Welcome to Winnipeg Building!
If you are one of the lucky people who gets to call Winnipeg home, this blog is for you. If you are even more lucky and planning an addition to your home, this article is for you! The most important part of your new addition is not the countertop, flooring selection or even size. The success of your addition will bear directly on the success of choosing the best foundation for your Winnipeg addition!
What Options Do I Have?
While the list of ways to detail a foundation are practically limitless, they generally boil down to two options. Deep foundations (piles or piers) and shallow foundations (footings or basements). Each one has a plethora of options to choose from. Should your foundation be a deep foundation on screw piles? Cast-in-place concrete piles? Should you rather choose a full basement, or a crawl space with an insulation skirt to prevent frost heaving?
When considering a foundation for your new addition it is crucial to have a qualified engineer review and recommend solutions for your project. Every project is different and needs a unique solution. However we’d like the opportunity to give you a bit of our experience and help equip you with the concepts to have meaningful conversation with your chosen engineer.
What are Deep Foundations?
Deep foundations are foundations that transfer the load of your addition or home down to soils and granular below the surface. This transfer of load is done via piles or piers. Concrete piers can be friction based (that the surface area of the concrete pile “grabs” the soil that it is drilled into), or end-bearing (when you are able to hit refusal or bell out the bottom of the pile to bear in soil). Concrete piers can be cast in place (when you drill a hole and fill with concrete) or driven (when you pound pre-built concrete piers into the ground). You can also use galvanized steel screw piles to transfer the load. They are large steel columns with a helix on the bottom to screw into the ground like a giant construction screw.
Typically in Winnipeg the deep foundation of choice would be cast-in-place concrete piles or screw piles for a residential addition. They are the most economical and easiest to schedule, with the least interruption to the neighbourhood and yard site (and screw piles win on the least intrusive scale hands down!). The city currently has some tougher regulations to try getting a project on screw piles approved and designed, though the results are more certain as you are able to see the exact torque on the pile that the engineer specified to ensure you are getting proper load bearing capacity. Rusting concerns are mitigated through galvanizing.
What are Shallow Foundations?
Shallow foundations are what are most common in Winnipeg for existing homes to rest on. These would be slab on grade (like a detached garage, where the concrete slab rests directly on grade), or basements and crawl spaces on footings. You can have concrete or wood foundations in this category, though concrete is more common. Depending on the depth of your shallow foundation you may be required to install an insulation skirt around the foundation to prevent frost ingress.
What Foundation is Your Existing Home On?
You may find yourself asking “Why does this matter? Should I not demand piles for my foundation?” But the joys of building in Winnipeg means that we have soil here that can expand or contract 1″ for every foot of soil that goes from dry to wet or vice versa. Most areas are sitting on about 30-40′ of this poor soil, so that means that the ground under and around your home and new addition can shift between 30 and 40″! You can combat that movement with proper drainage, good sloping of the grade around your home, and a well built foundation.
When choosing a foundation your prime goal should be to ensure the health of the whole home, including the new addition. What you want to do is minimize the differential movement between the home and the addition. When you have the 30″ of soil movement you want that to stay outside of your home, not affect the home.
What Foundation is Best for my Winnipeg Addition?
To that end, in general the best foundation for your Winnipeg addition is to make it as similar as possible to the foundation of your existing home. While there certainly are exceptions (and this is why you must have a qualified engineer involved!) it is typically best for the health of the whole home to have the addition bearing as similarly as possible to the home.
Exceptions to this would be areas near riverbanks and bank stability is an issue, foundations that are suspect where you would rather ensure your addition is solid and doesn’t move, and allow the existing home to move. In this case we recommend slip joints be incorporated so that the addition and house can move differentially with minimal inconvenience to you as the home owner.