Decks, Patios, Porches and Docks - More posts or not more posts

Hi,

I am having a contractor building a deck for me.
It's 20x14 with 10 feet high to a W/O basement.

The contractor provided 3 posts spacing 10 feet span with laminated beam.
I am not a deck builder, so I ask him to add another post. He agreed but changing the design to have cantilever. The original designed was having 2x10 joist post and beam without cantilever.

I wonder why with 3 posts. The joists are attached to the beam, but with 4 posts the joists are over the beam and extend out and let them cantilever over by two feet. And with 3 posts, we are using laminated beams, and with 4 posts not using laminated beams.

Thanks for your help.
Luan

Ask your building inspector about whether it is adequate and meets the minimum code standards.

The inspector works for you just as the contractor does.

Your contractor should be following your approved plans or the local minimums the city/county usually has available.

If you do not have the luxury oe benefits of an inspector, you will have to provide more information to get a definite answer.


Do it right or you could suffer when you go to sell and something is found inadequate, especially for a 10' high deck.

Dick

Hi Dick,

Thanks for your response.

Which method would you prefer if assumes all are met with building inspector?

Luan

I am not is a method to make a recommendation since I do not have all the details and am not there.

If you have 4 posts, you may have a better chance of stability if you have some lateral braces in the direction prallel to the house. This also reduced the sway from the higher elevation.

I assume you have a ledger mount to the house, so I would be very critical of the moisture barrier, having the flashing go under the moisture barrier and possibly double flashing. Make sure the proper connectors (nails and ledger through bolts) are adequate for contact with treated wood. The ledger should not be over the siding.

Dick

If the question you are asking about methods relates to the cantilever versus no cantilever, I prefer the cantilever because I feel it looks better. I agree with Concretemasonry's suggestions as far as the rest of the structure and flashing go.

Thanks guys,

Bill, cantilever versus no cantilever, which method is stronger? I don't really mind the look of both of them. However, it seems like there's no better methods. It depends on how beam, joist, and other factor to decide a strong deck.

Hi Luan,
I think you can see how my deck was built by the pictures I posted. http://decksummer08.shutterfly.com/
Pictures 5, 8, 10, and 11 give you a good idea of how the Beams were done. I like how my contractor notched the 6"x6" post so that the 2x10 beam rests on it and is connected through it for stability. IMO this is one of the strongest ways to do it. In my city, just south of yours in the same state ;), the holes/footings need to be dug out 42" down and be a certain width at the bottom based upon the deck dimensions. My deck dimensions were 16' wide by 18' out. The size of the posts matters and initially my plans included four 6"x6" posts for the first row of posts, but I decided to go down to 3 so that I wouldn't have to look through a forest of posts from my window. This caused the footing size for the middle post to increase from 18" to 20" and the outside posts to increase from 16" to 18". The rest of the posts including the landing didn't have to support as much so they could be 14" footings. Another thing that is code in my area is that the posts can't be more than 2 feet in from the edge of the deck. In MN it is important to get the footings right so that frost doesn't heave the posts. In the pictures my contractor added pink panther foam around the posts so that frost won't grab the side of the post and heave it (something he has seen happen).

My basement is not finished so my contractor was able to put a combination of lag bolts and screws into my ledger board. He stressed the importance of flashing it properly, and flashed behind the entire ledger board and also along the top edge. So when looking at my ledger from below I can see flashing underneath it and on top of it. You might be able to see the bottom flashing if you zoom in on picture 4.

Normally the contractor pulls the permit, but because I was so involved with the details of the plans and the materials for my deck I pulled it. In the process I got a brochure on all the deck codes for my city. Stuff like hand rail height, spacing between deck and railing, and tables for the footings. If you want me to dig up the link for these codes in my area let me know, your city probably has the codes posted too.

The inspector should visit your construction site twice. Once immediately after the footings are dug and again when the deck is complete.

One more comment. There is absolutely no wobble at all in my deck. I've tried to sway it back and forth but it doesn't budge. My contractor likes to put the cross supports in (as seen in some of the pictures) and he says that really helps. I've heard blocking between the joists will also help with movement. The only places that my joists are blocked is near the 4"x4" wood posts for the railing.

I was there for the final inspection and the inspector said my deck was very well built. :)

I would venture a guess that the cantilever method is technically stronger due to the fact the joist are sitting on the beam instead of hanging on it. You would also have less deflection in the joist (again this is technical, it would be hard to tell the difference when using 2x10 or larger joist). As far as footing size is concerned you need to talk to your local officials, around here it used to be three times the size of the post you were using. I have not built a deck in a while so I am not current on codes for footings and beam spans. I would make sure the contractor uses rack braces under the bottom of the joist as dgbehrends shows his contractor did.