Reverse Slope Driveway
A reverse slope driveway is a driveway that leads down from a public street to a parking area, such as a below-grade garage or in the lower levels of a building, which is common to many land uses including in most large buildings, such as offices and apartments.
The issue that is of concern in this situation is where a reverse slope driveway leads down from the public street into a parking area in the lower level of a house – usually detached or semi-detached houses, and individual townhouse units that front onto a street.
A reverse-slope driveway goes downhill toward the below-grade garage, rather than downhill toward the street. Reverse sloped driveways create a significant flood risk as they offer a distinct pathway for stormwater towards the below-grade garage, from the street. The street is typically part of the overland flow route of a major storm drainage system – part of the storm drainage system that is used to provide drainage of storm runoff when the municipal storm sewer system is full, generally every 2 to 5 years.
Catch basin/trench drain/drainage grate typically located just in front of the below-grade garage on reverse slope driveways (negative slope driveways ) to capture any stormwater runoff or snowmelt from the reverse sloped driveway. However, if the street is flooding with the overland stormwater flow and stormwater is coming down from the street and, often the catch basin/trench drain/drainage grate has insufficient capacity to handle all that flood water. This creates a risk of flooding to the basement, whereby stormwater can enter the basement via the below-grade garage. Stormwater that enters basements through reverse sloped driveways can cause significant flood damage to houses and can also contribute to sewer backup problems if this flood enters basement floor drains.
Catchbasins/trench drains/drainage grates servicing reverse-sloped driveways should be connected to the storm sewer, not the sanitary sewer. Ensuring that reverse sloped driveways do not have a constant slope into the below-grade garage from the street can also limit or prevent the chances that stormwater will enter the below-grade garage. If not provided by a sidewalk or otherwise, a 15 cm high point between the surface of the street and the point where the reverse-sloped driveway begins to slope down toward the below-grade garage can reduce the chances that overland flooding will enter the basement through the reverse-sloped driveway.
The use of reverse slope driveways is actively discouraged and will not be permitted for any type of new residential development.
Reverse slope driveways have been the subject of a number of criticisms, ranging from safety to aesthetics; but the prime focus of attention is on the high risk of basement flooding posed by reverse slope driveways. Several municipal zoning regulations prohibit the construction of any new reverse-sloped and below-grade garages for single-dwelling residential homes. Some builders apply to the Committee of Adjustment to allow reverse sloped driveways when they are currently not permitted. Now municipalities in Ontario require that any proposed new reverse slope driveway design shall address 100-year storm protection.
The use of Reverse Sloped Driveways is actively discouraged by the Town of Oakville. If a Reverse Sloped Driveway is proposed, the Town of Oakville will require the owner to ensure that a suitable degree of flood protection is provided. Reverse slope driveway drainage facilities may not be connected by gravity to the municipal storm sewer system in the Town of Oakville unless it can be proven that surcharging by the municipal storm sewer system during a 1:100-year storm will not cause them to flood.
As per the City of Burlington's Grading & Drainage Requirements, Reverse Slope Driveway shall be between 2% (minimum) and 5% (maximum) and shall only be permitted when it is proven by a Professional Municipal Engineer licensed in Ontario, that the reverse slope driveway will not flood during a 100-year storm event.
No portion of a garage should be located below the lowest grade of the lot on the street as per the City of Vaughan's requirements. Reverse slope driveways are not permitted as per the City of Vaughan's Zoning By-law 1-88 and the City of Vaughan’s Engineering Design Criteria and Standard Documents.
Markham zoning by-laws require that the garage floor elevation is above the elevation of the public street to prevent reverse slope driveways. The only possible exception is where the City of Markham would approve a reverse slope driveway where the first floor of the proposed house is lower than the elevation of the public street due to natural topography, in which case, a garage floor maybe 1.0 m lower than the first floor of the proposed house.
Reverse sloped driveways may only be considered by the City of Mississauga where the topography of the lot permits gravity drainage like a ravine lot) or where a Region of Peel's storm sewer exists of sufficient capacity and depth to permit a storm sewer lead to drain via gravity from the low point of the reversed slope driveway to the Region of Peel's storm sewer. The below-grade garage sill elevation shall be 1.0 m (3¼ft) above the municipal sewer obvert and the lead must be constructed to municipal standards.
The City of Toronto’s Zoning By-Law 569-2013 prohibits the construction of below-grade garages and reverse slope driveways (negative slope driveways) for single-dwelling residential buildings anywhere in the City of Toronto. If you want to build a below-grade garage that needs a reverse slope driveway in the city, you must apply for an exemption through a Minor Variance Application or a Re-zoning Application, depending on the development type.
As part of the process of applying for a reverse sloped driveway, the City of Toronto may request a Toronto Water Technical Review, if the City of Toronto's Committee of Adjustment’s Notice of Decision or a Toronto Local Appeal Body decision requires a technical review and approval by Toronto Water for a reverse slope driveway (negative slope driveway). A technical review is requested through a re-zoning application approval process for a reverse slope driveway. The typical reverse-sloped driveway design would propose a storm connection to the City’s sewer system to discharge water from the reverse-sloped driveway’s catch basin/trench drain/drainage grate. We prepare a stormwater flow analysis to identify the stormwater flow at the reverse slope driveway and the required features to drain it out for any proposed construction containing a reverse slope driveway and a below-grade basement garage.
We always propose a high point of the reverse slope driveway higher than the centerline of the public street elevation and design a catch basin/trench drain/drainage grate and a sump pump. No area other than the reverse slope driveway (negative slope driveway) shall drain to the proposed trench drain up to a 100-year storm event. Estimated flow from a 100-year storm is utilized to establish the required settling tank volume and sump pump capacity.
We also calculate the required backup electrical power (inverter/charger and batteries) for both primary and backup pumps in the event of temporary electrical failure.
The duplex sump pump system for the reverse slope driveways shall be factory pre-assembled with pumps, discharge pipe nipples, and floats pre-mounted in the basin. Floats shall be tethered to a removable standpipe/access cover assembly. The cover shall be a “heavy duty” 6mm steel plate, enamel-coated on both sides. The cover shall be fitted with two 400mm diameter pump openings and one 250mm diameter inspection cover with an integral standpipe for float tethering. All cover hardware shall be stainless steel. The basin shall be constructed of heavy-duty polyethylene. The inlet hub shall be 100mm in diameter and preassembled to the basin.
The basin shall have “torque stops” to locate and retain the pump in its proper position.
The vehicle geometry that causes the undersides of vehicles to drag on the pavement surface is a combination of ground clearance height and the wheelbase. Adequate axle-to-axle ground clearance shall be provided to prevent underside drag at the sloped driveway for a typical vehicle with a wheelbase from 2.6 m to 2.8 m.
A splash pad shall be provided at the outlet of the pump and outflow shall not enter into the adjacent property. The catch basin/trench drain/drainage grate and the sump pump shall be inspected after every storm event and shall be kept clean and free of debris and silt.
Our Licensed Professional Municipal Engineers offer Stormwater Management Design and Site Grading/Drainage Plans, Erosion/Sediment Control Plans, Site Servicing Plans to obtain site plan approval and building permits to construct commercial, industrial, institutional and multi residential new construction in Ontario including Ajax, Amherstburg, Arnprior,Aurora, Aylmer, Bancroft, Barrie, Belleville, Blue Mountains, Bracebridge, Bradford, Brampton, Brant, Brantford, Brockville, Burlington, Caledon, Cambridge, Carleton Place, Cobourg, Collingwood, Cornwall, East Gwillimbury, Elliot Lake, Erin, Espanola, Essex, Fort Erie, Gananoque, Georgina, Goderich, Grand Valley, Gravenhurst, Grimsby, Guelph, Haldimand County, Halton Hills, Hamilton, Hanover, Hawkesbury, Huntsville, Ingersoll, Innisfil, Kawartha Lakes, Kingston, Kingsville, Kitchener, Lakeshore, LaSalle, Lincoln, London, Markham, Midland, Milton, Minto, Mississauga, Mississippi Mills, Mono, Napanee, New Tecumseth, Newmarket, Niagara Falls, Niagara-on-the-Lake, Norfolk County, North Bay, Oakville, Orangeville, Orillia, Oshawa, Ottawa, Owen Sound, Parry Sound, Pelham, Pembroke, Penetanguishene, Perth, Petawawa, Peterborough, Petrolia, Pickering, Plympton-Wyoming, Port Colborne, Prescott, Prince Edward County, Quinte West, Renfrew, Richmond Hill, Sarnia, Saugeen Shores, Sault Ste. Marie, Shelburne, Smiths Falls, South Bruce Peninsula, St. Marys, St. Catharines, St. Thomas, Stratford, Sudbury, Tecumseh, Thorold, Timmins, Tillsonburg, Toronto, Vaughan, Waterloo, Wasaga Beach, Welland, and West Gwillimbury.
Having vast experience in stormwater management design, we offer effective, innovative, and cost-efficient stormwater management designs and stamped engineering Site Grading/Drainage Plans, Erosion/Sediment Control Plans, and Site Servicing Plans to our clients. Our professional engineering team's proficiency in conceptualizing designs and plan in accordance with our client's requirements has made us very successful. Our licensed professional structural engineers prepare thorough, detailed, and clear stamped stormwater management reports, stamped engineering Site Grading/Drainage Plans, Erosion/Sediment Control Plans, and Site Servicing Plans to suit your needs while also adhering to the design requirements of the municipality and or conservation authority, Niagara Escarpment Plan, City of Toronto's Ravine and Natural Feature Protection, and Oak Ridges Moraine Conservation Plan and submit to the municipality for review and approval to obtain site plan approvals and building permits.
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