Case Study Overview
How Rimkus Delivered Design, Specifications, Tendering, and Construction Administration for a Full Backyard Site Upgrade at an Occupied Residential Co-operative in Toronto, Ontario
A Rimkus Building Sciences engagement for Church Isabella Residents Co-operative in Toronto, Ontario delivered end-to-end consulting for a comprehensive site rehabilitation program at the property: design and specifications for a new cast-in-place concrete retaining wall, backyard concrete pads, drainage improvements, below-grade waterproofing, and fencing restoration across eight occupied residential units. Rimkus managed a competitive tender that produced five bids, recommended contract award, administered three change orders, and conducted nine field reviews from mobilization through substantial completion. The project reached substantial performance on November 21, 2025, with a final contract value of $324,325.19 (excl. HST), below the original base bid.
Who this is for: Residential co-operatives, condominium corporations, and property managers planning structural site rehabilitation: retaining walls, backyard improvements, drainage, and below-grade waterproofing on occupied multi-unit properties requiring design, tendering, and independent construction oversight. Also relevant to trustees and boards requiring defensible procurement documentation, and to insurers and legal teams seeking documented field review reports, corrective action records, and a certified Certificate of Substantial Performance.
What We Did
- Designed the new cast-in-place concrete retaining wall, knee walls, and backyard slab layout; prepared full specifications, permit drawings, and bid documents.
- Managed a competitive tender: invited five qualified contractors, held a mandatory pre-bid site meeting, issued one addendum, received five bids, and provided a written award recommendation.
- Conducted nine field reviews from mobilization through substantial completion; administered three change orders; issued two payment certificates; and certified substantial performance on November 21, 2025.
How We Helped
- Identified and directed correction of a reinforcing steel non-conformance before the footing pour, ensuring the deficiency was on record and corrected before concrete was placed.
- Adapted the retaining wall design in-field to encase seven unanticipated H-piles, issuing revised structural drawings and a change order without disrupting the construction schedule.
- Directed correction of a concrete slab placement non-conformance (100% coverage instead of specified 75%/25% ratio) and a post-completion coating adhesion deficiency, both before final acceptance.
|
SERVICE LINES |
SECTOR |
LOCATION |
ENGAGEMENT LEAD |
|---|---|---|---|
|
Building Sciences |
Residential Co-operative |
Toronto, Ontario |
Marc Winters, P.Eng. — Rimkus BES, Canada |
|
9 |
5 |
3 |
$324K |
|---|---|---|---|
|
FIELD REVIEWS |
BIDS RECEIVED |
CHANGE ORDERS |
FINAL CONTRACT |
What Was the Challenge? Structural Site Rehabilitation on an Occupied Co-operative Property
For a residential co-operative managing an aging site, structural deterioration in the backyard areas creates both safety and functionality challenges that cannot be deferred indefinitely. At Church Isabella Residents Co-operative in Toronto, the existing wood retaining wall and fencing system in the rear yards of all eight units had reached the end of its serviceable life. Drainage deficiencies, deteriorated concrete and brick paving, and inadequate below-grade waterproofing on the existing building foundation wall compounded the problem.
The co-operative required a consultant who could design an appropriate structural solution, prepare enforceable specifications, manage a competitive tender, and then provide rigorous construction oversight on a site with several complicating factors: seven existing steel H-piles adjacent to the proposed retaining wall alignment, a protected bur oak tree requiring arborist coordination, an occupied residential building that had to remain functional throughout construction, and a parking garage foundation immediately behind the excavation zone.
Without independent design and oversight, the co-operative had no mechanism to specify what was needed, obtain competitive pricing, or verify that the structural work met the drawings before it was permanently concealed in concrete.
“On a constrained urban co-operative site, construction oversight is not optional. Seven existing steel piles, a protected bur oak tree, and an adjacent parking garage foundation mean that every pour, every anchor, and every excavation decision has structural consequences if not verified before the concrete is placed.” – Chander Thusu, B.Eng., BSS, Practice Leader, Building Sciences
How Did Rimkus Help? End-to-End Building Sciences Consulting
Rimkus was engaged in December 2024 to deliver complete building sciences consulting across all phases of the rehabilitation program, from preliminary design through substantial performance certification.
Design and Specifications |
Competitive Tendering and Contract Award |
|---|---|
|
Attended the site for measurements and assessment. Prepared design drawings, structural details, and full specifications including concrete retaining wall, backyard slab layout, drainage improvements, waterproofing systems, fencing restoration, and permit drawings for the City of Toronto. Design adapted in-field to address unanticipated H-piles and end-unit foundation conditions exposed during excavation. |
Invited five qualified contractors, conducted a mandatory pre-bid site meeting on July 7, 2025, managed the question period and Addendum No. 1, received five bids by July 18, 2025, and provided a written bid award recommendation. Contract awarded under CCDC 2 stipulated price contract. Pre-construction meeting held July 30, 2025. |
Construction Administration and Field Reviews |
Occupied-Site and Tree Protection Coordination |
|
Conducted nine field reviews from mobilization in August 2025 through substantial completion in October 2025. Reviewed and approved rebar shop drawings, structural drawings, and fencing shop drawings. Coordinated third-party concrete testing and geotechnical subgrade verification. Administered three change orders. Issued two payment certificates. Certified substantial performance November 21, 2025. |
Required plywood hoarding over all unit sliding doors and windows before demolition. Directed contractor to coordinate with ISA Certified Arborist (Bartlett Tree Experts) for all work within the Tree Protection Zone of the protected bur oak at Unit 1. Root pruning report confirmed only dead roots pruned; no live roots damaged. Three-year post-construction monitoring program in place. |
How Our Services Address Common Challenges
Common Challenge |
What Rimkus Provides |
|---|---|
|
Structural non-conformances concealed by concrete placement |
Hold points and field reviews at critical pre-pour milestones verify reinforcing, dimensions, and anchorage before concrete is placed; deficiencies are correctable before they are permanent |
|
Unanticipated site conditions requiring design adaptation |
In-field design revisions and change orders issued promptly, including revised structural drawings and a change order for H-pile encasement at seven locations |
|
Protected tree and adjacency risks on constrained urban sites |
Contractor direction and coordination with ISA Certified Arborist; all work in the Tree Protection Zone conducted under arborist supervision per City of Toronto requirements |
|
Contractor deviations from specified layout or materials |
Documented non-conformances with corrective direction before work is accepted; compliance confirmed through follow-up review and contractor-submitted documentation |
Deliverables: What the Co-operative Received
- Design drawings and full specifications for the retaining wall, backyard slabs, drainage, waterproofing, and fencing restoration
- Building permit application drawings and supporting documentation for the City of Toronto
- Competitive tender management: pre-bid site meeting, question period, Addendum No. 1, receipt of five bids, and written award recommendation
- CCDC 2 contract coordination; pre-construction meeting minutes
- Rebar shop drawing review (September 4, 2025); structural drawing review (September 15, 2025); fencing shop drawing review (October 17, 2025)
- Nine formal field review reports documenting construction progress, deficiency observations, and directed corrective actions
- Third-party concrete testing coordination (three pours: September 26, October 8, and October 16, 2025) with 7-day and 28-day results
- Geotechnical subgrade inspection and approval for reuse of excavated material as engineered backfill
- ISA Certified Arborist root pruning report and three-year post-construction tree monitoring program
- Three change orders: CO1 (+$19,000 H-pile encasement), CO2 (-$574.81 security credit), CO3 (-$23,500 unused contingency and elastomeric coating allowances)
- Two payment certificates: Payment Certificate No. 1 ($110,242.80 incl. HST, October 9, 2025) and Payment Certificate No. 2 ($215,019.42 incl. HST, November 27, 2025)
- Certificate of Substantial Performance under the Ontario Construction Act (substantial performance date: November 21, 2025; certificate signed December 9, 2025)
Technical Scope of Work
The rehabilitation program addressed the following civil and structural site systems across all eight unit backyard areas:
- Concrete Retaining Wall: New cast-in-place reinforced concrete retaining wall and footing along the rear elevation, encasing seven existing steel H-piles. 15M vertical bars at 250 mm o.c., 15M horizontal bars at 250 mm o.c. (two-layer mat). Concrete placed at 32 MPa (exceeding specified 25 MPa minimum). Compressible separation material between new footing and adjacent parking garage foundation wall. Engineered shop drawings required and reviewed.
- Knee Walls and Partition Walls: New cast-in-place concrete knee walls between units with reinforcing designed to match the retaining wall footing. New wood partition fence and metal posts on new concrete knee walls at all locations.
- Wood Retaining Wall at Unit 1: New wood retaining wall at the corner adjacent to Unit 1, with salvaged fence panels and posts reinstalled on the new structure at original spacing. New wood boards installed to bridge the gap between the wood wall and the new concrete retaining wall.
- Below-Grade Waterproofing and Drainage Board: CM-100 below-grade waterproofing membrane applied to the foundation wall of the existing building and exterior face of the new concrete retaining wall. Continuous dimpled drainage board installed from footing to top of wall.
- Epoxy Coating: New epoxy coating applied to the exposed above-grade sections of the existing building foundation wall. Defective areas of coating (poor adhesion, washing off) identified at Field Review 9 and directed for correction prior to final acceptance.
- Backyard Concrete Pads and Drainage: New 150 mm reinforced concrete slabs (35 MPa, C-1 exposure, Xypex crystalline admixture, 10M bars at 300 mm o.c.) covering 75% of each backyard, with positive slope away from the building. Crusher run limestone base over 25% of each backyard. New 100 mm weeping tile with filter cloth and 19 mm clear stone. New Zurn FD2283-PV4 surface drain at each unit connected to the weeping tile.
- Fencing Restoration: Salvaged wood fence panels and aluminum posts reinstalled on new concrete retaining wall using galvanized threaded rods per approved shop drawings, trimmed to minimum 72″ height. New aluminum posts anchored into concrete knee walls. Existing chain-link fencing reinstated at end units.
- Engineered Backfill: Excavated native soil approved by geotechnical engineer for reuse as engineered backfill; placed in controlled lifts behind the new retaining wall. New sod installed between the concrete curb and the retaining wall.
- Foundation Crack Repair: Approximately 10 linear metres of crack repair on existing building foundation wall prior to membrane installation.
- Tree Protection Zone: All excavation within the Tree Protection Zone of the protected bur oak at Unit 1 conducted under supervision of ISA Certified Arborist Michael Brown (Bartlett Tree Experts). Only dead roots pruned; no live roots damaged. Three-year post-construction tree monitoring program.
Specified Materials
|
System |
Specified Product |
Notes |
|---|---|---|
|
Concrete (retaining wall footing) |
25 MPa minimum (specified); 32 MPa placed |
Higher-strength concrete accepted by Rimkus; does not negatively affect structural performance |
|
Concrete (backyard slabs) |
35 MPa C-1 exposure, Xypex crystalline admixture |
Third-party 7-day and 28-day testing conducted on three separate pours |
|
Reinforcing Bars |
Deformed grade 400 (CAN/CSA-G40.21) |
15M bars; vertical and horizontal at 250 mm o.c. in wall; shop drawings reviewed September 4, 2025 |
|
Adhesive Anchor |
Hilti HIT-HY 200 |
All dowel connections into existing concrete; confirmed by contractor photo prior to pour at FR 6 |
|
Bonding Agent |
Sika Armatec 110 EpoCem |
At all new-to-existing concrete interfaces |
|
Surface Drain |
Zurn FD2283-PV4 with adaptors and elbows |
One per unit backyard; connected to new weeping tile system |
|
Below-Grade Waterproofing |
CM-100 membrane |
Applied to existing foundation wall and exterior face of new retaining wall |
|
Drainage Board |
Continuous dimpled drainage board |
Exterior face of new wall, footing to top of wall |
|
Epoxy Coating |
Epoxy coating on above-grade foundation wall |
Adhesion deficiency identified at FR 9; corrective work directed before acceptance |
|
Weeping Tile |
100 mm with filter cloth and 19 mm clear stone |
Min. 1,200 mm x 1,200 mm clear stone surround with filter fabric |
Tendering and Contract Award
Rimkus managed a competitive tender that produced five bids from all five invited contractors. A mandatory pre-bid site meeting was held July 7, 2025. Addendum No. 1 was issued during the bid period. Bids closed July 18, 2025.
|
Contractor |
Base Bid (excl. HST) |
Projected Start |
Duration |
|---|---|---|---|
|
Quality Connect Construction Inc. (awarded) |
$329,400 |
15 days |
60-80 days |
|
Kabo Construction |
$526,250 |
30 days |
80 days |
|
Heritage Restoration Inc. |
$684,500 |
15 days |
5 months |
|
K.I.B. Building Restoration Inc. |
$687,700 |
TBD |
100 days |
|
Restorex Contracting Ltd. |
$949,500 |
10-15 days |
120-130 days |
Contract awarded to Quality Connect Construction Inc. at $329,400.00 (excl. HST), the lowest of five bids and $196,850 below the second-lowest submission. Three change orders were subsequently administered: CO1 added $19,000 for H-pile encasement (unanticipated site condition); CO2 credited $574.81 for co-operative security costs; CO3 credited $23,500 for unused contingency and elastomeric coating allowances. Final contract value: $324,325.19 (excl. HST), below the original base bid. Cost figures are project-specific; actual costs vary based on scope, site conditions, and market conditions at time of tender.
The Process: Construction Administration Across Nine Field Reviews
Rimkus provided full construction administration from contract award through substantial performance, with nine field reviews conducted from August through October 2025.
- FR 1 (August 11, 2025) — Mobilization: Contractor mobilized. Building permit and notice of project confirmed posted. Existing fencing removed at Unit 1 to facilitate access. Seven existing H-piles exposed during excavation; retaining wall design reassessed by Rimkus. End-unit concrete foundation elements directed to remain. Contractor directed to notify arborist regarding excavation near the protected bur oak.
- FR 2 (August 15, 2025) — Excavation and existing conditions: H-piles confirmed to be fully encased in new footing and wall; contractor directed not to cut or alter piles. Existing weeping tile removed. Existing brick wall at Unit 8 removed; existing footing to remain and receive dowelled connection per revised Rimkus drawings.
- FR 3 (September 2, 2025) — Foundation preparation: Below-grade waterproofing coating and drainage board completed. Gravel base placed and compacted to specified requirements. Compaction test results directed for submission.
- FR 4 (September 17, 2025) — Reinforcing steel non-conformance: Rebar layout did not conform to structural drawings; one footing section found to be insufficient width. Concrete placement withheld; contractor directed to reinstate all rebar to full compliance. Root pruning performed by ISA Certified Arborist at this date.
- FR 5 (September 25, 2025) — Reinforcing steel conformance confirmed: Footing widths at all locations confirmed to meet specified dimensions. Extra dowels installed to encase H-piles at locations requiring additional reinforcing. Geotechnical engineer verified subgrade bearing capacity.
- FR 6 (October 4, 2025) — Wall formwork and concrete placement: Footings placed using 32 MPa concrete (exceeding 25 MPa specified minimum). Wall reinforcing installed at 250 mm o.c. vertically and horizontally. Hilti HIT-HY 200 adhesive anchor not observed in use at Unit 8 dowel locations; contractor directed to confirm with photographic documentation before placement. Documentation provided and accepted.
- FR 7 (October 14, 2025) — Retaining wall and knee walls complete: Cast-in-place concrete retaining wall and knee walls fully constructed. Localized honeycombing on one knee wall directed for grinding. Waterproofing membrane and drainage board installed on exterior face of new wall.
- FR 8 (October 17, 2025) — Concrete slabs non-conformance: Backyard concrete pads completed. Surface drains installed and connected to weeping tile. Non-conformance identified: contractor placed concrete across 100% of each backyard instead of specified 75%/25% ratio. Corrective removal directed; perimeter sawcuts completed at time of review.
- FR 9 (October 21, 2025) — Substantial completion review: All items of work substantially complete. Fencing and posts reinstalled on new retaining wall and knee walls per approved shop drawings using specified galvanized threaded rods. Engineered backfill placed using approved excavated native soil. Wood retaining wall at Unit 1 corner completed. Epoxy coating on above-grade foundation wall found to have areas of poor adhesion and premature deterioration; contractor directed to remove defective areas, re-prepare substrate per manufacturer requirements, and reapply coating.
Notes on Methods and Limitations
Field reviews are discrete site observations and do not constitute continuous inspection. The contractor remains solely responsible for on-site health and safety. Observed non-conformances were documented and corrected at critical hold points prior to acceptance or concealment in concrete. Substantial performance was certified November 21, 2025 under Section 32 of the Ontario Construction Act.
“Two structural non-conformances were identified and corrected at the pre-pour hold point: reinforcing steel layout before the footing pour and missing adhesive anchor documentation before the wall pour. Neither would have been visible or correctable after the concrete was placed.” – Chander Thusu, B.Eng., BSS, Practice Leader, Building Sciences
What the Field Reviews Found: Key Observations and Corrective Actions
|
Finding |
Condition Observed |
Rimkus Direction and Outcome |
|---|---|---|
|
Arborist protocol not followed |
Excavation conducted within the Tree Protection Zone of the protected bur oak at Unit 1 without arborist supervision (FR 1) |
Contractor directed to immediately notify the arborist. Root pruning subsequently performed by ISA Certified Arborist Michael Brown on September 17, 2025; only dead roots pruned |
|
Reinforcing steel non-conformance |
Rebar layout did not conform to structural drawings; one footing section insufficient width (FR 4) |
Concrete placement withheld. Contractor directed to reinstate all rebar and excavate to required footing width. Conformance confirmed at FR 5 before pour approved |
|
Adhesive anchor not confirmed |
Hilti HIT-HY 200 adhesive not observed in use at Unit 8 dowel locations into existing footing (FR 6) |
Contractor directed to provide photographic confirmation before concrete placement. Documentation submitted and accepted by Rimkus |
|
Honeycombing on knee wall |
Surface-level honeycombing at one localized area on the newly completed concrete knee wall (FR 7) |
Contractor directed to grind the affected area to remove loose and poorly consolidated concrete |
|
Concrete slab layout non-conformance |
Contractor placed concrete across 100% of each backyard; specified layout is 75% concrete / 25% gravel (FR 8) |
Contractor directed to remove excess concrete and reinstate required gravel section. Perimeter sawcuts completed at time of review; corrective work underway |
|
H-pile encasement (unanticipated condition) |
Seven existing steel H-piles exposed during excavation; not shown on original drawings (FRs 1-2) |
Rimkus redesigned retaining wall to fully encase piles. Revised structural drawings issued. Change Order 1 issued at $19,000 (excl. HST) for the additional scope |
|
Epoxy coating adhesion deficiency |
Portions of epoxy coating on above-grade foundation wall washing off; poor adhesion at several localized areas (FR 9) |
Contractor directed to remove all defective coating, re-prepare substrate per manufacturer requirements, and reapply to achieve a uniform, durable finish before final acceptance |
Construction Administration Finding: Three non-conformances directly affecting structural integrity or drainage performance were each identified and directed for correction before the relevant work was accepted: reinforcing steel layout (corrected before footing pour), adhesive anchor documentation (confirmed before wall pour), and concrete slab layout (corrective removal directed before acceptance). A fourth non-conformance in the epoxy coating was identified at the substantial completion review and directed for correction before final acceptance. All were only detectable through timely, on-site field review at the critical milestone.
The Value Delivered
The value of end-to-end building sciences consulting on a structural site rehabilitation is most clearly demonstrated at the moments when the contractor’s work deviates from the specification. On this project, that happened four times, and each time independent field review identified the issue at the right moment.
Results Summary
- 5 bids received from all 5 invited contractors; contract awarded at $329,400 (excl. HST), $196,850 below the second-lowest submission
- Final contract value $324,325.19 (excl. HST), below the original base bid after three change orders including $23,500 in returned unused allowances
- 9 field reviews conducted from mobilization through substantial completion
- 4 non-conformances identified and directed for correction: 2 structural (pre-pour), 1 slab layout (pre-acceptance), 1 coating deficiency (pre-final acceptance)
- Retaining wall design adapted in-field to encase 7 unanticipated H-piles; revised drawings and change order issued without disrupting the construction schedule
- Substantial performance certified November 21, 2025 under the Ontario Construction Act
Structural integrity protected at the pre-pour hold point. Reinforcing steel non-conformances in the footing were identified at Field Review 4 and directed for full correction before concrete placement was permitted. Field Review 5 confirmed compliance. Without a hold point at this milestone, the non-conformances would have been permanently encased in the new retaining wall structure.
Adhesive anchor compliance verified before the wall pour. During Field Review 6, the specified Hilti HIT-HY 200 adhesive anchor was not observed in use at the Unit 8 dowel locations. The contractor was directed to provide photographic documentation of compliant installation before the pour could proceed. The documented confirmation provides the co-operative with a verifiable record of structural compliance.
Concrete slab layout non-conformance corrected before acceptance. At Field Review 8, the contractor had poured concrete across the full backyard surface at multiple units, contrary to the specified 75%/25% concrete-to-gravel drainage layout. Corrective removal was directed and underway before the work could be accepted, preserving the drainage performance the design was intended to provide.
Design adapted to unanticipated site conditions, at no net additional cost. Excavation exposed seven existing steel H-piles not visible prior to construction. Rimkus reassessed the retaining wall design in-field, issued revised structural drawings, and administered Change Order 1 for $19,000 (excl. HST) to cover the additional scope. The same change order process returned $23,500 in unused contingency and allowance credits through Change Order 3, resulting in a final contract value below the original base bid.
Competitive tender produced defensible pricing with full documentation. Five bids from all five invited contractors, managed through a structured process with a mandatory pre-bid site meeting and one addendum, produced a written recommendation that gave the co-operative’s board documented confidence in the award decision. The winning bid at $329,400 was $620,100 below the highest submission.
Why Rimkus Built Environment Solutions
Structural site rehabilitation on an occupied residential co-operative requires a consultant who can do more than write specifications. When unexpected conditions are exposed during excavation, the consultant needs to reassess the design quickly and issue revised drawings. When the contractor deviates from the specifications, the consultant needs to identify it at the right moment, before the concrete covers it permanently. And when the project is complete, the consultant needs to certify substantial performance under the Ontario Construction Act and assemble the close-out record that protects the owner.
Rimkus Building Sciences brings engineering expertise across structural and civil systems, combined with the construction administration capability to manage a project from initial design through close-out. For co-operatives, condominium corporations, and property managers managing structural rehabilitation on occupied properties, Rimkus provides the independent technical oversight that protects the owner’s investment from the first site visit to the Certificate of Substantial Performance.
We serve residential co-operatives, condominium corporations, property managers, building owners, and institutional asset managers requiring technical consulting for structural site rehabilitation, retaining wall design, condition assessment, reserve fund studies, and construction administration across residential and commercial properties throughout Canada.
Key Takeaways for Co-operatives and Property Managers
What Every Co-operative and Property Manager Should Know
- Pre-pour hold points are essential on structural concrete work. On this project, reinforcing steel non-conformances and missing adhesive anchor documentation were each identified and corrected before the pour. Both would have been permanently concealed and undetectable once concrete was placed.
- Unanticipated site conditions are common on urban co-operative properties. Seven existing H-piles not visible before excavation required a full design reassessment and revised structural drawings. A consultant who can adapt in-field prevents these discoveries from becoming delays or disputes.
- A managed tender process with five bids produced a spread of $620,100 from the lowest to the highest submission. A structured process with a mandatory pre-bid site meeting, a managed question period, and a written recommendation gives the co-operative board a defensible, documented basis for the award decision.
- Final contract value can be below the original base bid. On this project, unused contingency and allowance credits returned through Change Order 3 resulted in a final contract of $324,325.19, which was $5,074.81 below the original award. Transparent change order administration is how that happens.
- Substantial performance certification under the Ontario Construction Act is a legal milestone that starts the lien clock. Having a payment certifier administer the contract means the certificate is prepared and published correctly, protecting the owner and triggering the required statutory holdback releases.
Related Services
- Building Sciences Consulting
- Structural Site Rehabilitation
- Construction Administration
- Reserve Fund Studies and Condition Assessments
- Specification Writing and Tender Management
Frequently Asked Questions
Connect with Our Expert
Chander Thusu, B.Eng., BSS
Practice Leader, Building Sciences
+1 416 970 3107
[email protected]
View Chander’s Expert Profile
Chander has 32 years of experience in building sciences, structural rehabilitation of parking and balcony structures, and forensic investigation of high-humid buildings such as swimming pools and steam rooms. He holds a Building Science Specialist (BSS) designation from the Ontario Building Envelope Council and a Building Science Certificate from the University of Toronto.
This case study is intended to provide general information and insights into prevailing industry practices. It is not intended to constitute, and should not be relied upon as, legal, technical, or professional advice. The content does not replace consultation with a qualified expert or professional regarding the specific facts and circumstances of any particular matter.