Most roofs in America are covered with either dimensional shingles, asphalt, shingle types, or fiberglass shingles. The two look extremely similar and in fact are, with the only significant difference being that fiberglass shingles use a fiberglass mat as the base, while more traditional asphalt shingles use a paper base. But that one difference makes the asphalt shingles more water resistant and fire resistant than dimensional shingles, with the ability to work well in hotter climates. However, fiberglass shingles won’t last as long in colder climates.
However, it also makes them somewhat more expensive. If fiberglass shingles are installed a number of shingles on a home, the material costs will go up by about 20 to 30 percent. For that extra money, the homeowner receives a shingle that will last longer. Asphalt shingles are generally considered to be good for about 20 years, while fiberglass ones will last from 25 to as much as 50 years, with 30 years being typical.
Looking at the most common types of the roofing material available, we find:
- Composition shingles last 12 – 20 years
- Asphalt shingles last 15 – 30 years
- Wood shingles last 20 – 25 years
- Fiberglass shingles last 25 – 50 years
- Rubber roofs last 30 – 50 years
- Metal roofs last 50 – 75 years
Even so, the biggest factor in how long architectural shingles on any roof lasts is the weather that it is subject to. Any and all forms of weather have an impact on the life of architectural shingles on a roof, including the summer sun. Hail is a bid destroyer of roofs, allowing many homeowners to get a new roof paid for by their homeowner’s insurance. But the biggest factor in roof life isn’t the weather or even the architectural number of architectural shingles; it’s ventilation in the attic.
Whatever shingles are installed on a home, they are installed over roofing felt (or paper) and plywood or OSB sheathing. The roof shingles protect the home from rainwater, by providing a path for the rain to flow off the roof of the home, while preventing it from getting through the roof shingles onto the sheathing inside. But that doesn’t mean that attics are totally without moisture.
Humidity
Humidity can be trapped in there, if there isn’t adequate ventilation. This will encourage mold and fungi to grow on the bottom side of bundles of shingles and the sheathing, weakening it. Allowed to go far enough and the roof becomes wavy, with the flexing causing cracking in the metal shingles below.
One of the big questions that homeowners face is knowing when an asphalt roof needs to be replaced. There are several signs which can indicate this:
- Water stains on the ceiling of the home
- Missing or loose shingles; probably blown away by the wind
- Shingles are curling, cracking, or blistering
- The roof is sagging (this is different than the edges curling up)
- Dark or dirty-looking areas on the roof, indicate that the gravel is coming off
- Gravel from the roof in the gutters
- Visible exposed nail heads
- Water damage in the attic
- Flashing becomes damaged or is missing
Of course, hail or hurricane damage can greatly accelerate the destruction of roof shingles, lowering their lifespan.
Even specialty shingles, bundles of shingles, or brand-new roofs can be destroyed by severe weather events, causing tab shingles on most roofs it to need replacement. Failure to replace the shingles on a timely basis invites further damage, increasing the cost of eventual repair and replacement.
How Much Roofing?
Most homeowners will hire a roofing contractor to replace their own roofing squares, as they are not comfortable doing the job themselves. But the roofing square itself is actually rather simple for those who don’t mind working on the same roofing square themselves.
The one big problem is the quantity of work. Replacing the many how many bundles of shingles that are used in a bundle of roofing products requires a lot of man-hours, due to the size of the area that has to be done. A significant amount of stamina is required, due to the weight of the shingles themselves. Even so, one person can re-roof a home, if they decide to dedicate the time to do so, or they could talk a few of their buddies into coming over and helping.
Before anything, it’s necessary to calculate how many bundles or much material is needed. Roofers calculate the number of “squares” of a roof and how many bundles there are to replace. One square equals 100 square feet.
Since shingles are either sold by the bundle or by the square, this is an important number to calculate. Shingles are packaged in packs of 33.3 square feet of finished roof (not of how many shingle bundles or by area, which will be higher due to overlap), so every 100 square feet of roof requires three packages of the shingles needed.
A standard package of shingles contains 29 – 12”x 36” shingles. That works out to how many square shingle bundles full square amount of shingles and a total of 87 square feet of material. But because the shingles in a square are normally overlapped by a bit more than 50%, it is considered to have 33.3 square feet of shingle.
However, due to the slope of the roof, the number of squares of roofing can’t be calculated by dividing the home’s own square feet of footage by 100. Besides, the same roofing crew used will usually overhang areas that are not included in the total square footage of other materials of the home, like the garage, porches, and eaves.
These make the roof’s size bigger than the home. But with a two-story home, the roof with many square feet will be smaller than the home’s 100 square feet of footage, as the floor space will be divided between the first and second floors.
To calculate the square footage of the roof’s area start by measuring the dimensions of the home. But don’t just take flat roofs, measure the walls, measure to the edges of the eaves, as that’s what you really need to know.
In the diagram below, if only the yellow rectangle, which represents the walls is measured, then it will be as if the whole roof and area covered were only the part represented by the pink triangle. But in reality, we have to add the blue square footage of the roof area as well. If the home’s perimeter isn’t an exact rectangle, don’t worry, just measure it as if it were. That might cause the purchase of too many bundles, but they can always be returned.
The challenging part of this is measuring the height of the roof peak above the eaves. That usually means climbing up a ladder, with the help of a buddy to hold the lower end. If that’s not possible, then make an estimate, erring on the high side.
As with the roof dimensions and outer perimeter of the home, erring high will mean buying three bundles of shingles, more shingles per bundle than needed; but three bundles once again, the unused three bundles, can be returned.
From that information, it is about how many squares bundles are possible to calculate the total of 100 square feet of total square footage of the whole roofing project by using the Pythagorean Theorem. Let me see if I can simplify that.
Roofline
To start with, we need a right triangle. If you remember, a right triangle is any triangle that has a right angle or one that is 90 degrees. Since your roof area probably doesn’t have that, we’re going to cut the triangle in half, vertically, right at the roof peak. That will give us two mirror-image triangles of the same size, shown as “A” and “B” above.
When we pull one of those triangles out, we can give the three sides their own names, as in the diagram below. Remember, the dimensions of triangle B will be the same, with the exception that the triangle is a mirror image.
Triangle from roof
What we need to know is the length of side Z, but what we have is the measurements of the length times sides W and Y. To get the length of side X, we merely need to divide the length of side W in half. Then it’s time to apply the dreaded Pythagorean Theorem. Here it is.
X2 + Y2 = Z2
Let’s walk through that slowly for those who don’t like math. You’re going to want a calculator which has the ability to do square roots for this. For convenience’s sake, I’m going to apply some numbers to those letters, so that we can better see how it works. So:
- W = 24
- Y = 6
- A (the length of the roof, which isn’t shown) 30
- That means that X =12
StepAction Shown as FormulaShown as ExampleStep 1Put numbers in formulaX2 + Y2 = Z2122 + 62 =?Step 2Square the numbers (multiply them by themselves)X X =Y Y =12 12 = 1446 6 = 36Step 3Add the squared numbers together Z2144 + 36 = 180Step 4Find the square root of that, using a calculator (the calculator included in Windows OS will do it)Z13.4Step 5Multiply the result by the length of the roof Z A = Sq. Ft. 13.4 30 = 402Step 6 Multiply that by 2 to account for the other side of the roofs. Ft. 2 = Total roof402 2 = 804Step 7Divide by 100 to get squares Total roof ÷ 100 = Squares804 ÷ 100 = 8(add an extra package)
So in our example, we find that the “Z” side of the roof is 13.4’, which gives us a roof square footage of 804 square feet. Since we can only buy whole packages of laminated shingles per bundle, it means buying an extra package for those four square feet. But then, it’s a good idea to have some extra shingle bundles on hand anyway, as there’s always something that makes it necessary to use one bundle of more laminated shingles than expected.
Some of the things that might require using an extra bundle of ridge shingles are dealing with dormers, valleys, and the roof peak. So keep that in mind when buying your ridge shingles material and make sure you buy enough bundles of shingles to account for the extra bundle of shingles material and extra scrap those situations will cause.
One final point on this measurement; if the whole roof slope and roof pitch of the house is L-shaped, it makes sense to cuft it into two pieces and calculate them separately, adding them together. Otherwise, the area calculated for the whole roof pitch and slope will be way too big, as the vast majority of it will include filing in the inside of the L.
A Few Notes on Shingling the Roof
Most homeowners who shingle their own roof will start by removing the existing roofing shingles first. There’s nothing wrong with that, but it may not be necessary.
Building code
Building code for three roofs on a house, so unless the building code in your municipality is more restrictive or there is such extensive damage to the other roofing shingles in a bundle or the roof sheathing as to require removing a layer of the old roofing shingles first, putting the new two roofing shingles on over the old one can save a lot of labor.
How many shingles
The trick to how many shingles when doing this is using the existing how many shingles in a bundle as a guide for how many shingles on the new ones, butting the shingles up against the existing overlap tab shingles. That helps prevent unsightly humps in tab shingles on the roof, which can lead to leaks.
Lay asphalt or fiberglass shingles
While not common, it is also possible to lay asphalt or fiberglass shingles in a square, over cedar shakes, or even shingles in a bundle. This is tricky, as the old shingles roof won’t be as smooth as the new one. It’s best to get some help from a professional if this is the decision that’s made.
It isn’t necessary to lay a new single layer of shingle or of roofing felt over the existing shingles when installing a second shingle roof over the first shingle one. In fact, it’s better not to, as it makes it easier to see the edges of the existing shingles. However, some professionals will add a single-row layer of waterproof shingle underlayment at the eave ends of tab shingles, to help prevent ice dams.
New flashing
New flashing should always be installed to help prevent leaking at that point. This includes a drip edge. Make sure that the flashing used is for re-roofing, as the dimensions and roof area will be different. Flashing in valleys should also be replaced, even if it looks good. That flashing is going to have to last another 30 years.
Roofing job
Any roofing job is done from the bottom up. Special care must be taken at any point where the roof is pierced, as that is a prime location for a leak. This piercing is usually by some sort of vent, which will have flashing built into it.
Always make sure that the flashing overlaps the bundle number of shingles downhill of it and is overlapped by more than how many shingles are up above it. As for the exact number of shingles that are on line with it, to either side, that’s up to personal discretion; but overlapping the shingles over the flashing will look better and be easier to seal.
Replace Vents
It’s a good idea to replace vents at the same time that the roof is being replaced. All vents, regardless of the type, are affected by weather. So unless they look like new, they should probably be replaced. The additional cost of the vents is minor, in the total cost of the roofing project budget.