Installing lap siding: 4 golden rules
Generally speaking, installing fiber cement lap siding is fairly straight forward. However, there are four very basic practices that can make or break your installation.
1. Fastener placement
Lap siding is typically blind nailed, meaning that you place the fastener near the top of the plank, and you cover the fastener with the next course of siding. James Hardie lap siding planks are intended to overlap each other by 1¼ inch -- in other words, you have a 1¼-inch space in which to place the fastener so the next course can cover it. James Hardie recommends placing the fastener 1 inch from the top of the board, near the bottom of the nailing box. It's simple enough to do and can make a huge difference in the appearance of your installed siding.
When nailed properly, the lap siding should sit tight to the wall. In fact, it should be tight enough that you would have a hard time getting your fingers under the siding. It should never be loose or show significant gaps. The odd, bowed stud might create a gap, but in general, you should not see gaps between the laps. Moving the fastener placement from a half-inch from the top of the plank to one inch from the top can produce a night-and-day difference in the tightness of the plank to the wall.
2. Hit studs
When installing lap siding, the fasteners should hit a stud. Many folks think nailing lap siding to OSB or plywood is good enough, but not nailing siding to the studs can have more of a far-reaching impact than you think.
Lap siding is subject to all of the forces of Mother Nature, including wind, which is always pulling at the siding. Fasteners placed firmly in a stud are in a better position to prevent wind from pulling the siding off than fasteners placed into OSB or plywood. The science of nail pull-out value, simply put, dictates that a 2-inch siding nail is extremely difficult to pull out of a stud but relatively easy to pull out of OSB or plywood. Hitting studs is key to the long-term durability of the siding installation.
3. Overdriven fasteners
Fiber cement siding has the same look and feel of wood, but it does not have the same mechanical properties as wood. One important difference is fiber cement's inability to rebound and grip a fastener. When you drive a fastener through wood it rebounds and grabs the fastener. A fastener driven through fiber cement just makes a hole. Fiber cement relies on the head of the nail to hold the plank to the wall. The head of the nail now becomes a crucial player in keeping the plank tight to the wall. Overdriving the fastener decreases its hold. Fasteners should be snug to the surface of the board, but never over-driven.
Illustrations from James Hardie's Best Practices Guide
4. Joints
How much does fiber cement siding expand or contract? In the case of James Hardie products the expansion or contraction should be extremely small and, in most cases, imperceptible. For this reason planks creating a butt-joint, where two planks meet each other, should be placed tightly together. No gap should be left. A simple flashing should also be placed behind each butt-joint to prevent moisture from getting behind the siding.
Your manufacturer includes instructions with the product for good reason. Follow them, and also pay attention to these four very basic installation practices. They can make a huge difference in the look and performance of your fiber cement lap siding.
Matt Spencer is the National Installation Manager for James Hardie Building Products, the largest manufacturer of siding in North America. Matt and his team educate installers, builders, and design professionals on the proper techniques to install fiber cement siding. Matt also works with James Hardie's R&D group to develop and improve installation practices for new and existing products. Matt has been with James Hardie for eleven years holding prior positions in sales and product development. He earned a master's from Northwestern University in product design and development.
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