Roof pitch is an essential metric when it comes to choosing the right materials and accessories for your new roof. Of course, you will most often go with what’s aesthetically pleasing for you, and fits the budget. However, it is very important to consider the pitch of your roof, before making the decision on materials.
Many roofing materials are designed for a certain roof slope and will not work properly, if at all, if the correct pitch is not met. The most common example is with asphalt shingles and most types of metal roofing, which are designed for a minimum of 3 in 12 pitch roofs.
Everything below the 3 pitch, is considered a low slope, and requires a special low-slope or flat roofing material, to work properly. Therefore, while asphalt shingles will not work on low-slope roofs, they often still get installed, in violation with manufacturer’s minimum pitch requirement, and thus voiding the warranty.
Low Slope Roofs – Pitch Below 3 in 12
Though many contractors will insist that “they’ve installed 100s of such roofs, and none ever leaked” – this is not true, unless you live somewhere in Florida or other southern states, where there is never any snow. As you go up north into the snow country, most roofs will get affected by ice dams in one way or another, and even the most insulated / well ventilated roofs are not immune to ice-dams leaks. Due to the nature of ice dams, the lower pitch roofs are more prone to such leaks than the higher pitch roofs.
All too often, roofing contractors will tell you that using an ice & water shield will protect your roof against ice dams, on high and medium slope roofs, and even on the low-slope roofs. However, in our experience, we have replaced over 20 medium to low sloped asphalt shingles roofs in the past few years, all of which were under 5 years old, with ice & water shield installed underneath. This shows that not only pitch was NOT considered when choosing the roofing materials, but also that ice & water fails all too often, even with adequate pitch, when there are ice dams.
Most metal roofing systems are also designed for a minimum of 3 in 12 pitch, and though they have a much higher chance of not leaking on low slope roofs, you are still taking a chance, if you decide to install a metal roof, when the minimum pitch requirement is not met. However, on a proper roof pitch – even 3/12 – a metal roof will always outperform asphalt shingles. It will last longer and will be pretty much immune to ice dams even without ice and water shield underneath (assuming there is a layer of synthetic underlayment installed). However a cost of metal roofing often scares homeowners away, and they still go with asphalt shingles, taking a risk of having to deal with the stress and additional expenses of having to fix leaks.
The best solution in a low slope roofing situation, which in a residential setting is often found on shed dormer roofs, is to use a low-slope / flat roofing membrane, such as IB PVC or IB Traditions, which has aesthetically pleasing asphalt shingles pattern printed on it. This is the material that we install for our customers to resolve their leaks issues, with 100% satisfaction and zero leaks going forward!
Medium-To-High Slope Roofs – Pitch Between 6 and 12
Even on higher pitch roofs, it is important to know that not all types of materials will work for you. For example, I would not recommend installing a slate roof or synthetic slate imitations on any roof pitch below 8 in 12. Because of slate’s slippery surface, the potential for wind-driven water increases exponentially, as the roof pitch goes down. On a roof pitch below 8, it becomes too easy for water to travel all the way up, beyond the hidden edge of the slate, and then find its way inside your home. Even when using proper underlayment (not felt paper, as a slate roof will far outlast felt, which will dry out and break / crack in multiple locations under the slate, in as little as 10 years), you don’t want to take the chance of having leaks on a very expensive new roof. One great thing about slate roofs, is that they will shed ice and snow, and are pretty immune to ice dams, just like metal roofs.
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