When do you need a geotechnical engineer for your home development project?
In Ontario, a wide range of site conditions and custom home development can make it challenging to know when or if the project requires the assessment or recommendations of a geotechnical engineer. Unconventional building or foundation design further complicates the matter. For most lightweight homes, you will likely not need to have a geotechnical engineer consult on the foundation design, but we provided a decision-making matrix below to help navigate those ambivalent situations.
Know Your Site: The Planning Stage
Even before you have chosen the site, you may want to bring in a geotechnical engineer to avoid selecting highly problematic sites that present with the potential for costly issues such as slopes, surface and subsurface water, and challenging soil types. Knowing the history of your site can reveal altered landscapes or hazards on-site that may require consultation with a geotechnical engineer. Your local municipal office may have building records that documents if anyone has done work on the site.
If any of those issues are present on-site, then an assessment by a geotechnical engineer will give you a basis to determine whether you should buy the site. The report will also give you a forewarning of what’s to come in the subsequent stages even if you decide to proceed with purchasing the site.
Building Permit Requirements: Following Your Local Requirements
In Ontario, the municipal government is responsible for managing and issuing building permits for home construction and renovations, and they can differ from municipality to municipality. In other locations across Canada and the U.S., the authority having jurisdiction (AHJ) may at a separate level, which makes it difficult to outline here precise rules for building permits. In all cases, identify first the AHJ for your proposed home construction and the zone to determine what the requirements are, which may include drawings and letters of assurance, and whether they need to be stamped by a certified professional.
Potential Issues That May Benefit from a Consultation with a Geotechnical Engineer
- Natural Hazard Assessments
- Foundation Subgrades
- Foundation Backfill and Engineered Fill
- Foundation Drainage
- Sediment and Erosion Control
- Slope Stability
- Surface and Subsurface Water Management
- Retaining Walls
- Flood Construction
Designing and Planning Your Foundations
We have a mantra when designing foundations for a new building that we let the site do the talking. For a site with few if any of the potential issues listed above, you may be able to use conventional foundation design and may be able to avoid incurring extensive costs in foundational design and construction.
Before you begin construction, you will want to implement best practices for soil and erosion control throughout the site as well as a soil management plan. For builders in Ontario, there are strict regulations for controlling any soil that you remove from the site and controlling erosion. Planning for both scenarios will prevent arranging for last-minute soil disposal. We have written an article specifically on O.REG 406/19 that can provide guidance on managing soil.
During Construction: Excavation and Quality Assurance
To ensure that the house is built according to design, you may want to have an inspection by a geotechnical engineer. Even the best foundational design can fail if not properly executed and if the materials do not meet your site specific standards or of your local AHJ.
During excavation of the site, most AHJs have safety rules that govern the area needed around the excavation and the walls of the excavation. If in doubt, then consulting an engineer before and during excavation can help meet safety requirements and prevent issues during inspection.
What happens when you don’t consult a geotechnical engineer?
In short, consulting a geotechnical engineer at all phases of home development is a sound strategy for risk management and the sooner you bring one in, the better chance you have of mitigating cost overruns later. Some issues that may be prevented by a professional assessment can be sorted into three main categories from the source of the damage: water, soil compaction or swelling, and slope stability.
- Water damage occurs from flooding hazards not considered in building elevations and inadequate or compromised drainage systems.
- Structural damage, settlement, or cracking of the foundations and retaining walls may occur when the fill material is inadequately compacted or the subgrade material is poor. Swelling from frost or water may cause movement and/or cracking of the foundations.
- Slope failure can cause damage to retaining walls, the structure, and loss of yard space.