Have you noticed that there are few flat roofs on homes in the Pacific Northwest? There is a reason that goes beyond how they look.
The reason roofs are pitched?
Though the slope of roofs vary, its purpose doesn’t. That purpose is to ensure proper drainage of water.
In areas like he Pacific Northwest, with the amount of rainfall we receive, flat roofs simply cannot drain enough water fast enough with the smaller square footage of most homes. The same applies to homes in states prone to heavy snow falls.
The pitch is design to prevent water build-up
Deciding on the pitch.
Pitch is the measure of how steep a roof is. It’s calculated as rise to run – how many inches the roof gains in elevation for every 12 inches in distance, expressed as a ratio. The greater the rise, the steeper the roof. A 3/12 pitch would be a relatively flat roof whereas a 12/12 pitch would be relatively steep.
The decision as to the pitch of a given roof, not getting into local building codes, is determined by the amount of water flow it will need to handle. Adding into the calculation is the amount of snow and ice likely to accumulate on it. A steeper roof means less snow and ice build-up and faster drainage as the accumulation melts. This minimizes water refreezing on the roof surface.
And yes, as long as the pitch is enough to handle the water flow, it can be steeper.
So why do commercial buildings have flat roofs if they have the same concern over drainage? Cost. What comes with it is an entirely different set of maintenance and care issues.
The need for maintenance on pitched roofs
Unless your home is rectangular, you’ll have multiple pitches meeting. The point they meet is the valley.
Water flows off the shingles into the valley and then to the gutters.
It’s more than water that will flow into the valleys and gutters. Any debris on the roof will be picked up by the flowing water and collected in them. With valleys protected from the wind, unless the water runoff is strong enough, the debris will build up over time, damming the valley. Water can now back up on the roof – exactly what the pitched roof was intended to prevent.
As water pools behind the debris, it can damage the valley or work its way between or underneath shingles (depending on how the valley was designed). This is a big issue on lower pitched roofs. There isn’t enough water flow or help from gravity to clear the valley.
On a roof with two pitches meeting, the end of the valley will meet in a corner of a gutter system. What debris is pushed off the roof will collect at that point. If the gutters aren’t cleaned out regularly, even with a steeply pitched roof, the debris will collect at the base of the valley.
The point where the gutters and valley meet is extremely vulnerable. Water collecting will get wicked up under the edge of the shingles along the roof edge, eventually rotting the roof deck. Left untreated too long this will create large openings allowing water, insects, and critters to get inside as well as continued water damage. Over time, the added weight from the debris and water pooling will damage the gutters, pulling them away from the fascia (creating more potential water damage) and leaks.
The more valleys, the greater the risk.
More valleys mean more opportunity for debris to build up. The pitch itself matters less. With shallower pitches, debris can build up quicker in the valleys due to slower water flow but with steeper angles, valleys are more protected from the wind.
Where steeper pitches have a greater impact, is with gutters. The steeper angle means faster water flow off the roof surface. While this minimizes damage to the roof, it requires gutters to be completely free of debris. Any debris in the gutters can limit their ability to handle the water rushing off the roof without overflowing.
With any pitched roof, maintenance is vital to maintain water flow and the longevity of the roof. The more pitches and valleys, the more maintenance necessary. For homes in wooded areas and likely to see more leaf litter (even pine needles can be an issue), maintenance is needed more often.
To determine how often your roof should be cleaned, talk with a professional. Have an inspection and create a maintenance schedule based on your home’s roof design and location.
If you’re in the Tacoma/Gig Harbor area here in the PNW, schedule an inspection or cleaning today to protect your investment and maximize the lifespan of your roof.