6×6 post breaks in two story deck with roof
user-433254
| Posted in General Questions on
Looking for some guidance on where to break the 6×6 posts on a multi level deck that also carries a roof.
Splicing posts doesn’t seem to make sense because of structursl integrity and twisting. Can I stack the posts at decking level allowing them to twist at that point? This would divide post into three sections, ground to first level decking, first level decking to second level decking and then second level decking to roof.
What do I do about uplifting forces in this case?
Should I just leave it to an engineer?
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Replies
Terrell,
You can't splice them as you need the structure at each level to bear on the top of the posts. See figure 9 in the linked guide. https://www.awc.org/pdf/codes-standards/publications/dca/AWC-DCA62015-DeckGuide-1804.pdf
At each level the post will stop under the beam that is supporting the deck or roof, and start on top of that beam.
I don't think you need an engineer unless there is something else at play (which will depend on both your location, and whether the decks will have sheathing to resist shear). The simplest way to specify the appropriate hardware is probably to use the Simpson guide.
https://www.strongtie.com/solutions/deckcenter
That being said, it's not a straightforward structure. You should have an experienced carpenter working with you.
Generally you run posts as long as possible as each section needs to be laterally braced in both directions. More runs more bracing which tends to take away form the look. Sometimes it is better to run a full height steel column and wrap it in wood. Besides lasting longer, it won't twist or check like a 6x6 would.
As for the actual structural details of a two story deck, that is definitely best left to an engineer. This is something that is very easy to build incorrectly.
+1 for using steel columns here. Get steel tubing from a structural steel fabricator. Have the tube run the full height of the column, and have them weld bearing plates to the tube at the appropriate places to support your deck platforms. Have them punch holes in the plates for you to bolt the deck platform structure to. Note that the bearing plates should have a lip or channel for the joists/beams to rest on so the bolts aren’t in shear but are only holding the joists/beams in the plate/saddle assembly.
You’ll find structural steel fabricated like this isn’t very expensive. Make sure the fabricator primes it for you, then paint it with a good protective paint (I like the Rust-Oleum stops rust enamel line for this). You can wrap the columns with wood to make them look like wood, or leave them as steel painted to look good as a “modern” deck structure. You’ll probably only need 3” square or round tubing for this column, so you can still get in a 6x6 footprint even if wrapping the column with wood.
Make sure to allow for lateral bracing with these columns. Sometimes using some steel channel beams or flitch plate style construction will allow for bolted steel connections to handle shear forces on the columns to provide the required bracing with minimal visual impact on your overall structure. This is how commercial steel construction works, with the steel part ultimately getting hidden within the finish materials.
Bill