The Canadian Funding Corporation reports on Brick cladding repairs in Ottawa, Ontario
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The City of Ottawa has found residential buildings that represent a safety concern. Consultants are looking for ways to repair these buildings. The Canadian Funding Corp. reviews a report from the CMHC about these brick cladding repairs.
Introduction
This 11-storey, concrete-framed residential building was constructed circa 1974. It is clad primarily in brick veneer with a concrete block backup wall and has a rectangular footprint. The brick veneer at non-balcony locations was intended to be supported at every floor by steel shelf angles anchored to the slab edge. The backup wall comprises concrete block, which bears on the floor slab. Lateral support of the brick veneer to the backup wall is provided by horizontal truss type reinforcement. Incidental moisture is managed by through-wall flashings made of copper and woven polyolefin fabric. Weep holes are spaced at 600 mm (2 ft). Suspended slabs support the brick veneer at the balcony locations. Prior to 2003, the brick veneer maintenance program consisted of applying brick surface sealers and caulking replacement. Tenants in certain areas complained of mold smells after rainstorms. These areas exhibited visible deterioration of grout and brick veneer. In October 2003 exterior swing stage water testing revealed water infiltration occurring in the same areas due to the localized brick veneer and mortar deterioration. In June 2004, the consulting firm that conducted a building envelope investigation discovered that the brick veneer exhibited numerous deficiencies, which is not uncommon for a building of this vintage. The major issue was the severe shelf angle corrosion on the east elevation, which represented a safety and serviceability concern. The east elevation was slated for rehabilitation in 2005. The project was tendered by invited bids. The successful contractor was awarded the first phase of the project for a bid of $ 266,547 plus GST. The first phase was completed in October 2005. All work was completed in November 2005 at a final construction cost of $378,561.00 (excluding GST).
Consultant’s Observations (from both visual inspection and invasive openings)
Bricks and mortar were generally in fair to good condition. Vertical brick and mortar cracking was noted at corners of the buildings. The cracking typically occurred on the upper floors. Attempts had been made to seal some of the cracking with caulking. Localized brick deterioration with varying degrees of severity. Mortar erosion. Some weep holes (located at steel shelf angles) were plugged. Previous repointing and brick fracture repair efforts were evident. Steel shelf angle joints had been recaulked at some point in the past. The sealant was in good condition. When the sealant was locally removed, the underlying steel shelf angle leading edge was found to have moderate to severe corrosion. The joint at the steel angle between the narrow brick veneer locations on the east and west elevations were filled with grout, possibly from the original construction. The shelf angles at the southeast corner of the building exhibited severe corrosion from the 3rd to the 11th floor. At test openings, the copper and woven polyolefin fabric (Fabrene®) throughwall flashing was found to be deteriorated. Volumetric expansion due to corrosion had resulted in hard contact between brick veneer and the steel shelf angles. At most openings, the air space between the backup concrete brick wall and brick veneer was filled with mortar droppings. Water remained behind the brick veneer several days after significant rainfall.
Problem Analysis
The investigation showed that localized brick and mortar joint deterioration and fracture was occurring, primarily at the building corners. This was attributed to a lack of vertical control joints at corner locations. Typically vertical control joints allow thermal expansion and contraction to take place without incurring stress buildup due to restraint. Brick ties, horizontal truss, lock type, exhibited minor to moderate corrosion; however, the condition of the steel shelf angles was of greater concern. Test openings revealed the steel shelf angles were in an advanced state of corrosion. Corrosion products had caused the steel to undergo significant volumetric expansion, which filled any expansion joint space (soft joint) provided at original construction and created a stress buildup between brick and steel. Elimination of the soft joint beneath each angle resulted in the full height (and weight) of the brick cladding being supported by the lower levels of brick coursing and steel angles. Frame shortening was considered, which would cause further stress in the veneer. Test openings revealed that the deterioration of through-wall flashing material was caused by long-term exposure to moisture infiltration which essentially rotted the membrane. Copper-fabric wall flashing is no longer used for this reason. Building envelopes of this vintage typically fail due to inadequate water penetration control and moisture-related degradation of wall assembly components.
Repair Recommendations
The consultant recommended the following scope of work. Remove the brick veneer to access the existing shelf angle and concrete block wall on the east elevation and approximately 600 mm (2 ft) around the building’s corners (install a vertical control joint at these locations). Install new hot-dipped, galvanized shelf angles; repair and reinforce concrete block backup wall where applicable. Install through wall membrane flashing and weep holes for moisture control. Install new soft joints in narrow brick panels. Backer rod and caulk. Repoint brick at non-brick replacement locations as required with non load-bearing type N Mortar. Install new brick. The south, north and west elevations exhibited a similar pattern of distress as the east elevation. However, the shelf angle corrosion was not as advanced as the east elevation. Wind driven rains often cause problems on the east elevations of high-rise building in Ottawa. The upper three floors, (9th, 10th and 11th) exhibited the most advanced state of corrosion. A program to address the deficiencies was recommended for implementation over three to five years. The rehabilitation program will consist in replacing the steel shelf angles on the 9th, 10th and 11th floor, applying the same methodology as the one used on the east elevation.
Design and Construction
The design, based on the repair recommendations, was prepared in February 2005; competitive tendering was completed in March 2005. Construction began in August 2005 and remained onschedule for completion in November 2005. The consultant provided periodic construction reviews, and no significant issues developed during construction.
Costs
Jan Luistermans says that the pre-tender cost estimate was $290,000, plus GST. Four contractors were invited to tender. Upon review, the contract was awarded to the lowest bidder for $266,547, plus GST. The bids were as high as $472,550, excluding GST, averaging $388,000.
A breakdown of the winning competitor bid contained the following (excluding GST):
Mobilization/Demobilization $21,182
New Brick Veneer $207,200
Testing Cash Allowance $1,000
Unit Rates Items $34,500
Bonds $2,665
Total $266,547
New Air Barrier $25,367*
*The new air barrier installed was an elastomeric bitumen, trowel-applied on the concrete block backup wall.