Who this guide is for
- Homeowners choosing a horizontal siding profile
- People deciding between lap and shiplap looks
- Renovators planning reveal and board lines
- Anyone briefing an installer on horizontal siding
Lap versus shiplap profiles
Traditional lap siding overlaps each board over the one below, creating a stepped shadow line, while shiplap uses a rebated joint so boards sit flatter and interlock. The profile sets the facade's character and the way water runs down it. Choose the profile as a deliberate look-and-performance decision.
- Lap: overlapping boards with a stepped shadow line
- Shiplap: rebated interlocking joints sitting flatter
- Profile affects both shadow and water shedding
- Reveal sets the visible board depth and rhythm
Reveal and board lines
The reveal is how much of each board is exposed, and consistent reveal gives the facade its rhythm. Coursing has to stay level and line up around openings and corners. Planning the reveal and how lines meet windows is part of a tidy result.
How the boards shed water
Horizontal siding sheds water down the face and across the laps or joints, so the profile and how boards meet openings matter for keeping water out. The boards are the screen; the barrier behind is the real defence. Plan both together.
Corners, openings and trim
How the horizontal boards terminate at corners and frame windows and doors needs trim that suits the profile, and these junctions are where water and looks can go wrong. Coordinate the siding with the trim plan so edges resolve cleanly. Plan terminations from the start.
Assembly and professionals
The barrier and any drainage gap behind the siding, and the way boards meet openings, affect durability, so a qualified installer should handle the work and coordinate the assembly. The visible profile is a style choice within a performance system. Requirements vary by location and project.
Lap and shiplap planning checklist
- 1Choose between lap and shiplap profiles
- 2Decide the reveal that sets the facade rhythm
- 3Keep coursing level and aligned around openings
- 4Plan how boards shed water across laps or joints
- 5Coordinate corners and openings with the trim
- 6Plan the barrier and any drainage gap behind
- 7Resolve board terminations cleanly at edges
- 8Use a qualified installer to coordinate the assembly
Common mistakes to avoid
- Picking a profile for looks without considering water shedding
- Inconsistent reveal so board lines wander
- Failing to align coursing around windows and corners
- Ignoring the barrier and drainage behind the boards
- Leaving terminations and trim as an afterthought
- Assuming the siding profile is the whole weather defence
When to involve a professional
- Use a qualified installer to coordinate boards and assembly
- Confirm the barrier and drainage gap behind the siding
- Treat openings and terminations as weather-relevant junctions
- Coordinate the siding profile with the trim plan
- Requirements vary by location and project; verify with your professionals
Frequently asked questions
Questions readers ask about this topic
What's the difference between lap and shiplap siding?
Lap siding overlaps each board over the one below for a stepped shadow line, while shiplap uses a rebated joint so boards sit flatter and interlock. The profile affects both the facade's character and the way water runs down it.
What is the reveal on siding?
The reveal is how much of each board is left exposed below the one above, setting the rhythm of the facade. Keeping the reveal consistent and the coursing level, especially around openings, is central to a crisp horizontal siding.
Does the siding profile keep water out by itself?
No. The boards are a screen that sheds most water down the face and across the joints, but the weather barrier behind is the real defence. Both have to be planned together for the wall to stay dry.
How do horizontal boards meet windows and corners?
They terminate against trim that suits the profile, and these junctions are where water and looks can go wrong. Coordinating the siding with the trim plan so edges resolve cleanly is part of a tidy, durable result, and requirements vary by location and project.
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