Page 153 - 2018 National Home Improvement

2018 National Home Improvement Estimator, All Rights Reserved Page 127

Built-up Roofing
A built-up roof that isn’t worth repairing must be stripped off before the new roofing is installed. Once the
deck is clean, pound flush or pull all exposed nails and make repairs to the deck and flashing as
needed.

The base sheet for a built-up roof can be either resin-coated or asphalt-coated organic felt or fiberglass.
On a wood deck, nail the base sheet to the deck. Use a Type I or Type II venting base sheet on a
concrete deck.

The felt layers are applied on top of the base sheet. Type I (15-pound) and Type II (30-pound)
asphalt-saturated organic felts are the most common. Asphalt-impregnated fiberglass felts are Types III,
IV and V. Type III fiberglass felt is lower quality than Type IV. Coal tar-saturated felts are popular in
some areas. Polyester felts are stronger than fiberglass felts, and fiberglass felts are stronger than
organic felts.

Lay each 100 square feet of felt in 25 to 30 pounds of hot asphalt, 20 to 25 pounds of coal tar or 2 to 4
gallons of cold-applied roofing adhesive (lap cement). If the last layer is a mineral surface cap sheet, use
the same quantity of asphalt, coal tar or adhesive. For a topping of gravel or slag, flood each 100 square
feet of surface with 60 pounds of hot asphalt or 70 pounds of coal tar or 3 gallons of emulsion. Then
install 400 to 500 pounds of gravel or 300 to 400 pounds of slag per 100 square feet of roof surface. If
gravel or slag is set in emulsion, apply an aluminum reflective coating to protect against UV damage.

Modified Bitumen Roofing (APP and SBS)
In the 1970s, chemists in Europe discovered that asphalt took on rubber-like properties when combined
with certain additives. These additives include APP (atactic polypropylene) and SBS (styrene butadiene
styrene). Adding about 30 percent APP to asphalt creates a product that can be stretched up to 50
percent without breaking. SBS modified roofing was developed by French and German chemists. They
found that asphalt took on the character of rubber when 10 to 15 percent SBS was added. SBS modified
asphalt will stretch up to six times its original length without breaking. Unlike APP, SBS modified
asphalt returns to its original size when released. This elasticity makes asphalt roofing more durable.
The roof surface can shift, or expand and contract, without breaking.

APP roofing uses a polyester mat that matches the pliability of APP modified asphalt better than a
woven glass mat. You apply APP membranes using a torch. The back of the sheet has extra asphalt
that bonds to the surface below when heated. That’s convenient on smaller jobs with limited working
area, because you need very little equipment.

You can use many mat materials with SBS, including fiberglass and polyester. Fiberglass SBS mats
weigh from 1.0 to 2.5 pounds per 100 square feet. Polyester SBS mats weigh from 3.5 to 5.0 pounds
per 100 square feet. You can apply SBS membranes with hot asphalt, a torch, or cold adhesive.