Picture-Frame Borders with Cumaru Decking: Plan the Details

Understanding the Cumaru Product for Picture Frames

When working with Cumaru, note that it gives off a scent of cinnamon and vanilla.

For decking, Cumaru is typically available in kiln-dried (KD) profiles such as 1"x6" (actual 3/4" x 5.5") and 5/4"x6" (actual 1" x 5.5"). These dimensions are crucial for planning your picture frame, as they dictate the finished height and width of your border elements. The consistent milling of these boards helps ensure a uniform appearance for your perimeter.

Cumaru is naturally resistant to termites and weather changes, making it a dependable material for outdoor use. Its Class A fire resistance rating is another characteristic that contributes to its suitability for demanding builds. While Cumaru is dense and hard to work with, proper tools and techniques can manage its silica content and high oil content.

Sub-Structure and Blocking Requirements

A critical aspect of a successful picture frame border is the underlying sub-structure. The border boards, running perpendicular to the main deck boards, require continuous support. This means installing additional blocking between joists along the perimeter of your deck frame.

For a single picture frame border, you will need to install blocking parallel to the rim joist, set back by the width of the border board plus any desired gap. If you plan for a double picture frame, two rows of blocking will be necessary. These blocks provide the necessary fastening surface for the ends of the field boards and the long edges of the border boards.

Ensure all blocking is securely fastened to the joists and rim joists. The blocking material should be compatible with your deck framing and adequately sized to support the Cumaru decking. Proper spacing of this blocking is vital to prevent deflection or movement of the border boards over time.

Board Selection and Layout for the Picture Frame

When selecting Cumaru boards for your picture frame, aim for consistent color and grain patterns, especially for the visible perimeter. While Cumaru weathers to a silver-grey if left untreated, initial color consistency will contribute to a more uniform appearance if you choose to oil it to maintain its color.

Consider the width of your Cumaru decking boards. The common 5.5-inch face width (for both 1"x6" and 5/4"x6" profiles) will define the visual thickness of your picture frame. A single board width creates a clean, minimalist border, while a double board width can offer a more substantial look.

The layout of your picture frame will also influence the main deck board layout. The field boards will butt into the inner edge of the picture frame boards. Precise measurements and cuts are essential for tight, consistent joints between the field and border boards. Plan for appropriate spacing between all boards as per manufacturer recommendations for Cumaru to allow for natural movement and drainage.

Integrating Fascia and Edge Finishes

The picture frame border is often complemented by fascia boards, which cover the rim joists and provide a finished edge to the entire deck structure. Selecting Cumaru for your fascia ensures a cohesive look with your decking. Cumaru's durability makes it well-suited for this exterior application.

When planning, consider how the fascia will meet the picture frame boards at the corners. Mitered corners are a common choice for a clean, continuous look. Ensure that the fascia boards are installed plumb and level, aligning with the bottom edge of the picture frame for a polished finish.

The thickness of your fascia board should be chosen to cover the exposed rim joist adequately. Cumaru's natural resistance to decay and insects also extends to fascia applications, contributing to the long-term integrity and appearance of your deck's edges.

Worked Example: Single Picture Frame Border

Let's consider a hypothetical deck project measuring 12 feet by 16 feet, using Cumaru 5/4"x6" decking (actual 1" x 5.5"). We want a single picture frame border.

First, determine the interior dimensions of the deck field. If the picture frame board is 5.5 inches wide, the field area will be reduced by 2 x 5.5 inches (11 inches) in both length and width. So, the field would be 10 feet 1 inch by 14 feet 1 inch.

Next, calculate the blocking needed. This forms a continuous perimeter of support for the picture frame boards. For the 16-foot length, you'll need two 16-foot boards for the long sides of the picture frame. For the 12-foot width, you'll need two 12-foot boards for the short sides. This assumes mitered corners for a clean finish.

For the main field, the Cumaru boards will run parallel to the 16-foot dimension, spanning the 10-foot 1-inch width between the inner edge of the picture frame boards. The ends of these field boards will be fastened into the blocking.

To calculate the Cumaru needed for the picture frame: two 16-foot lengths and two 12-foot lengths of 5/4"x6" Cumaru. If you are ordering in specific lengths, always account for waste from cuts and potential imperfections. For a 12'x16' deck, the perimeter is 2*(12+16) = 56 linear feet. With a single 5.5" wide picture frame, you'll need approximately 56 linear feet of 5/4"x6" Cumaru for the border itself, allowing for miter cuts. It's prudent to add 10-15% for waste.

Before you order

• Confirm desired width of picture frame (single, double, etc.)
• Verify Cumaru board dimensions (e.g., 3/4" x 5.5" or 1" x 5.5")
• Plan for additional blocking in the sub-structure to support border boards
• Determine how main deck boards will terminate against the picture frame
• Select Cumaru fascia to match or complement the border
• Consider mitered corners for a clean, finished look
• Calculate linear footage of Cumaru needed for the picture frame, including waste

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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