Roof Pitch Part 1 - What Is It and Why Does It Matter?
Let's start with a very simple looking and slightly stretched out drawing of a house.
If you remember graphs in math, pitch is synonomus with slope. It is calculated by taking the rise of a length and dividing it by the length of run. Laying that math over our house it would look something like this.
In roofing, we talk about pitch by saying the number of rising inches per twelve inches of length. A roof that rises 3 inches per 12 inches would be described as having a pitch of 3/12. So, when you hear a roofer say, "Your roof has a typical pitch, it is a five twelve." Math wise they mean for every twelve inches, your roof goes up five inches.
When building a house, considerations involved in selecting a roof pitch include availability and cost of materials, aesthetics, ease or difficulty of construction, climatic factors such as wind and potential snow load.
To a regular home owner, in more practical terms, aka, money, why does pitch matter?
Depending on the pitch, it will cost more money to maintain a roof. With asphalt roofs, lower pitches a little bit more expensive because they require specialized underlayment practices and steeper pitches are more expensive because of the increased fall risk. The safety hazard and physical difficulty of working at steeper slope means contractors will charge more.
For some roofers, the way this cost is calculated is per roofing "square". A square is a 10 foot by 10 foot area or 100 square feet.
If a roof has 8/12 or 9/12 pitch, a roofer might charge an extra $10 per square to install that roof. A 10/12, 11/12, or 12/12 roof might cost $50 more per square.
Comparing costs:
A 20 square roof with at 6/12 pitch would cost around $11,000.
That same roof, but with a 11/12 pitch would be $1,000 more.
If you're already in your home, there's not much you can do about your roof pitch! If you're thinking of buying a home, you can now add the extra maintenance cost of a steep roof pitch to what is already probably a very long list of considerations.
Check out Part 2! How to figure out your home's roof pitch.