cost in specific cases. The main one is when you want the ducts and air handler in a hot attic brought inside an airtight roof deck. Walls, crawl spaces and garages each have their own best fits. A radiant barrier can help in our sunny climate, but it does not replace insulation.

This guide covers which type fits which part of the house, the R-values that apply in Bexar County, and how to tell what your home actually needs.

Quick Answer: Best Insulation by Area of the Home

Why San Antonio Homes Need Their Own Insulation Plan

San Antonio sits in climate zone 2A, a hot and humid zone with a long cooling season. On a summer afternoon the attic is the hottest part of the house, and that heat pushes down through the ceiling into the rooms below. That is why the attic floor is usually the first place to look.

Two more local factors shape the choice.

• Ducts in the attic. In hot climates, ductwork is often run through the attic. Cool air then travels through the hottest space in the house before it reaches your rooms. This affects whether a radiant barrier, sealed and buried ducts, or roof-deck spray foam makes sense.
• Humidity. Moist air affects crawl spaces and roof decks more than attic floors. Some materials handle it better than others, and some setups need a moisture plan before any insulation goes in.

R-Value Targets for San Antonio (Climate Zone 2)

R-value measures how well insulation slows heat flow. A higher number means more resistance. The total R-value of your attic comes from the material's R-value per inch multiplied by how deep it is installed, so a "lower" material can reach the same target if there is enough room for more depth.

The code numbers apply to new construction and permitted work, and your city's adopted code is what governs. The ENERGY STAR numbers are its cost-effective recommendations for existing homes.

A quick self-check: ENERGY STAR suggests measuring the depth of your attic insulation and multiplying the inches by 3 for a rough R-value. If the insulation is at or below the top of the floor joists, you probably need more.

How deep does R-38 or R-49 need to be?

Loose-fill products have different R-values per inch once they settle, so the depth needed to hit the same target is different.

These are rough figures worked out from U.S. Department of Energy settled values. The real number comes from the coverage chart printed on the product bag, which lists the minimum settled thickness and how many bags it takes for a given area. Your paperwork at the end of the job should show the R-value that was installed.

The Main Insulation Types, Compared

Blown-in fiberglass

Blown-in fiberglass is loose glass fiber that a machine blows across the attic floor. It settles very little over time and is light, which matters when you are adding a deep layer over old ceiling drywall.

The trade-off is a lower R-value per inch, so it needs more depth than cellulose to reach the same R-value. It can also be "fluffed," which means installed below the maker's minimum density. Fluffed insulation can look deep and still fall short of the label R-value. Ask how many bags will be used for your attic size and compare that with the bag chart.

Good fit when: the attic floor is open, there is plenty of height, and you want a top-up over existing insulation.

Blown-in cellulose

Cellulose is made from recycled paper treated with fire retardants. It has a higher R-value per inch than blown fiberglass, so it reaches R-38 or R-49 with less depth. That helps in low attics where there is not much room between the ceiling and the roof.

Cellulose settles more, roughly 10 to 20 percent. A good installer blows it deeper than the target so the settled depth still hits the R-value. It is also heavier per cubic foot than fiberglass. Like any fiber insulation, it needs to stay dry, so roof leaks have to be fixed first. Cellulose can also be packed into closed wall cavities through small holes.

Good fit when: the attic has limited height, or the walls are closed and empty.

Fiberglass batts and rolls

Batts are pre-cut pieces and rolls are long blankets. They work best where framing is open and evenly spaced: walls during a remodel, garage walls, and floors above a crawl space.

How well they perform depends on the fit. Gaps, squashed sections and batts stuffed around wires all lower the real R-value. On an attic floor full of wires and blocking, blown-in usually covers better. If rolls are laid over existing attic insulation, ENERGY STAR advises using unfaced rolls so moisture is not trapped.

Good fit when: the framing is open and regular and the installer can fit each piece cleanly.

Spray foam (open-cell and closed-cell)

Spray foam goes on as a liquid and expands into place. Unlike fiber insulation, it also seals air. There are two main kinds:

• Open-cell foam: about R-3.6 per inch. It is softer and lets water vapor pass through.
• Closed-cell foam: about R-6 per inch. It is denser, more rigid and resists water vapor.

In a San Antonio home, the main reason to choose spray foam is usually the roof deck. This turns the attic into a sealed, unvented space, so ducts and the air handler up there sit inside the insulated part of the house instead of in a hot attic. The Department of Energy notes that the roof deck in an unvented attic must be very airtight. Unvented attics also have their own code rules, so the design needs to be right before anyone starts spraying.

Spray foam has clear trade-offs. Sealing and insulating an attic with spray foam costs more than adding insulation to the attic floor. The sloped roof also has more surface area than the flat ceiling below it, so there is more area to cover. During installation, the EPA says only workers with proper protective gear should be in the space, and residents should stay out until the product's re-occupancy time has passed.

Good fit when: ducts and equipment are in the attic and you want them inside the insulated space, the attic is finished or partly used, or the space is too tight for blown-in.

Radiant barrier

A radiant barrier is a reflective foil, usually installed on the roof side of the attic. It reflects the heat that radiates down from a hot roof. It does not slow heat moving through materials the way insulation does, so it has no R-value of its own.

The Department of Energy says radiant barriers work better in hot climates than cool ones, especially when ducts are in the attic. It also notes that some studies show 5 to 10 percent lower cooling costs in warm, sunny climates. Dust on the shiny surface reduces how well it works. That is why foil laid flat on top of attic floor insulation tends to lose effect over time.

Good fit when: the attic floor is already well insulated and sealed, and you want an extra layer against roof heat, especially with ducts in the attic.

Mineral wool and rigid foam board

Mineral wool (rock or slag wool) is a denser fiber insulation that handles high temperatures well. It comes as batts and loose-fill, and loose-fill mineral wool settles at about R-3.0 to R-3.3 per inch.

Rigid foam boards are made from polystyrene, polyisocyanurate or polyurethane. They are often used on crawl space and foundation walls, under floors, and as continuous insulation behind new siding. You will usually see both in specific spots rather than across a whole attic.

Which Insulation Fits Your Home? Common San Antonio Situations

A vented attic with thin or uneven insulation

This is the most common case. Seal the leaks in the attic floor first, add baffles at the soffits, and then blow fiberglass or cellulose to an even depth that reaches about R-38 to R-49. Old insulation can usually stay if it is dry and clean. If it is wet, moldy or contaminated, it should be removed before the new layer goes in.

Ducts and the air handler in a very hot attic

You have two main paths. You can keep the attic vented, seal the ducts, and insulate the attic floor heavily; ENERGY STAR notes that burying sealed ducts in insulation is fine and can even improve efficiency. Or you can spray foam the roof deck so the whole attic, ducts included, sits inside the insulated space. The second path costs more and needs a careful design, but it deals with the duct heat directly.

A pier-and-beam house

Homes raised on piers have open space under the floor. The target for the floor is R-13. Batts held up tight against the subfloor, closed-cell spray foam, or rigid foam board can all work. Moisture is the first thing to check, because damp air or standing water under the house can ruin fiber insulation and lead to mold.

Older walls with little or no insulation

If the walls are closed and mostly empty, cellulose or fiberglass can be blown in through small holes drilled from inside or outside, then patched. If you are replacing siding anyway, ENERGY STAR suggests blowing insulation into the empty cavities before the new siding goes on.

A bonus room over the garage that never cools down

These rooms often lose to heat from several sides at once: the garage ceiling below, short knee walls, and a sloped ceiling close to the roof. The fix usually means insulating and sealing all of those surfaces, not just one. Spray foam is one option for sloped ceilings with little space. Batts or blown-in can work on the garage ceiling below the room.

A remodel or addition with open framing

Open walls are the easiest time to insulate well. Batts fitted with care, blown-in behind netting, or spray foam all reach R-13 in a standard wall. This is also the cheapest time to seal around outlets, pipes and wiring holes.

Stop and check before any insulation goes in

Some attic conditions need attention before any material is chosen:

• Vermiculite insulation. ENERGY STAR describes it as a lightweight, pea-size, flaky gray mineral. It may contain asbestos and should not be disturbed until a lab has tested it.
• Knob-and-tube wiring. It is found mostly in homes built in the 1930s and earlier and can be a fire hazard when covered with insulation.
• Wet insulation, roof leaks or mold. The cause needs fixing first.
• Bath fans, kitchen vents or dryer vents that blow into the attic. They should vent outdoors.
• A gas furnace or water heater in the attic. ENERGY STAR advises having an HVAC contractor do combustion safety testing after air sealing.

Air Sealing Comes Before Any Insulation Type

Insulation slows heat moving through materials, but most of it does not stop air from leaking through gaps. ENERGY STAR advises sealing the attic floor before adding insulation. It even says that if a contractor will not agree to seal before insulating, you should call another one.

Common leak points include the gaps around recessed lights, the plumbing vent pipe, the furnace flue, wiring holes, the tops of interior walls, and the attic hatch. Once new insulation covers them, these spots are much harder to reach. That is why air sealing should happen before any new insulation goes down.

Common Mistakes When Choosing Insulation

• Picking the material before looking at the house. The attic height, the existing layer, the ducts and the roof design should drive the choice, not a brand name or a sales pitch.
• Comparing only R-value per inch. Total R-value depends on depth and even coverage. Blown fiberglass at the right depth can match cellulose at a shallower depth.
• Blocking soffit vents. In a vented attic, insulation piled against the eaves can block airflow. Baffles keep that path open.
• Using a radiant barrier instead of insulation. It is an add-on for hot climates, not a replacement for proper attic floor insulation.
• Laying faced rolls over existing insulation. The facing can trap moisture between layers.
• Not getting the result in writing. ENERGY STAR says the contractor should give you paperwork showing how much insulation was added and the new R-value.

Rebates and Tax Credits in 2026

CPS Energy attic insulation rebate. CPS Energy residential customers can get up to $0.35 per square foot for contractor-installed attic insulation, or $0.25 per square foot if they install it themselves. The current program covers projects completed between February 1, 2026 and January 31, 2027. Applications are due within 30 days of finishing the work.

Key rules for attics with more than 24 inches of clearance: the final level must be at least R-38, and the existing insulation must be no higher than R-14. Lower attics have their own R-19 and R-11 thresholds.

The rebate covers insulation installed between the air-conditioned living space and an unconditioned attic. If you are planning roof-deck spray foam instead, ask CPS Energy whether your project qualifies before counting on it. Program terms can change without notice.

Federal tax credit. ENERGY STAR lists the federal insulation tax credit as applying through December 31, 2025. Check with a tax professional before assuming it covers work done in 2026.

Frequently Asked Questions

Does insulation help during San Antonio winters too?

Yes. Insulation slows heat moving in either direction. In summer it keeps attic heat out of your rooms, and during winter cold snaps it helps keep heated air inside. Air sealing helps in both seasons as well.

Can new insulation go on top of old insulation of a different type?

Usually, yes. ENERGY STAR says that unless the old insulation is wet, moldy, smelly or contains animal waste, new insulation can generally go on top without removing it. The new layer does not have to be the same material as the old one, as long as the old layer is dry and clean.

Is cellulose a fire risk?

Cellulose sold as insulation is treated with fire retardants, and ENERGY STAR certified insulation has to pass flame-resistance testing. Any insulation still needs safe clearances. ENERGY STAR recommends special covers over older recessed lights and sealing gaps around flues with metal flashing and high-temperature caulk.

How long do I need to stay out of the house after spray foam?

It depends on the product. The EPA notes that some manufacturers recommend 24 hours after a professional two-part spray foam job before residents return, but times can vary. Ask your installer for the specific product's re-occupancy time before work starts.

Will insulating the attic floor make the attic cooler?

Not really. Insulation on the attic floor keeps attic heat out of your rooms, so the attic itself can stay just as hot. This is why ducts in a vented attic matter: they still sit in that heat. Sealing and burying the ducts, adding a radiant barrier, or moving to a sealed roof deck are ways to deal with it.

Can I install insulation myself?

ENERGY STAR rates batts and rolls as basic skill and loose-fill as intermediate. Sprayed foam is rated advanced and needs a certified installer. If you do it yourself, ENERGY STAR suggests sealing the attic first, wearing protective gear, walking only on joists, and working early in the day because attics get very hot.

The Bottom Line

For most San Antonio homes, the best first step is a well-sealed attic floor with blown-in fiberglass or cellulose at about R-38 to R-49. Spray foam on the roof deck fits homes with ducts and equipment in the attic or limited space, and it costs more. Closed walls usually get blown-in insulation, crawl space floors need R-13 once moisture is under control, and a radiant barrier is an extra layer, not a substitute.

The right answer for your house starts with what is already there. If you would like a second opinion, we can measure your current attic insulation, check for air leaks and problem conditions, and explain which options fit before you commit to anything. Request a free estimate to get started.

References

• ENERGY STAR. Recommended Home Insulation R-Values (opens in a new tab)
• ENERGY STAR. Well-Insulated and Sealed Attic (opens in a new tab)
• U.S. Department of Energy. Loose-Fill Insulation (opens in a new tab)
• CPS Energy. Ceiling-Attic Insulation Rebate (opens in a new tab)