Shiplap Siding: How It Works on an Exterior and Which Products to Use

Shiplap siding is made of boards with a rabbet (an L-shaped notch) along each long edge, so neighboring boards overlap while their faces sit nearly flush. The result is a flat wall with a crisp, narrow shadow line between boards instead of the stepped look of lap siding. Outdoors it is made in real wood, in fiber cement such as Hardie Artisan Shiplap, and in engineered wood such as LP SmartSide Nickel Gap. Installed horizontally, the overlap has to face the right way so water is shed outward, and that orientation is the most important detail of the whole job.

Shiplap vs nickel gap vs channel siding

These three names get mixed up, and some products blur the lines. This is how they usually differ on an exterior:

All three have a flat face, which is the main visual difference from lap siding, where each board sits at an angle and casts a thicker shadow underneath.

Interior shiplap is a different product

The shiplap you see in kitchens and living rooms is often primed MDF or pine, sometimes square-edged boards set with spacers rather than overlapping rabbets. It isn't made to handle rain, sun or wet-dry cycles, and it doesn't belong on an exterior wall. For outside use, choose a product sold as exterior siding and install it to that manufacturer's instructions.

Exterior shiplap products

Fiber cement: Hardie Artisan Shiplap and Square Channel

James Hardie makes shiplap as part of its Artisan line, which is 5/8 inch thick, twice the thickness of standard Hardie lap. According to Hardie's catalog:

• Artisan Shiplap is 10.25 inches wide with a 9-inch exposure, 12 feet long, with a narrow 0.15-inch channel between boards.
• Artisan Square Channel is the same size with a 1-inch square channel, for a bolder line.
• Artisan V-Groove is 8.25 inches wide with a 7-inch exposure and a 0.5-inch V-shaped channel.

These flat-wall profiles use a lock joint between boards, come primed with a smooth texture for field painting, and can be installed horizontally, vertically or as soffit. Outside corners can be mitered on site. Fiber cement is noncombustible (ASTM E136), which matters on lots in fire hazard zones. Our San Jose Artisan V-Groove project shows the same Artisan flat-wall family on a full house. Availability varies by region, so confirm with the supplier before you design around a specific profile.

Engineered wood: LP SmartSide Nickel Gap

LP SmartSide Nickel Gap is LP's flat-board profile. LP's spec sheet lists it at a nominal 1/2 inch thick and 8 inches wide with a 7-inch reveal. It comes in cedar texture or brushed smooth, primed or in LP's ExpertFinish factory colors, and LP lists it for horizontal or vertical installation. Locking flanges with a fastener groove hide the nails. It is lighter than fiber cement and cuts like wood. It is combustible, so check fire-zone requirements before choosing it. Our LP SmartSide siding page covers how we install LP products.

Real wood

Cedar and redwood are milled in standard shiplap and channel patterns, and wood shiplap remains the most authentic version. The Western Red Cedar Lumber Association notes that shiplap and tongue-and-groove profiles are made with interlocking or overlapping joints, so they work horizontally, vertically or on an angle. Its guidance also recommends channel and bevel patterns, which allow for shrinkage, when siding is unseasoned. Wood shiplap needs regular refinishing and is limited on many wildfire-zone lots unless it is a listed fire-retardant-treated product or part of a listed wall assembly.

Keeping horizontal shiplap dry

Flat-face siding with horizontal grooves handles water differently from lap siding. These are the details to get right:

• Lip orientation. On horizontal shiplap, the rabbet that is open toward the back of each board goes at the bottom, so its outer lip hangs down over the board below. Water running down the face then steps outward at every joint. Installed upside down, each joint becomes a small ledge that directs water toward the wall.
• The ledge in each groove. Square channels and nickel gaps have a small horizontal surface where water and dirt can sit. Keep the paint film intact there, and on field-painted products make sure cut edges and grooves are fully coated.
• Butt joints. Where two boards meet end to end, manufacturers require flashing or an approved detail behind the joint. LP's Nickel Gap instructions, for example, call for flashing behind each butt joint, a 3/16-inch gap, joints over studs, and joints staggered at least 16 inches.
• Weather barrier. A continuous, shingle-lapped weather-resistive barrier behind the boards is the real waterproofing. Shiplap's job is to shed most of the water before it gets there.
• Windows and trim. Flat profiles butt tightly into window trim, so head flashing and the gap at trim edges have to follow the manufacturer's spacing.
• Flat walls. Flat-face siding shows every bump in the wall. Old houses often need shimming or sheathing repair first so the lines read straight.

Installed vertically, shiplap behaves like other vertical board siding: water runs straight down the grooves, and any horizontal joint between stacked boards needs Z-flashing. Our vertical siding guide covers that detail.

Where shiplap siding looks right

• Modern farmhouse: horizontal shiplap or nickel gap in white or light gray, with dark windows.
• Coastal and cottage homes: narrow-gap shiplap in a soft color.
• Contemporary homes: square channel or V-groove in a single dark color, often vertical.
• Accent areas: an entry wall, a bump-out, a gable or an ADU, mixed with lap siding or stucco elsewhere.

Flat boards make color the main design tool. Our siding and trim color guide covers how light and dark colors read in Bay Area fog and sun.

What affects the cost

• Product. Thick fiber cement boards like Artisan cost more than standard lap siding, engineered wood usually sits in the middle, and clear cedar is at the top.
• Labor. Flat profiles need straight walls, careful layout and tight joints at trim. Mitered corners add time.
• Painting. Primed products need a full paint job after installation; factory-finished products don't.
• Wall prep. Tear-off, sheathing repair and flattening an old wall can outweigh the difference between products.

For a price on your house, we give a free written estimate after a walkthrough. See our James Hardie siding page for how we install Artisan profiles.

Frequently asked questions

Can shiplap be used as exterior siding?

Yes, if it is a product made for exterior use, such as cedar or redwood shiplap siding, Hardie Artisan Shiplap or LP SmartSide Nickel Gap. Interior shiplap boards, often MDF or pine, are not built for weather. On horizontal installs, the overlap must face the right way so water is shed outward.

What is the difference between shiplap and nickel gap?

True shiplap has overlapping rabbeted edges and may show a small V or square reveal. Nickel gap boards are set with a narrow, uniform gap about the thickness of a nickel, which gives very even lines. Exterior nickel gap products such as LP's use interlocking edges so the gap doesn't leave the wall open.

Does James Hardie make shiplap siding?

Yes. Hardie Artisan Shiplap is a 5/8-inch fiber cement board, 10.25 inches wide with a 9-inch exposure and a narrow channel. It is primed for paint and can be installed horizontally or vertically. Availability varies by region.

Should shiplap siding go horizontal or vertical?

Either works when the product is rated for it. Horizontal shiplap reads as farmhouse or coastal, and vertical reads taller and more modern. Vertical installs need flashing at any horizontal joints; horizontal installs need the overlap facing down.

Is shiplap siding more likely to leak than lap siding?

It doesn't have to be. Lap siding is more forgiving because each board overlaps the next by more. Shiplap depends more on correct lip orientation, flashed butt joints and an intact weather barrier, so installation quality matters more.

Sources

• James Hardie: Hardie Artisan siding, shiplap
• James Hardie: National product catalog, Artisan profile specifications (PDF)
• LP: SmartSide Nickel Gap siding installation instructions
• LP: Achieve a modern look with SmartSide Nickel Gap siding
• Western Red Cedar Lumber Association: How to design with and specify cedar siding