Water should NOT stand on a sloped roof!
While performing a one-year warranty inspection at a new home, a home inspector noticing standing water on a sloped roof. It was clear that the roof pitch over this new patio addition was too shallow for the composition shingles that had been installed above it. And there was really no excuse for such a mistake.
The owner of this particular one-year old home said she had paid a private contractor to build the addition a few months earlier. Unfortunately, she – like most home owners – did not know about the importance of matching the roof covering material to the angle of the roof pitch. Not following a manufacturer's installation instructions can lead to serious roof leaks, even mold. The home inspector reported the identified defect to the home owner, and advised her to ask the contractor to come back and repair it. He agreed to a phone consultation with the contractor, if it became necessary.
The Roofer Is Supposed to Match the Material to the Roof Pitch
In construction-speak, "roof pitch" is a term used to describe the angle, or slope, of the roof surface. Pitch is usually expressed by a phrase like "5 in 12," or "5:12," or sometimes just "5 pitch." In this example, the phrase means that for every 12 "of horizontal measure away from the roof edge, the roof surface gets 5" higher. It's easy to see that the water shedding ability of a roof will have a great deal to do with how high the pitch angle is. Saying it another way: "the higher the pitch, the faster the water will run off a roof."
Let's say it again: Water SHOULD NOT STAND on a sloped roof!
Manufacturers of composition shingles (the type that is installed on most US homes) have to provide product warranties for their shingles. For that reason, they have a keen interest in those shingles being installed correctly. So these manufacturers print the installation instructions ON EVERY BUNDLE OF SHINGLES. And, in those instructions they recommend that the roof pitch be greater than 4 in 12, so that water will run off properly and efficiently. If a roofer uses composition on a roof with a pitch of less than 4, special preparations must be performed, like doubling up the roofing felt, and using sheet metal flashing at valleys, etc.
Now, here's where it gets interesting in our particular story. EVERY MANUFACTURER of roof shingles insists that composition shingles NOT BE USED when the roof pitch is less than 2 1/2: 12. In fact, violating that instruction (and a few others) will void the warranty on the entire roof. In other words, composition shingles are not designed or intended to be used with a shallow roof pitch. Wind-driven rain will actually blow water back up under the shingles, under the melt and the wood deck will get wet, and fail to dry properly. Over time, this wet deck will warp and rot, and leak. So, while it may be keeping the interior (ie, the attic and ceiling) dry early on, it will be slowly losing the fight.
If a home inspector or a roofer sees water standing on a pitched roof, it is a pretty good clue that there is not enough pitch angle to the roof deck. It is a definite sign that the roofer should not have used composition shingles on that surface. The contractor who built this lady's patio addition, did not know, or just did not care. This home owner should complain, and the roof covering should be changed out at no charge.
What Is the Proper Way to Roof a Low-Sloped Roof?
But, what materials should you use to cover a low-sloped roof?
Roofing materials manufacturers make a product with similar surface granules and matching colors, called roled roofing, which comes in 36 "wide rolls.This" roled roofing "is to be applied by, first doubling up on the layers of roofing paper, overlapping each run as it progresses away from the lowest roof edge. Then, starting again at the lowest roof edge, the composition roled roofing is rolled parallel with the roof edge, and the overlapping portions / seams (no less than 1 "wide) are hot mopped with tar or roofing cement.
There are other types of materials that are available for these low-sloped applications, but generally speaking, they all roll out and are sealed at the seams to keep standing water or wind-driven rain from getting up under the roof covering. After all, the purpose of your roof covering materials, and the flashings that supplement them, is to keep the rain and moisture out.
An Inspector Can Provide a Little Peace of Mind If You Are Going to Remodel
If you are considering a roof replacement for any reason, call a professional real estate inspector. And, that goes for any and all remodeling projects around your house. In most states, inspectors are called by the generic term "Home Inspector." If your state requires a license to perform these services, by all means use a licensed inspector. Some companies are willing to act as a consultant between you and your contractor. It's a good idea to contact an inspector early, before things get testy between you and your contractor.
If you have already had an addition done or a roof replacement, and you want a second opinion, call a home inspector. Most inspection firms perform "system" inspections, where they only look at the individual systems and components that were remodeled or updated. Do a little research and check with your friends, or with inspector trade associations, like the American Society of Home Inspectors (ASHI), or the like, to find companies who hold the highest standards or professionalism.
What's the Take-Away?
If you, or someone you know, are about to plan a remodel or upgrade, it's a good idea to get someone on your side who knows how the work is supposed to be performed … someone who can advise you and / or your contractor about the right way to do it. Call a professional home inspector near you.