Roof Systems

Modified Bitumen SystemsModified Bitumen (MB) is asphalt that has had modifiers added to it to give it plastic or rubber-like properties. The most common types of modifiers being used are APP (Atactic Polypropylene) and SBS (Styrene Butadiene Styrene). 

Rolls of modified bitumen membrane come in widths of 36″ (0.9 m) to approximately 39″ (1 m) and cover an area of approximately 100 square feet to 112 square feet per roll. Surfacings for these roll materials consist of a smooth surface, or mineral granules, aluminum, copper, or an aggregate such as gravel or slag that is set it hot asphalt.

Modified Bitumen roof systems consist of one, two, or three ply systems. The type of substrate will often determine the type of system being installed. Modified membranes can also be installed in conjunction with built-up roof materials (such as multiple plies of fiberglass felt) to form a “hybrid” roof system. Modifieds have proven performance on residential, commercial, and industrial applications.

Roofhelp recommends that all modified roofs be installed on slopes not less than 1/4″ per horizontal foot (stated “quarter in twelve” or “quarter-inch slope”) in order to achieve positive drainage.

BASE SHEETS

Asphalt-Coated Organic Base Sheet – Perforated and Non-Perforated

Asphalt-Coated Glass Fiber Base Sheet

Asphalt-Coated Glass Fiber Venting Base Sheet, Types I and II

FELTS AND FABRICS

Asphalt-Saturated Organic Felt – Types I (A.K.A. No. 15) and II (A.K.A. No. 30)

Coal Tar-Saturated Organic Felt

Smooth-Surfaced Asphalt Roll Roofing – Types I, II, III, and IV

Asphalt- or Coal Tar-Saturated Cotton Fabrics

Asphalt- or Coal Tar-Saturated Woven B.U.R.lap Fabrics

Asphalt-Impregnated Glass Felt – Types III, IV, and VI

Coal Tar-Impregnated Glass Felt – Type I

Thermoplastic Fabrics for Built-Up Roofing – Types I, II, III, and IV

BITUMENS

Asphalt – Types I, II, III, and IV

Coal Tar – Types I, II, and III

Lap Cement – A.K.A. Cold-Applied Liquid Adhesive, A.K.A. Solvent Based (Cutback) Asphalt – Type I (Grades 1 and 2), and Types II and III

SURFACINGS

Mineral Aggregate – Gravel or Slag

Asphalt Roof Coatings – Asbestos and Non-Asbestos

Aluminum-Pigmented Asphalt Roof Coatings – Non-Fibered, Asbestos Fibered, and Fibered without Asbestos

Emulsified Asphalt – Fibered and Non-Fibered

Mineral-Surfaced Asphalt Roll Roofing (Organic)

Mineral-Surfaced Asphalt Roll Roofing (Glass Felt)

Other items not listed are flashing materials, mastics, caulking material, fasteners, and roof insulation, to name a few. 

Now that you see the wide variety of materials available, you are probably wondering what the differences are. The difference in the base sheets is simple. Venting base sheets are specially-designed for use with moisture-cured substrates such as light weight insulating concrete or poured gypsum. Neither of which you homeowners will have to worry about. Regular base sheets are generally used with nailable decks such as plywood. The differences in the felts are determined by the types of reinforcement materials used. For instance, polyester felts are stronger than fiber glass felts which are stronger than organic felts. The fiber glass felts will vary among themselves in quality with Type III being the lowest quality and Type VI being the highest. 

Gravel or slag surfacings are probably the most popular. The next most popular surfacings are probably the granule-surfaced cap sheets, commonly called 90 pound because they used to weigh approximately that much per square. Now they weigh around 72 pounds per square. Then come the emulsions which can be spray, brush, or roller applied. 

Now we’ll talk about how B.U.R.’s are put together. Base sheets are usually the first piece of Built-Up Roofing material installed and are usually mechanically-fastened (nailed) to the deck or substrate. Then come the felts. These can be installed with either hot asphalt or coal tar, or cold-applied liquid adhesive, a.k.a. solvent-based asphalt or “cutback” asphalt. Approximately twenty-five to thirty pounds of hot asphalt or twenty to twenty-five pounds of coal tar per 100 square feet (roof square) is used between each ply. Three to five gallons of the cold-applied adhesive is used per square. Last is the surfacing. With a cap sheet, the same amount of bitumen or lap cement is used to install the cap sheet as is used to install the plies. With gravel or slag, a flood coat of about sixty pounds per square of asphalt or seventy pounds per square of coal tar is applied and 400 – 500 pounds per square of gravel or 300 – 400 pounds per square of slag is embedded. Emulsion surfacings will vary. Usually it’s around three gallons per square that is used. If emulsion is what is preferred, an aluminum reflective coating should be applied after the emulsion cures to help reflect damaging UV rays.

Built-up roofs can be installed over just about any type of roof deck as long as the proper substrate is used. BUR’s can’t be mopped to a wood roof deck. In this case a rosin sheet and base sheet are needed first. With steel roof decks, the thickness of the deck should be a minimum of 22 gauge and some type of approved insulation should be mechanically-attached to the deck to provide a substrate. Manufacturers should be consulted before mopping to Polyisocyanurate (“iso” for short) insulation. Many manufacturers will not warrant a roof if the felts are mopped directly to the iso and a coverboard such as wood fiber or perlite is needed. In some cases adhesives are being used to attach the insulation to the deck but be sure the roofing materials manufacturer is consulted before this is done. With structural concrete roof decks, the roof is often mopped directly to the deck after it’s cleaned. Sometimes a thermal insulation is used to provide a substrate. Thermal insulation can be attached by mechanical means, adhesives, or even hot-mopped. If the insulation is hot-mopped with bitumen, then care needs to be taken so as not to allow the bitumen access to the interior of the building at joints in the roof deck. Also, if Isocyanurate insulation is used, only 4′ X 4′ sheets can be mopped due to its propensity to warp and curl. With lightweight insulating concrete, pre-cast gypsum panels, or poured gypsum, venting base sheets are attached with special fasteners and then insulation may or may not be installed over the base sheet and then the roof membrane installed. In some cases a vapor barrier will be necessary. Built-up roofs cannot be mopped directly to lighweight insulation or gypsum. Cement fiber roof decks should have a base sheet or insulation mechanically-attached to it before installing the roof. Insulation should be installed in two layers with all joints offset and staggered a minimum of twelve inches.

How Long Do They Last?

The service life of a roof is dependent on many factors: geographical location & weather conditions, foot traffic, materials used, conditions under which the roof was installed, slope of roof, type of surfacing material, etc. Under ideal conditions, a 3-ply built-up roof should last at least fifteen years, a 4-ply should last at least 20 years, and a 5-ply should last at least 25 years. This author has seen ten year old 4-ply roof that needed to be replaced and twenty year old 3-ply roofs that were still functioning.

APP MODIFIEDS

In order to create roofing grade asphalt, asphalt flux is air-blown at elevated temperatures which converts the flux to roofing grade asphalt. In the early 1970’s, the Italians, lacking the blowing equipment, were looking for a product that would convert asphalt flux into a usable roofing product. They discovered that if Atactic Polypropylene (APP) – a by-product of propylene polymerization – was added to asphalt then it gave the asphalt some plastic properties. They found that by adding about 30% of APP modifier, they could stretch the modified asphalt up to fifty percent of its original length before it would break. 

Next came the need to make it into a usable roll product. Some type of reinforcement would be needed. They looked into various reinforcement materials and decided on a polyester mat because polyester would accommodate the APP modified asphalt’s elongation properties whereas the more commonly used woven glass mats would not. The reinforcement material is dipped into the hot modified bitumen mix, then goes through a rolling cylinder, cooled, and then wound into a roll. 

APP membranes are applied using a torch. The back of the sheet has extra asphalt on it which, when heated, bonds to the substrate. This was especially convenient for the smaller, more cut up roofs because less room and equipment is needed on site to torch-apply a membrane than is necessary for application using hot bitumen.

BUR Systems or Built-Up Roof are a roof consisting of multiple plies of roof felts laminated together with bitumen. Built-up roof material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate (gravel or slag), emulsion or a granule-surfaced cap sheet. 

This section was written simply to give people an idea of what a Built-Up Roof (B.U.R. for short) is and how it’s put together. The materials and information listed here are not comprehensive nor do they represent all types of built-up roof materials available.

Built-Up Roofing is one of the oldest and most reliable ways of installing a new roof. It was first known as composition roofing and started in the 1840’s. B.U.R.’s come in two basic types, asphalt and coal tar, and three basic components – (1) the waterproofing component, (2) the reinforcing component, and (3) the surfacing component which is used to protect the other components from the elements.

Wood Shake: Wood Shakes are thicker than Wood Shingles. There are two main types: (1) handsplit and resawn and (2) tapersawn. Handsplit and resawn shakes have the split face exposed with a naturally rustic appearance, and are sawn on the back. Tapersawn wood shakes are sawn on both sides for a semi-textured look with a stronger shadowline than a wood shingle. Used for both roofing and sidewalls. Recommended for use on pitches of 4:12 and steeper. All Wood Shakes are cut from clear heartwood with no defects. Heavy split and resawn Sawn on the backside, while the face is split with the natural grain of the wood. Has a highly textured surface on the exposed face. This is the heaviest type of Wood Shake, with a very rugged or rustic appearance. Available thicknesses for these shingles is 3/4", 7/8", 1" and 1 1/4"+.

Medium split and resawn Similar to the heavy split and resawn shake, but not as thick or heavy. It produces a roof with a very textured appearance. Available thicknesses are 1/2" and 5/8".

Tapersawn Sawn on both sides like a Wood Shingle, only thicker. This shake gives a naturally tailored look of a shingle accented by the sharper shadow-line of a shake due to the thickness of the butt. It's the most popular type of wood roof. Available thicknesses: 5/8", 7/8" and 1".

Packaging: Shakes are packaged five bundles per 100 sq. ft.

Tile: Tile roofs have been around for centuries. Like any roofing product, they were created to provide a barrier between the inside of a structure and the harsh outside elements. Roof tiles are made of local, natural and recyclable materials such as terracotta (also known as clay), slate and concrete. All three of these roofing materials offer lifelong durability and fireproofing; two superior qualities that continues to set them apart from the competition. Concrete roof tiles, like those manufactured by Eagle Roofing Products, offer additional benefits including: versatility in design and color, energy efficiency, greater protection against high winds, hail and freeze/thaw climates, and they are less expensive than genuine clay or slate.

Spray Foam: Spray Polyurethane Foam (SPF) roofing provides excellent insulation and custom slope to avoid ponded water issues and improve water flow to drainage. SPF roofing systems require a roof coating to be applied over the foam in order to cover and protect the spray polyurethane foam from deteriorating due to the sun’s harmful UV rays. Spray foam coatings all contain low levels of VOC’s, provide energy cost savings and create minimal disruption to the tenants and occupants inside the building during construction. These coatings have been successfully used on spray foam roofing systems for over 30 years, providing renewable and sustainable systems that are seamless and have outstanding waterproofing capabilities.

Silicone: a silicone roof coating system is a layer of silicone that is applied to a flat roof. It usually dries as a single-ply membrane that protects a roof from moisture, mold, UV radiation, and severe weather. It can be applied to roofs of any size as long as they are flat and in relatively good condition. The roof is one of the most critical parts of any building, but it’s also one of the most difficult and most expensive components to fix. A good roof will last between 25 and 50 years depending on what kind of roof it is, but it can also cost thousands of dollars to replace or repair it when it is too heavily damaged.

It’s easy to assume that there is no way around having to fix a roof, but there is a much cheaper solution that can extend its life and help you avoid costly repairs. It is known as a silicone roof coating system, and when you have it applied correctly, you can make it so you can go for years without having to replace your building’s roof.