How to Install Composite Decking on a Slope?

Sloped decks require more precise planning and sturdier structural support. Composite decking boards are the best choice for building a sloped deck because they are strong and don’t need much upkeep. To put composite decking on a slope, you need to dig a deep concrete footing to make sure the base is stable and level. Make sure the structure is well anchored so it can handle side pressure.

Key construction steps include excavating down to solid soil, installing posts, and joists. Additionally, ensure a 1% slope for drainage. Keep clear of any adjacent structures. This post will explain step by step how to put composite decking on a slope.

Planning Before Building a Sloped Deck

Before constructing a deck, thorough preparation is essential. Preliminary planning includes:

Site Assessment and Analysis

The first stage in creating a deck on a slope is to carefully look at the site circumstances. This means not just looking at the slope angle, but also knowing the type of soil, drainage problems, and other things. Think about these things:

• Slope Measurement: Use a laser level or traditional spirit level to accurately measure the slope. Write down the entire difference in height and see if the slope is the same all the way across.
• Soil Analysis: The stability of the slope directly depends on the soil type and condition. Assess the soil type and composition to determine its load-bearing capacity.
• Check the Water Table: Areas with high water tables usually need special drainage treatment. Also, in areas with cold weather, observe how deep the frost line is.

Solid Capped Composite Decking Board CO-03

Capped with an HDPE layer, Capped Composite Decking is made excellent at resisting stains, scratches, weathering, and fading.

View More

Regulations and Safety

Building decks on slopes typically involves stricter building codes. Pay attention to the following aspects:

• Building Permit Requirements: Most decks that are attached to houses need building permits. Get building permits from your local building department and know the rules on deck height, size, and location.
• Railing Standards: Install required railings to ensure safety. Railing gaps must not exceed 4 inches to prevent children from slipping through.
• Stair Standards: Follow specific regulations for slope, tread depth, and riser height.
• Structural Loads: Calculate deck loads, including lateral earth pressure for slope decks.

Functional Zoning

The design of the sloped deck should consider clear functional zoning. This directly influences the deck’s layout, dimensions, and structural choices. Areas can be divided based on usage requirements as follows:

• Entertainment Zone: Dining, barbecuing, and gathering spaces.
• Recreational Zone: Sunbathing, reading, and viewing areas.
• Transition Space: Pathways connecting the house to the landscape.
• Special Features: Hot tub, fire pit, and outdoor kitchen.

Planning the Drainage System

Drainage design for sloped decks is more critical than for flat decks. Improper drainage can lead to erosion, structural damage, or even landslides. The drainage system should be designed with the following aspects in mind:

• Surface Drainage System: Establish a 1%-2% slope on the deck surface. Construct gutters and downspouts to direct accumulated water away from the building.
• Subsurface Drainage System: A drainage system beneath the deck prevents water accumulation around foundations. Waterproof membranes and drainage boards are commonly used.
• Material Drainage Design: Make sure there are enough spaces between the composite deck boards. Choose types of composite decking that are better at keeping water out.

Learn More: How To Install An Under-Deck Drainage System?

Material Selection

Composite wood decking consists of wood fibers and plastic polymers. It combines the natural appearance of wood with the durability of plastic. Different brands and styles of composite decking vary in material composition and performance. Common types of composite decking include:

• Solid Composite Decking: Features a fully dense internal structure with excellent mechanical properties. Its load-bearing capacity easily accommodates the weight of heavy outdoor furniture.
• Hollow Composite Decking: Features a honeycomb or channeled design. It’s very light, which makes it easy to move and set up, making it perfect for DIY jobs. Compared to solid decking, it also offers a notable cost reduction.
• Capped Composite Decking: uses a multi-layer co-extrusion method to cover the core material with a layer of polymer to protect it. This style is very good at withstanding bad weather.
• Uncapped Composite Decking: It has a wood-plastic composite core that is directly visible, which keeps the wood grain and texture more realistic. However, not having a protective covering speeds up ageing.

Each material has its own benefits. COOWIN offers many types of composite decking so that you can choose the one that best fits your building needs.

Learn More: What Is the Difference Between Hollow and Solid Composite Decking?

Construction Steps

When building a deck on a slope, hiring professional contractors is the safest option. If you wish to install it yourself, follow these steps:

Site Preparation and Surveying

First, survey and prepare the site according to your design plan. This includes:

• Marking the boundaries of the work area. Reserve space for material storage and equipment access.
• Clearing all vegetation, including turf, shrubs, and tree roots.
• Removing topsoil down to stable soil layers.
• Consider installing landscape fabric for weed control over drainage gravel.
• Find the places where the deck connects to the house. These will be used as the starting point for all measurements.
• Mark all post locations, accounting for design loads and span requirements.
• Measure and record ground elevation at each post location.

Installing Deck Footings

Footings form the foundation for deck installation. Steps for constructing footings on a slope include:

• Dig Footing Holes: Excavate footing holes on the slope. Ensure holes reach solid soil layers and are below the frost line.
• Install Deck Posts: Place posts into each hole. Measure the length from the bottom of the post to the desired deck height. Leave one foot of length at the top of each post.
• Pour Concrete: After setting the deck posts, fill the holes with concrete and allow it to cure completely. Once the concrete begins to set, use a level to check that the posts are horizontal.

Installing the Frame Structure

After preparing the foundation, you can start building the frame structure of the composite deck. This is mostly made up of support beams and joists:

• Install Joists: After securing the posts, assemble the joists. Joist dimensions should be set based on deck span and design load. Use galvanised rust-resistant hardware for connections to ensure long-term stability.
• Install Joists: Usually, composite deck joists are 16 inches apart, but for heavy loads, 12 inches is better. For better strength, use galvanised steel hangers when installing.
• Consider Drainage: To make sure the water drains properly, either slightly slope the joists or use joists that already have drainage holes built in. Also, make sure there is enough airflow under the frame to keep moisture from building up.

Installing Composite Deck Boards

The installation method for decking boards depends on your chosen material. Generally, there are two installation approaches:

• Hidden Fastening System: Utilises edge clips integrated with a groove system. This installation method offers the most aesthetically pleasing solution. Its advantages include no visible fasteners on the surface and allowing boards to expand and contract freely.
• Surface-Fastened System: Installed using composite deck screws. Pre-drilling is required to prevent deckboard splitting. Screw heads should be flush with or slightly below the deck surface.

Additionally, observe these installation guidelines:

• Acclimatisation: Deck boards should be laid flat in the shade for 48 hours so they can get used to the weather. Do not place during very hot or very cold weather.
• Board Orientation: Lay boards parallel to the slope direction to facilitate drainage.
• Expansion Gap: Leave a 1/8-inch to 1/4-inch gap between deck boards.
• Installation Sequence: Install from bottom to top for ease of operation and safety.

Installing Railings and Accessories

Finally, you can begin installing railings and other accessories to complete your deck. Always adhere to local building codes during installation. Understand requirements for railing spacing, height, and post width. The railing installation process generally includes:

• Cut all railing posts and top rails to the appropriate height.
• Secure each railing post to the outer edge of the deck using expansion bolts.
• Ensure correct spacing between each railing post. Use a level to verify the vertical alignment of each post.
• Fasten support posts and beams to the top rail using deck screws.

Conclusion

Building a composite deck on slopes requires precise engineering calculations and strict construction standards. Every step, from planning to building, affects the deck’s safety, sturdiness, and appearance. If you have further questions about composite decks, feel free to contact COOWIN. Our service team provides professional answers.

FAQ

How Should Trees on Slopes be Handled?

Removal isn’t always necessary—several solutions exist:

• Design Detours: Adjust deck layout to bypass trees.
• Integrated Design: Incorporate trees into deck plans.
• Selective Pruning: Remove branches interfering with the structure.

How Should Areas Beneath Slope Decks be Cleared?

Debris tends to accumulate beneath slopes. Implement these prevention and cleanup strategies:

• Design Phase: Ensure sufficient clearance height for maintenance.
• Preventative Measures: Install debris screens or grates.
• Regular Maintenance: Inspect and clear quarterly.

What Considerations Apply for Composite Decks on Slopes in Cold Climates?

In cold weather, adhere to these installation requirements:

• Frost Heave Protection: Ensure deck foundation depth is adequate.
• Snow Load: The deck must withstand the region’s maximum snow load.
• Slip Resistance: Select composite decking types with textured, slip-resistant surfaces.
• Snow Removal Safety: To get rid of snow, don’t use metal shovels. Instead, use plastic shovels or snow blowers.
• Thermal Expansion/Contraction: Allow appropriate expansion gaps during installation to accommodate temperature variations.