A Vital Choice for Your Frames
It’s crucial that you pay attention to the size of the timber components when specifying your frames. Inaccurate sizing, whether undersized or oversized, can compromise the structural integrity of the garage once the build is installed.
A self-supporting structural frame, unlike a conventional gravity-based structure that relies on gravitational support, necessitates a harmonious balance in its design. This balance involves aspects such as proportion, size, strength, and positioning, with the inclusion of appropriate bracing. If elements within this self-supporting structure are either too small or too large, they can upset the overall balance of the frame. This imbalance could lead to structural instability, known as racking, and in extreme cases, it might result in partial or total collapse of the structure.
Additionally, the braces within the frame must be proportionate to the overall structure, and the joints on the braces should fit correctly with the tenons. It is not uncommon for framers to make the tenons on the braces smaller for ease of installation after the main beams are in position. However, this approach should be avoided as it turns the peg into the primary joint. The peg should only serve as a locator for the mortise and tenon joint calculated for the structural level.
Furthermore, the positioning of the peg must ensure sufficient material of the tenon surrounds it, establishing a structurally sound peg/joint connection.
Racking and Preventing Tilting
Racking refers to the tilting or leaning of a building, caused by horizontal pressure exerted by wind forces. Buildings must withstand these forces to comply with building regulations. Structural calculations performed by a qualified engineer are essential, accounting for the specific site orientation because wind strength varies in different directions.
Methods of resisting racking differ depending on whether the side is open or enclosed. For open sides, knee braces across the corners between eaves, beams, and posts are typically used. Their size is determined by the engineer, based on the building’s dimensions. Enclosed sides may require diagonal stud work braces or the application of OSB3 or plywood sheathing. In some cases, knee braces can also serve as interior design features.
Sagging and Beam Deflection
Sagging, also known as deflection, occurs when a beam experiences downward displacement due to the load it carries. An example of this might be the weight of the roof on an eaves beam. In the case of vaulted roofs, sideways deflection can also occur. Structural beams are appropriately sized to withstand this deflection. However, it’s important to note that oak, being a natural material, will exhibit some degree of sagging or bowing. Structural calculations account for this movement, which can be up to approximately 8mm.
As a result, garage doors on a building may require periodic adjustments as the roof settles and the beams adapt. This natural occurrence is completely normal and will have been considered in the initial calculations when you purchase a garage from us.
Emphasising the Importance of Joints
The mortise and tenon joint holds fundamental significance in timber framing. Some oak framers may undersize the tenon, making it considerably smaller than the mortise. This approach facilitates construction by allowing the installation of eave beams on the posts before inserting the braces.
In this scenario, the peg (originally intended as a locator) becomes the primary joint. Undersizing the tenon also increases the risk of insufficient wood around the drill hole, which fails to meet minimum standards and significantly heightens the potential for racking.
By prioritising accurate timber sizing, understanding the risks associated with inadequate joints, and taking measures to prevent racking and sagging, homeowners can ensure the long-lasting stability and structural integrity of their garages built by The Garage Specialist.