On a residential sloped roof, there are generally 2 styles of fiberglass shingles that are used; 3-Tab and dimensional.  3-Tab shingles were created first.  Each sheet contains three individual shingles of equal size.  When installed on a roof, the style is identifiable due to slits between each individual shingle, allowing for the full shingle to be viewed from the ground.

Dimensional shingles were created after 3-Tab shingles.  A sheet of dimensional shingles is the same size as 3-Tab, but contains five individual shingles per sheet consisting of different sizes overlapping one another to create a more dynamic look.  There is no difference in effectiveness between the two styles other than appearance.

Roofing is measured in terms of squares. One square is equal to a 10’x10’ area or 100 square feet.  Both styles of shingles are sold in packages containing one-third of a square.  They are also installed the same way.

When installing a new roof, work must begin at the bottom and continue toward the peak.  The top half of a sheet of shingles contains lines of roof tar.  This is where the nails are applied to secure the shingles.  Nails should never be applied into the bottom  half of the shingle as this will cause a leak in the roof .  The next row of shingles are installed as such that the shingles themselves overlap the top half of the row below, covering the tarred area and the nails.  There are two reasons for this:

#1 – To cover the nails in order to prevent leaks.

#2 – In hot weather, the tar on the sheets of shingles melts causing the overlapping shingles to glue themselves down.

In the past, new roofs were installed directly on top of the old roof.  This was done with as many as three, four, or even five layers of roofing.  Today, the building code only allows for up to two layers of shingles.  If two or more layers of shingles currently exist on a roof, they must be stripped off down to the plywood.  The newly installed roof becomes the first layer.  In the future, a second layer of roofing may be installed on top.

In some cases, the original layer of installed roofing maybe cedar shingles installed directly to the framing of the roof.  In this scenario, the cedar shingles must be removed and new plywood installed in its place before installing the new fiberglass shingles.