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A Condominium Siding Option

Fiber Cement Building Materials

Article written by Jack Carr, P.E., R.S., LEED AP, Criterium Engineers
Published in Condo Media, December 2012

Many condos built in the late 1970s and 80s need to retire their current facades or siding. I am often asked for suggestions for new siding and I thought it might be helpful to discuss one of these siding options - fiber cement products.
Fiber cement building materials are being used more in new condominium construction. It is used by most large builders in about 20 percent of the new condo market. The reasons are pretty simple - it looks like wood but is termite-resistant, water-resistant, non-combustible, can resist hurricane force winds (when face-nailed) and is warranted to last from 15 to 50 years.
Fiber cement siding is composed of cement, sand and cellulose fiber that have been autoclaved (cured with pressurized steam) to increase its strength and dimensional stability.While current manufacturing processes do not allow for the reprocessing of fiber cement siding, the manufacture of the material itself utilizes wood chips reclaimed from wood processing (the cellulose). When combined with the long lifespan of the siding, the integrated wood fiber qualifies the material for "green" points under several different programs.

It's All in the Details

Fiber cement siding is generally molded to resemble wood products. Applications are designed to be installed in place of conventional clapboards, shingles and vertical siding. Manufacturers are also introducing more alternate designs, such as those that resemble stone or shingles.
Products are manufactured generally as planks or boards. Trim materials such as soffits are also available. Ensuring that trim is installed at the corners and around windows will help guard against leaks. When fiber cement materials are not available, vinyl should be used, as aluminum trim will react adversely with the siding's ingredients. Although greater lengths may be special ordered at premium cost, standard stock order length is 12 linear feet for both siding and trim. Joint-malting will therefore generally constitute a greater labor factor than is usually the case with wood or other synthetic materials available at greater lengths. Moisture entry is a problem for all types of siding. For this reason, I recommend joints be both flashed and caulked.
Products are generally available unfinished or pre-primed. I recommend the use of pre-primed materials as that ensures coverage and improves installation efficiency. Ends should be primed in the field when cut.
There are at least three drawbacks to specifying pre-finished siding. One is the potential problem of slightly varying color between dye lots. A second is matching the recormnended touchup at cut ends. The third is that recommended caulk joints become difficult to disguise.
Because manufacturers demand a premium for pre-finished siding, there is very little economic incentive compared with a field-painted building.
Field painting also offers the advantages of providing the owner and architect with a limitless color palette. Painted finishes on fiber cement are far more durable than on wood, due to the uniformity and high density of the product, and because fiber cement does 110t absorb water as readily as wood.
While fiber cement siding is purported to be easier to install than other types of siding, paying attention to the manufacturer's specifications is critical. That may not always be easy since these specifications can sometimes be vague. Language such as "leave appropriate gap between planks and trim," and "install planks in moderate contact" can leave installers scratching their heads. Although fiber cement is relatively dimensionally stable, we have observed situations where the manufacturer's specified spacing has not been provided. The result can be extremely problematic as the siding may buckle or wave and create opportunities for moisture to enter. Further, this type of siding will mirror defects in the sheathing or substrate if it is not properly supported.
Lastly, boards contain crystalline silica. Although installers tend to treat this material like wood, proper respirators should be worn when using a chop saw or other tools that create dust. The preferred method is to scribe and snap, but since installers are used to working with wood, they must be educated to the health hazards.
In the final analysis, fiber cement products represent a major product class with excellent performance results when used with proper attention to details, at a cost that is slightly more than pine, but significantly less than cedar and other long-lasting wood products.