Installing concrete siding is a project where the weight of the material changes how you work. Concrete siding, whether it is fiber cement planks, concrete composite panels, or precast concrete siding units, is significantly heavier than vinyl, wood, or engineered wood. A 12-foot fiber cement plank weighs 20 to 30 pounds. A concrete composite panel four feet by eight feet weighs 80 to 120 pounds. The weight means the wall framing must be adequate, the fasteners must be correctly specified, and the installation sequence must account for handling material that cannot be carried up a ladder by one person. Concrete siding is a permanent exterior cladding. It is fireproof, rot-proof, and insect-proof. It is also heavy, brittle, and unforgiving of installation errors. The material properties dictate the installation methods.
Concrete siding is made from portland cement, sand, and cellulose or polymer fibers. The fibers provide tensile strength. The cement provides compressive strength and durability. The combination produces a material that behaves like concrete in compression and like a fiber-reinforced board in bending. It does not burn. It does not rot. It does not expand significantly with temperature changes, roughly one-eighth the thermal expansion of vinyl. It does absorb moisture and must be installed with the appropriate gaps, drainage plane, and paint to manage that moisture. A concrete siding installation that traps moisture behind the siding will cause the siding to fail, not from rot, because concrete does not rot, but from freeze-thaw damage, efflorescence, and paint failure. The moisture management principles are the same as for any siding. The consequences of getting them wrong are different.
Structural Loading and Wall Preparation
Concrete siding adds dead load to the wall. The weight must be accounted for in the structural design, particularly for retrofit installations where the original wall was designed for a lighter siding material. A house framed for wood clapboard siding that is being re-sided with concrete siding is gaining roughly two to three pounds per square foot of dead load. For a 2,000-square-foot exterior wall area, that is an additional 4,000 to 6,000 pounds distributed across the foundation. The foundation can almost certainly handle the additional load. A deck ledger board attached to the same wall needs to be re-evaluated. The ledger fasteners that were adequate for the original lighter siding may not be adequate for the additional load of concrete siding bearing on the ledger connection. If you are re-siding a house with concrete siding and the house has an attached deck, have the deck ledger connection inspected before the siding goes on.
The wall sheathing must be sound. Concrete siding is unforgiving of uneven substrates. The planks are rigid. They do not conform to irregularities in the wall the way vinyl does. A dip in the sheathing of an eighth of an inch over four feet will be visible in the finished siding. The sheathing must be flat and securely fastened. Replace any sheathing that is delaminated, swollen from moisture, or loose. The fasteners for the siding must penetrate into the studs, not just the sheathing. The sheathing alone does not have sufficient holding power for the weight of concrete siding.
The water-resistive barrier behind concrete siding must be installed with the same care as for any siding, with one additional consideration. Concrete siding holds less moisture than wood but more than vinyl. It can absorb water from the back side if the drainage plane is inadequate. A rainscreen gap, a space between the back of the siding and the face of the house wrap, is recommended for concrete siding in all but the driest climates. The rainscreen allows any water that penetrates the siding to drain out the bottom and allows air circulation to dry the back of the siding. The rainscreen is created by vertical furring strips or a plastic drainage mat. The gap is typically three-eighths to three-quarters of an inch.
Fire Resistance and Code Requirements
Concrete siding is non-combustible. It does not burn, does not contribute fuel to a fire, and does not emit toxic smoke. This property makes it suitable for wildfire-prone areas where building codes require non-combustible or ignition-resistant exterior cladding. In wildfire zones, the siding must be installed with additional requirements: the gaps at the bottom of the wall must be screened with one-eighth-inch metal mesh to prevent embers from entering, the soffit vents must be screened, and any gaps larger than one-eighth of an inch must be sealed. The concrete siding itself meets the code requirement. The installation details determine whether the wall assembly as a whole meets the code requirement.
In urban and suburban areas, concrete siding provides a fire-rated exterior that can reduce the required setback from property lines in some jurisdictions. A wall clad in non-combustible siding may be allowed closer to the property line than a wall clad in combustible siding. The building code provisions vary by jurisdiction. Check with the local building department. The fire rating of the siding is documented in the manufacturer’s evaluation report.
Frequently Asked Questions
Is concrete siding too heavy for my house?
For a standard wood-framed house with sheathing and studs at 16 inches on center, concrete siding is not too heavy. The additional dead load of two to three pounds per square foot is well within the capacity of the framing and foundation. The exceptions are houses with structural deficiencies, houses with inadequate sheathing, and houses where the siding is being installed over existing siding rather than over sheathing. If you are unsure, have a structural engineer evaluate the wall before ordering materials.
Does concrete siding meet wildfire building codes?
Yes. Concrete siding is non-combustible and meets the requirements for ignition-resistant construction in wildfire-prone areas. The siding itself is compliant. The installation details, screened gaps, screened vents, and sealed penetrations, determine whether the wall assembly as a whole meets the code. Follow the manufacturer’s wildfire installation guide for the specific product you are using.
Does concrete siding need a rainscreen?
In wet climates, coastal areas, and anywhere with more than 30 inches of annual rainfall, a rainscreen is strongly recommended for concrete siding. In dry climates with less than 20 inches of annual rainfall, concrete siding can be installed directly over house wrap without a rainscreen gap. The rainscreen provides drainage and drying for any water that gets behind the siding. The cost of adding a rainscreen is roughly $0.50 to $1.00 per square foot for furring strips or drainage mat. The cost of replacing siding that fails from trapped moisture is the entire project done twice.
The Bottom Line
Concrete siding is heavy, fireproof, and permanent. It requires a flat substrate, adequate fasteners, and a drainage plane behind it. The weight adds dead load to the wall that the framing and foundation can almost always accommodate. The fire resistance makes it the right choice in wildfire zones. The rigidity means the sheathing must be flat and the fasteners must be correctly specified. Install concrete siding over a rainscreen in wet climates. Install it over house wrap in dry climates. Paint it with acrylic latex. The siding will outlast every other component of the wall except the concrete foundation.
