Roofing Basics

Roofs have two main styles: sloped and flat. The pitch, or slope, of a roof is measured in a ratio of run vs. rise. In other words, the number of inches the roof rises across 12″.

The ratio for the average sloped roof in our region is 4 in 12. Flat roof is a construction term. All flat roofs must have some slope or ponds of water will form on the roof. A minimum slope is ½” in 12.

There are several common roof types in this area: shingles, tile, torch down, and hot mop. The pitch of the roof can be a factor in which type of roofing is used. Shingles can be used on roofs with a slope as slight as 2 in 12 but a roof flatter than that requires hot mop or torch down.

Shingles come with 20, 25, 35, or 40 year warranties depending on the thickness and expected life. The most popular shingle style now is the “dimensional” shingle. They are designed to give the illusion of thickness. Dimensional shingles start at the 25-year level and hide bumps when roofing over existing roofs.

Tile roofs come in many styles. Although more expensive than shingles, they are called lifetime and will last 50 years or more. Tiles are much heavier than shingles and not all roofs can handle their weight. If you are not sure if yours can, don’t take a chance–consult an engineer. There are lightweight tiles available that don’t require an engineer’s report, depending on your roof style, although these are more expensive than the regular tile.

Torch down is a modern method using a modified bitumen torch-applied system. A fiberglass base sheet and all metal trims are applied first. The torch down roofing is rolled out and heated with a hand-held torch. It melts to the fiberglass base and welds itself to the adjoining roll. This is a very popular method because it is easy to work with and fairly durable. A torch down roof will last for 10-15 years.

Hot mop is less popular lately. Asphalt is melted in a kettle and pumped up to the roof and mopped onto the felt. The most common roof consists of three layers of felt and tar. Gravel or a cap sheet is installed on top to protect the asphalt from the sun.

Re-roofing is one of the most important jobs around your home. If you wait too long or have a poor job done, you will have leaks that cause other expensive damage.

The average re-roof costs around $4000 and lasts 25 years. This means the cost per year of that roof is $160. If you try to make your roof last “one more year”, you are saving $160. Put that into perspective: if that roof leaks and your drywall and carpet get wet, the $160 you saved represents only the down payment on the repairs you will need.

Once you have decided to invest in a new roof, you will have several decisions to make about the project. For example, one decision you will have to make is regarding tear off. The City says you can have three layers of the same kind of roofing material. Your roof is designed to hold this weight. One advantage to tearing off is being able to inspect the wood below. One disadvantage is that it adds approximately $1000 to most roofs. Some roofing materials cannot go over an existing roof and must be torn off to install properly.

Another decision is the warranty. Warranties vary on all these roofs. Some are from the manufacturer, some from the installer. Some are transferable, and some are not. Be sure to check this out and think about what is best for your situation.

One decision that should be a slam-dunk is to use a licensed contractor, and to check references. Be sure you also verify the contractor’s insurance coverage for both liability and worker’s compensation.

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