The Word - Siding ABCs
By Bruce Barker
Once again, The Word invites you to travel into the dark realm of subjects that are sometimes misunderstood by home inspectors. The Word hopes you will find this trip informative and maybe a little entertaining.
The Word’s topic this month is “siding ABCs.” The Word finds this topic interesting because we are required to describe the type of exterior wall covering and inspect it as well. It would help to know a little about some of the many different types of siding we might encounter.
A is for Aluminum Siding
Aluminum siding was first introduced in the late 1940s and was popular through the 1960s. While still available, this market niche has been filled by vinyl siding. You’re most likely to see aluminum siding on homes built between 1950 and 1980.
Most aluminum siding was installed horizontally in interlocking strips. It was also available in vertical strips. Aluminum siding is easily distinguishable from other siding by its metallic sound and feel; however, steel siding has a similar sound and feel. You can use a magnet to tell the difference -- the magnet will stick to the steel siding and not to the aluminum siding.
Aluminum siding is a good wall-covering material. It doesn’t rust, although it can oxidize if the bare metal is exposed, especially near the ocean. It’s durable and if properly maintained, can serve throughout the life of the structure. It originally came prepainted and accepts repainting well.
Complaints about aluminum siding include that it is easily damaged and repair can be difficult. It can be noisy in the wind and rain.
Some believe that aluminum (and steel) siding needs to be grounded/bonded. There is no requirement in the National Electrical Code to ground or bond aluminum (or steel) siding, although some local jurisdictions may require it. This is a little silly since only the piece to which the grounding/bonding wire is attached might be effectively grounded/bonded. The resistance of the physical and electrical connection to the other pieces is far too high to effectively ground/bond all of the siding.
Aluminum siding shares many of the installation techniques of vinyl siding. We’ll discuss vinyl and aluminum siding installation in another column.
A is for Asbestos Cement Siding
Asbestos cement siding was first introduced in the early 1900s and was popular from the 1920s through the 1950s. You could see this siding on homes built between about 1910 and 1974. Asbestos was banned in building materials in 1973, although existing stock was allowed to be used. This market niche has been filled by fiber cement siding.
Asbestos cement siding was manufactured as rectangular shingles measuring about 12 by 24 inches. It was also manufactured as horizontal lap siding. The siding was first produced with a smooth face. Vertical grooves and wood grain patterns were introduced soon thereafter. Some types have an uneven lower edge. This siding is usually about ⅛ inch thick.
Asbestos cement siding is a good wall-covering material. It resists fire, rot, and wood-destroying organisms. It’s durable and if properly maintained, can serve throughout the life of the structure. It accepts paint well.
Complaints about asbestos cement siding include that it is brittle, which makes it crack easily and makes it easy to damage. Repair can be difficult, but at least one manufacturer makes a similar-looking product from modern fiber cement siding.
Like all asbestos containing building materials, asbestos cement siding is not dangerous if it is intact and undamaged. Siding repair involving sanding, cutting or removal must be performed by a trained contractor, and disposal of this siding involves hazardous waste protocols. This makes repair and removal very expensive.
C is for Cement (Fiber) Siding
Fiber cement siding was first introduced to the United States market in the mid-1980s, has gained significant market share since the mid-1990s and has almost replaced wood-based siding in many markets. In fact, The Word was one of the first builders in Atlanta to use this material in the mid-1990s.
Fiber cement siding is available as horizontal lap siding, as panel siding, as simulated cedar shingles and shakes, and in shapes such as octagonal and half-round that are sometimes used as decorative accents in gables. The siding is available in smooth and textured finishes. Lap siding widths range between 5¼ and 12 inches wide. Panel siding is 48 inches wide and comes in lengths between 8 and 12 feet. This siding is usually between 5/16 and ½ inch thick.
Fiber cement siding can be difficult to distinguish from some wood-based siding, although most wood-based siding is thicker than fiber cement siding. Wood-based siding will readily compress when probed, whereas fiber cement siding won’t. Fiber cement siding has a distinctive sound when tapped.
Fiber cement siding is sometimes called “Hardie Board” after the company that first introduced the product to the U.S. market. Other companies manufacture this siding and inspectors should not describe fiber cement siding as “Hardie Board.” Inspectors should use the generic term fiber cement siding.
Fiber cement siding is a good wall-covering material. It resists fire, rot and wood-destroying organisms. It’s durable and if properly maintained, can serve throughout the life of the structure. It accepts acrylic paint well, but not stain and oil-based paint. Manufacturers don’t recommend using these coatings.
Complaints about fiber cement siding appear to involve improper installation. Lawsuits have been filed against James Hardie and Certainteed alleging product defects. These suits are recent and the allegations have not been substantiated.
Failure to comply with manufacturers’ installation instructions voids their warranties and is likely a significant factor in complaints about the siding. Lap siding should be lapped at least 1¼ inches. Lap siding should be blind-nailed, although face-nailing is allowed in high-wind areas. Blind-nailing is when nails are installed near the top of the siding and the nails are covered by the course above. Face-nailing is when nails are installed through both courses of the siding and the nails are visible. See Figure 1.
Nails should be installed not closer than ⅜ inch to the edge of lap and panel siding. Nails should be driven straight into and fit snug or flush with the siding. Snug means that the bottom of the nail head touches the siding and flush means that the top of the nail head is even with the siding. Overdriven nails (more than ⅛ inch) should have the holes filled and a correctly installed nail should be placed nearby. See Figure 2. Good luck doing this with a nail gun.
Panel siding should be installed vertically with joints aligned with studs. A horizontal joint should occur at each floor level and should be flashed with Z-flashing. Treatment of vertical joints depends on the manufacturer’s instructions for the specific type of siding. Typical vertical joint treatment instructions call for battens (vertical strips of wood), manufactured H-joints or caulking the joint. Caulked joints should be about ⅛ inch wide. Much less and there won’t be enough caulk in the joint. Much more and the caulk won’t effectively fill the space. Some manufacturers allow installation with no joint treatments or caulking.
Clearances between the siding and other materials are very important for avoiding siding deterioration. Although fiber cement siding resists rot, it will deteriorate if regularly exposed to moisture. This is why manufacturers recommend painting cut siding ends.
The following clearances apply to both lap and panel siding: (1) clearance between siding and the ground should be at least 6 inches; (2) clearance to other surfaces such as decks, roofs, sidewalks and driveways should be at least 1 inch; two inches is required in northern climates by Hardie; (3) clearance between gutter end caps and siding should also be at least 1 inch; (4) clearance above Z-flashing at windows, doors and panel siding horizontal joints should be at least ¼ inch and the gap should not be caulked.
Caulking and flashing is important for water control. Caulk should be applied at inside and outside corner boards. Caulking lap siding butt joints is generally not recommended for aesthetic reasons. The caulk will pull away, sometimes very soon after installation. Flashing under these butt joints is recommended by manufacturers (required for some products) and is especially important in areas subject to wind-driven rain. Kick-out flashing should be installed in the usual place where a sidewall extends past a roof. Kick-out flashing should be at least 4 inches tall and 4 inches wide. See Figure 3.
The Bottom Line
There’s a lot more to inspecting siding than looking for damage and rot. Now we have some more tools to take our siding inspection to the next level.
Memo to Hestia (goddess of the home and hearth): The Word does not reside on Mt. Olympus (just at its base) and welcomes other viewpoints. Send your lightning bolts or emails to Bruce@DreamHomeConsultants.com. The thoughts contained herein are those of The Word; they are not ASHI standards or policies.