Pre-fabricated Wall Systems Feasibility Study
This feasibility study examines what prefabricated cladding technologies might offer for deep energy retrofit projects. Our team chose a 30 year old residential apartment building in downtown Toronto as our case study. The building suffers from deteriorating windows and poor envelope thermal performance. The proposed pre-fabricated wall systems will improve the existing building performance, reduce the operation and maintenance costs, and eliminate conditions contributing to mold growth. Our proposal focuses on analyzing and assessing the specific benefits or constraints of current market offerings with respect to panelization, off-site fabrication, modular construction, and related systems. The goal of this study is to evaluate the costs, the logistics implications, and benefits and risks for pre-fab wall systems.
#HighPerformanceEnvelope #DowntownHighrise
Project Team
Principal-in-Charge: Kevin Stelzer; Project Architect: Kevin Pu; Project Manager: Jing Li
Location
Downtown Toronto
Study Completion
June 2022
The existing east and west EIFS cladding appeared to be aging with widespread surface staining. The EIFS system lacks continuous and durable air barrier. A complete wall replacement is recommended with a drained cladding system as a solution to the EIFS cladding deficiencies, air barrier deficiencies, and water penetration.
Existing Building
scope of work
Pre-fabricated Wall Systems: 4 Systems
Supplier 1 offers high-performance, customized rainscreen wall system that consists of triple-pane glazing and insulated pre-cast sandwich panels, that help to minimize thermal energy demand and maximize heating. cooling and natural light.
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Wall Assembly
• Rainscreen wall system includes:
• A.C.M. panel
• Trim attached to back section profile
• AVB
• Armorwall (insulated panel)
• Back section profile
• Steel stud framing
Effective R-Value 30
Air Tightness 0.035L/sm2 @300Pa
Fire Rating Passed
Pre-construction Preparation Time ~39 weeks
Installation Time 4-5 months/tower
Cost Estimates $$
Benefits
• No need for furring, system comes with metal studs
• Has discrete anchoring system that requires less structural steel framing materials
Risks
• Heavier duty crane is likely required due to the weight of the panel
Supplier 2 offers lightweight prefabricated EIFS wall system featuring their waterproof air barrier, continuous insulation and their patented drainage wedge design. It has limitless architectural and finish options. However, the system comes without windows.
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Wall Assembly
EIFS wall system includes:
• Finish
• Mesh with base coat
• 6.5” GPS insulation
• Air moisture barrier
• Sheathing
• Steel stud framing
Effective R-Value <30
Air Tightness 0.0014L/sm2 @75Pa
Fire Rating Passed
Pre-construction Preparation Time ~14 weeks
Installation Time 4-5 months/tower
Cost Estimates $$
Benefits
• No need for furring, system comes with metal studs
• Large panel size means fewer joints and gaskets
• Super light weight
• Least amount of panels
Risks
• Challenging to transfer panel from one spider crane to another on the roof due to size of the panel
• Windows are not included
Supplier 3 consists of four preassembled sections containing insulated panels, aluminum anchors, clips, angles, and shims, intumescent tape, and exterior panels. Together the system offers a uniquely designed pressure equalized rainscreen with triple-pane windows.
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Wall Assembly
Rainscreen wall system includes:
• A.C.M. panel
• Kingspan insulated foam panel
• Speedwall support framing
Effective R-Value 31
Air Tightness <0.02 L/sm2 @600Pa
Fire Rating Passed
Pre-construction Preparation Time ~35 weeks
Installation Time 4-5 months/tower
Cost Estimates $$$$
Benefits
• Superior thermal performance
• Has discrete anchoring system that requires less structural steel framing materials
• Relatively light weight
Risks
• Require furring to complete interior wall, means more cost and labor
• C shape panels might be challenging for transportation
Supplier 4 offers fully integrated high-performance window systems, non-combustible continuous insulation, and patented Thermal Plenum™ Technology provide unparalleled ‘bridge free’ thermal performance. The 100% non- combustible assembly is pre-manufactured as a fully unitized wall assembly ready for installation on new builds or deep energy retrofits.
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Wall Assembly
Rainscreen wall system includes:
• A.C.M. panel
• 6 7/8” Thermal plenum
• 7” Mineral wool insulation
• Galvanized sheet steel AVB sheathing
• 6” CFS subframe
• Closed cell cavity insulation
Effective R-Value 30
Air Tightness <0.5 L/sm2 @300Pa
Fire Rating Passed
Pre-construction Preparation Time ~10 weeks
Installation Time 4-5 months/tower
Cost Estimates $$$
Benefits
• High performance air leakage control and moisture management with patented Thermal Plenum
• Thermally broken Unibody designed to carry heavier loads of glass or ceramic claddings, triple glazed windows, etc.
• No need for furring, system comes with metal studs
Risks
• Heavy wall assembly due to sheet steel sheathing layer and robust framing system , means heavier duty crane is required for installation
• Highest panel counts, means more joints and gaskets
Construction Schedule Comparison
Conventional Construction vs Prefabricated Panels
Conventional Construction Schedule
Pre-fabricated Wall Systems Construction Schedule
Risks and Benefits
Compared to conventional stick-built method, prefab panel system offers ‘lean’ off-site manufacturing process, higher deliver efficiencies, and superior timeline predictability. Panels are manufactured in the factory; therefore they have better quality control. The sizes of the panels are highly customizable to work with the design. Prefab panel systems are also demountable upon end of life-cycle.
Preconstruction Preparation Time
The preconstruction period can vary to some degree depending on several factors including contract type and specific needs of a project. In theory, a conventional approach can have a relatively short pre-construction period but may incur increased risks/impacts from schedule delays due to unforeseen site conditions (not to mention costs). On the other hand, pre-construction period for prefab approach is estimated to be longer than conventional approach but can overlap a considerable amount with construction time. Therefore, the preconstruction time preceding construction time for pre-fab approach is 18 weeks compared to 8 weeks for conventional approach.
Construction Timeframe
In terms of overall construction timeframe, the pre-fab approach indicates an approximately 2 months schedule advantage when compared to conventional stick-built approach (11 months vs. 13 months).
There are many challenges with prefab panels system in terms of maneuvering large panels and installing them on the courtyard elevation. We believe the best approach would be lifting panels from the street to the roof, transferred to the set of courtyard cranes, and lowered into position for installation. This approach minimizes the need for road closures associated with mobile cranes (still required to initially lift the Spyder cranes) and minimizes hoisting above adjacent properties.
Installation
In addition to the cost for materials and installation, the cost for access equipment is also an important factor. The cost to rent the cranes will be dependent on the panel weights and actual activity durations; however, the anticipated cost is in the order of $500,000 per tower for prefab approach, compared to the cost of $1,000,000 per tower for mast climber for stick-built approach.
Access Equipment Cost