Freqently Asked Roofing Questions

The decision to recover or tear-off existing low slope roofing will influence the cost, performance, and insulating value of new roof installations.

"Recovering" the existing roof significantly reduces the cost of roofing replacement and preserves existing insulation value. This approach often provides the best value, but can prove to be a costly mistake if certain conditions are overlooked.

Building codes have long prohibited the installation of more than two layers of roofing. This limitation reduces the likelihood of overloading and of moisture entrapment. While the consequences of overloading may be obvious, moisture entrapment can be equally destructive since trapped moisture will accelerate the deterioration of new roofing, insulation, and even the supporting deck. Core samples provide the information for evaluating existing roofing.

Other factors can influence this critical specification, but trapped moisture is often the most important consideration when assessing the need to remove an existing roof.

"Ice dams" are accumulations of ice that prevent normal drainage from a roof, potentially causing heavy interior leakage. These types of leaks are made possible by heavy snowfall, followed by outdoor temperatures that remain below freezing for extended periods of time. Heat loss from the building interior causes the snow to melt, but the melted snow re-freezes at the colder overhangs and gutters. This cycle of melting and re-freezing continues as long as temperatures remain below freezing, causing "ice dams" to grow. Eventually, the "dam" causes drainage to back-up beneath the roof, and enter structure.

Weather conditions in the Greater Cincinnati area during February of 2010 were ideal for ice dam formation!

Leakage occurring during the conditions described, may be identified as resulting from ice dams if the leakage does not reoccur during normal rainfall. Once identified, ice dam leakage may be addressed in a number of ways:

• Do nothing. If leakage was minor, and has never occurred in the past, it may be reasonable to decide that the expense involved with possible remedies is unnecessary.
• Improve attic ventilation or attic insulation. For the ice dam to form, snow on the roof must first melt, in spite of the fact that outdoor temperatures are below freezing. Both attic ventilation and attic insulation serve to prevent rooftop snow from melting prior snow at the eaves and gutters.
• Install Ice and Water Shield beneath shingle, slate, or tile roofing. This material creates a barrier to ice dam leakage, and is most economically installed during the course of roof replacement.
• Install heating cables. There are some ice dam situations that cannot be resolved by anything other than heating cables. Electrical outlets must often be added to serve the new cables, and someone must remember to activate the cables when weather conditions warrant.

Molloy Roofing has worked in the Greater Cincinnati area for well over a century, and in recent decades we have noted an increase in the frequency of ice dam conditions occurring.

The hurricane winds that raced through the Midwest in 2008 brought new attention to the importance of proper shingle attachment. There are two common methods of attaching shingle roofing: driving nails with a hammer or with a pneumatic nail gun. To be effective, nails must be properly located, and driven flush with the surface of the shingle.

Nail guns are popular because they shorten training time and reduce effort. It takes years of practice to become proficient at hand nailing, but nail gun productivity can be achieved almost immediately. In spite of this apparent advantage, we prefer to hand nail shingle roofing.

Ideal nail placement is limited to a very small area. When a nail is driven outside of that area, the shingle's wind resistance is reduced and the manufacturer's warranty may be invalidated. Proper nail placement is certainly possible when using a nail gun, but placement tends to be considerably more accurate when hand nailing.

On pre-1960's homes, roof sheathing boards are typically 5-1/2" wide. When installing shingles over these relatively narrow boards, many nails will unintentionally be driven between the boards. If not pulled out and re-located, these nails will back-out over time. When hand driving a nail between the boards, you can feel that the nail missed (and you can use the claws of your hammer to pull the nail out). This feel is not present when using a nail gun, and nails driven between boards are more likely to be overlooked.

In addition to being properly located, nails must be driven flush with the surface of the shingle. This means that the nail cannot be over-driven or under-driven. This requirement is complicated by temperature, variations in wood type, and by the types of roofing and flashings that are being secured. Nail gun air pressure can be adjusted to compensate for some of these variations, and the best guns may be adjusted at the gun, and don't require a trip to the compressor. However, it has been our experience that air pressure is more often set too high, preventing the need to occasionally use a hammer to "finish" raised nails. Unfortunately, over-driven pneumatic nails tend to blast completely through the shingle, creating a problem that remains unseen until high winds test the installation. In cold weather, when shingles are less flexible, this problem may occur even when nail gun air pressure is carefully set. Hand nailing provides a clear advantage in this regard.

The photo on the left shows an incorrectly positioned and badly over-driven nail. This shingle may easily be lifted by wind, and would not meet manufacturer warranty requirements. The photo on the right shows two nails that were driven on an angle, and are not flush. In time, these nails will wear holes in the shingle tab that will lay over them.

There may be situations where nail guns are appropriate, but we believe that better quality shingle roof installations are achieved by hand nailing.