Deck beams, often referred to as girders, are fundamental structural components of a deck that provide essential support for its frame. They are integral to the deck's stability, bearing the weight from the deck's surface, the joists, and any live loads (like people or furniture), transferring that weight down to the support posts and ultimately to the foundation.
Function and Purpose of Deck Beams
The primary role of deck beams is to act as horizontal support members that span between vertical support posts or connect to the house ledger board. They are designed to carry the loads from the deck joists, which run perpendicular to the beams.
- Load Bearing: Beams are engineered to withstand significant downward forces, ensuring the entire deck structure remains stable and safe.
- Weight Distribution: They effectively distribute the weight from the joists and the deck surface to the support posts, preventing localized stress points.
- Frame Support: Beams are the backbone of the deck's substructure, supporting the entire framework that the decking surface is laid upon.
Placement and Installation
The placement of deck beams is crucial for structural integrity and depends on the deck's design and size.
- Common Placement: Beams are typically installed either alongside the rim joists (the joists forming the perimeter of the deck) or directly below the joists. This strategic positioning ensures efficient load transfer.
- Supporting Joists: When beams are placed below joists, the joists often rest directly on top of the beam, allowing for a strong and direct transfer of weight.
- Larger Decks: For larger or more complex deck designs, additional beams may be installed intermittently throughout the deck's footprint. These extra beams provide enhanced support, especially for areas that will bear heavier loads or for longer spans where a single beam might not suffice.
Beam Installation Scenarios
| Scenario | Beam Placement | Primary Function |
|---|---|---|
| Simple Deck | At the perimeter, supporting rim joists. | Main structural support for the deck frame. |
| Larger Deck | Perimeter and additional intermittent beams. | Enhanced support for longer spans and heavier loads. |
| Elevated Deck | Running below joists, supported by posts. | Direct load transfer from joists to vertical supports. |
| Cantilevered | Integrated into joist system, extending out. | Providing support for an overhanging section. |
Types of Deck Beams
Deck beams can be constructed from various materials, each offering different strengths, aesthetics, and cost implications.
- Solid Dimensional Lumber:
- Commonly used in residential deck construction.
- Typically composed of multiple pieces of lumber (e.g., 2x10s, 2x12s) bolted or nailed together to create a thicker, stronger beam.
- Examples include treated pine, cedar, or redwood.
- Glued Laminated Timber (Glulam):
- Engineered wood product made by bonding together multiple layers of wood with durable, moisture-resistant adhesives.
- Offers superior strength and longer span capabilities compared to solid lumber.
- Often used for larger, more demanding deck structures or where a clean, finished look is desired.
- Laminated Veneer Lumber (LVL):
- Another engineered wood product, created by bonding thin wood veneers with adhesives under heat and pressure.
- Provides excellent strength and stiffness, resisting warping, twisting, and shrinking.
- Suitable for long spans and heavy loads, often used in conjunction with other framing materials.
- Steel Beams:
- Less common for residential decks due to cost and specialized installation, but highly durable and capable of very long spans.
- Typically used in commercial or very large, custom deck projects.
Importance of Proper Sizing and Code Compliance
Correctly sizing and installing deck beams is paramount for safety and longevity. Beam dimensions (depth and width), material, and span length must comply with local building codes. These codes specify requirements based on:
- Load Calculations: Ensuring the beam can support the anticipated dead load (weight of the deck itself) and live load (people, furniture, snow).
- Span Tables: Guidelines that dictate the maximum distance a beam can span between supports based on its size and material.
- Connection Methods: Specific requirements for how beams are attached to posts and joists, including the use of appropriate fasteners and hardware (e.g., post caps, beam hangers).
Consulting a local building professional or reviewing your area's specific deck building codes is essential to ensure your deck beams are properly designed and installed.
