Restoration Guide: Hardboard Siding for Exterior Walls

Rob Sabo

Editor's Note: This is article 11 of 18 in Chapter 2: Exterior Walls of the Old House Web's Home 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.

11. HARDBOARD SIDING

Section 1--Overview

Hardboard siding is made of wood chips that are converted into fibers and combined with binding agents under heat and pressure. Hardboard siding first was introduced in the early 1920s and became more widely used in the following decades. By the 1950s, many manufacturers were producing hardboard siding, but during the 1970s, stricter policies enacted by the Environmental Protection Agency led to many plant closures. By the 1980s, hardboard siding accounted for just 30 percent of the residential siding market, and today that number has dipped to around 15 percent.

Currently, there are only six building product manufacturers still producing hardboard siding. The main factors behind market contraction are the widespread use of vinyl siding, fiber-cement siding, and exterior insulation finishing systems (EIFS), which are discussed in detail in Article 15: Exterior Plywood Siding of the Old House Web Exterior Wall section.

1.1: Problems with Hardboard Siding

Numerous class-action lawsuits have been filed against makers of hardboard siding due to problems that arose when the siding was exposed to moisture. However, those lawsuits have been settled, and most hardboard siding manufacturers offer 25- to 30-year warranties on their products and point to the material's long history of strong performance in variable climates. Manufacturers say field errors in the installation of flashing, caulking and nailing were the main reasons behind the product's degradation.

Some hardboard siding manufacturers continue to change their manufacturing processes in order to extend product life and increase durability, while other manufacturers have hardly tinkered with their processes over the years.

Section 2--Repairing Existing Hardboard Siding

If you are remodeling a home with older hardboard siding, it's likely you've come across sections where the siding has deteriorated due to age or weathering. Small portions of damaged lap siding can be cut out and replaced with siding of a matching pattern. Make sure to inspect the exterior wall sheathing as well; chances are if water has penetrated the siding, then the sheathing has been compromised as well. See article 4 for more information on replacing exterior sheathing.

Large sections of damaged siding should be removed entirely and new siding hung in its place. Depending on styles, patterns, and how well the existing siding has withstood the test of time, new hardboard siding may not exactly match the existing wall cladding.

Section 3--Replacing Old Siding With New Hardboard Lap Siding

Hardboard lap siding is made in many popular patterns and styles, although some remodeling work may not match existing siding, depending on when it was manufactured. The majority of hardboard siding is pre-primed at the factory, but it requires two coats of paint for best coverage and to further protect the siding from moisture damage. Masonite Corp. makes a pre-finished hardboard siding that has a 15-year warranty on the finish.

Hardboard siding can be hung over existing exterior wall cladding provided it is sound and in relatively good shape--if you notice excessive areas that have weathered over time during your home renovation you should remove the damaged siding.

Hardboard siding also can be installed over solid or insulated sheathing, or directly to studs over a vapor barrier (more information on vapor retarders can be found in article 5).

Like all siding products, hardboard expands and contracts with humidity and temperature. Minimum spacing requirements are as follows:

  • 3/16-inch from windows, door frames, and corners
  • 1/16-inch between vertical joints, which always must land in the middle of a wall stud

Joints and seams must be caulked to ensure the integrity of the siding--and remain within warranty specifications in most cases.

Section 4--Replacing Old Siding With Hardboard Panel Siding

Hardboard panel siding represents only about one-third of the total hardboard market. Hardboard sheet siding is sold in 4-by-8-foot or 4-by-9-foot square-edged or ship-lapped panels. When remodeling, hardboard siding can be run over exterior sheathing or attached directly to wall studs with use of a vapor retarder. All panel edges must fall on a stud for nailing. Framing must be blocked for horizontal edges, and Z-flashing must be installed.

Hardboard panel siding has no knots, grain variations, or other defects on its surface. The material holds paint extremely well. It is sold in a wide variety of styles and patterns that imitate many popular wood siding products.

When using hardboard siding during a home restoration, it's important to protect the unfinished siding during construction--it cannot get wet for long periods of time. Hardboard siding also should not be hung over wet exterior sheathing. The material requires regular painting to help maintain product integrity.

When remodeling a home, don't let periods of slipshod manufacturing deter you from choosing hardboard siding. It's less expensive than many wood products, and when properly applied and maintained it lasts as long in the field as other siding products.



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