Roofing Materials and Structure – How It Works

Date Published: November 2, 2020

The roof over your head is an especially important aspect of the overall performance of your house. A properly installed and maintained roof and attic system are key components that prevent moisture intrusion, manage water from roof runoff, and promote good energy efficiency and indoor air quality.

Much like a crawlspace, an attic space can fall into disrepair from neglect. Who besides an occasional home inspector or contractor spends much time in an attic space or on a roof?

Understanding the building science principles that underlie a roof system can prevent manageable maintenance items from developing into much more costly repair conditions.

The Purpose Your Roof Structure

All roof systems are designed to manage and shed water. Water and ice should not be allowed to pool or collect anywhere on a roof, no matter the materials present.

Whether it is a more common asphalt shingle roof, a concrete tile or metal roof, or a rubber membrane flat roof system, all roof coverings should discharge collected rain and melted snow into a gutter and get that water away from the foundation of the house.

It is common knowledge that gutters need to be cleaned regularly, even when there is a gutter guard present, but it is also important to clear debris off the roofing materials.

We have written extensively in other posts about the dangers of poor grading and drainage around the property and a professionally installed roof and a complete gutter system are significant parts of the overall drainage plan for a house.

Roof Material Types

The most common roofing materials found today are asphalt products.

roofing material - asphalt shingle

roofing material - asphalt shingle

These shingles consist of a felt paper with asphalt granular adhered to the top. Dimensional or Architectural shingles can have a life expectancy of twenty years and even as much as forty years, depending on the product. In Colorado, asphalt shingles are very popular because of their lower cost and our climate.

Another popular roofing material in Colorado is concrete tile.

roofing material - concrete tile

roofing material - concrete tile

These tiles are molded out of concrete and attached to a home in a lap fashion just like other shingles. Concrete tiles are typically rated for a 50-year lifespan or more!

Because the material is much heavier than a standard roof, an installer may need to ensure the roof structure can support the additional weight by hiring a structural engineer. Also, the material may be rated for 50 years, but maintenance, such as repairing cracked or loose tiles, may be needed.

Although less common in our snowy climate, flat roofs are present and require different roofing materials. These materials are typically rolled on to create one solid barrier instead of having individual shingles. The two main types consist of rolled asphalt and rubber membrane.

roofing material - rolled asphalt

roofing material - rolled rubber membrain

Rolled asphalt is a similar material to asphalt shingle, but comes in large rolls. The edges of the rolls are sealed together to create one continuous barrier. While it is an inexpensive roofing material, it doesn’t last long. It has a roughly 10-year lifespan.

Rubber membrane roofs are similar but made out of a more robust material which makes their lifespan much more comparable to other materials. This is a much more common flat roof material on new installations.

The last type of roofing material we will touch on is metal. Metal roofs have been making a big comeback lately. While it has always been widely popular on outbuildings and barns, corrugated/standing-seam roofs are seen installed on more and more new homes in our area. These roofs have a long lifespan and are cheaper than concrete tiles roofs. However, metal roofs can be very noisy during storms which can be bothersome.

roofing material - standing seam metal roof

While there are many other roofing materials that have been used over the years, those are some of the widely used ones. During our home inspections, we define the type of roofing material that is present on the home and also the condition. We typically will walk the roofs where possible, although many materials we do not walk to prevent damage.

But what about hail?

A common misconception about hail damage is that any hail will damage a roofing material and that the affected roof will fail shortly after the damage has taken place.

This is not a correct understanding of hail damage. Smaller hail can fall onto your roof and have negligible effects on its performance. It takes larger hailstones, more than one-inch diameter typically, to cause impact damage on a roof.

The largest issue with hail damage is that it strips away the overall life expectancy of the product, particularly for asphalt shingles. Each sizeable impact of larger hail destroys the shingle and the roof will shed its roofing granules.

You can imagine that your “twenty-five” year shingle now only has half of that life left in it after significant hail damage.

What’s Underneath The Roof?

An underlayment is a product that is installed over the roof decking but underneath the selected roofing material. Older homes may feature tar paper or felt products while newer homes may have synthetic products applied.

These underlayments are installed so that even in the event of a roofing material failure the wood decking underneath is protected from water penetration.

synthetic underlayment

One of the largest culprits of active roof leaks is found at roofing “penetration points” where plumbing vents and mechanical systems penetrate through the roof deck and underlayment.

These areas should be monitored as they pose the greatest risk of failure over time, although a professionally installed vent or “boot” should not leak.

My Roof Has Soft Spots!

Below the underlayment is the roof decking, also known as roof sheathing. This is typically sheet wood such as plywood or OSB particle board in newer homes. This provides a flat surface to lay the roofing material on.

Not all building components are created equal. Some older homes that were built to be more economical may feature thinner roof sheathing or wider installation of rafters and trusses. This can give a roof deck a “soft” feeling when walking over the roof covering, where the roof bends slightly as you walk over it. This is not necessarily a roof defect and can simply be a consequence of the material choices made when the house was built.

Also, older homes with plywood sheathing are more prone to soft spots in the sheathing. As the material ages, the sheets of wood adhered together start to separate, particularly with the high temperatures in the attic or if a past roof leak was present. Occasionally when replacing a roof, the sheathing will need to be replaced as well in softer spots. A roofer will make this determination.

What About The Attic?

It is quite common to find an attic space above the ceiling in a single-family home. These spaces are a great indicator of the overall condition of the house.

An attic space can reveal the overall structure, insulation, and ventilation of the house which we will detail in other posts. In older homes, it is common to find wood rafters and plywood sheathing, while newer homes will feature engineered trusses with OSB sheathing.

There are advantages and disadvantages to each type of roof structure, like all components of a house, but each system requires the same attention to moisture, insulation, and ventilation concerns.

A complete evaluation of an attic space will of course include an evaluation of the roof structure, identifying damaged rafters or roof trusses, and looking for signs of water penetration where a roof has failed.

During our inspections, we will view the attic where accessible to look for structural or moisture concerns.

If you are looking for a home inspection in the Colorado Front Range area, contact us today!

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About the Author: Joe Ophoff

Joe Ophoff has been working as an energy efficiency specialist since 2014. He is the Energy Services Manager at Scott Home Inspection in Colorado.

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