Concerns frequently crop up about not following manufacturer’s installation instructions, both from a code and warranty perspective. I thought some discussion around this might bring some clarity. Here is my take on it:

From a code perspective a distinction needs to be made between violating installation instructions that affect the performance of a material or appliance, and those that have other purposes. So for instance, not following the approved nailing pattern for roof shingles would be a code violation, but I doubt a case could be made for a manufacturer insisting you use their flashing tape with their house wrap, if there were others that could be shown to provide equal performance.

Similarly, I doubt deviating from a manufacturer’s installation instructions would void their warranty unless the deviation could be shown to have affected the deficiency. So if for instance, you install a siding which isn’t approved for use on wood furring you might void the warranty claim was that there were gaps, or the boards came loose, but not if the boards delaminated, lost their finish, or had some other defect that couldn’t be traced to the unapproved practices.

Im not a lawyer, but this seems to me to be in keeping with practices in other fields, especially insurance. There has to be a strong connection between the claim and the cause. I’d be interested in other’s opinions on this.