Membrane Roofs & Insulation
QE Roofing is a preferred installer of Weatherbond and Mule Hide membrane roofing systems. We have installed over 1,000,000 square feet of membrane roof systems and we still have a flawless reputation. This should make any potential customer feel comfortable knowing we take pride in our work. We appreciate the opportunity to serve you and will strive to make your roofing project an unforgettable great experience.
Membrane Roof System Overview
A majority of low-slope roof systems in North America use roof membranes to serve as the weatherproof coverings for roof assemblies. A roof membrane protects underlying roof assembly components, such as the insulation and roof deck, and the building from water entry. Most low-slope roof membranes have two principal components: weatherproofing layer or layers and reinforcement.
The weatherproofing component is the most important element within a roof membrane because it keeps water from entering a roof assembly. In built-up membranes, the weatherproofing component is the mop-applied bitumen or cold-applied bitumen-based adhesive. In polymer-modified bitumen membranes, the primary weather proofing component is the polymer-modified bitumen. In single-ply roof membranes, the weather proofing component is the thermoplastic or thermoset polymers. In fluid-applied systems, the waterproofing is the cured, fluid-applied membrane material.
The reinforcement adds strength, puncture resistance and dimensional stability to a membrane. In bituminous membranes, the reinforcement helps hold the weather proofing bitumen in place and provides tensile strength to the membrane. In built-up membranes, the reinforcement may be a fiberglass ply sheet or polyester fabric embedded between the layers of weatherproofing bitumen or cold adhesive. In polymer-modified bitumen membranes, the reinforcement generally is fiberglass, polyester fabric or a composite of both that has been fabricated into the finished sheet in the manufacturing process. In single-ply roof membranes, fiberglass or polyester scrims, fabrics and mats are used for reinforcement. However, some types of single-ply membranes, such as unreinforced EPDM, do not use reinforcement.
A roof is composed of several primary parts, and collectively these parts are referred to as either a "roof assembly "roof system."
An assembly of interacting roof components including the roof deck, air or vapor retarder (if present), insulation and membrane or primary roof covering designed to weatherproof a structure.
A system of interacting roof components generally consisting of a membrane or primary roof covering and roof insulation (not including the roof deck) designed to weatherproof and sometimes to improve the building's thermal resistance.
In general, a roof assembly consists of the structural deck and roof system. A roof system includes every component above the roof deck.
Membrane roof systems typically consist of three primary parts: insulation, roof membrane (the weatherproof covering) and membrane surfacing, if present.
Membrane roof systems employ a weatherproof membrane covering, or roof membrane, to keep water from entering
the structure. Examples of common roof membrane types include but are not limited to built-up roof membranes, polymer-modified bitumen roof membranes, EPDM, other single-ply and liquid-applied roof membranes.
Generally, membrane roof systems are installed as low-slope roof systems; however, in some instances, membrane roof systems can also be used on steep-slope roof systems.
A category of roof systems that generally includes weatherproof membrane types of roof systems installed on slopes at or less than 3:12.
A category of roof systems that generally includes water-shedding types of roof coverings installed on slopes greater than 3:12.
Membrane Roof Insulation
The purpose of roof insulation is to provide a substrate for the application of a roof membrane and thermal resistance. A roof can be one of the largest surface areas of a building envelope through which interior heat escapes. Insulation within a roof assembly may help to maintain the inside temperature of a building at a more constant, comfortable level.
Roof insulation that is properly manufactured, designed and installed serves several vital purposes:
- It can reduce the energy required to heat and cool buildings.
- It can reduce the potential for condensation occurring on interior surfaces.
- It can stabilize deck components by reducing their temperature variations and consequent thermal expansion and contraction.
- It can provide a relatively smooth substrate upon which roofing materials may be applied.
- It can provide fire resistance for certain low-slope roof assemblies.
- Tapered insulation can be used to provide slope for positive drainage where the deck does not.
Including rigid roof insulation in a roof assembly requires several design considerations. Depending on the type and thermal resistance of the insulation to be used, there may be a resultant need for changing or upgrading the design of the roof membrane. For example:
- Because insulation resists heat transfer, its use directly under a roof membrane does not allow solar heat to readily pass through to the interior of the building, as normally occurs if insulation is not present. Therefore, in compact roof assemblies, insulation contributes to an increase in roof membrane temperature during hot weather and a possible decrease during cold weather, thereby accelerating the aging process of roofing materials.
- In a roof system with insulation, a higher thermal-resistance value may increase the magnitude of the thermal expansion and contraction of the roof membrane compared with a roof system without insulation.
- While reducing the potential for interior moisture condensation, rigid roof insulation sandwiched between a roof deck and roof membrane can increase the probability of condensation occurring within the roof system. For many projects in moderate and cold climates, the addition of insulation may add to the need for an effective vapor retarder. Condensation control is an important consideration in the thermal design of most roof assemblies.
An ideal roof insulation would have the following properties:
- Compatibility with Bitumen and Other Adhesives--It would be able to withstand the effects of being in contact with adhesives, solvents and hot bitumen at the application temperatures required for installation of a roof membrane without degradation.
- Component Compatibility--It would be formulated to be compatible with the other components of a roof assembly.
- Impact Resistance--It would have strength, rigidity and a density high enough to resist impact damage during and after roof system installation.
- Fire Resistance--It would be noncombustible and comply with the requirements of insurance underwriters and building codes.
- Moisture Resistance--It would resist the effects of moisture vapor and water without degradation over the life of a roof system.
- Thermal Resistance-- It would have a low thermal conductivity (k-value) so that the highest possible thermal resistance (R-value) can be achieved in the thinnest possible piece of material.
- Stable R-value--The R-value would remain constant and not drift or lose thermal resistance with age.
- Attachment Capability--Its surfaces would accommodate secure attachment. Also, its resistance to moisture absorption would not impair its physical properties and attachment capabilities.
- Dimensional Stability--It would be dimensionally stable under varying temperature and moisture conditions.
- Compressive Strength--It would have sufficient strength to resist damage from roof system construction operations and normal rooftop traffic.
The 10 properties listed would be found in an ideal roof insulation. In reality, no single commercially available rigid board insulation product currently available has all these ideal properties. Therefore, designers need to choose rigid board insulation materials that have properties best suited to specific project conditions.
The following are the generic types of rigid roof insulation and are currently among those most commonly used or found in low-slope membrane roof systems in North America:
- Cellular glass
- Expanded polystyrene (EPS)
- Extruded polystyrene (XPS)
- Faced gypsum
- Fiber-reinforced gypsum
- Mineral fiber
- High-density polyisocyanurate
- Wood fiberboard
The following criteria should be considered by designers of roof assemblies containing rigid roof insulation:
- On steel roof decks, the steel deck flutes' direction, rigid insulation board, orientation and membrane layout should be designed to accommodate the satisfactory anchorage of roof system components and facilitate application of the membrane and installation of temporary tie-ins and water cutoff details.
- On steel roof decks, rigid insulation boards, if rectangular, should be placed with their longer dimension edges supported on the top flanges of the steel roof deck. The insulation boards placed directly over steel roof deck should not cantilever over the open steel deck flutes.
- In practice, steel decks are often installed incorrectly with minor curves or small incremental errors in overlaps. As successive insulation boards are installed on the deck, at some point the insulation edge may begin to cantilever off at the top flange of the steel deck panels. Unless corrected, some of the insulation panels may be misaligned, with the long dimension of the boards not directly supported by the top flange of the deck panels. When this condition is encountered, additional labor will be required to cut the rigid board insulation or align the board joints with the top flanges of the steel roof deck to correct the installation.
- In low-slope membrane roof system construction, use of two or more layers of rigid board insulation is preferred. The board joints in the second layer of rigid board insulation should be offset from the joints in the first layer to reduce thermal losses and reduce membrane stress.
Guidelines Applicable to All Membrane Types
Slope and Drainage: Membrane roof assemblies should be designed to provide positive drainage. The criterion for judging proper slope for drainage is that there be no ponding water on the roof 48 hours after a rain during conditions conducive to drying. To satisfy this requirement, designers should make provisions in their roof assembly designs for positive slope. Slope generally is provided by:
- Sloping the structural framing or deck
- Designing a tapered insulation system
- Using an insulating fill that can be sloped to drain
- Proper location of roof drains, scuppers and
- A combination of the above
Single-ply roof membranes are a category of roof membranes that are field-applied using just one layer of membrane material, either homogeneous or composite, rather than multiple layers.
There are two broad types of single-ply membranes based on their chemistry: thermoset single-ply membranes and thermoplastic single-ply membranes.
For thermoset roof membranes, the materials' principal polymers are chemically cross-linked. This chemical cross linking of thermoset membranes means the membrane sheet material is cured or vulcanized.
Thermoset single-ply membranes, such as ethylene propylene diene monomer (EPDM), are cured or vulcanized during manufacture, or they cure on the roof during weathering, such as chlorosulfonated polyethylene (CSPE).
Unlike thermoplastic materials, once fully cured, thermoset polymers can only be bonded to like material with a liquid applied adhesive (glue) or adhesive seam tape because new molecular linkages may not be formed.
There are three common subcategories of thermoset roof membranes.
- Ethylene propylene diene monomer (or terpolymer) (EPDM)
- Chlorosulfonated polyethylene (CSPE)
- Polyisoburylene (PIB)
With thermoplastic single-ply membranes, the materials' chemical and physical characteristics allow them to repeatedly soften when heated and harden when cooled. Typically, there is no chemical cross-linking in the molecular composition of a thermoplastic membrane's com-
pound. Because of the chemical nature of thermoplastic membranes, thermoplastic membrane sheets typically are seamed by heat-welding with hot air.
There are four common subcategories of thermoplastic membranes:
- Ketone ethylene ester (KEE)
- Polyvinyl chloride (PVC)
- Thermoplastic polyolefin (TPO)
- PVC alloys, including copolymer alloy (CPA), ethylene interpolymer (BIP) and nitrile alloy (NBP)
The principal components used in constructing single-ply membranes are:
- Single-ply membrane material
- Membrane flashings
Single-ply membrane roof systems are typically designed and installed in three configuration types: loose-laid ballasted, mechanically attached and adhered. Descriptions of each of these configuration types follows.
Loose-laid, ballasted systems seldom require field-membrane securement other than perimeter and base flashing attachment. As the system's name implies, the weight of the ballast and force of the gravity serve to secure the entire root system. A design professional has the responsibility to determine the capability of a structure to carry the weight of a membrane roof system, including the ballast. As roof slope increases, consideration should be given to the type of ballast used. Ballast should be specified and installed in accordance with manufacturers' recommendations and local building code and wind requirements. The most common application rate for aggregate or stone ballast is 1,000 pounds to 1,200 pounds per 100 square feet for 1½ inch to ¾ inch round, river-washed gravel designated as Size Number 4 in ASTM D448, "Standard Classification for Sizes of Aggregate for Road and Bridge Construction." Ballast, aggregate size, application rates and ballast configurations also may change with the type of aggregate and ballast used. Ballast rates may need to be increased at perimeters and corners per local code requirements.
Fasteners should not be used to attach rigid board insulation or field sheets of a roof membrane to a substrate in a ballasted single-ply roof system.
Perimeter attachment of loose-laid ballasted single-ply membranes is accomplished in a variety of ways. There are proprietary fastener systems that include penetrating and nonpenetrating methods. Each method is unique in its design and installation.
Mechanically attached systems use a variety of fasteners and fastening patterns to secure a membrane to a substrate. Among these methods are metal disks placed within a seam and attached through a membrane to a roof deck; metal or plastic bars placed within a seam and attached through a membrane to a roof deck metal and plastic disks and/or bars placed over a membrane
and covered with membrane stripping; and specialized proprietary securement systems. Mechanically attached systems apply significant dynamic loads to the substrate, which need to be accounted for.
At roof perimeter and corner regions, membrane perimeter sheets (half sheets) that are about half the width of the membrane sheets used in the field are generally used. The use of these half sheets results in the installed membrane at the roof perimeter and corner regions having additional fastener densities to account for the greater wind loads in these areas of the roof.
Fasteners for use with mechanically attached single-ply membrane system vary. Although some manufacturers will allow use of readily available screws and plates, other manufacturers require specialized, reassembled fastening components where specified. Specific deck types, warranty requirements and manufacturer's guidelines should be considered when selecting a proper fastener. The specific membrane manufacturer should be consulted for its perimeter securement recommendations and requirements.
An alternative method of mechanical attachment of single ply roof membranes provides for adhering a single-ply roof membrane to specially-coated fasteners plates using a heat-induction welding tool.
Adhered membrane systems are generally applied using a liquid-applied contact adhesive. Some membranes are made with a factory-laminated fleece backing that allows adhesion with alternative types of adhesives, such as hot asphalt and low-rise polyurethane foam. Self-adhering membrane systems also are available. Membrane sheets should be set in continuous applications of adhesives or as recommended by the membrane manufacturer.
The method of attachment of the insulation or base sheet underlying a membrane provides wind-uplift securement for a roof system. Securement can be affected by roof slope, and the number of fasteners to be installed may vary based on the requirements of a membrane manufacturer or the building code of jurisdiction.
Perimeter mechanical attachment of single-ply membranes is accomplished in a variety of ways. There are proprietary fastener systems that include penetrating and nonpenetrating methods. Each method is unique in its design and installation.
Membrane Thickness Sizes
PVC membranes are produced in a range of thicknesses, including 36 mils, 45 mils, 60 mils, 72 mils and 90 mils.
TPO membranes are produced in a range of thicknesses, including 45 mils, 60 mils, and 80 mils.
Reference: National Roofing Contractors Association, The NRCA Roofing Manual: Membrane Roof Systems, National Roofing Contractors Association 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018, 2011