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Construction
Deck Building Tips for DIYers
Building your own deck can be a rewarding project and a great way to save on labour costs. However, it also comes with significant responsibility. A deck must safely support its own weight, furniture, and the people using it for many years, while withstanding British Columbia's wet winters, hot summers, and seasonal ground movement.
A simple ground-level deck may be manageable for experienced DIY homeowners, but larger or raised decks require a solid understanding of structural framing, local building codes, and proper construction techniques. If you're unsure about any structural part of your project, hiring an experienced deck builder is often the safest investment.
This guide explains the basic structural components of a residential deck commonly built in the Lower Mainland and throughout British Columbia. It isn't intended to replace local building codes, but it will help you understand how a properly built deck is constructed and why each structural component is important.
Deck Footings
Every deck begins with its foundation. Regardless of the decking material you choose—pressure-treated wood, cedar, composite, or PVC—the strength and longevity of your deck depend on properly installed footings.
If you plan to build a free-standing ground-level deck over cracked concrete or a poorly growing grass area, you'll most likely use deck blocks or precast concrete patio slabs as your foundation. Deck blocks are precast concrete supports designed to hold a wood post or beam. They are typically installed on compacted gravel or a concrete pad.
Deck blocks are one of the simplest and most affordable footing systems because they require no digging and no concrete pouring. However, they also have limitations. Since they rest on the ground rather than extending below the frost line, they cannot fully resist frost heave or seasonal soil movement. Over time, your deck may settle unevenly or develop a slight slope.
If your goal is simply to create a functional, low-level outdoor living space, deck blocks may be an acceptable solution. However, if you're building a raised deck, a larger structure, or a deck you expect to last for decades, poured concrete footings are the better long-term investment.
Raised decks should not rely on deck blocks. Without a proper foundation, seasonal movement can affect both the structural stability and safety of the deck.
The most common permanent deck foundation in British Columbia uses concrete footings poured into cardboard form tubes that extend below the local frost depth. Galvanized post bases are embedded into the concrete, supporting the deck posts above ground and protecting them from direct moisture contact. Although this system requires more labour, skills and costs more than deck blocks, it provides a much stronger, more reliable foundation and greatly reduces the risk of future movement.
Important: Local building codes throughout British Columbia may specify minimum footing depth, diameter, reinforcement, and soil requirements. Always check with your local building department before choosing any footing system.
Post-to-Beam Connections
The connection between the deck posts and beams is one of the most important structural connections in any raised deck. A properly constructed post-to-beam connection transfers the weight of the entire deck safely into the beam, then into the posts, and finally down into the footings.
Here are some of the most common post-to-beam connections used by deck builders throughout British Columbia.
• Solid wood beam. A solid wood beam is the traditional (old-school) way to create a strong and aesthetically pleasing deck substructure. A solid beam is made from a single piece of timber cut directly from a tree log.
• Multi-ply beam. A multi-ply beam is the type of beam most commonly used by today's deck builders. It is created by placing three or four standard framing boards side by side, clamping them tightly together, and fastening them with nails or structural screws. Once securely fastened, the individual boards act as one solid structural beam. The strength of a multi-ply beam comes from the rigid connection between all of the boards, allowing them to work together as a single structural member.
Important: Both solid wood beams and multi-ply beams must bear directly on top of the supporting posts and be secured with approved galvanized steel connectors (see picture below).
• Double beam (double-board or "sistered" beam). A double beam is created by fastening two framing boards side by side. If your deck design requires a double beam, the tops of the supporting posts should be notched so the beam bears directly on the wood post. The connection is then secured using galvanized carriage bolts or other code-approved fasteners.
• "Sandwich" beam. A "sandwich" beam is created by bolting two boards to the opposite sides of a supporting post. This construction method is generally not recommended and is prohibited by many modern building codes. It is structurally weaker because the entire weight of the deck is supported by the carriage bolts instead of being transferred directly into the post. Over time, or under heavy loads, the carriage bolts can begin acting like wedges against the beam boards, increasing the risk of the boards splitting and the entire post-to-beam connection failing.
Ledger Board
If you plan to attach your deck to your house, you'll need to install a ledger board. The ledger board is one of the most important structural components of an attached deck because it transfers approximately half of the deck's weight, along with the live load created by people, furniture, and other objects, into the house framing, which is supported by the home's foundation. The remaining load is carried by the beam, posts, and footings along the outside edge of the deck.
Before installing a ledger board, take the time to research the correct installation method for your home. Factors such as the type of exterior cladding or siding, the wall structure, waterproofing details, and local building codes can all affect how the ledger board should be attached. A properly installed ledger board is essential for the structural safety and long-term performance of your deck.
Joists
Deck joists are the repeated framing members that form the structural base of your deck. They are typically attached to the ledger board using galvanized joist hangers. In most residential decks, the joists run perpendicular to the house wall, while the decking boards installed on top usually run parallel to the house.
In Canada, the maximum joist spacing for most residential decks is 16 inches on centre when installing decking perpendicular to the joists. If you plan to install decking at a 45-degree diagonal angle, the maximum recommended joist spacing is typically reduced to 12 inches on centre to provide proper support for the decking boards.
The required joist size, spacing, and allowable span depend on the deck design and the loads the structure is expected to support. Before starting construction, always check your local building codes to determine the correct joist size and maximum span for your project.
If you want to learn more about joist spans, I'd recommend reviewing the Residential Exterior Wood Deck Span Guide, published by the Canadian Wood Council. It provides detailed span tables and structural information for residential deck construction in Canada.
Blocking
Solid blocking is installed between deck joists to strengthen the deck frame and help prevent the joists from twisting or moving over time. Proper blocking improves the rigidity of the deck structure and helps distribute loads more evenly.
As a minimum requirement, joists with a span greater than 8 feet should have solid blocking installed at mid-span. Larger decks with two or more beams will also require blocking directly above each beam. If the distance between supporting beams exceeds 8 feet, additional mid-span blocking should also be installed.
Solid blocking is highly recommended for traditional wood decking and is considered essential when installing composite, PVC, or other manufactured decking products. Because composite and PVC decking systems require a more rigid framing structure, proper blocking helps improve the long-term performance of both the framing and the decking.
Cantilever or Overhang
A cantilever, also known as an overhang, is the portion of a deck that extends beyond the supporting beam. It allows builders to create a larger deck surface without moving the beam or adding additional posts.
The maximum allowable cantilever depends on the joist size and span. According to the Canadian Wood Council Residential Exterior Wood Deck Span Guide, the maximum cantilever is generally:
• 16 inches for 2×6 and 2×8 joists.
• 24 inches for 2×10 and 2×12 joists.
As a general rule, the cantilever should never exceed one-quarter of the actual joist length. The cantilever length must also be included when calculating the total joist span.
Where guardrails are required, deck joists should be a minimum nominal size of 2×8, and the deck perimeter should be reinforced with a double 2×8 rim joist under ideal conditions. Always verify the current requirements with your local building codes, as they may vary depending on your municipality and deck design.
If You Cut It, Seal It!
Don't take shortcuts—treat every cut you make.
Whenever you cut pressure-treated lumber, you expose untreated wood that is no longer protected by the original pressure-treatment process. Every cut, notch, hole, or drilled opening should be treated with a wood preservative to help protect the exposed wood against moisture, fungal decay, and rot.
Remember, Mother Nature doesn't accept excuses. If exposed wood is left untreated, it may begin to deteriorate within just a few years.
One commonly used product in British Columbia is Cut-N-Seal from MicroPro Sienna, a water-based, colour-matched wood preservative designed for cuts, holes, and notches in pressure-treated lumber. It helps restore protection to exposed wood in above-ground applications and is available in both brown and green colours.
Treating every cut only takes a few extra minutes, but it can significantly extend the life of your deck framing.
DIY Deck Building vs. Hiring a Professional
Building your own deck can be a great way to save on labour costs, and many homeowners successfully complete smaller projects themselves. However, deck construction requires much more than basic carpentry skills. A properly built deck must safely support structural loads, comply with local building codes, and withstand decades of changing weather conditions.
Unfortunately, some homeowners begin building a deck only to realize partway through the project that it is more challenging than expected. At that stage, finding a professional deck builder willing to take over and correct someone else's work can be difficult.
If you're confident in your skills, willing to learn, and prepared to follow local building codes carefully, building your own deck can be a rewarding experience. But if you're unsure about any structural aspect of the project, hiring an experienced deck builder from the beginning is often the safer and more cost-effective decision.
If you're planning a new deck and have questions about the construction process, decking materials, or design options, don't hesitate to contact us. We'll be happy to answer your questions and help you choose the right solution for your project.
Important to Remember
Before starting your deck-building project, always check your local building codes, zoning regulations, and permit requirements. Building code requirements may vary between municipalities throughout British Columbia. If you're unsure about any structural aspect of your project, it's always better to ask your local building department or hire an experienced deck builder.
Your deck footings, posts with beams, and ledger board form the structural foundation of your deck. They provide the support for your joists, decking boards, railings, furniture, and, most importantly, the people using your deck. Take their installation seriously, because every other part of the deck depends on them.
Ignoring basic deck-building principles may result in a springy, uneven, or unsafe deck. In the worst-case scenario, poor construction can eventually lead to structural failure or even a deck collapse while your family or guests are using it. Building your deck correctly the first time is always easier and less expensive than repairing it later.
