Finishing Corners with Hardwood Siding

Understanding Corner Types for Hardwood Siding

Hardwood siding corners generally fall into two main categories: those that create a seamless, integrated look, and those that use trim pieces to define the corner. Each approach has distinct visual characteristics and installation requirements. The choice often depends on the desired architectural style, the specific siding profile, and the project budget.

Integrated corners, such as mitered joints, aim for a continuous appearance, making the corner seem like a natural fold in the siding. Trimmed corners, conversely, use distinct trim boards to cap the siding ends, creating a framed or articulated edge. Both can be effective, but require careful planning and execution.

The Mitered Corner: A Seamless Appearance

A mitered corner involves cutting the ends of the siding boards at a 45-degree angle so they meet precisely at the corner, forming a 90-degree angle. When executed correctly, this method creates a clean, continuous look where the wood grain appears to wrap around the building. This is often preferred for contemporary designs or when a minimalist aesthetic is desired.

However, mitered corners are more challenging to install. They require precise cuts and careful alignment. Hardwood, especially in exterior applications, will expand and contract with changes in humidity and temperature. A mitered joint offers less tolerance for this movement compared to a trimmed corner, potentially leading to visible gaps over time. Proper fastening and potentially a weather-resistant adhesive may be necessary to maintain integrity.

Trimmed Corners: Defined Edges and Protection

Trimmed corners utilize separate trim boards to cover the ends of the siding at the exterior corners. This is a common and often more forgiving method. The siding boards are cut square and butt against the trim, which then caps the corner. This approach creates a distinct visual frame around the building's edges.

There are several variations of trimmed corners, including simple butt joints against a single trim board, or more elaborate assemblies with multiple trim pieces. Trimmed corners offer practical advantages: they are generally easier to install, provide better protection for the siding end grain from weather, and can accommodate more material movement. They also allow for contrasting trim materials or colors, adding another layer of design opportunity. Trim boards should be chosen to complement the siding in terms of material, durability, and finish. Maximo Accoya or thermally modified wood can be excellent choices for trim due to their stability and resistance to decay.

Planning for Material Movement and Drainage

Regardless of the corner detail chosen, planning for material movement and effective drainage is paramount for hardwood siding. Wood naturally expands and contracts, and corners are particularly vulnerable points if this movement is not accommodated. For mitered corners, leaving a very slight gap or using a flexible sealant can help manage movement. For trimmed corners, ensuring proper spacing between the siding and the trim allows for expansion.

Drainage is also critical. Water must not be allowed to collect within the corner assembly. This means ensuring that any horizontal surfaces shed water away from the building and that vertical joints are designed to prevent capillary action. A rainscreen assembly, which creates a ventilation gap behind the siding, is highly recommended for all hardwood siding applications, including corners, to promote drying and prevent moisture buildup.

Worked Example: Designing a Trimmed Corner for a Shed

Consider a hypothetical 10-foot by 12-foot shed with 8-foot tall walls, clad with horizontal hardwood siding. We want to use a trimmed corner detail for a classic, robust look. Our chosen siding is a 5.5-inch face width (nominal 1x6) and we plan to use 1.5-inch wide (nominal 1x2) corner trim boards.

For each corner, we will need two trim boards. Let's assume the trim boards will extend from the bottom of the siding to the top. The siding boards will be cut square and butt into the trim boards. To calculate the trim needed for one 8-foot tall corner, we need two 8-foot long pieces. For the entire shed, with four corners, this would mean eight 8-foot trim pieces. It's always advisable to order 10-15% extra material to account for cuts, waste, and potential future repairs. So, we'd aim for nine or ten 8-foot trim pieces.

When installing, the first trim board would be fastened to the sheathing or furring strips. Finally, the second trim board would be installed over the ends of the siding and the first trim board, creating a neat, weather-resistant corner. This method provides a clear, defined edge and protects the end grain of the siding.

Before you order

• Desired Aesthetic: Do you prefer a seamless look (mitered) or a framed, articulated edge (trimmed)?
• Installation Skill Level: Is precise cutting and fitting for mitered corners achievable, or is the more forgiving trimmed approach better suited?
• Material Stability: How much expansion and contraction is expected from your chosen hardwood siding species?
• Weather Exposure: How exposed are the corners to rain and sun? Trimmed corners often offer better end-grain protection.
• Budget: Mitered corners typically require more labor, while trimmed corners require additional material for trim boards.
• Complementary Materials: Will trim boards be the same material and finish as the siding, or a contrasting material like Maximo Accoya or thermally modified wood?
• Drainage and Ventilation: How will the chosen corner detail integrate with your rainscreen assembly and ensure proper water shedding?

Confirm installation details, approved uses and warranty terms in the current instructions for the exact product and profile. Your installer should verify the substrate, structure and applicable project requirements.

Questions to help you decide

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