2.1.5 Roofs and Parapets | Chicago Public Schools

Planning Rationale

Roofing System

The Standard roof type for new construction is a hybrid cold applied SBS modified bitumen roofing system. A hybrid system allows for the use of asphalt coated base sheets or interply sheets in combination with an SBS modified bitumen cap sheet.

A cold applied SBS modified bitumen system is optimal for occupied buildings where:

Safety and/or odors are a concern
On smaller roofs
On roofs where access logistics are difficult
When there is the possibility of roofing system installation scheduling delays due to multiple adjacent construction activities associated with various other trades
When ambient temperatures are not conducive to the installation of hot applied asphalt roofing systems

Cold applied systems are less disruptive than hot applied modified bitumen roofing systems, as there is no hot roofing kettle on site.

Hot applied systems are also acceptable when feasible (with CPS approval), because hot applied roofing systems are slightly more cost effective than cold applied roofing systems. Hot asphalt is utilized for adhering the insulation and roof membrane materials. A hot applied system is best used when school is not in session.
There are provisions in both the CPS standard cold applied and hot applied SBS modified bitumen specification sections for a fluid applied liquid flashing. This liquid flashing is intended for limited and localized use at very special conditions with prior CPS consideration and approval. It is not intended for widespread application on new construction projects.
Torch-down or self-adhering sheet roofing products are not allowed on CPS modified bitumen roofing projects.
A field applied reflective roof coating is required over the granulated field cap sheet and granulated flashing cap sheet, following a 30 day roofing system curing period. The reflective coating is required to meet the City of Chicago Code requirements and LEED for Schools Cool Roof credit requirements. Factory coated cap sheets are not acceptable.
Stainless steel Fasteners are required at all roof applications where fasteners are secured to treated wood or cementitious/masonry substrates.
No changes to the CPS standard SBS modified bitumen specification sections (other than the required wind design pressures and wind uplift pressures) are permitted without prior CPS approval.

Cold Applied SBS Modified Bitumen Membrane System:

Where determined by CPS to be applicable, the typical cold applied SBS modified bitumen membrane system for the roofing field areas is to be typically configured as follows:

Field-applied reflective coating over;
One layer of granulated modified bitumen cap sheet in cold adhesive, over;
Two layers of reinforced base ply sheets in cold adhesive, over;
Cover board in low rise foam adhesive, over;
Flat stock and/or tapered polyisocyanurate insulation (as specified), in low rise foam adhesive, over;
The underlying deck assemblies with associated preparations (including vapor barriers/temporary roofs).

The typical cold applied SBS modified bitumen membrane system for the base flashing areas is to be typically configured as follows:

Field-applied reflective coating over;
One layer of granulated modified bitumen flashing cap sheet in cold adhesive, over;
One layer of reinforced base ply sheet (backer sheet) in cold adhesive.

Hot Applied Modified Bitumen Membrane System:

Where determined by CPS to be applicable, the typical hot applied SBS modified bitumen membrane system for the roofing field areas is to be configured as follows:

Field-applied reflective coating over;
One layer of granulated modified bitumen cap sheet in hot asphalt or in cold adhesive, in lieu of hot asphalt, (at roofing manufacturer’s option and per roofing manufacturer’s recommendation - for field cap sheet only), over;
One layer of reinforced base ply sheet in hot asphalt adhesive, over;
One layer of type VI glass-fiber ply sheet in hot asphalt, over;
Gypsum fiber or coated wood fiber cover board in hot asphalt adhesive, over;
Flat stock and/or tapered polyisocyanurate insulation (as specified) in hot asphalt adhesive, over;
The underlying deck assemblies with associated preparations (including vapor barriers/temporary roofs).

The typical hot applied SBS modified bitumen membrane system for the base flashing areas is to be configured as follows:

Field-applied reflective coating, over;
One layer of granulated modified bitumen cap sheet in hot asphalt or in cold adhesive, in lieu of hot asphalt, (at roofing manufacturer’s option and per roofing manufacturer’s recommendation - for flashing cap sheet only), over;
One layer VI glass-fiber ply sheet (backer sheet) in hot asphalt.

The AOR is to identify the new roof system construction (listing all components from the new deck type(s) up to the exposed roofing membrane on the drawings to clarify which specified scope(s) of work are required by the contractor.
The drawings to identify the new roof system construction (listing all components from the new deck type(s) up to the exposed roofing membrane on the drawings to clarify which specified scope(s) of work are required by the contractor.
Clearly identify drain locations, equipment locations, slope and thickness of insulation, tapered insulation layout, walkway pad locations, and all types(s) of deck (e.g. metal, concrete, etc.).
Where tapered insulation is required, provide a four-way sloped, tapered insulation system.
Use R-30 as the minimum insulation value.
With full understanding of the recognized roofing industry standard for an 8 inch minimum mounting height for parapet and roof top accessory flashings, the CPS standard recognizes and goes beyond this industry standard and requires a minimum flashing dimension of 1’-2” for maintenance and performance enhancements to the roofing system.
Per Chicago Energy Transformation Code: At least 40 percent of the available roof area must be designated as a solar-ready zone and designed with structural capacity to accommodate an additional weight (dead load) of at least 5 pounds per square foot. The construction documents must show a reasonable path for future installation of conduit from the solar-ready roof zone to the main electrical service panel.

The ANSI/SPRI/FM 4435/ES-1 wind design standard is specified for the manufacturing and installation of pre-engineered, factory fabricated, pre-finished aluminum copings and roof-edge flashings tested according to ANSI/SPRI/FM 4435/ES-1 and capable of resisting the calculated design pressures.
No field fabricated metal or exposed fasteners will be accepted.
Shop welding is required at corner and end/termination pieces.
Fully integrated with the roofing and exterior wall construction providing a continuous air and water barrier. Install metal saddle flashing at coping terminations from low parapets to higher wall interfaces.

Locations: Consider roof slope, roof area, crickets, and roof-top equipment when locating drains. Provide perimeter roof drains where practical, a minimum of 6’-0” from parapet walls. Do not locate roof drains under or near rooftop mechanical units.
Drains & Scuppers: AOR to provide all dimensional information on roof plans and details (Slopes, High Points, Low Points, etc.) The drains and scuppers (including canopies) shall be located to drain over water permeable surfaces.
4-way Roof Drainage Systems: Required per the standard modified bitumen specification sections to avoid ponding of water. Actual and realistic roof slopes need to be shown. Deflection of roof shall be considered in lay out of roof plan.
- Secondary (Emergency Overflow) Roof Drains: Required for new construction projects. They are to be provided for each primary roof drain as a Combination Roof Drain unit, manufactured as a single assembly, including a primary drain with an adjacent secondary (emergency overflow) drain.
- Piping for secondary drains is to be insulated and remain separate from primary drains for the horizontal run.
- Only one Secondary Drain per roof area shall be separately routed both horizontally and vertically, terminating to daylight via a lamb’s tongue spout near the ground (elevation depending on conditions).
- The Lamb’s Tongue (with manufacturer’s bird screen option) shall be located to facilitate visual monitoring of overflow events, and is to drain on an appropriate permeable surface such as stone, gravel or grass. The secondary roof drainage system is to be sized as required for the primary storm drainage system as required by the Chicago Building Code and is to comply with all other applicable codes and CPS specifications and standards. “Lambs tongue” is not a substitute for overflow drains, it is simply a device used for monitoring that the existing roof drains are not clogged.
  
  NOTE: Lambs Tongue Downspout shall be graphically shown and dimensionally located on roof plans and exterior elevations.
  
  The scuppers shall have a vertical clear opening of 4-inches (minimum) in height. The scuppers shall not be located above underlying doors, sidewalks, window assemblies or area wells. The scuppers shall be located over water permeable surfaces. The scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed (per CBC).

Water Cooled Chillers: Towers shall be located on roof platforms with acoustical/vision screening. Refer to the mechanical section of design guidelines for information and requirements of equipment.
Air Cooled Chillers: Provide air-cooled chillers on grade with sound / visual screening. Consideration for individual project air cooled chillers to be located above grade requires CPS approval based on life cycle analysis including energy, material and maintenance costs for all trades. Refer to the mechanical section of design guidelines for information and requirements of equipment. Ensure at grade equipment conforms to zoning setback requirements.
Screening: Required for visual screening and to minimize noise pollution to the surrounding neighbors as well as the school.
Roof Curbs: Position of roof curbs should consider roof drainage and not obstruct drainage flow.

Rooftop Maintenance: Shall be a key consideration for the roof layout. Access for personnel and materials shall be along a safe and well lit path.
- Access to Roof Structures: Every roof area and level shall have a permanent method to access it from the interior, not from an adjacent higher or lower roof and shall be secured from unauthorized access.
- Roof Hatches: shall not to be located within 10 feet of any roof edge. All roof hatch assemblies shall be insulated and raised per CPS standard mounting height.
- Ship’s Ladder: Where space allows, a Ship’s Ladder is optimal, otherwise a Ladder is required. Provide with an access hatch sized to a suitable dimension per manufacturer’s requirements to meet applicable codes and standards.
- Ladders: Ladders shall be affixed to structure and not exceed 24’-0” in height without a fall restraint system. Cages are not permitted at top of ladder. Ladders shall be architecturally and structurally designed by AOR to accommodate and coordinate adjacent structure.

Height: Parapets shall be a minimum height of 1’-2” at the high point above the finished surface of roof, with consideration given to the effect of increased height on the exterior wall system.
Flashing: Shall conform to requirements of roofing system.
Movement Joint: The exterior wall assembly moves vertically, therefore detail the parapet wall to provide the expansion joint at the parapet wall or to the underside of the roof structure. Alternative parapet wall construction will be considered where no interior component of the wall type assembly occurs.