Installing LP SmartSide Siding and Trim
LP SmartSide is engineered wood siding made from wood strands that are glued and pressed under heat. It comes in lap siding, trim, and soffits. The product is treated with zinc borate for decay and insect resistance. That treatment is part of the manufacturing process and does not require anything additional from the installer, though the cut edges left exposed after you saw into the panel are untreated and need protection. I started working with this material around 2016 when it first became a major competitor to fiber cement in the mid-range market. The main reason contractors moved to it was weight. A four-by-eight sheet of SmartSide lap siding weighs roughly eighty pounds, compared to well over a hundred for an equivalent cement board. That makes a real difference when you are lifting panels to a second story or working a whole crew on a re-skin project. The substrate matters more than most people expect. LP requires a minimum of one-half inch APA-rated plywood or OSB sheathing, and the sheathing must be flat within a quarter inch over ten feet. If your existing sheathing is uneven, you will see every bump telegraph through the siding. I have torn out three whole sides of a house because the original OSB had settled and swollen unevenly over twenty years. It was cheaper to fix it at the start than to deal with the callbacks.
You will also need a moisture barrier. LP recommends their own ZIP System tape and fluid flashing, but any code-compliant housewrap works as long as you seam it correctly. The tape is where most mistakes happen. Installers tend to stretch the tape rather than lay it flat, which creates bubbles that look fine until rain gets behind them.
Cutting and Handling
SmartSide cuts with a standard circular saw or a table saw. Use a fine-tooth blade, at least sixty teeth for a ten-inch blade, and cut with the good face up. The material is dense enough that a dull blade will tear the edges and create a rough finish that shows up once paint goes on. I switch blades more often than I do with regular lumber, and my blade life is shorter because of the glue content. Exposure of cut edges is the single most important step that gets skipped. After every cut that exposes raw wood, you need to apply a coat of primer to that edge before the panel goes on the wall. LP sells a touch-up primer in a small can, but any high-quality latex or oil-based primer will work. If you skip this, the wood strand at the cut edge absorbs water faster than the treated surface, and you will get swelling and delamination within a few seasons. I learned that the hard way on a project in Louisiana where humidity runs above seventy percent for most of the year.
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Nailing and Spacing
Use galvanized or stainless steel nails. The zinc borate treatment interacts with some coatings, and the wrong nail will corrode and stain the paint within a year. Roofing nails work for soffit work, but for siding you want either a thirteen-gauge ring-shank siding nail or a hot-dipped galvanized common nail at fifteen penny weight for most applications. Nail placement follows a specific pattern. Drive the nail through the center of the upper weatherlap, not through the middle of the panel. The nail goes into the sheathing or stud behind it, and the head should sit just flush with the surface without breaking the paper face. If you over-drive the nail, the paper tears and water can wick behind the siding. If you under-drive it, the panel will not seat properly against the layer below and you get a visible gap. Spacing between panels depends on the product line. LP lap siding is designed to overlap by about five-eighths of an inch, but the exact dimension changes based on the nominal width you chose when ordering. Check the spec sheet for your specific product before you start hanging anything. I once ordered six-inch reveal siding and installed it with an eight-inch overlap because I assumed it was standard. The result looked like mismatched flooring and had to be removed.
Window and Door Rough Openings
Flash the rough opening before you bring the siding up to it. This means applying flashing tape or building paper to the header, jack studs, and sill pan. The sill pan is non-negotiable. Water that gets behind the siding and hits an unflashed sill will sit there until it rots the frame. I use a two-piece metal sill pan with outward-turned lips for every window and door on a SmartSide job. It takes an extra ten minutes per opening but saves hours of repair work later. When you cut the siding to fit around a window, leave a gap of about a sixteenth to an eighth of an inch on each side. Do not butt the siding tightly against the trim. Wood moves with temperature and humidity changes, and if you nail it flush there is nowhere for it to go except up or down. The gap allows for expansion and keeps the paint film from cracking at the joint.
Trim and Corner Details
SmartSide trim comes in pre-primed boards. The primed surface is suitable for direct painting, but if you are working in a high-UV environment or an area with heavy rain exposure, adding a second coat of exterior paint to the trim faces is worth the time. The primer on the factory board is thin and not designed to be a final finish coat. Corner boards need a slight gap at each miter joint. Use a shim or a nail set to hold the gap open while you caulk. Siliconized acrylic caulk works here, but do not use pure silicone because paint will not adhere to it. I mix a bead of caulk with a little bit of the exterior paint color so the joint blends in after the trim is painted.
Common Mistakes That Cost Money
Installers who come from fiber cement often try to cut SmartSide with a grinder or a chop saw without a blade guard. That creates dust that gets everywhere and the material chips badly. A standard saw blade gives a clean cut every time if the blade is sharp. Another frequent error is running the siding directly over existing vinyl without removing it first. Vinyl expands and contracts significantly more than wood, and that movement transfers into the new siding and causes nails to pop. If the existing substrate is solid and flat, you can install over it with a proper furring system, but skipping the furring is a mistake that shows up within two years as a series of raised nail heads.
Where SmartSide Falls Short
The material is not a solution for every situation. In areas prone to prolonged moisture exposure without good drainage, such as coastal regions with driving rain or areas with poor roof runoff management, fiber cement or engineered polymer siding may be more durable over the long term. SmartSide handles moisture well when installed correctly, but it is still wood-based and will fail if water gets behind it and stays there. The warranty covers defects and decay under normal conditions, but it does not cover damage from improper installation, which is most of the failures I see in the field. There is also the issue of dimensional stability during transport and storage on the job site. Panels left uncovered in direct sun can develop a slight bow, especially in hot weather. I always keep a pallet of SmartSide under a tarp or in a shaded area until I am ready to use it. A bowed panel is harder to fasten flat and creates visible waviness in the finished wall.
Where to Find the Official Guide
LP provides a full installation manual on their website that covers every product line they make. The document is free to download and includes the current nailing schedules, flash details, and expansion gap requirements. I keep a copy on my phone when I am on site because the paper version gets damaged by weather and glue. The online version is searchable, which helps when you need to look up a specific detail for a particular product rather than searching through a thick printed book.
