Why you Should Use Expansion Joints in Flooring and Sub-flooring

Flooring will contract and expand with changes in temperature and ambient moisture. Your sub-flooring and flooring is made from different materials or utilizing varied manufacturing methods. This means that they will react to heat and moisture conditions differently and expand and contract at different rates. When your flooring and substrate don’t have the space they needs to expand, it can result in buckling, uneven or spongy flooring. Using expansion joints allows your flooring and sub-flooring to expand without affecting the look and feel of your floors.

The Advantages of Expansion Joints

The LRFD Specification (AISC, 1999); “Adequate provision shall be made for expansion and contraction appropriate to the service conditions of the structure.”

While ASCE 7-02 Minimum Design Loads for Buildings and Other Structures (ASCE, 2002) states: “Dimensional changes in a structure and its elements due to variations in temperature, relative humidity, or other effects shall not impair the serviceability of the structure.”

Expansion joints are the perfect solution—allowing the flooring to expand and contract without compromising building design or the integrity of the structure.

Expansion and contraction of a flooring system builds up over the whole floor which can result in uneven floors, tenting of tiles, nail pops, squeaky or ‘soft’ floors and a wealth of other issues. Think about this math; a 12’ wide room with 3 ½ wide hardwood has about 40 joints. If each board expands 1/16” the cumulative expansion is about 2 ½”. When expansion joints are included in the flooring system, they contract when the floor expands and expand when the floor contacts so as to prevent buckling and its associated issues.

What are Expansion Joints

Expansion joints for commercial use are 0.2 to 0.3 inches wide and filled with permanently flexible filler like neoprene, urethane or polysulfide for flooring applications in high traffic areas (sealants in high traffic areas must have a shore hardness of 35). Where traffic is not a concern, silicone is often utilized.

From the American Wood Council: “An expansion joint of at least one half-inch must be provided at the edge of flooring strips adjacent to parallel partitions and exterior walls. The joint is covered by the baseplate and toe molding.”

Consult the manufacturer’s and designer’s specifications for expansion joint placement. If your flooring is in direct sunlight or near a fireplace or other heat source, expansion and contraction is likely to be more common and expansion joints should be placed closer together.

It’s important to note that expansion joints must be included in addition to the 1/8-inch subfloor panel spacing and may not be necessary for smaller rooms. It is also recommended that expansion joints be placed between rooms where different flooring or ambient moisture or heating conditions occur.

Expansion joints in wood floor systems are also a requirement in building over 80’ in length according to the APA (The Engineered Wood Association. You can download the document here).  Roof sheathing in buildings over 80’ must also be installed in a specific pattern to ensure there is allowances for expansion and contraction.

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