A Home Inspector’s Basic Guide to Fiber Cement Siding Inspections

Welcome to the Inspection Insider. Here, seasoned home inspectors share their technical expertise and experience to help you improve your own inspections.

Fiber cement siding has become a favored material for residential exteriors due to its durability against the elements, resistance to pests, and capability to mimic traditional wood or stucco finishes. 

Nonetheless, despite its exceptional resistance, fiber cement siding demands meticulous installation and routine inspections to ensure it performs optimally over its lifespan. For home inspectors, understanding the critical elements—like installation best practices, water management strategies, common defects, maintenance requirements, and repair protocols—is paramount in providing accurate, informative reports to homeowners and prospective buyers.

I’m Henry Sander of Heartland Home Inspections in Illinois. I have more than 4,000 inspections under my belt. I serve the industry as an AHIT Instructor and Field Trainer, President of the Northern Illinois Chapter (NIC) of the American Society of Home Inspectors (ASHI), and an ASHI mentor. In this article, I help you identify brands of fiber cement siding, discuss key indicators of proper installation, and how to spot and report common fiber cement siding problems.

How can I tell different cement siding manufacturers apart?

Different brands have different installation instructions, so it’s important to know which brand you’re examining. To tell major brands of fiber cement siding apart, look for manufacturer markings:

• James Hardie often imprints their name on the underside of the siding planks, typically near the edge where it was nailed in. This can be visible only upon removing a siding board. Typically Hardie wood grain does not display any wood grain knots.
• LP SmartSide may have knots with “L” and “P” stamped into them. 
• CertainTeed can be identified by markings or codes, which might be found on the back of the siding or in installation records. CertainTeed wood grain may have knots embossed in the pattern, but their knots are not as distinct as LP’s. 

Looking for markings but still unsure which brand you’re dealing with? Consult with a siding professional who can identify the siding based on its features and installation.

How can I tell if fiber cement siding has been properly installed?

The foundation of a long-lasting fiber cement siding system is correct installation. Poor installation methods can lead to fiber cement siding issues, like accelerated deterioration, water intrusion, and aesthetic problems. 

Industry standards emphasize the need for:

• Clearance requirements.
• Proper fastening techniques.
• Correct overlaps.
• Sealing.
• Flashing.
• Support or penetration blocking.

Let’s discuss what red flags to look for.

Clearance Requirements

Fiber cement siding systems have clearance requirements. Typical clearance standards are two inches to the roof, six inches to the ground, and an inch from the gutter end caps.

Fiber Cement Siding Fasteners and Attachment Methods

Fiber cement siding should be secured with corrosion-resistant nails or screws, such as hot-dipped galvanized or stainless-steel fasteners. 

These fasteners should be driven flush with the panel surface, not overdriven, which can cause cracking or bowing. They should also be spaced properly—generally 16 inches on-center for typical siding installations—and nailed into framing members rather than just sheathed in. Over time, fiber cement siding fasteners can loosen, so it’s essential to check for any that have backed out or are missing altogether.

Fasteners that are less than ⅜ of an inch to the siding edge can also fail.

Board Overlap and Joints

Consistent overlap is vital for effective water shedding. Most manufacturer specifications recommend overlaps of approximately 1 1/4 to 1 1/2 inches for horizontal strip siding. During siding inspections, verify that the overlaps are even across the façade and that control joints are appropriately placed to accommodate contraction and expansion.

Additionally, all vertical seams should be sealed properly with exterior-grade sealants or paint designed for fiber cement siding products. Keep in mind that best practices for joints, sealants, flashing behind joints, and separation distance varies slightly by manufacturer and age. For example, Hardie previously allowed joint caulking years ago but recommends only joint flashing now.

Regardless of the brand and age, follow best practice. I look for up to 1/8 in separation in the joints, flashing behind the joint, and if the manufacturer allowed joint caulking at the time of installation. 

Sealing Cut Edges

All cement siding manufacturers require cut edges and penetrations to be sealed with compatible sealants or primer-based paints. Failure to properly seal these cut edges can lead to water wicking into the core of the material, resulting in internal damage, swelling, or mold growth. 

Inspectors should look for any visible sealant gaps, cracks, or deterioration and recommend resealing where needed.

Water Management and Flashing

Water intrusion is one of the most significant threats to fiber cement siding’s longevity—not because the material itself is vulnerable, but because improper water management can lead to underlying substrate damage, rot, mold, and structural issues. 

The primary defense is correctly installed flashing systems, especially Z-flashing, which directs water away from vulnerable areas. 

Inspectors need to verify that Z-flashing is installed at all horizontal joists and critical junctions: around windows, doors, and transition points where siding terminates or intersects with other building trim and components. The flashing should overlap the siding, extend beyond the siding’s base, and be supported by solid blocking or framing. Unsupported or improperly supported Z-flashing can sag or shift, compromising its function. A small ⅜ to ½-inch gap above the Z-flashing and the panel above may allow for paint.

Penetration Blocking

Supporting blockings behind the flashing provide stability and prevent sagging or shifting that could lead to water leaks. These blockings should be solid, rot-resistant, and securely fastened into framing members, extending the entire width of the flashing to provide a sturdy support surface. On a normal visual home inspection, you may not be able to see this because the support is in the walls, covered by interior and exterior cladding. Do your best to verify support blocking with other methods.

In addition to Z-flashing, inspectors should verify that all penetrations, such as pipes or vents, have appropriate blocking, flashing, and sealant. Sealant should be compatible with fiber cement and applied evenly to all entry points to prevent gaps that may trap moisture.

What common defects are associated with fiber cement siding? How do I identify them?

Even with proper initial installation, fiber cement siding can develop issues over time. For home inspectors, recognizing these common defects is essential to providing accurate assessments in your siding inspection reports

Cracks, Chips, and Impact Damage

Cracks can develop from impact, shifting substrate, or thermal expansion and contraction. By comparison, chips and impact damage are often caused by accidental impact, like from lawn equipment or hail. 

Cracked or chipped panels should be noted, especially if water can infiltrate through these breaches.

Paint and Finish Deterioration

While fiber cement siding typically holds paint well and requires less maintenance than wood, issues can occur. 

Peeling, cracking, or blistering usually indicate moisture infiltration or UV damage. In older homes, the finish may fade or chalk, and it is advisable to recoat or repaint every 10-15 years to maintain protective integrity.

Water Intrusion and Mildew

Signs of water intrusion behind siding include:

• Discolored or damp-looking areas on interior walls, which may be visible around windows or on walls.
• Mildew and mold growth, including visible mold patches on interior walls and ceilings or around wall penetrations. Musty odors, black or greenish mold spots, and discoloration at the seams and joins are also indicators of moisture penetration and mold growth.
• Bubbling, blistering, or peeling paint on the exterior, indicating moisture trapped beneath the surface.
• Warped, bulging, or buckled siding panels.
• Soft or spongy sections of siding, especially when pressed. This may suggest internal damage, rot, or delamination caused by persistent moisture.

To identify water intrusion during siding inspections:

• Conduct a thorough visual inspection around windows, doors, vent openings, and any areas with flashing.
• Look for improperly installed or missing flashing, unsealed joints, or damaged panels that water can get through.
• Use a proper deep-scanning moisture meter to check the moisture content of the siding and underlying sheathing, particularly at the joints, penetrations, and low points.
• Pay attention to the condition of caulking and sealants, which should be intact, flexible, and free from cracking or gaps. When these areas are compromised, water can seep behind the siding, leading to wood rot, framing damage, or compromised sheathing.
• If accessible, examine the sheathing or framing behind the siding to assess the extent of water damage and growth. If inaccessible, advise the homeowner to hire a contractor to removing a small section of the panel or access an interior wall cavity.
• If you have an access point to get behind the siding, and you have an intrusive EIFS certification and endorsement, you may want to use a probing moisture meter to test behind the siding.

If you detect signs of water infiltration during your siding inspections, recommend further investigation by a qualified contractor. The repair process often involves replacing damaged panels, resealing and re-flashing penetrations, and correcting any drainage or grading issues causing water pooling.

The Importance of Inspecting Fiber Cement Siding

Thorough inspections not only safeguard against costly repairs. By emphasizing proper installation practices, regular fiber cement siding maintenance routines, and responsive repairs, inspectors also play an essential role in extending the life of fiber cement siding and maintaining the home’s overall health and safety.

 We hope you enjoyed Henry Sander’s article on fiber cement siding. Worried about potential claims? Learn more about how errors and omissions insurance can give you peace of mind and protection.