Restoration Guide: Fiber Cement Siding for Exterior Walls

Rob Sabo

Editor's Note: This is article 14 of 18 in Chapter 2: Exterior Walls of the Old House Web Restoration Guide. This guide was developed and edited for old homes from original material in the U.S. Housing and Urban Development (HUD) Rehab Guide.


Section 1--The Basics:

Fiber-cement siding was introduced to the building trades in the late 1980s. Prior to fiber-cement siding, asbestos-cement siding was widely used throughout the U.S. and Europe beginning in the 1920s. However, as the health risks associated with the fibrous material became more well known, asbestos was eliminated as a building material in the 1970s. Asbestos siding still can be found on many old houses, and special care must be taken when remodeling a home that contains this material. Under no circumstances should contractors remove the material themselves; rather, they should hire a licensed environmental hazard contractor who specializes in asbestos removal.

Note: Asbestos fibers only pose a health hazard if they become airborne. If they are encapsulated in whole, intact cement siding, they pose virtually no health risk. They only become a hazard if the siding is sawn or broken into pieces and the fiber is released. Before undertaking any home renovation project that includes removal of old cement-style siding, a professional should be brought in to determine if the siding contains asbestos fibers.

1.1: What Is Fiber-Cement Siding?

Fiber-cement siding is made from Portland cement, sand, clay, and specially treated wood. Fiber cement siding is easier to work with than its asbestos-based predecessor, and it comes in a much wider range of styles. Trade names for fiber cement include: Hardie Board and Certainteed. Other fiber-cement products on the market include backer board, panel siding, trim pieces, and facia board.

Fiber-cement siding looks nearly identical to wood when painted. It's a great product for humid environments. In addition to its high durability, it's also termite resistant. Most fiber-cement siding is warrantied for up to 50 years.

1.2: Why It's Become Popular With Builders

Fiber-cement siding is almost impervious to rot. It's extremely durable, fire-resistant, and weathers much better than wood siding products. For these reasons, fiber-cement siding continues to gain market share. As new products hit the market, such as fiber-cement shingles for siding, its use is expected to increase even more.

1.3: Working with Fiber-Cement Siding

The siding can be cut with regular wood-working circular saws, but many home renovation professionals prefer masonry-cutting blades. Fiber-cement siding also can be scored and snap-cut like sheetrock. The siding is sold either primed or pre-painted. Paint holds extremely well to the siding due to its rough and porous surface texture.

Section 2--How to Repair Existing Fiber-Cement Siding

If the siding has been dented or is cracked, it can be patched with compounds sold by various fiber-cement siding manufacturers such as James Hardie Building Products or CertainTeed. Repairs of larger sections are similar to replacing wood siding products--cut out the damaged section and install a new piece of similar size. Joints should be caulked to prevent moisture penetration.

A word of caution: Depending on when the existing siding was manufactured, you may have trouble finding a similar pattern. Styles and patterns have changed as the product evolved.

2.1: Replacing Existing Siding with Fiber-Cement Lap Siding

Fiber-cement siding is typically sold in 6 or 12 inch widths up to 12 feet long. It can be applied directly to framing members over an air infiltration barrier such as Tyvek, or a moisture retarder such as asphalt-saturated felt. It also can be applied directly over existing siding, but furring strips may be necessary to make a flush wall face. Furring strips also are required if laying the siding over masonry-covered walls.

The siding can be used with regular wood trim, fiber-cement trim, or even vinyl trim depending on your cost and style preferences. Fiber-cement siding is attached with galvanized nails or with corrosion-proof screws.

2.2: Fiber-Cement Panel Siding

Fiber-cement panels are most commonly sold as 4x8 to 4x10 foot sheets. They are available in a wide range of textures and patterns, but there still are not as many choices as wood panel siding. Fiber-cement panel siding can be applied directly to framing without plywood sheathing, or it can be applied over plywood shear paneling. Rust-proof screws or nails should be used to attach the siding. Vertical joints should be caulked, and horizontal joints require flashing.

Fiber-cement panels can be difficult to work with because they are much heavier--and more brittle--than wood panel siding. Hanging these panels requires two workers at a minimum. Fiber-cement panels also can be used as a soffit material.

Special care also must be taken when cutting fiber-cement panels. Cut only in well-ventilated areas, as prolonged exposure to the silica-laden dust could pose a health risk. Major manufacturers such as James Hardie and Certainteed also market specialized tools to make cutting easier and to reduce materials damage.

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