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Matthew Steger WIN Elizabethtown

Common Roofing Types

In south-central PA, there are 5 types of roof coverings that we commonly seen in my home inspection travels. In order of how common they are (1.) Asphalt/Fiberglass Composition Shingles, (2.) EPDM (Ethylene Propylene Diene Monomer), (3.) Rolled Asphalt (Modified Bitumen), (4.) Slate, and (5.) Metal. With any type of roof material, regular maintenance and inspection is key to a long service life and a lower possibility of leakage.

Asphalt shingles are the most commonly found on homes in this area on 4:12 and high-pitched roofs. Roof pitch measures the roof’s steepness. A 1:12 roof pitch, for example, is nearly flat as it only rises 1’ in height for every 12’ of vertical distance. A 12:12 pitch, for example, would be a 45° angle looking along the home’s rake edge.

Asphalt shingles can be installed on 4:12+ pitches although some shingle manufacturers will allow 2:12 pitched installs as long as a proper membrane (such as an ice and water shield) is installed between the roof sheathing and the shingles under the complete roof. The lower the roof pitch, the more likely rain water can leak under the shingles or wind damage can occur. An ice and water shields adds an extra protective layer under the shingles to help prevent leakage.

 

Asphalt shingles come in 2 styles: flat 3-tab and architectural.  3-tab shingles (seen in the 1st photo) were common up until about 10 years ago. These shingles generally lasted from about 15 years to about as long as 25~30 years for newer varieties. As of about 10 years ago, architectural shingles (also called laminated shingles) became pretty much the standard for reroofs and new installations. You’ll be hard-pressed to find new installations of flat 3-tab shingles although the major shingle manufacturers still do manufacture 3-tab shingles. The minimal design life of architectural shingles is about 25 years and some manufacturers offer 40+ year varieties. The difference between a 25 year and 40 year shingle is generally its thickness; a slightly thicker felt base and thicker asphalt granule layer is what differentiates 25 year and longer lasting designs. As this material starts to wear, the asphalt granules will start to come loose.

Building standards permit 2 layers of asphalt shingles to be installed (a new layer on top of an old layer) although doing so makes the roof framing and sheathing take on considerably more weight. Also, additional attic ventilation may be needed due to the extra heat the attic will likely experience. Adequate attic ventilation is critical to proper shingle service. An extra hot attic, such as due to insufficient attic ventilation, can make the attic (and the rest of the home) very hot and may void the shingle warranty since the shingles can be baked from underneath. Also, adding a new layer of shingles on top of old shingles will, in most cases, cause the new shingles to not last as long as they are designed. For example, installing 30 year shingles over another layer of old shingles may cause these new shingles to possibly only last 15~18 years. Not removing the old shingles saves money initially, but also leads to wasted money down the road since 30 year shingles are more expensive than 25 year shingles and you are getting maybe half the actual life by using the 2-layer method.

Also, for architectural shingled roofs, only ridge shingles or flat 3-tab shingles cut to size (color-matching, of course) should be used at the ridge. Architectural shingles should NOT be used on ridges as their increased edges may allow for wind damage (tear-off). Shingle manufacturers generally list this installation requirement in their instructions as well as in their product warranties.

EPDM (Ethylene Propylene Diene Monomer) is commonly found on flat (or low pitched) roofs. Of course, no roof should be perfectly flat since the roof needs to be able to drain water. A roof of 2:12 and less is considered ‘flat’. EPDM is also commonly called ‘membrane’. For the average flat roof, multiple pieces of EPDM are installed with rigid foam panels underneath. The seams (of where the various pieces of EPDM join) are sealed down with a special adhesive. The other perimeter is also terminated with EPDM strips to help prevent leakage at edges, vents, etc.  When the material meets sidewalls, such as a chimney, masonry, parapets, etc., the material should terminate up the wall approx. 12” using termination bars to help prevent leakage at the junction.


EPDM used on residential flat roofs is most commonly black and comes in 0.045” and 0.060” thicknesses. This product generally wears at about 0.001”~0.0015” per year so a properly installed and maintained 0.060” EPDM roof should last at least 40 years.

Rolled Asphalt (Modified Bitumen) is a flat roof alternative to using EPDM. It is a material similar to asphalt shingles. Instead of being cut into shingle form, however, it comes in roll-form and is applied with a hot torch, not nails. The material is normally 39” wide so rolls of which are overlapped slightly as it is installed. This material’s design life is approx. 8~15 years (again assuming proper installation and maintenance) dependent upon the pitch and grade of the material.

When a roof has a low pitch, sunlight and rain water can sit on the roof for an extended time and can cause faster material deterioration. The life of rolled asphalt can be extended if resealed with UV silver coating (this UV silver coating is not designed to make the roof water tight, but instead reflect UV energy which can destroy the asphalt over time). As this material starts to wear, the asphalt granules will start to come loose. Rolled asphalt roofs are generally the cheapest type of flat roof.

Slate roofs are very common on older homes in the Lancaster area. There are hard slate and soft slate varieties. Slate is a mined rock and is a durable roofing material. Pieces of slate are held in position using 2 nails. Over time, should one of the nails rust and fail, the remaining nail will be the sole support of the slate very often causing the piece of slate to rotate like a hinge.

Slate mined in different areas (most commonly from Vermont, but also can be found in some other states including PA), comes in different colors. Since slate can’t be bent, like an asphalt shingle can, making a slate roof water-tight over ridges or hips can be difficult. In many cases, a metal strip piece of flashing is installed at these areas to help prevent leakage.

Assuming it is properly maintained as repaired as needed, a slate roof can easily last 75+ years and, sometimes, 100~200 years. Hard slate should last longer than soft slate since hard slate doesn't absorb water or warp. For roofs over 50 years old, however, it is common to find evidence of repairs due to non-color matching pieces of slate. Again, since the slate’s color depends upon the location it was claimed, it is often difficult (and sometimes impossible) to find pieces of slate to color match an existing older slate roof. When going into an unfinished attic below a slate roof, it is common to see evidence of some past leakage and sometimes even pin-holes of daylight. Ideally, slate roofs should be inspected annually by a roofer uniquely trained and qualified to work on slate roofs. Asphalt-based and rubberized versions of slate-look-alike shingles do exist.

Metal roofs have been around for hundreds of years. They can be made of copper, tin, aluminum, etc. and are quite durable. Each type of metal has its own unique wear characteristics. Copper tends to be the most expensive. Over time, however, once the top (exterior side) coating deteriorates (such as rusting), rain water can contact the metal and lead to rust holes and leaks. Once a small amount of light rust is visible, it is a good time to repaint a metal roof. Modern metal roofs have their paint baked on at the factory. A properly maintained metal roof can easily last 40+ years. Again, the maintenance of metal roofs should be left to a proper trained roof.

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My full list of technical and home maintenance articles can be found here.

© 2020 Matthew Steger

Matthew Steger, owner/inspector of WIN Home Inspection, is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at: 717-361-9467 or msteger@wini.com.

WIN Home Inspection has provided a wide array of home inspection services in the Lancaster, PA area since 2002. This article was authored by Matthew Steger, ACI - owner of WIN Home Inspection in Lancaster, PA. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.