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The roof is your home's umbrella. If it has holes, it will leak.
Your home's roof is more than a layer of asphalt shingles, clay tiles, or metal sheets. It is a system with an extremely important job: protect the occupants and the rest of the home from the environment, including rain, snow, sunlight, and moisture.
Your roof as a system
A typical asphalt roof system is composed of shingles, underlayment, flashing, decking, framing, ventilation, and insulation.
Shingles shed water. They are far from water proof, but their job is to quickly move water off of the roof. They should be installed so that gravity allows them to do their job. Shingles are mostly 3-tab or architectural. They must be durable to withstand wind, rain, sunlight, animals, and traffic.
The roof's underlayment is the next layer of protection, and is usually the most water resistant layer. Felt paper is the most common underlayment in our area. Moisture will get through the asphalt shingles on a regular basis. The underlayment provides a drainage plane for the moisture, rather than your home's interior. In the event of shingle failure, the underlayment will act as a secondary level of protection. Similar to shingles, it should be installed so that gravity allows it to sufficiently do its job!
Flashing is a broad term. There are many types of flashing but they all serve a similar purpose- waterproof parts/components of the roof. It is usually thin metal, but there are some alternatives. Flashing is used in areas where underlayment and shingles are just not enough. Common areas where flashing can be observed is around the perimeter of the roof, in valleys, and around penetrations. These are all areas prone to leaks.
Curious if your roof is properly flashed? While this will not provide a definitive answer, it may give you an idea. Walk outside and from the ground see if there flashing along the edge of the roof under the shingles. This flashing is called a drip edge, and it prevents water from running along the bottom of the shingle and rotting out the fascia board.
The next two components are the roof decking and framing. The decking is the flat boards, usually plywood or OSB, that the underlayment, shingles, and flashing are attached to. The decking should be flat and rigid enough so that the shingle fasteners do not back out when the roof is being walked nor does hail have as significant of an impact. The decking is attached to the roof framing. Framing members that hold the decking are trusses or rafters and sometimes battens. These are part of the home's structure and must be protected from moisture damage.
Roof venting is an often overlooked component. Venting prevents excess temperatures and moisture in the attic. High moisture content will cause wood rot and lessen the effectiveness of insulation. High temperatures will increase energy bills and can cook shingles from below! The diagram shows how ridge and soffit vents work, but gable and turtle vents are also common in our area. Gable vents work by drawing air from one end of the attic to the other. Gable vents need about 1' of free ventilation for every 150 square feet of attic space. Turtle or ridge vents used with soffit vents only need about 1' of free ventilation for every 300 square feet of attic space, provided that 40-50% of the vent space is provided by ridge/turtle vents.
Finally, we have insulation. Insulation and air sealing have been the craze of the 21st century. They are extremely important and can significantly lower energy bills when properly installed. There are many types of insulation including fiberglass (batts and blown-in), blown-in cellulose, mineral wool (batts and blown-in), closed cell and open cell foam, and various types of foam/plastic boards and battens to name a few.
A word of caution: Insulation and air sealing correctly installed in the right location- lower energy costs and less moisture intrusion. Insulation and air sealing incorrectly installed and or in the wrong location- worthless at best, moisture and mold trap at worst.
It is important to understand that these components rely on each other and other components of the home. Adding insulation to an old house's attic just might cause your moisture to be trapped in your walls. Covering solid board decking with a new ZIP system may just rot out your rafters. For these reasons, it is important to consult a professional before making changes to any home.
Have questions? Feel free to call or text, no purchase necessary.
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