The lifespan estimate is based on average conditions, and many factors contribute to a longer or shorter life of the roof. The life can vary depending on circumstances and conditions. Some conditions may be:
- Color of roof – A dark roof absorbs more heat, which may shorten the lifespan.
- Angle of roof slope – Higher pitch roofs tend to last longer due to less exposure to the direct sun and weather
- Multiple-layer roof – A roof installed over an existing roof will have a shorter life. Two layers of shingle roof are allowed by building codes, so it is possible to put a new shingle roof over an existing one—just once. While a homeowner saves the tear-off labor and dump fees for removal of the old roof, the shorter life of the new roof and double expense of the tear-off and dump fees when it’s time for a roof again make it a poor long-term choice.
- Quality of roof material – Lower quality materials typically have a shorter life span
- Vegetation – Branches or vines rubbing on a roof or the acidity from the accumulation of leaf debris on a roof shortens its life. This also gives pests a route to get on the roof and even into the attic
- Attic ventilation – An unventilated or poorly ventilated attic may shorten the life span of the roof
- Climate conditions – Severe weather, heavy winds, and both harsh winters and hot summers tend to shorten lifespan