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Community and Q&A

Porch posts

cibula11 | Posted in Building Code Questions on

We are building a wrap around porch that extends 6′. Since we know, because of code we have to use 6×6 for the posts for the deck, I have question about the posts that supper the roof.

One way is to use the same 6×6 and extend it from footer to header. We think that since these posts will be 6′ apart going around the porch it might seem a bit too bulky.

Does code allow you to replace 6×6 posts with a PVC reinforced porch posts (they are turned and look like traditional porch posts)? Or do we have to stick with 6×6 lumber?

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  1. GBA Editor
    Martin Holladay | | #1

    To answer your question, we would need to know more about your roof loads and your climate (to determine your snow load).

    We would also need to know more about the specs of the PVC posts you are considering using.

    You might be able to get some useful information from the manufacturer of the PVC posts.

    Then you can consult an engineer to determine whether the posts will support your roof loads.

    Finally, you can contact your local code official to determine if your plan complies with your local building codes.

  2. cibula11 | | #2

    Okay, Thanks.

    I went to the manufacturers website and found this statement right at the top:
    "International Residential Code & International Building Code Compliant when properly installed. See ICC-ES Report #2601"

    The current posts are 4x4 cedar, and these posts are far substantial than the old ones. We live in Iowa and certainly snow is an issue, the porch has a fairly low pitch 4/12. We are setting them 6' apart because of this, just to be safe.

  3. Expert Member

    Matt, Post size rarely determines spacing. 6"x6" holds up an extraordinarily large load. You usually go at it the other way round: Figure out your roof load, what size beam you can use, and that gives you the approximate span. You then finalize the span and post spacing by looking at the elevations and deciding where you would like the posts. With common dimension lumber that span is usually in the ten to twelve foot range. Larger spacing means less posts, footings, excavation and not so bulky a look.

  4. cibula11 | | #4

    From what I've found my roof load looks to be 40 as a max. The current header is a doubled 2x8. I don't want to get too much larger than that because the porch eave is slightly below the height of a door (it's lower than the normal 8ft.) Anything larger than a 2x8 header starts to take up significant sightline from the porch. It's my understanding that a doubled 2x8 should span a max of 8ft. Is this correct?

    The reason for asking about the 6x6s initially was because I've been told, according to code, these are the only acceptable posts to use in framing a deck/porch. If that's the case, I agree the only way i can make the porch seem less bulky is to space them farther apart than 6',....if that's possible given my header size.

  5. Expert Member

    Matt, the length your beams can span depends both on the loading required and the area of roof they are supporting. You can beef up the beams by using more 2"x8"s without increasing the depth. It's probably worth going someone who can do the calculations for you so you can increase the spans and open the porch up a bit.

  6. cibula11 | | #6

    So, is it true that 4x4s can no longer be used as support posts for porch roofs? Because of where the windows/doors are located, I'd prefer to use 4x4s every 6 ft. Otherwise, I've got to span at least 12' to make it look correct and avoid placing posts right in the middle of windows and also Be offset from the corners of my house... given my porch depth will only be 6' around 3 sides of the house.

  7. Expert Member

    Matt, Here in Canada 4"x4"s aren't recognized by our code as structural members. Perhaps someone familiar with the code you are under can comment as to whether that's true there too.

    A number of other materials, like steel or manufactured products - perhaps even the ones you referred to in your OP - meet the code. And if your porch is only six feet deep a twelve foot span is easily achieved. What you are missing is someone who can put this all together for you. Most people at this point consult an architect or contractor. If you don't want to spend the money I'd suggest talking the options over with your building inspector.

  8. wjrobinson | | #8

    My lumber yard just did loads for me and I have the sheets in my vehicle right now. I also use software I bought beamchek and there are load tables and books and online software. And there are pros to go to.

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