What Does Roof Pitch And The Type Of Roof System On Your Home Have To Do With How Well Your Roof Holds Up In A Storm?
Roof pitch is how much your roof rises in inches for every foot horizontally. For instance a 6/12 pitch means your roof rises 6″inches for every foot horizontally.This is the average pitch for a roof on most homes. A 1/12 to 2/12 is a low pitch. A 7/12 and up is considered a steep pitch and insurance companies pay extra for the steep pitch when there is a claim on the roof. There is a point where your roof becomes what roofers call unwalkable.
Rooftops with steep pitches are excellent for moving water. The steep slope helps get rid of water in hard rain falls in snow. However, this also creates extra hardship on your gutters that need to withstand a heavier flow of water. Sometimes you would need 6 inch K style gutters versus the typical 5 inch K style gutters.
A lower pitched or flat roof change to hold moisture longer of course. Standing water is the enemy of a roof. Wind shear is another issue. Wind shear refers to the wind velocity around a roof. High pitched roofs tend to experience more wind shear. If you live on the coast for instance you may want to consider a lower pitched roof.
That being said there is an article on sciencedaily.com that states according to a study conducted on behalf of The Roofing Industry Committee on Weather Issues through a cooperative research and development agreement with Oak Ridge National Laboratory’s Buildings Technology Center – determined that steep sloped roofs held up better due to the fact the building materials composing the roof structure defend better against wind uplift forces that occur during hurricanes.
The study, led by ORNL engineer Andre Desjarlais, concludes that construction of these structures should adhere to current local building codes that have been upgraded over previous codes, closely following manufacturers’ guidelines and using compliant edging systems.
The funding source is DOE’s Office of Building Technologies.
Asphalt shingles have been utilized as a roofing material for more than one hundred years. The first asphalt shingles were manufactured in 1901 but were not mass produced until 1911. Asphalt shingles were originally made from cotton rags that were coated with asphalt and surfaced with slate particles.
In the early 1960s, glass fiber mats were introduced as the base material for asphalt shingles which made the shingles lighter and less apt to retain detrimental moisture. Relatively inexpensive asphalt along with advancements in mat and sealant technology quickly led to asphalt shingles becoming the primary choice for steep slope roofing.
In 2009, asphalt shingles comprised 57 percent of the roofing market covering 138.5 million roofing squares. Today, there are literally billions of roofing squares covered by asphalt shingles in the United States. One square is a 10’ x 10’ area or 100 square feet.
Not surprising, a large percentage of steep slope roofing in hurricane prone regions is asphalt shingles because asphalt shingles are more economical than their tile or metal counterparts. Further, stringent building codes and standards have led to tougher demands on the asphalt shingle industry. Today, asphalt shingles can be rated for high wind zones up to 150 mph at a three-second gust.
The installation method used to install your roof is also very important. Your roof should be installed with a high wind rated laminated shingle also called a dimensional or architectural shingle. Six nails should be used on shingles in areas with frequent high winds. The perimeter edges of the roof should be sealed solid with roof cement. Each protrusion in the roof, plumbing boots, vents, should be coated with roof cement and each shingle going around the vent should also be coated with roof cement.
Valleys should be coated with roof cement also. Dead Valley should use peel and stick and then the area should be shingled over top with roof cement between the peel and stick and the shingles. If there is a very low pitch or the dead Valley is flat then single ply should be used over the peel and stick.
Although recent Studies have shown steep roofs hold up to high winds better they are saying it is only due to upgraded material. All roofs from low slope to steep slope roofs are using upgraded materials. I find this irrelevant and those same study participants still agree that high slope roofs get more uplift on shingles similar to an aircraft because of the angle of the roof.
The best alternative seems to be the average 6/12 pitch with an upgraded laminated shingle designed to withstand 130 mile per hour or 150 mile per hour winds. Another alternative would be metal roofs. That will be a subject for a future article.