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So you want to build a deck?

Updated: 05/27/2017

You might think, it's just a deck. Why do I need a city building permit? However, last month, a young girl was injured in a deck collapse in Cottage Grove.

A deck is an extension of your home, and just as you would not want your house to collapse, why build a deck that could fall apart due to frost heave, water intrusion, rambunctious activities and other forces of nature?

When you apply for a deck permit, the Building Inspections Division reviews your submitted plans to verify that the decking, floor joist, beams and footings are adequate to support the weight. For example, did you know that a 14-foot-by-20-foot deck must be able to support 14,000 pounds?

You might think, Dave, we will never have that many people on our deck. No, but what about in the winter when there's 30 inches of snow out there? That translates into 6,720 pounds, plus the weight of the deck. Then you and a number of friends go out to watch that magnificent sunset. I'd be a little nervous.

In addition to reviewing the loading on your deck, the city is also concerned with how the deck is fastened together, e.g., the deck ledger to the house, the floor joist to the deck ledger, on the other end the floor joist to the beam, the beam to the posts, the posts to the footings, the anchoring of the footings in the ground, etc. We are worried about two things here:

  1. The weight of the deck pushing down on the ground
  2. What happens to the deck when a big wind comes along and tries to lift the deck

Now, let’s talk about the railing system. Did you know that the posts that support the railing system need to withstand 200 pounds of force? A common 4” x 4” post has been tested and found to snap at 325 pounds of force. You buy a notched post and its breaking strength is less than 200 pounds. Intermittent rails need to withstand 50 pounds of force and must be screwed in place, not nailed. A 4-inch sphere should not be able to pass between the pickets or the bottom rail and the decking.

If you want further information on how to build a deck, the city website has a deck handout [PDF] to guide you in building a safe structure. If you still have questions, give us a call at 952-233-9397.