Home Inspection FYI

Providing Help, Knowledge and Other Useful Information To Home Owners Everywhere

Home Inspection FYI - Providing Help, Knowledge and Other Useful Information To Home Owners Everywhere

ASPHALT SHINGLE WEATHERING

Shingle “weathering” is a general term used to describe the effects of a shingle due to long-term exposure to the elements.

A weathered shingle isn’t necessarily a damaged shingle, although weathering will eventually damage shingles. Weathering is a natural process that causes the shingle to deteriorate over time. The rate at which shingles weather can be affected by a number of things.

Shingle Quality

A low-quality shingle will fail before a high-quality shingle. Quality can vary widely among manufacturers, and even within a single manufacturer’s product line.

Structure Orientation

South-facing roof slopes have shorter lifespans due to increased thermal cycling and UV exposure. Some portions of the roof are affected by prevailing winds more than others.

Degree of Roof Slope

Flatter roofs have shorter lifespans because they shed moisture more slowly and are more directly exposed to UV radiation than roofs with steeper pitches.

Climate

Harsh climates shorten roof lifespans. Wind, moisture and thermal cycling all contribute to deterioration of roofing materials.

Thermal Cycling

Climates with large daily temperature swings shorten roof lifespans because they cause greater amounts of expansion and contraction. This increases the roof’s rate of deterioration.

Roof Color

Darker roofs absorb more heat, which shortens shingle lifespan by accelerating the loss of volatiles and increasing thermal cycling.

Elevation

Homes at higher elevations are exposed to more UV radiation, which deteriorates most roof-covering materials, including asphalt shingles.

Roof Structure Ventilation

Poor ventilation of the roof structure shortens shingle lifespan by failing to keep shingles cool, resulting in accelerated loss of volatiles and greater amounts of thermal cycling.

Quality of Maintenance

Failure to repair damage and keep roofs clean can result in damage and deterioration from moisture intrusion and wind.

Now that you have a good idea of the kinds of conditions that contribute to deterioration, let’s look at an overview of the process of deterioration.

ASPHALT SHINGLE LIFESPAN, Part 1

Asphalt shingle lifespan is strongly affected by weathering. Even though the rate at which shingles weather varies, they still go through a generally predictable lifecycle.

Shingle deterioration chart ASPHALT SHINGLE WEATHERING

 The lifespan of asphalt shingles is related to the rate at which they deteriorate. The long-term deterioration pattern of an asphalt shingle can be broken into three parts:

  • incipient deterioration;
  • accelerating deterioration; and
  • decelerating deterioration.

“Incipient” mean “early,” so incipient deterioration is the first stage. During the incipient stage, deterioration takes place very slowly.

As time passes, deterioration starts to worsen, and shingles enter a period of accelerating deterioration.

By the time the deterioration curve begins to flatten out and the decelerating period begins, the shingles have reached the point of functional failure.  They’re no longer protecting the roof and are trying hard to turn back into the raw materials from which they’re manufactured.

Let’s examine the lifecycle of an asphalt shingle from the time of manufacture onward.

Packaging

Shingles start to age and deteriorate as soon as they’re packaged. This is the beginning of the incipient stage. The deterioration process is very slow at first, and is mostly driven by oxidation, the chemical processes taking place within the asphalt, and sometimes also by heat and pressure, depending on storage and transportation conditions.

Shingle Installation

Deterioration accelerates dramatically once the shingles are installed and exposed to weather. The asphalt layer is new and hasn’t yet had a chance to cure, so this rapid aging continues for a short time until the asphalt layer becomes tougher. This period typically includes minor granule loss as excess granules adhered during manufacturing separate from the shingles and are washed away by runoff.

Slow, Prolonged Aging of a Shingle

Once the curing period is complete, shingles enter a long period of aging at an ever-increasing rate.

At first, the pace will be so slow that it won’t really be visible. Shingle deterioration starts on a very minute scale with micro-cracks in the asphalt, the loss of a few granules, dissipating volatiles, and chemical changes in the asphalt.

The rate at which aging increases depends on a number of factors, such as shingle quality, roof orientation, slope, and other factors. This is the end of the incipient period and the beginning of the accelerating slope.

Accelerating Deterioration of a Shingle

During accelerating deterioration, these factors become more important. Multiple factors can combine to drastically extend or shorten the service life of the shingles.

As they approach the end of the accelerating-deterioration slope, most shingles will have common failures.

asphalt shingle craze cracking ASPHALT SHINGLE WEATHERING

Random surface cracking, called “craze-cracking,” can expose more asphalt to UV radiation.  In cold climates, the potential for damage is increased due to the expansion of moisture as it turns to ice. Craze-cracking will be covered in more detail in the articles to come.

Thermal cycling can cause a shingle to split. Splitting may be due to:

asphalt shingle bridging split2 ASPHALT SHINGLE WEATHERING

• contraction of the shingles themselves; or

asphalt shingle substrate splitting ASPHALT SHINGLE WEATHERING
• contraction of the roof deck.

A shingles can become more brittle as volatiles, which keep them flexible, dissipate. Loss of volatiles can degrade the bond between the asphalt and the granules, resulting in an increase in the rate of both uniform and localized granule loss.

asphalt shingle wind creasing ASPHALT SHINGLE WEATHERING

It also increases the chances of creasing or splitting of a shingle from flexing.

organic shingle distortion ASPHALT SHINGLE WEATHERING

As shingles lose volatiles, they may also become more moisture-absorbent, which can lead to distortion. Shingle distortion exposes more of the under-surface of the shingle to moisture, and increases the chances of roof leakage because wind-driven rain can more easily penetrate the roof.

organic shingle delamination ASPHALT SHINGLE WEATHERING

An organic shingle is more strongly affected by the loss of volatiles because, as the volatiles dissipate, the mat becomes more absorbent. As they deteriorate, organic shingles sometimes delaminate, which can leave the mat directly exposed to weather.

organic shingles trashed ASPHALT SHINGLE WEATHERING

Loss of granules on a shingle increases the amount of UV radiation reaching the asphalt. Although UV rays deteriorate asphalt, leaks from UV-caused deterioration are rare because properly installed shingles are typically at least two layers thick.

Thanks to Kenton Shepard and Nick Gromicko

How Wind Can Damage Your Roof

Wind and How It Can Damage Your Roof

We know that hail is associated with storms. Usually, storms that drop hail also bring wind, as low-pressure fronts move in and out of the area.

What Causes Wind?

In talking about wind damage, we should first cover some basics.

Wind is air moving from areas of high air pressure to areas of low air pressure. The greater the difference in air pressure between two points on Earth, the faster the air will move between them.

How Wind Creates Damage

Wind Uplift

One of the destructive forces created by wind is uplift, which is the tendency of materials to be lifted into a wind-created vacuum. Uplift can be created by either of two physical conditions:  loss of laminar flow, or increased wind speed. Both of these processes reduce the air pressure immediately above the roof-covering material.

Laminar Flow

wind force damage 300x155 How Wind Can Damage Your Roof

Air flowing close to a surface is in a state called “laminar flow.”  According to the laws of physics, flowing air will try to maintain contact with a surface. When that surface bends or curves sharply, the air flow can’t turn quickly enough to maintain contact, and it separates from the surface. We say that it “loses laminar flow.” This creates a vacuum, and anything that can move will be lifted up into that vacuum, if the vacuum is strong enough.

1 42 2 How Wind Can Damage Your Roof

The other process that creates uplift is related to the fact that increasing wind speed lowers air pressure. Wind speed on the roof can be up to 2½ times the approach speed, which is the speed of the wind as it blows toward the home. Reduced air pressure from fast-moving air just above the surface of the roof also increases the amount of uplift.

Wind Damage Location

Uplift can develop when wind blows across a roof.

The location of damage on a home will be affected by the orientation of the wind to the roof structure, and by the shape of the roof. In these illustrations, areas of uplift are shown in blue.

1 42 3 How Wind Can Damage Your Roof

When wind blows perpendicular to the eaves and ridge, uplift is created along the upwind side of the lower roof slope and along the downwind side of the ridge.

1 42 4 How Wind Can Damage Your Roof

When wind blows parallel to the eaves and ridge, uplift is created along the upwind rakes.

1 42 5 How Wind Can Damage Your Roof

Wind blowing at the side of the building was deflected up and over the low-slope section, creating an area of strong uplift, which sucked shingles and underlayment right off the roof.

If uplift can lift a portion of the roofing material, more of the surface of that material will be exposed for the wind to push against, and it will be more easily displaced or blown off the roof.

Uplift is strongest at areas of the home where the wind loses laminar flow. The areas most commonly affected include:

  • upwind eave edges;
  • upwind rakes;
  • upwind corners; and
  • the downwind side of ridges.

It’s at these areas that we’ll most closely see wind-related damage.

In addition to uplift, areas which lose laminar flow also experience turbulence. This buffeting or fluttering effect can also loosen and displace roofing materials.

Positive Pressure

Positive air pressure is really just the wind pushing against something that offers resistance, such as a shingle tab that’s been raised by uplift, and flashing that protrudes enough for wind to push against it. Eaves and rakes are areas where roofing materials terminate, so they are especially vulnerable to damage from wind pressure.

Wind Inflation

Wind inflation is similar to what happens when you blow up a balloon. It’s a result of positive air pressure. An extreme example of inflation is when wind blowing at the gable side of a home enters the space between the underlayment and roof-covering material. By inflating this space, wind can create damage by breaking the bonds of asphalt shingles.

1 42 6 How Wind Can Damage Your Roof

In this photo, we see the results of all three factors. The left side of the structure was the downwind side, and you can see that roofing materials were lifted into the vacuum created by loss of laminar flow.

The far-left corner had roof sheathing removed by a combination of uplift due to loss of laminar flow and inflation.

The near-right corner had roof sheathing removed by a combination of positive pressure and inflation.

Many other convection-related wind events occur both with and without storms. Another condition that creates winds which can damage roofs is large-scale weather patterns that produce a strong, deep flow of air which passes over a mountain chain.

 

Wind and Weather

Asphalt Composition Shingle Fasteners

Fasteners Used For Asphalt Composition Shingle Installation

 

Jurisdictional Requirements

The type of fasteners that can be used on new construction may be limited by jurisdictional requirements. Areas that commonly experience hurricane-force winds typically don’t allow staples to be used.

Fastener Types

The type of fastener used to fasten the shingles is especially important for resisting wind uplift and pull-through. Fasteners for asphalt shingles should be roofing nails or staples. The head of a roofing nail and the crown of a staple are the parts that actually hold the shingles in place. The minimum width for the staple crown is 15/16-inch.

Although both nails and staples have historically been used to secure shingles, staples are usually not recommended in areas subject to high winds, and they’re also not allowed by most building codes in new construction.

Fastening shingles with staples may void the manufacturer’s warranty against wind damage.

Both nails and staples have sufficient strength to resist the small uplift load on the fasteners as long as the adhesive strips are fully bonded. If staples are properly installed, they offer close to the same resistance to wind as nails.

Staples

 stapled shingle fasteners Asphalt Composition Shingle Fasteners

The problem with staples is orientation. As an installer uses an air-compressor staple gun, his natural tendency is to rotate his body. Unless he also rotates his wrist at the same time, the orientation of the staple crowns will reflect this rotation.

Properly installed, stapled shingles will usually withstand wind speeds of up to 60 mph. Upgrading the fastening system requires re-fastening the shingles with roofing nails. The shingles may need to be hand-sealed afterward because the adhesive bond may not re-seal adequately.

Nails

Some shingle manufacturers specify that their shingles be fastened with nails. Nails should be corrosion-resistant, wide-head roofing nails of the proper length. Corrosion-resistant nails can be made of galvanized steel, copper, aluminum or stainless steel.

 

Proper Fastener Installation

proper stapling shingles Asphalt Composition Shingle Fasteners

protruding nail Asphalt Composition Shingle Fasteners

 

Fasteners should not be over-driven, which will cause them to cut part-way through the shingle and lower its wind resistance.  They should also not be under-driven, which will cause the protruding nail head to eventually wear a hole through the overlying shingle.

proper nailing shingles Asphalt Composition Shingle Fasteners

Fasteners driven at an angle can cause both problems, depending on how deeply they’re driven.

 

Fastener Placement

strip shingle normal wind Asphalt Composition Shingle Fasteners

 laminated shingle normal wind Asphalt Composition Shingle Fasteners

Fasteners should be placed according to the manufacturer’s instructions. Generally, they should be installed below the adhesive strip, equally spaced across the shingle, and placed in slightly from the ends, as shown in the two photos above.

t lock fastening Asphalt Composition Shingle Fasteners

T-lock shingles have their own requirements for fastener placement.

strip shingle high wind Asphalt Composition Shingle Fasteners

Laminated shingle high wind Asphalt Composition Shingle Fasteners

 

Shingles in areas designated as high-wind areas should have additional fasteners installed at the two inner positions, as shown in the two photos above.

Heavy architectural shingles often have different fastening requirements. The fastener placement may vary by slope rather than by wind designation.

heavy laminated shingle standard slope Asphalt Composition Shingle Fasteners

Standard-slope fastening

heavy laminated shingle steep slope Asphalt Composition Shingle Fasteners

Steep-slope fastening

 

The Holding Power of the Substrate

The holding power of the substrate affects the holding power of the fasteners. Decayed or rotten sheathing will not anchor fasteners well.

 

Inadequate Penetration

inadequate fastener penetration Asphalt Composition Shingle Fasteners

Fasteners should be long enough to completely penetrate the roof deck. This can be a problem when newer shingles have been installed over old ones, as well as with ridge and hip cap shingles, and with continuous ridge vents.

Thanks to Kenton Shepard and Nick Gromicko