Widen deck support spacing for carport use

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Old 08-11-13, 02:28 PM
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Widen deck support spacing for carport use

I have a deck that is roughly 12' deep and 25' wide. It currently has 4x4 posts supporting the deck at just shy of 6' spacing.
I will be excavating the dirt near the deck dropping the level 2.5' and will have to replace the support posts to make them longer but would like to beef up the deck support so that I can remove every other post leaving enough space between to have two car ports underneath the deck. Height above the new ground level will be about 9' and the two car ports will be roughly 11'6" wide each.

What would I need to do to ensure the deck is structurally sound enough with fewer support posts?
 
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Old 08-11-13, 03:03 PM
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Got some pictures?
Need to know what the joist size and spans is, how it's attached, if there's any diaginals and about a dozen other questions.
A picture may answer a bunch of them.
 
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Old 08-12-13, 12:28 PM
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The 4x4 post are probably attached to a beam that runs perpendicular to and has the floor joists supported. The beam will need to be increased in size in order to support the deck. If you are spanning 11'6", you should be able to use a double 2x12 for the span.
 
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Old 08-15-13, 11:09 AM
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Sorry for the late response guys, been busy lately. Below is a very basic layout of the deck. Forgive my poor drawing skills and I left out the joists.

Name:  Deck.jpg
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The top of the picture would be the edge of the deck attached to the house.
The joists extend out from the side of the house 12' and the last 4' of the deck is supported by a board coming at a 45 degree angle between the support post at 8' and the bottom of the joist.

Dimensions are approximate. The support posts are currently 4"x4". I believe the joists are 2x12 but I will have to check. There are cross pieces between the joists at the posts of the same dimension. I will also have to check what the joist spacing is.

The deck boards run parallel to the house across the joists and are 2x6.

I am looking to remove the second and fourth rows of support posts creating two sections under the deck wide enough to park one car each. I figure that the 4x4 posts would be inadequate to carry the addtional load. I am an adequate carpenter but do not know how to determine what would be required to carry the load of the deck and whatever may be on top of it with the decreased support posts.

The extra 2.5' at the right end of the deck is where it actually wraps around to the side of the house which is not shown but follows the same support structure as the section shown.

Thanks guys.
 
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Old 08-15-13, 12:21 PM
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So, on the left is a 2x12 with it’s end (at the top) attached to the house. Then at 6’, 12’, 18’and so on there is another 2x12. These are supported by 4x4 posts. Are there joists between these?
 
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Old 08-15-13, 12:44 PM
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Yes, there are joists between though I will have to check what the spacing on the joists are as well as their size. They might be 2x10 rather than 2x12.
A correction to above, I believe the posts are spaced 5' and 10' out from the house with a 2' overhang.

The deck design is pretty straight forward and I should be able to modify it easily enough I just need to determine what size posts, joists and beam I need if I want to have an 11' gap between posts along the length of the deck. Hopefully not much will need to be replaced and I know that will all depend on current joist and beam size and what the joist spacing is but I am a lot further along if I know what will be required to fit specific spacings. I may have to replace the posts with 6x6 simply due to the height but will have to do some more accurate measurement of what the height will be after I excavate the yard down to driveway level. I might push over 10' in the length of the posts once I have excavated.
 
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Old 08-15-13, 08:42 PM
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For a touch of overkill, I would replace posts 1,3 & 5 with a 6x6 post and use a tripple 2x12 with staggered joints on top of that. The joists all need to be the same size so they all rest on the new beam. You may also need some bracing from the posts to the beam if there is an issue with the deck swaying.
 
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Old 08-19-13, 06:54 PM
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I finally got the measurements.
The joists are 2x10 at 16" on center spacing.
The first row of posts parallel to the house are 4' 2-1/2" out and the next row is 7' 8-1/2" from the house. The outside of the second row of posts has two 2x6 boards and the joists are notched about 1/2" sitting on top of it. The overhang is 4'. The outside edge of the deck has a 2x6 on top with a 2x10 below it on the inside and a 2x10 over top of them on the outside.

One thing I saw that I did not like was that at least one row of posts did not line up with the joist spacing (new deck was built over old deck frame with existing posts) so they used two cut pieces of 2x6 to sandwich between the joist and side of the post. But the joists are supported by the two 2x6 boards being used as a beam so it is probably sound. If I am going to be replacing the posts anyway I would pour the concrete pads in the correct locations so everything lines up correctly.
 
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Old 08-20-13, 01:43 PM
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