By Robert Rymell, P.Eng., C.Eng., CSC
Over the years, this author’s firm has been involved in several cases of water damage problems that turned out to be mismanaged water management. Anyone who has ever walked by a building during or just after a rainstorm knows a person can get more wet from rooftop runoff than the rain itself. Worse, there are cases of ice falling off of high structures onto lower ones or the sidewalks below. These problems seem to have become more prevalent (possibly due to changing climate patterns), resulting in increased possible safety issues.
There is a lot of information on runoff of surface water, and increasing building science data regarding water migration through walls and ground, but unfortunately little to connect this knowledge on a practical level.
This article presents a few brief case studies to illustrate how things can go wrong when the whole picture is not initially considered. In each example, the original building owners were not consulted by the new building developer/builder to try and ward off future problems. In each case, the problem’s resolution required ‘fixes’ that could have otherwise been avoided.
Since Building A (a high-rise) was being constructed next to Building B (a mid-rise in a downtown core), the new walls had to be built right at the property line. The existing building had a podium all around that covered the underground parking and office spaces and also extended to the property line.
The wall design of Building A included small shelves and windowsills. Unfortunately, this meant the water and ice fallout ended up on the podium of Building B, resulting in possible injury issues and water damage to the interior of maintenance offices located in the first level below grade. Additionally, since the owners of A did not talk to the owners of B, there was no connection at grade level to prevent water from going down between the buildings below grade causing further damage to Building B.
Had discussions between the owners occurred earlier, construction measures could have been taken to ensure a proper tie-in between the two buildings. It is possible the ledges on the side of the new building would also have been eliminated.
In this particular case, the tie-in between the buildings had to be accomplished to newly complete precast walls that did not have a through-wall flashing. This made the durability of the resulting flashing questionable, but it was the only option available. Each owner now knows of the future maintenance costs. As for public safety, the area directly along the side of the new building was to be cordoned off.
Building C is a mid-rise constructed decades ago on the side of a hill. In order for Complex D to be constructed lower on the hill, a retaining wall was built at the property line between the two buildings. Unfortunately, the wall was not constructed with provisions for drainage. As a result, the wall acted as a dam to underground water. The water then upwelled at the lower perimeter of Building C, washing out footings and moving large cast-in-place concrete slabs used as ground floor balcony walk outs. Again, the Developer of Complex D did not talk to the owner of Building C.
This problem could have been avoided had the retaining wall been correctly constructed with water-drainage provisions—simply, weeping tile placed along the stone’s back side.
To avoid stability issues for the building, surface water was redirected on the upslope side and any voids at the building walls were hard filled to prevent further wash out. Additionally, the damaged footings of the building were widened and reinforced to provide stability.
Building E is a two-storey low-rise, constructed many years ago at the property line on three sides. Building F is also two storeys, but approximately 3 m (9.8 ft) higher, and a more recent construction. Even though they were both at the property line a narrow gap was created between them. Water ingress resulted in damage to Building E.
A failed attempt was made to try and seal the gap at grade, however the space was too narrow—it could not be effectively done and access from either end was impossible. To further compound matters, the builder of Building F constructed a small roof over the gap with a slant onto Building E’s roof.
Since Building E’s owner did not know about the roofing (and therefore did not upgrade the roof drains), the subsequent rainfalls overloaded the existing roof resulting in damage to the interior.
Again, had the developer of Building F talked to the owner of Building E, provisions could have been made in the initial designs to either utilize the adjoining wall for both or allow for enclosure of the space between the buildings.
Existing Complex G was constructed on a slope with swales that redirected runoff to street catch basins that had performed well. A new retaining wall—which did not have drainage provisions—was built by the developer of a new home development site on a lower elevation of the hill. As a result, the construction of the retaining wall redirected ground and surface water, damaging some of the new homes. Blame was incorrectly laid on the original complex.
Had the home developer installed correct drainage provisions for the new retaining wall, and discussed with the Complex G owners possible easier rework of existing swales, the whole problem could have been avoided.
To resolve the problem, Complex G reworked the swales, which required removal of trees, such that surface water drained directly onto the street.
Dealing with failures
Unfortunately, each of the situations profiled in this article required significant negotiation between the parties to try and avoid litigation. Difficulties arose on both sides with the primary arguments being, “Why should I pay to alter your building?” and “Why should I pay for damage your construction caused?” Much of the animosity could have been averted if the parties had negotiated at the time of design.
Further, these situations were not directly covered by existing legislation. Therefore, the unique solutions that followed had to be accepted by all parties including the authority having jurisdiction (AHJ).
What the code says
The National Building Code of Canada (NBC)—and, similarly, the provincial codes—requires consideration for the handling surface water, but does not specifically address ground water or shed from an adjacent structure. In 126.96.36.199−Accumulation and Disposal, it requires:
- Where water, snow, or ice can accumulate on a building, provision shall be made to minimize the likelihood of hazardous conditions arising from such accumulation.
- Where precipitation can accumulate on sloped or horizontal assemblies, provision shall be made for drainage conforming with the relevant provincial or territorial regulations or municipal bylaws or, in the absence of such regulations or bylaws, with Article 188.8.131.52. of Division B of the National Plumbing Code of Canada 2010.
Where downspouts are provided and are not connected to a sewer, provisions shall be made to:
a) divert the water from the building; and
b) prevent soil erosion.
- Junctions between vertical assemblies, and sloped or horizontal assemblies, shall be designed and constructed to minimize the flow of water from the sloped or horizontal assembly onto the vertical assembly.
Unfortunately, these sentences of the code relate to the new construction; in simple terms, they require water be redirected away from the building. Unfortunately, it leaves what happens to that water to other municipal or provincial legislation. Therefore, this requires the designer look for possible other legislated provisions that may or may not provide guidance.
In Section 5.7.1−Protection from Surface Water, NBC goes on to state:
184.108.40.206. Prevention of Accumulation and Ingress
- Except as provided in Sentence (3), the building shall be located, the building site shall be graded, or catch basins shall be installed so that surface water will not accumulate against the building.
Except as provided in Sentence (3), foundation walls shall be constructed so that surface water will not:
a) enter the building; or
b) damage moisture-susceptible materials.
- Buildings specifically designed to accommodate the accumulation of water at the building or the ingress of water need not comply with Sentence (1) or Clause (2)(a).
Again, as with 220.127.116.11, the code tells us to redirect water away from the building. However, it does not provide direction as to what to do with it afterward.
In Section 5.8.1−Foundation and Floor Drainage, NBC examines drainage materials and installation requirements:
18.104.22.168. Required Drainage
- Except where a wall or floor is subject to continuous hydrostatic pressure, or unless it can be shown to be unnecessary, the bottom of every exterior foundation wall and every floor-on-ground shall be provided with drainage. (See Appendix A.)
In Appendix A-22.214.171.124.(1)−Required Drainage, the code says:
A wall or floor located below the water table or in the path of a watercourse will be subject to continuous hydrostatic pressure. In such cases, the provision of drainage will be ineffective and the wall or floor must be made waterproof to prevent water ingress.
Where a wall or floor is subject to intermittent hydrostatic pressure, as may result from seasonal flooding, proper drainage will facilitate the drying out of the soil. In some cases, reducing exposure to high moisture levels will extend the life of the moisture protection.
Where a wall or floor is not subject to hydrostatic pressure, drainage again reduces the exposure to high moisture levels and allows less than waterproof treatment of the wall or floor.
126.96.36.199. Drainage Materials and Installation
- Drainage shall be specified and installed to accommodate the drainage load.
In 188.8.131.52. Required Moisture Protection, NBC requires:
- Except as provided in Sentence (2), where a building element separates interior space from the ground, materials, components, or assemblies shall be installed to prevent moisture transfer into the space.
Materials, components, or assemblies need not be installed to prevent moisture transfer from the ground where it can be shown that such transfer will not adversely affect any of:
a) the health or safety of building users;
b) the intended use of the building; or
c) the operation of building services.
Again, for 184.108.40.206 and 220.127.116.11, the sentences relate to the control of water at the building—not on the site or what to do with it. For these measures, the designers must go to other legislation that may or may not exist in the particular jurisdiction.
Similarly, in Part 9−Housing and Small Buildings, NBC requires accounting for water’s flow away from the structure:
18.104.22.168. Surface Drainage
- The building shall be located or the building site graded so that water will not accumulate at or near the building.
Additionally, at the provincial and municipal levels, an outline of the rights of property owners and some guidance for the handling of surface water has been provided in documents such as:
- Ontario Ministry of Agriculture Food and Rural Affairs’ (OMAFRA’s) Drainage Conflict: Surface Water; and
- Municipal Program Development Branch Environmental Sciences Division’s Stormwater Management Guidelines for the Province of Alberta.
Building right at the property line will pose a different set of problems than those of buildings constructed on slopes or even floodplains. Structures such as retaining walls or out-buildings can be relevant when taking a holistic viewpoint.
There is a high cost in removing and rebuilding retaining walls or working in difficult access areas which, if handled early in the construction process, could be avoided. The key to the whole problem is for the players to sit down at the time of design and think through the possibilities and come up with those creative solutions early. It may be that not every eventuality can be covered, but there will be a level of due diligence established so both sides are knowledgeable of the possibilities.
With the high price of real estate, there may now be a need for the policy-makers to look at these types of issues in much the same way ‘sunshine laws’ are being implemented.
In this article, water has been the focus of the discussion. However, there are other issues that may occur, such as:
- ice and snow shed;
- more storms, more rain, more frequent intense storms;
- greater swings in temperature;
- less greenspace; and
- higher water tables that eliminate natural drainage runoff.
Each would have a different effect on the buildings, possibly leading to damage, a decline in real-estate value, or an impact on the health and safety of the occupants and visitors.
It is important for design professionals to study the conditions prior to construction, as well as to help ensure neighbourly agreements are reached. In other words, one should remember it tends to be cheaper to pay the lawyers at the beginning of the project, rather than after construction has finished.
Robert Rymell, P.Eng., C.Eng., CSC, is president of RBS Consulting Engineering Group in Innisfil, Ont. He is a professional engineer and a registered consulting engineer licensed to practice in Ontario, Alberta, Prince Edward Island, and Nova Scotia. Rymell is a member of the executive committee of the Canadian Commission on Building and Fire Codes (CCBFC), as well as the Toronto Chapter of Construction Specifications Canada (CSC), the Ontario Building Envelope Council (OBEC), and the National Building Envelope Council (NBEC). He can be contacted via e-mail at firstname.lastname@example.org.