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  1. Design and Construction /
  2. Vol. 4 Renovations /
  3. 2.0 Project Types and Typical Scope Elements /
  4. 2.2 Exterior

2.2.3 Chimney Stacks

Planning Rationale

Existing chimney stacks were originally constructed to direct heating plant combustion gasses (from coal) away from the school and the neighborhood. The venting of the heated combustion gas provides a “stack effect” and draws air into the combustion device which is necessary for its operation. Although coal is no longer used to heat the schools, many older buildings in the CPS inventory still have stacks which provide ventilation for the heating plant that they have. A limited number of stacks are leased by CPS to cellular telephone providers for the mourning of service antennas. Chimney stacks are sometimes included in envelope projects if in disrepair. Other times, the chimney stacks are subject to a project targeted at the stack.

Chimney stacks no longer need to be the height that they were when they serviced coal fired heating plants. Tall stacks are difficult to maintain and are an unnecessary maintenance issue. Normal practice is to reduce the stacks to the lowest practical height consistent with the underlying architecture of the building, which is usually the height of the parapet or just above the adjacent roof level. Stacks with cell phone antenna leases are ordinarily maintained by the cell phone providers.

For all new and renovated Exterior Masonry Construction, refer to the New Construction Guidelines: Volume 3, Chapter 2.1 Construction.

Typical Considerations for Chimney Stack Renovation shall include, but are not be limited to the following:

Masonry

Evaluate mortar and brick conditions to determine need for tuckpointing and repair of cracking, movement, bulging, vandalism, exterior wall leakage, efflorescence. Also consider the existence and condition of tension bands, and coping. Quantify extent of repairs and need for masonry cleaning.

Height

Normally stacks will be reduced in height to the level of the parapet or just above the roof level. Determine if the stack is providing ventilation for any operational equipment. If the stack is providing ventilation for a heating plant, a stack effect analysis will be needed to determine the mechanical viability of reducing the stack height Verify the existing height and compare to original drawings to identify if the stack has been previously reduced to ensure drawings and pricing will be accurate. When stacks are to be reduced in height, the new height shall be coordinated between the AOR and the Structural and Mechanical Engineers. New caps are provided at the top of the stack at the new height in an architecturally compatible manner.

Mechanical Coordination

Coordination with mechanical requirements are mandatory when renovating existing chimney stacks.

  • When chimneys are lowered or flues are altered, the associated boilers and water heaters shall be calibrated as part of the scope.
  • In some cases, mechanical equipment is abandoned. Typically, due to budget constraints, abandoned oversized equipment shall remain in place. This scope shall be verified and documented.
  • Access the boiler room to evaluate the existing breeching connection to stack and develop scope as required.
  • Boiler flues shall be re-routed directly through the roof or exterior walls.

Structural Coordination

Chimney stack renovations often require new openings in the existing roof structure to facilitate the mechanical upgrades and for the reduction or removal of the stack. The AOR shall engage a structural engineer to review the existing building conditions and determine the structural scope required to support the mechanical renovation.

Environmental

The Managing Environmental Consultant (MEC) shall perform inspection, testing and design services for the chimney scope of work prior to, during the work and upon its completion.

  • Asbestos Containing Materials (ACM): Many existing chimney stack systems have (ACM) located in the boiler, the incinerator flue gaskets, the exterior roofing materials, stack insulation and other suspect ACM that may be impacted by the required scope of work.
  • Lead Based Paint (LBP): LBP may be present on all interior painted surfaces, exterior chimney clean-out doors, exterior ash dump chute doors, or other components impacted by the scope of work.
  • Miscellaneous Environmental Items: MEC shall assess and design the handling of any soot, ash, contaminated materials, or loose interior debris, including animal excrement and carcasses, from the existing boilers or incinerators (to be abandoned) in the Ash House

Access Doors

Review existing conditions and operability of the chimney access door. Determine if replacement or repairs are required. Existing clean-out doors are replaced if the chimney stack remains in use. The clean-out door shall be removed and infilled with masonry or metal panel if the chimney stack is lowered and no longer utilized.

Interior & Liners

Identify the conditions, materials, and depth of debris via video documentation. Documenting the existing condition is especially important for chimney stacks whose tall heights shall remain. Determine if a sleeve or gunnite (sprayed cement liner) needs to be installed, replaced, or repaired. Coordination with the environmental consultant is required to determine the extent of removal of debris from the base of the stack. Existing chimney stacks are not usually lined, however, when stacks are to be reused, liners are required to be installed. The nature and extent of the liner must be shown on the demolition drawings.

Chimney Cap

All new chimney caps shall be provided with stainless steel through-wall flashing and stainlesssteel anchors to the existing stack structure shall remain.

  • Stacks that are taken out of service shall be provided with a new reinforced cast-in-place concrete cap to fully enclose the stack.
  • Reduced heights stacks to remain in service shall be provided with a new  reinforced cast-in-place concrete ring cap.

Joints

Identify condition of sealant and mortar and identify if replacement is required.

Step Irons

Corroded step-irons can create significant issues in the adjacent masonry at the stack.

  • Step-irons are not typically utilized at CPS schools and shall be removed from existing chimney stacks to ensure adequate performance of the repaired chimney stacks.
  • Removal scope at existing step-irons shall be coordinated with the telecom operator to ensure access to equipment at the stack is maintained.

Lightning Protection System

Existing tall masonry chimney stacks at CPS buildings typically have existing lightning protection installed. Lightning protection is typically removed during masonry chimney stack projects. If the chimney stack height is not altered, the existing lightning protection shall be repaired in kind. Identify the condition of lead wires, ground wires and the need to re-anchor or reduce in length.

Telecom Equipment

Many CPS stacks include existing telecom equipment. Long lead times are associated with telecom equipment, so the telecom operator shall be contacted as early as possible in the design phase to avoid potential delays to the project schedule.

  • Stacks with telecom equipment cannot be reduced below the height required for the operation of the equipment.
  • If the stack extends above the equipment, partial reduction of the stack shall be considered by the AOR. Existing mechanical systems shall be coordinated with the Mechanical EOR.
  • Chimney stacks that are deficient at the location of telecom equipment shall receive the appropriate repair scope to ensure the structural integrity of the stack.

Adjacent Roofs

If portions of the stack are required to be rebuilt and may impact an adjacent roof, identify the existing roofing system and extent of roof replacement with the assistance of a roofing consultant.