Installation of vinyl or horizontal steel exterior cladding: Is an air space mandatory?

A widespread belief is that all exterior cladding must be installed with an air gap (capillary break) behind the siding. However, this statement is inaccurate when referring to horizontally installed vinyl or steel exterior cladding.

According to the Quebec Construction Code, more specifically article 9.27.2.2 and paragraph 9.27.2.2(1)(c), certain types of exterior cladding are recognized as meeting the minimum requirements for protection against water, without requiring the addition of a continuous air gap behind the cladding.

Vinyl and horizontal steel cladding are examples of such coverings. Their very design incorporates a form of capillary break. Interlocking profiles, overlaps, drainage ribs, and assembly gaps create a discontinuous space that allows water to drain away by gravity and limits capillary rise into the substrate. In other words, the capillary break is intrinsic to the cladding system itself.

Thus, when these materials are installed in accordance with the manufacturer's instructions and best practices, the absence of an additional air gap does not constitute a non-compliance with the Building Code.

It is important to understand that the Code sets minimum requirements. Adding a continuous air gap may represent a performance improvement in certain contexts, but an improvement is not a regulatory requirement. Confusing advanced best practices with mandatory requirements too often leads to erroneous conclusions of poor workmanship.

In summary:

– The Building Code does not require an air gap behind horizontal vinyl or steel siding.

– These two types of cladding already incorporate a capillary break by their design.

– The absence of an additional air gap does not constitute a defect.

– Compliance is based on adherence to the Code in force at the time of construction and the manufacturer's instructions.

Before concluding that there is faulty workmanship, it is essential to refer to the applicable code, the type of coating involved, and the context of its implementation. In construction, technical nuances make all the difference.