What Type of Insulation Can I Use With Fiber Cement Siding?

  • Product Knowledge

No matter what type of climate you’re working in, fiber cement siding gives owners an exterior that protects the building and helps to insulate it effectively. The siding is weather-resilient and impact-resistant, and it even offers a code-compliant siding solution in regions with strict building requirements, like California. Fiber cement has become one of the most popular types of cladding in the States because of its long-term durability.

Fiber cement siding works well as an exterior material because it protects the layers of insulation underneath it. But many wonder what the best insulation for exterior walls is or what types of insulation they can use in conjunction with fiber cement — let’s explore more.

How Fiber Cement Optimizes Home Insulation

Fiber cement brings a few benefits to a building’s insulation:

  • Keeps pests and moisture out
  • Seals the home for optimal energy-efficiency
  • Provides exceptional durability over time

“It’s the only type of siding that combines the performance of masonry—minimal upkeep; rot-, fire-, and termite-proof; unaffected by wind or cold—with the look of painted wood clapboards, shingles, even stone or brick. Yet fiber cement goes for just a fraction of the cost of these other materials,” according to Sal Vaglica for This Old House.

Types of Insulation and How They Compare

From rigid boards to insulating concrete blocks, there are several types of insulation. Depending on which type of insulation you choose, you’ll want to check with the manufacturer and local building codes for the appropriate thickness of that insulation layer.

Understanding the difference between R-value and U-value is important. You’ll want to add enough insulation to meet R-value recommendations, which ENERGY STAR® provides, according to the climate zone you’re building in (pictured below). Residential energy codes dictate minimum insulation requirements, found in chapter 4 of the International Energy Conservation Code.

Allura energy map

ENERGY STAR® climate zones

You should install Allura products over a rigid sheathing that provides a flat surface that is no more than one inch thick.

Here are a few types of insulation that work well with fiber cement.

Concrete Insulation Types

“Insulating concrete forms (ICFs) are basically forms for poured concrete walls, which remain as part of the wall assembly,” according to the Department of Energy. “This system creates walls with a high thermal resistance, typically about R-20. Even though ICF homes are constructed using concrete, they look like traditional stick-built homes.”

By using foam boards or blocks and reinforcing them with rebar, ICF systems provide continuous insulation and a highly durable wall assembly.

Concrete blocks can then be filled with insulation, but studies show that thermal bridging can occur. “Placing insulation on the exterior has the added advantage of containing the thermal mass of the blocks within the conditioned space, which can moderate indoor temperatures,” according to the Department of Energy.

Installing fiber cement siding on a concrete assembly requires an experienced contractor, and it will also require furring strips to anchor any siding panels installed on the exterior.

Loose-Fill or Blown-In Insulation

This type of insulation works well for retrofit projects. Materials like fiber and foam are used to fill in wall cavities and other spaces, either by pouring or blowing the insulation material into the empty space. Fiber cement siding could then be installed on the sheathing or any structural framing on the assembly.

Allura graphic

Loose-fill insulation is most commonly made from fiberglass, mineral wool or cellulose, and it is produced using recycled materials. “Cellulose, fiberglass, and rock wool are typically blown in by experienced installers skilled at achieving the correct density and R-values. Polystyrene beads, vermiculite, and perlite are typically poured,” according to the Department of Energy.

Spray-Foam Insulation

Spray or liquid-foam insulation is sprayed or poured into walls, attics or under floors to provide insulation and reduce air leakage. Small pressurized cans of insulation also work for holes or leaks around doors and windows for DIY insulation projects.

Fiber cement siding can then be installed on the sheathing or any structural framing on this type of assembly.

Allura Painting Siding


Rigid Boards and Panels

Rigid insulation panels like EPS or XPS foam boards, or structural insulation panels (SIPs), can be used to insulate almost any part of the home. These types of insulation are a highly effective form of protection and provide thermal resistance that often outperforms most other types of insulation.

These boards are sometimes covered in a foil face, as a reflective surface that also helps with vapor diffusion. Fiber cement can be added to this assembly by being installed over sheathing or to structural framing.

Ask a Professional

Whichever type of insulation an owner selects, it’s best to work with a professional who knows best. “The type of insulation you should choose depends on how you will use it and on your budget,” according to the Department of Energy. “Consult a professional insulation installer to decide what type of insulation is best for you.”

If you’re working with fiber cement siding, you should consult with the product manufacturer on the most appropriate type of insulation. Manufacturers like Allura provide installation guides to help owners and professionals install the insulation chosen as the best product for their project.

The best way to meet fastening requirements for Allura products is to install three-quarter inch structural sheathing over any non-structural sheathing. However, the wall assembly must be designed in such a way that the re-established structural fastening surface (e.g. OSB, plywood, lathe strips, or 1x or 2x framing lumber) is sufficient to meet the requirements of ICC-ES Evaluation Report ESR-1668. The wall assembly should be designed in such a way that the fastening surface meets the requirements of building and energy conservation codes.

Finishing Your Home With Fiber Cement

Allura finished building


Once you select the type of insulation that works for your project, fiber cement siding can help the assembly achieve a high-performance exterior and energy-efficient building. Because it comes with a 50-year warranty, Allura fiber cement products help owners rest easy knowing the building will be protected for decades.

All of Allura’s products are tested to performance and strength standards to ensure exterior protection. If you’re looking for more information on fiber cement, find an Allura dealer near you.

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