The most common cause of warping in siding is moisture, humidity, and heat. Heat can cause manufactured products, like vinyl, to expand and shrink, so don’t park the barbecue too close. Prolonged sun exposure can cause sagging. If vinyl siding is attached too tightly to the house, with no flexibility, it can contribute to warping. Moisture and humidity can cause wood to expand and contract. Strong sealants are used that prevent this, but eventually wood will deteriorate and sealants fade, so you need to be diligent about proper care and maintenance.