Addition and Deck Structural Design in Lake Oswego, OR
Most Lake Oswego addition work heads toward the water, which means it heads downhill, which means it ends up elevated. A room or deck standing eight or twelve feet above grade on posts is a fundamentally different structure from one sitting on the ground, and the difference is lateral rather than vertical.
Vertically the design is simple: posts carry load to footings. Laterally, a set of tall slender posts is a mechanism that will sway unless it is braced, and on these lots the bracing has to be designed rather than assumed — partly because the loads are seismic here as well as from wind and occupancy.
Footings on the downhill side are the second design decision. A footing placed on the face of a slope has considerably less lateral confinement than one on level ground and has to be carried deeper to find both competent bearing and enough soil in front of it to resist being pushed out. Setting those at the same depth as the uphill footings is a common and consequential shortcut.
What We Look At Here
- Lateral bracing design for tall post systems, including seismic demand
- Post size and slenderness against unbraced height
- Downhill footing depth for both bearing and lateral confinement on a slope
- Connection back to the main structure, and whether it is relied on for lateral support
- Cantilever back-span and hold-down where structures project over slope
- Drainage effects of new footings and decking on the slope below
More on the service itself: Addition & Remodel Structural Design. More on the area: Lake Oswego.
Questions
Frequently Asked Questions
Why do downhill footings need to be deeper on my Lake Oswego lot?
A footing on a slope face has less soil in front of it to resist lateral push and reaches competent bearing later than one on level ground. Matching it to the uphill footing depth leaves it under-founded in both respects.