I N S TA L L AT I O N I N F O R M AT I O N United States COMMERCIAL Protected Membrane Roof Installation Guidelines P M R F I R S T . . . T O L A S T.
O V E R V I E W ...................................................................2 G L O S S A R Y ...................................................................4 C O M P O N E N T S .............................................................6 STYROFOAM™ Extruded Polystyrene Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Fabric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OVERVIEW Overview 2 CHANGING THE SEQUENCE Protected membrane roofing’s breakthrough contribution to flat roof technology was the incorporation of an “upsidedown” approach to insulating the roof: placing the insulation on top of the waterproof membrane to improve the membrane’s effectiveness and the insulation’s efficiency.
CHANGING THE SEQUENCE Advantages of PMR All flat roof assemblies consist of the same basic elements assembled in a seemingly logical order: a deck (composed of wood, metal or concrete), covered with insulation and topped with a waterproofing membrane. A protected membrane roof can employ the same elements, but the membrane is positioned under the insulation, offering superior long-term performance and durability.
GLOSSARY Glossary Absorption: the ability of a material to absorb quantities of gases or liquids, such as moisture. Accelerated Weathering: an experimental test where a material is exposed in a controlled environment to various elements (heat, water, condensation or light) to magnify the effects of weathering. The material’s physical properties are measured before and after the process to identify any detrimental effects of weathering.
Fabric: a woven cloth or material of organic or inorganic filaments, threads or yarns. Can be used as a reinforcement in certain membranes and flashings or used in a protected membrane roof application to reduce the ballast requirements. Loose-laid Membrane: membrane that is not attached to the substrate except at the perimeter of the roof and at penetrations. Typically, a loose-laid membrane is held in place with ballast.
COMPONENTS – STYROFOAM Extruded Polystyrene Insulation Components STYROFOAM ™ EXTRUDED Description STYROFOAM extruded polystyrene insulation is a rigid, closed-cell insulation, ideally suited and designed for PMR installations. Because of the properties imparted during the extrusion process combined with the hydrophobic nature of polystyrene, STYROFOAM insulation has a high resistance to both water and water vapor, providing demonstrated longterm mechanical and thermal performance.
STYROFOAM ™ EXTRUDED Function Provide thermal properties: STYROFOAM™ extruded polystyrene insulation has a high aged thermal resistance (R-value) when compared with competitive roof insulations. Provide membrane protection: By installing the insulation over the membrane, the membrane is kept at a relatively constant temperature year-round and protected from weathering, mechanical damage and abuse.
COMPONENTS – Fabric Components FABRIC Description Ballast reduction fabric, commonly known as filter fabric, is used in PMR installations between the ballast and insulation. This water-permeable material must have proven longterm weather resistance, be strong enough to withstand traffic abuse and prevent displacement of the insulation under flotation conditions. Specification Apply fabric unbonded and shingle fashion over the installed insulation (Figure 3).
Components Extend the fabric up the roof perimeter cants and roof protrusions by at least 3" above the top level of the ballast (typically about a 6" upturn) and place it loose under the metal counterflashings (Figure 5). Fabrics, such as Fabrene V.I.E.,† should meet or exceed the guidelines listed in Table 1.
COMPONENTS – Ballast Components BALLAST Description Crushed stone or washed, rounded riverbed rock, ASTM D448 Gradation #2, 4, 5 or 57 depending on membrane type, building height, wind zone and parapet height (Table 2). Depending on the ballast design, the range of ballast is 10 to 15 lb/ft2 with additional ballast around perimeters and penetrations (15 to 20 lb/ft2). In some cases, pavers can be used. See “Pavers” on page 12 for additional details.
BALLAST Design Approach Refer to TechNote 508 for the recommended amount and placement of ballast. The ballast design depends on: • Type of membrane (adhered, loose-laid or mechanically attached) • Building height • Design wind speed • Site exposure • Parapet height • Gravel stop height Specification ASTM D448 Gradation #2, 4, 5 or 57 washed free of fines or stones. Spread stone ballast uniformly over installed insulation to provide minimum weight or thickness.
COMPONENTS – Pavers Components PAVERS Description Concrete slab pavers or interlocking pavers can be used to supplement or replace conventional stone ballast requirements and create a surface for rooftop decks, walkways, terraces, gardens and similar applications. Note: For structural plaza deck design, such as for parking decks and other high-traffic areas, the design is the responsibility of an architect and/or structural engineer. Function Note: For additional information, see “Ballast” on page 10.
ALL OTHER COMPONENTS Description MEMBRANES The membrane is the flexible or semi-flexible waterproofing layer on the roof deck. In a PMR application, the membrane is sandwiched between the roof deck and the insulation. Membranes fall into three general categories: built-up roof (BUR), two-ply modified bitumen, single-ply (sheet) or liquid membranes. Note: PMR assemblies should be installed with adhered membranes only.
COMPONENTS – All Other Components Components 14 ALL OTHER COMPONENTS Function The roof deck should: • Provide structural support to accommodate both live and dead loads without significant deflection. • Provide dimensional stability by forming a stable substrate not affected adversely by cyclical thermal- and moisture-induced movement. • Provide fire resistance as determined by the building type and intended use. • Provide a substrate for the roof system. • Accommodate building movement.
SPECIAL CONDITIONS Cold Rain Phenomenon THE ISSUE “Cold rain phenomenon” (or “cold water wash”) occurs during periods of cold rain and/or melting snow or when the ambient condition is 33°F to 50°F. In these conditions, the deck temperature may be temporarily reduced. The issue is that there may be additional heat loss, and in buildings with high humidity, such as pulp and paper mills, the likelihood of condensation increases.
C O N D I T I O N S , I S S U E S A N D R AT I N G S – S p e c i a l C o n d i t i o n s a n d I s s u e s Conditions, Issues and Ratings 16 SPECIAL CONDITIONS Moisture Absorption AND ISSUES STYROFOAM™ extruded polystyrene insulation will absorb water and the insulation value will be reduced. Always ensure that the roof deck has proper drainage; if the PMR system has significant ponding (e.g., standing water), the insulation will not be “diffusion open.
SPECIAL CONDITIONS Green Roof Design THE ISSUE Can PMR assemblies be used for “green roof” designs? DISCUSSION In a “green roof” design, the ballast in a PMR assembly is essentially replaced with green material – usually soil and plantings – plus a drainage layer directly on top of the insulation (Figure 6). Replacing conventional ballast with vegetation can limit storm water runoff and, by filtering the runoff through the plants, also improve the quality of the runoff.
C O N D I T I O N S , I S S U E S A N D R AT I N G S – S p e c i a l C o n d i t i o n s a n d I s s u e s Conditions, Issues and Ratings 18 SPECIAL CONDITIONS Finding Leaks in a PMR THE ISSUE Is it more difficult to locate a leak with a PMR or conventional roof assembly? DISCUSSION Building upon years of in-field experience, the majority of roof leaks in PMR systems occur at flashing as opposed to the interior field area.
SPECIAL CONDITIONS Membrane Seam Failure AND ISSUES Plant Growth on PMR Assemblies THE ISSUE THE ISSUE Failures at the seams in thermoset membranes may be worse with PMR because the membrane stays damp. Periodically, plant growth will occur on PMR and other low-sloped roofs. Can this be avoided? DISCUSSION DISCUSSION Thermoset membranes (such as EPDM and neoprene) were historically seamed with a contact adhesive.
C O N D I T I O N S , I S S U E S A N D R AT I N G S – F i r e a n d Wi n d R a t i n g s Conditions, Issues and Ratings FIRE AND WIND RATINGS Overview Fire and wind ratings are required to meet building code requirements. Typically, a PMR assembly, including roof deck, membrane, insulation and ballast, is tested in exactly the same configuration as would be constructed in the field. No deviation from the component specification is allowed. Underwriters Laboratories Inc.
FIRE AND WIND RATINGS ULI Hourly Fire Resistance Ratings for PMR – Steel Deck Assembly # Rating (hrs) Description P-225, P-226, P-235 (New PMR) 1, 1-1/2 Steel deck 1/2" or 5/8" Type X gypsum (varies) Bar joists Suspended ceiling P-404 (New PMR) 1-1/2 Steel deck 1" mineral or fiberboard Bar joists Plaster ceiling P-801, P-805 (Retrofit PMR) 1, 1-1/2, 2 Steel deck Mineral or fiberboards Spray fiber fireproofing Beam construction P-803 (Retrofit PMR) 1, 1-1/2 Steel deck Mineral or fiberboards
C O N D I T I O N S , I S S U E S A N D R AT I N G S – F i r e a n d Wi n d R a t i n g s Conditions, Issues and Ratings 22 FIRE AND WIND RATINGS ULI Hourly Fire Resistance Ratings for PMR – Concrete Deck Assembly # Rating (hrs) Description P-904, P-909, P-912, P-915 (Retrofit PMR) 2 Precast concrete units Mineral fiberboard P-904, P-909, P-912, P-915 (New PMR) 2 Precast concrete units 1" gypsum board ULI Hourly Fire Resistance Ratings for PMR – Other Assembly # Rating (hrs) Description P
FIRE AND WIND RATINGS ULC Hourly Fire Resistance Ratings for PMR – Metal Deck Assembly # Rating (hrs) Description R-202, R-217 (New PMR) 1 Steel deck 1/2" gypsum Beams or bar joists Suspended ceiling R-702, R-703 (New PMR) 1, 1-1/2 Steel deck 5/8" gypsum Spray cementitious mixture Beams or bar joists R-804 (New PMR) 3/4, 1, 1-1/2, 2, 3 Steel deck 5/8" Type X gypsum Spray fiber fireproofing Beam construction R-805, R-806 (New PMR) 1 Steel deck 1/2" or 5/8" Type X gypsum (varies) Spray fiber
C O N D I T I O N S , I S S U E S A N D R AT I N G S – F i r e a n d Wi n d R a t i n g s Conditions, Issues and Ratings FIRE AND WIND RATINGS ULC Hourly Fire Resistance Ratings for PMR – Concrete Deck Assembly # Rating (hrs) Description P-229, P-505, P-507 (New PMR) 1, 1-1/2 2' poured gypsum deck Bar joists Suspended ceiling FM Hourly Fire Resistance Ratings for PMR Assembly # Rating (hrs) Description RC-227 (New PMR) 1 Steel deck 1/2" Type X gypsum Gypsum board ceiling RC-264 (New PMR) 1
IN THE U.S.: • For Technical Information: 1-866-583-BLUE (2583) • For Sales Information: 1-800-232-2436 THE DOW CHEMICAL COMPANY • Building Solutions • 200 Larkin • Midland, MI 48674 • www.dowstyrofoam.com/architect NOTICE: No freedom from infringement of any patent owned by Dow or others is to be inferred.
