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Hardboard Siding Woes

The problems associated with hardboard siding have received a lot of press coverage in the past few years. Class-action suits have been brought against the manufacturers of Masonite® Omniwood® siding (Georgia-Pacific) and Inner Seal siding (Louisiana Pacific) for alleged early failure characterized by rotting, buckling, discoloring, deteriorating, as well as causing damage to other structural parts of the buildings into which it was incorporated. Products cited in the suits included both lap siding and panel siding.

The cause of failure

Lap siding and panel siding are both composite wood products. Wood fibers are coated with resin and formed into a mat. A resin-impregnated overlay is placed over the mat. The complete layup is pressed into sheets under heat and pressure. Sometimes a design such as imitation wood grain is formed into the surface. The thickness of the sheets is usually either 7/16 or 1/2 inch. The sheets are then cut up into boards to make lap siding or into panels to make panel siding. Lap siding is usually 16 feet long and from 4 to 16 inches wide. Panels are typically 4 x 8 or 4 x 10 feet. Hardboard siding is usually pre-finished with primer in the factory and finish-painted once installed.

The problems associated with both lap and panel siding are associated with moisture. If water from any source gets past the finish and into the siding itself, the wood fibers will absorb and retain this water. The wet wood fibers will swell, causing the siding itself to expand. When the siding expands, it can swell and buckle with enough force to pull fasteners. Wet siding will eventually rot.

Moisture can enter siding around fasteners that have been over-driven and not sealed properly, through cut ends that have not been sealed, and through the faces if they have not been primed and painted thoroughly.

Who’s to blame? Lawyers for the plaintiffs allege that the failure of the siding was caused by an inherent defect in the material itself. The manufacturers claim that the problems were the result of improper installation. Whatever the cause, the problem remains, and property owners are faced with the difficulty of developing an effective repair strategy.

Cover up or replace?

Although the problems have been documented at length, there is confusion about what an appropriate repair solution might be. Generally, there are two possible scenarios. The first is to cover the existing siding with new siding. The second is to remove the existing siding and replace it with new siding.

The main argument for the first option is economics. The contractor is not faced with costs for tearing off the existing siding, haulage and dump fees, and preparation of the subsurface for new siding and, therefore, is able to submit a lower quotation. However, the economic gains of this “cover it and forget it” solution are short term.

Replacing the siding is preferred, but is not without problems.

We generally do not recommend covering the existing siding. If the siding has deteriorated to the point that replacement is being considered, then there has almost certainly been water penetration behind the siding. Siding that has buckled has lost its integrity as a rain barrier. Therefore, wind driven rain can easily find its way behind the siding. If the siding is rotten or swelled due to high moisture content, then it is permanently wet. Water trapped in and behind the siding can cause a number of problems with the other components in the structure, including rotten sheathing, wet insulation, mold, and even rot of the structure itself. These conditions are also favorable for termites. Steel-framed buildings are subject to rust. In extreme cases, water penetration can penetrate to the inner walls of a building and cause deterioration of these. None of these conditions may be evident unless the existing siding is removed so the structure behind it can be thoroughly inspected.

The procedure of installing a second layer of siding directly over existing siding poses problems of its own. The extra thickness of the second layer usually means that the siding will stand proud of exterior trim. This creates an ugly detail that detracts from the value of the building. The alternative, building up the trim to match the thickness of the two layers of siding, is expensive.

Sealing around wall penetrations is next to impossible to do correctly when one layer of siding is installed over another. pically, the details of base flashing and counter flashing are tricky to work out and install. This attention to detail is not what one expects from a low-

bid job. Caulking is not a substitute for proper flashing details. Improper sealing results in further water penetration into the building facade. This re-creates the original problem and compounds it because now any water that finds its way into the building is effectively locked in by the second layer of siding that was installed to prevent the problem in the first place.

The hoped-for economic benefits of covering deteriorated siding with a second layer of siding are likely to be false. This repair solution will likely detract from the real and perceived value of a building. A knowledgeable buyer will not be fooled by this head-in-the-sand attempt to deal with the original problem.

Additional Sources of Information

Some class-action settlements have been reached. Owners of properties with hardboard siding may be entitled to compensation. Check with manufacturers for details. A few helpful numbers are:

Additional information and service are also available from any of the 66 offices of Criterium Engineers.

Volume 12, Number 1

January 2001

Copyright © 2001

The Engineering Advisor is intended to enhance your knowledge of technical issues relating to buildings.  For additional information on any subject, please feel free to call us.  Our commitment is to provide you with timely, accurate information.