Insulating your home is one of the most important steps you can take to make your home more energy efficient. The type of insulation you use can have a big impact on energy savings, installation costs, and home comfort. Two popular types of insulation are cellulose and spray foam. But which one is the better choice for your home?
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What is Cellulose Insulation?
Cellulose insulation is made from recycled paper products, typically newspaper. It is treated with fire retardant chemicals and then chopped into small pieces to form loose fill insulation. Cellulose contains about 75% recycled content. It is an environmentally friendly option since it makes use of waste paper.
Cellulose is applied wet and allowed to dry in wall cavities. It settles over time to form dense packed insulation with an R-value of around R-3.7 per inch. Higher density installation boosts the R-value to about R-3.9 per inch. Most homes insulated with cellulose achieve insulation levels of R-13 to R-21 in standard wall cavities.
Advantages of Cellulose Insulation
- Made from recycled materials
- Relatively low cost insulation material
- Works well for retrofit in existing homes
- Good sound absorption qualities
- Does not require special respirators or protective gear for installation
Disadvantages of Cellulose Insulation
- Can settle over time, reducing insulation value in attic applications
- May encourage growth of mold if gets wet
- Loose fill application allows air movement through insulation
- Higher potential for insect or rodent infestation
What is Spray Foam Insulation?
Spray foam insulation starts as a liquid solution that is sprayed into wall cavities, attics, crawl spaces, and other areas. It expands quickly to fill all nooks and crannies before curing into a solid foam insulation. The typical spray foam insulation is polyurethane foam. It contains little or no formaldehyde.
There are two main types of spray foam insulation:
- Open-cell spray foam – Softer and allows vapor transmission. Typically has an R-value around R-3.7 per inch.
- Closed-cell spray foam – More rigid foam with higher density. R-value of R-6.0 to R-6.5 per inch.
Most homes insulated with spray foam have insulation values of R-13 to R-23 in standard wall cavities. Higher R-values can be achieved by adding thicker insulation.
Advantages of Spray Foam Insulation
- Air seals as it expands and cures
- Higher insulation value per inch compared to other insulations
- Conforms well to odd shaped spaces
- Provides some structural reinforcement
- Minimal vapor transmission through closed cell foam
Disadvantages of Spray Foam Insulation
- Higher material cost compared to other insulations
- Requires special equipment and contractor expertise
- Respirator and protective gear recommended during installation
- Can bow or warp wood studs as it expands if not installed correctly
- Difficult to remove or replace if remodeling
Cellulose vs. Spray Foam Insulation Cost Comparison
Insulation cost per square foot can vary quite a bit depending on whether you insulate yourself or hire a contractor. Here is a general comparison of material-only costs for common insulation levels:
| Insulation Type | Cost per Square Foot (Material Only) |
|---|---|
| Cellulose Insulation (R-13 walls) | $0.20 – $0.40 |
| Spray Foam Insulation (R-13 walls) | $1.00 – $2.00 |
| Cellulose Insulation (R-30 attic) | $0.75 – $1.25 |
| Spray Foam Insulation (R-30 attic) | $3.00 – $6.00 |
As you can see, the material cost for spray foam is significantly higher than cellulose insulation. However, installed spray foam costs are only 15% to 50% higher than cellulose when you factor in labor expenses. The higher insulating value of spray foam compared to cellulose can result in energy savings that offset the higher initial costs over time.
Comparison of Other Features
Beyond just costs, here is how cellulose and spray foam stack up on some other considerations:
Installation Locations
Cellulose insulation is primarily used for wall cavities, attic floors, and rim joists in new construction or retrofit applications. It can be dense packed into wall cavities to provide thermal and sound control. Cellulose blown into attic floors requires proper venting between roof rafters.
Spray foam insulation can be applied in all of the same areas as cellulose. It excels at air sealing and insulation for rim joists, old porous concrete foundation walls, cathedral ceilings, and awkward shaped cavities. Closed-cell spray foam is ideal for exterior wall insulation when continuous exterior rigid foam insulation is not used.
Air Sealing Ability
As wet-spray cellulose dries inside a wall cavity, it adheres to wood and other surfaces to provide a decent air seal. However, some settling will occur over time which can allow air gaps. Air infiltration through electrical boxes and other penetrations needs to be caulked and sealed.
Spray foam insulation expands to fill the entirety of a wall cavity or space. It seals around pipes, wires, outlets, and other penetrations as it cures. The rigid foam results in excellent air sealing qualities. Spray foam provides up to 50 times lower air permeability compared to cellulose.
Vapor Permeability
Cellulose insulation is vapor permeable, meaning water vapor can diffuse through it. This allows wall assemblies to “breathe” and dry out if any moisture accumulates inside. A vapor retarder paint or facing material is often applied to the warm-in-winter side of walls insulated with cellulose.
Open-cell spray foam is semi-permeable to vapor transmission. Closed-cell spray foam forms a rigid plastic barrier that inhibits vapor diffusion. For colder climates, the vapor impermeability of closed-cell foam makes it preferable for exterior wall insulation.
Fire Resistance
Cellulose insulation receives fire retardant chemical treatments during manufacturing. This results in a product that achieves Class 1 fire ratings for flame spread and smoke development. This makes cellulose very safe for residential insulation projects.
Polyurethane spray foam is naturally fire resistant and achieves similar Class 1 flame spread and smoke ratings. Foam plastic requires an approved thermal barrier, like gypsum wall board, for fire protection in habitable spaces. Overall, both cellulose and spray foam present minimal fire hazards.
Rodent and Insect Resistance
Loose fill cellulose insulation provides ample opportunity for rodents to burrow and nest. Professional dense packing helps limit settling and gaps for pests to enter. Insecticide sprays or powders can be applied during installation for added pest protection.
The rigid structure of cured spray foam resists invading pests. Rodents and insects cannot burrow through it. Occasionally ants or other pests may still manage to penetrate the barrier through cracks or utility penetrations.
Mold Resistance
Cellulose insulation is made from recycled paper products and provides a food source for mold if exposed to excess moisture. Proper moisture control, indoor humidity levels, and vapor retarders are important when using cellulose to limit mold growth.
Closed-cell spray foams are non-porous and resist mold growth within the insulation itself. Open-cell foams can potentially support mold if water infiltration occurs. Both types of spray foam require proper installation to avoid trapping moisture.
Sound Absorption
The porous and fibrous structure of cellulose insulation absorbs sound effectively. This helps reduce exterior noise and attenuate sound transmission between interior rooms. Dense packing cellulose into wall cavities provides excellent sound control.
Spray foam insulation provides less inherent sound damping compared to cellulose fiber. However, spray foam’s air sealing ability helps block exterior noise intrusion. Spray foam insulation will reduce sound transmission slightly between rooms but not as effectively as cellulose.
Environmental Impact
Cellulose is one of the most environmentally friendly forms of insulation. The recycled paper content gives it a very low carbon footprint compared to other insulations. No chemical off-gassing occurs after installation. Cellulose is biodegradable as well.
The chemicals and foaming agents used to produce spray foam insulation have moderately high greenhouse gas emissions during manufacturing. However, polyurethane foam itself has low global warming potential after installation and does not deplete ozone. Cured foam is inert and non-toxic.
Conclusion
Overall, spray foam is considered a superior insulation product based on insulation performance, air sealing ability, and resistance to pests and moisture. However, the higher cost of spray foam insulation keeps cellulose competitive for new construction and retrofit projects, especially for rim joist and attic applications.
Here is a quick comparison overview of some key differences between cellulose and spray foam insulation:
Cellulose Insulation
- Lower cost insulation material
- Effective air sealing in retrofits when dense packed
- Higher sound absorption
- More environmentally friendly
- Higher risk of settling over time
- Can support mold growth if exposed to moisture
Spray Foam Insulation
- Excellent air sealing ability
- Higher R-value per inch
- Minimal pest or mold issues
- Better suits exterior wall applications
- Higher material and installed costs
- Difficult to remove or replace
Homeowners should consider the pros and cons of each insulation type for their specific project requirements. An energy audit helps determine where air leaks may exist and how much insulation is needed. This allows selection of the best insulation solutions for your attic, walls, foundations, and other building cavities.