Roofing System- An Overview
Updated: Jan 2, 2021
Of the many systems on the home the roof might only be second to the foundation as far as importance. The roof system consists of multiple parts with a main purpose to act together to create a moisture barrier, preventing water from entering and damaging the home. Every homeowners should understand the various parts to the roof system and how to maintain them.
Understanding Your Roof
Your roof consists of layers of material that work together to repel water and other moisture away from the home. Roof systems can consist of different materials but there are 4 basic layers that are common among all residential roofing systems.
Layer 1- Roof Decking.
The roof decking is the structural layer of the system that attaches to the framing of the roof. The material is often CDX plywood or oriented strand board (OSB). This layer provides support for the rest of the roofing material so it is important it is sized and installed correctly to prevent roof sag or gaps which may allow moisture to enter the home.
Homeowners can view the roof decking from the attic of a home if access is available. Durring annual inspections of the attic the roof deck should be inspected for signs of water penetration, sagging, or pest damage. A lack of ventilation in the attic can also cause mold growth on the sheeting which will cause damage overtime. If any of these signs are observed a licensed roofing contractor should be consulted for repairs.
Layer 2- Underlayment.
Roofing underlayment is the last layer of defense when it comes to water pentation. There are three main types that are all applied directly to your roof decking and create a water proof or water resistant barrier depending on the type of material that is used. The three types of roofing underlayment are: asphalt saturated felt, and non-bitumen synthetic felt, rubberized asphalt.
Asphalt saturated felt (felt paper, tar paper) is the most popular type of underlayment used, although synthetic products are quickly taking over the market. This contains a base mat of various products including cellulose, tar, bitumen, and polyester. The base mat is then impregnated with asphalt to create a water resistant barrier. These products tend to be easily damaged and are applied over the whole roof in overlapping layers.
Synthetic Felt is becoming more popular even with its increased cost over traditional tar paper. The base mat of these products are reinforced with fiberglass to increase their durability and lifespan still creating a water proof barrier. These products are designed to be used across the entire roof surface.
Rubberized Asphalt (Ice and Water Shield) is much more expensive than traditional tar paper or synthetic felt because it contains more asphalt and rubber to make it water proof instead of water resistant. It often has a very sticky back to help it adhere, increase its durability, and create a waterproof seal. In Michigan this product is required to be installed on the eves to prevent ice buildup. The product should extend to a line at least three feet inside the exterior walls. It is often installed in valleys and around chimneys or other penetrations to create another layer of protection. It is not a replacement for metal flashing.
Once Installed there is not much a homeowner can do to maintain this layer as it will be sandwiched between the roofing material and roof decking. It is important to ensure this layer is installed properly when a new roof is being applied. In Michigan it is extremely important that ice and water shield be installed as required to prevent ice buildup.
Layer 3- Flashings
Flashings are often overlooked during roof installations although most of the roof leaks I observe during my home inspections are caused by improperly installed or damaged roof flashings. The material is most often aluminum, galvanized steel, or copper. There are many locations that roof flashings should be installed including in valleys, around chimneys, skylights, and other roof penetrations, at intersections with walls, at roof pitch changes, and at the edges of the roof. Each of these locations use special techniques to ensure the water will run off the roof properly, below are some basic guidelines for installation but they do not constitute all the techniques that must be used during all situations.
Valley flashing is most often used in open valley roof installations. While closed valleys are most commonly installed because they cost less they aren't the right choice for every installation. Thicker shingles consisting of multiple layers may not lie flat in the valleys or allow proper shedding of ice and water. This can cause granule loss and cause the shingles to age faster than expected. On an open valley a sheet of metal in attached to the roof decking and the underlayment and roof materials are sealed to this metal. This installation allows for water and ice to be shed faster. Properly installed the valleys tend to last longer and if a repair is needed it is usually easier and less expensive.
In my experience the penetration of a masonry chimney is one of the most prone to leak on a roof. This is because chimney flashing is often installed improperly or not replaced on a re-roof, even by professional roofing contractors. Properly flashing a chimney consists of 4
layers flashings that overlap to form a impenetrable seal to moisture. These layers are the head flashing, step flashing which is recessed into the brick of the chimney, counter flashing, and apron flashing. The forming or shaping of these flashings is just as important as installing them correctly and a qualified roofing contractor should always be hired when flashing these areas.
Wall intersections are also often installed improperly. The tricky thing with these areas is they can often hide damage inside walls. There are two basic types of intersections; rake and headwall. While not required the inspector suggests an installation using a vertical blocking of treated lumber combined with a multiple layered flashing system including step flashing and through the wall z-flashing. This type of flashing can be used for all types of siding including vinyl, stone, brick, or wood. I will be using writing a more detailed article about this type of flashing system in a later article.
Drip edge flashing is installed around the rakes and eves of a roof. This is made of either galvanized or painted steel or aluminum. It is important that these areas are installed correctly in order to prevent water penetration. Even roofing contractors that have been installing for many years may not be installing this trim correctly so I suggest to include pictures of how your want your flashing installed in your contract before you sign it.
I call this out missing kick out flashing on an estimated 80% of home inspections. Kickout
flashing should be installed in any area where the wall extends past an intersecting roof in order to direct water away from the wall and into a gutter system. Without this flashing water can easily find its way behind the siding and cause major rot. For more information check out my blog post "Kick-out Flashing".
There are many other types of flashing that could be used including those around pipe penetrations, sky lights, and hip and valley roofs. While roofs are often constructed by homeowners, handymen, and Do It Yourselfers it is not my recommendation. The major reason why I recommend a professional is because of the number of times I see subpar roof flashing installed. Roofing should be completed by an experienced and licensed contractor in order to avoid major damage to the roof and ensure flashing is installed correctly.
To maintain your flashing you should have a visual inspection performed annually to look for any deteriorated, rusted, or damaged areas. If caulking or another type of sealant was used it should be replaced if it is cracked, shrunk, or otherwise not creating a weatherproof seal. If any exposed fasteners are present they should be sealed with silicone caulk.
Layer 4- Roofing
The final layer of the roof system is the roofing itself. There are many types of roofing including multiple types of steel, sheet goods such as rubber and rolled asphalt roofing, slate, cedar, and the most popular is asphalt based shingles. Due to the vast majority of installed roofing being asphalt based shingles that is what we will cover here.
There are three basic types of asphalt shingles: 3 tab, dimensional, and luxury. While 3 tab shingles are still used often dimensional shingles have taken the market and continue to be the most popular roofing option in our area. For a more detailed breakdown on the construction of asphalt shingles see my article "Fixing Loose or Lifting Shingles".
The roofing is not often a waterproof layer, but works with the underlayment to create a waterproof barrier. This layers main job is to protect the underlayment from damage due to things like UV rays, hail, and tree branches.
To maintain your shingles you should first have them inspected at least twice per year, once in the spring and once in the fall. Look for signs of shingles lifting or not sealing (click here for repair options) or visible fasteners which should be sealed with a premium roofing sealant. If you observed cracking, missing, or large areas of loose shingles you should consult with a roofing contractor immediately. Also look for mildew or staining of the shingles. This is a sign of a fungus which can damage the shingles and reduce their lifespan. For more information on that please see my article "Cleaning Your Shingles"
If you notice shingles that are lifting or loose a repair by a licensed contractor should be made. Without repair the shingles could become further damaged by wind and cause leaks in the roof. For more information on lifting or loose shingles see our article "Fixing Loose or Lifting Shingles".
Also look for nail pops, areas the nails are standing proud of the shingle. Anytime you can see the top of a nail it should be set with a hammer to ensure it is holding tight and sealed with a premium grade roof sealant. There are areas where fasteners are purposely installed on the surface of the roof. These fasteners should be resealed often to ensure they do not leak.
Understanding and maintaining your roof is an important part of being a home owner., however I would suggest you rely on experts to evaluate this important system at least once per year. A roof inspection is usually inexpensive, especially when compared to a repair that could have been easily avoidable. As a certified home inspector and licensed residential contractor with over 18 years experience in the building trades I can help you evaluate your roof. For more information on my services as a home inspector in Central and West Michigan please visit my website at www.cardinspectionservices.com