Roofing FAQs

Q: Can I apply new shingles over existing shingles?

A: Yes. You can apply new shingles over existing shingles, depending on the condition of the roof. If the roof has one layer of shingles that are lying flat and the deck is in good condition, the existing shingles typically do not have to be removed. During re-roofing is a good opportunity to examine roof ventilation to ensure vents are sufficient in number, positioned properly and are unobstructed.

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Q: Why or when should I use an asphalt shingle underlayment

A: An asphalt shingle underlayment is typically dry felt that may be impregnated or coated with an asphalt saturant, or a synthetic sheet. The use of an underlayment is recommended for the following reasons:

• Resins may exude from the wood board decking. Underlayment protects roof shingles from the resins that may be released.
• Underlayments protect decking material from wind-driven rain that may penetrate the shingle layers.
• To validate their limited warranties, many manufacturers require the use of underlayment.
• The use of underlayments, particularly heavier grades, reduces “picture framing.” According to CASMA, picture framing is the visible outline of deck panels caused by irregularities in roof decking thicknesses.
• To obtain a Class A fire resistance rating, underlayments should be used underneath shingles.
• The underlayment should conform with CSA 123.3-M (No. 15 / ASTM D226 Type 1 No. 15 felt), ASTM D 4869, and/or CAN 2-51.32 (Breather Type Sheathing Paper) industry standards.

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Q: How do I get rid of algae growth on my shingles?

A: There are several ways to reduce the discoloration:

• For a new roof, install a zinc or galvanized type metal near the ridge of the roof. As the metal ions are oxidized and erode off of the metal strip, they wash down the roof inhibiting cellular algae growth.
• A dilute solution of chlorine bleach, trisodium phosphate and water can be applied – one part chlorine bleach to three parts water with a quarter cup of trisodium phosphate. Note: Trisodium phosphate should be available at any paint supply store. Gently spray the solution on the shingles. For stains that are hard to remove, scrub mildly. Scrubbing too harshly will remove granules. Rinse the shingles thoroughly with water. In the past, this has been a temporary solution and usually needs to be repeated every couple of years. Apply this solution carefully to avoid damaging other parts of the building or the shrubbery below.
• Some companies offer roof cleaning compounds or roof cleaning services. Ensure the roof cleaning process will not damage the shingles.

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Q: Can hail affect asphalt roofing shingles?

A: Hail can affect asphalt roofing shingles. The damage caused by hail can be classified into two groups: aesthetic damage and functional damage. Aesthetic damage results in slight granule loss and the life of the shingle is usually not affected. Functional damage is characterized by substantial granule loss or cracking or penetration of the shingle. Functional damage may result in short term leaks or a reduction of the life expectancy of the shingle.

According to CASMA Technical Bulletin No. 14, there are several factors that impact how roofing shingles perform in hail:

• Size and density of hail stones – Larger heavy stones will cause more severe damage.
• Age of the shingles – Newer roofing shingles are more resistant than older shingles, as the asphalt is less brittle and better able to absorb the impact energy.
• Angle of hail impact – Hail which strikes the roof at a 90° angle is more likely to cause shingle fractures, while hail that strikes the roof obliquely is more likely to result in spots of granule loss.
• Temperature – Colder temperature will be more likely to cause fractures as the asphalt will be more brittle than in warmer weather.
• Roof deck conditions – Solid roof decks on moderately spaced trusses offer better support to the shingle surface in resisting hail damage. Shingles on flimsy or rotted decking can be more easily fractured.

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Q: My gutter is filled with granules. Is there a problem with my shingles?

A: Not necessarily. An excessive amount of granules are applied during the shingle manufacturing process to make sure that the asphalt on the roofing sheet is completely covered. It is important to completely cover the sheet with granules so that the asphalt is not exposed to ultraviolet light.

The granules are then pressed in. Due to the excessive amount of granules applied, some of the granules are only held loosely in place. Most of the excess granules are removed by the shingle manufacturing process, but some of these granules do get packaged with the shingles. These excess granules are known as “hitchhiker” granules.

“Hitchhiker” granules will typically come off during the first few years of shingle exposure on the roof. They usually will be found in gutters or at the bottom of downspouts. The loss of these granules is normal and does not affect the performance of the shingle. Granule loss only becomes a problem when much of the asphalt becomes exposed on the surface of the shingle.

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Q: What is buckling?

A: Buckling is defined as ridges that form along the length of the shingle, with the ridge spacing usually coincidental with deck board joints. These ridges are caused by the shingle being distorted from the movement of the deck. Buckling can occur with any deck type, but is more common with board decks, and less common on plywood/OSB decks. Buckling can occur when a new roof is installed, even if the old roof did not show any buckles; when the roof is stripped, the deck may be exposed to moisture, causing dimensional changes in the supporting lumber.