# load bearing capacity of 1x6 box



## 1HandyWoman (Sep 23, 2015)

I want to replace the columns on my front porch.  They are load bearing and are presently made of 4 - 1"x6" made into a square box (each column).  I do NOT want to use that method to replace the columns and instead want to use solid wood or composite columns.  BUT I need to determine what the present load capacity is for these columns to make sure I can meet or exceed that load bearing capacity with the new columns.  

Does anyone know HOW to determine the load bearing weight capacity of a 1" x 6" wooden box?:help:


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## nealtw (Sep 23, 2015)

If those columns are carrying any load at all there will be 4x4 inside the box if you have reason to change them, treated six by six i or 4 treated 2x6s nailed together is  the normal today. Then wrap that with 1x8 or what ever.
If you use treated use galvinized nails or screws.


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## 1HandyWoman (Sep 23, 2015)

No I have investigated and the box is hollow.  I want to use some vinyl covered composite that has the strength of a 4x4 and I can determine its load capacity.  I just need to determine if that is enough to carry the present load.

Does anyone know of a calculation or table that can determine the load carrying capacity of a 1 x 6 box?


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## nealtw (Sep 23, 2015)

That's not how you would figure out what you would need . You woulod needto figure out what the load is. That is the weight that is supported by each post as it is and what ever other loads may be added like snow.
I could be wrong but I don't think anyone would be able to find a chart that includes a 6" box as a supporting member. Just because that is what you have dosn't make it right.


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## slownsteady (Sep 23, 2015)

The right answer requires an engineer to make that calculation. But out of curiosity, what is above the columns? A roof over the porch? No second floor? What are the dimensions? How did you determine that they're hollow? What kind of support is under the columns? There is a lot involved in that calculation.


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## 1HandyWoman (Sep 24, 2015)

"You woulod needto figure out what the load is. That is the weight that  is supported by each post as it is and what ever other loads may be  added like snow."

I disagree.  To have built the columns initially I would agree that someone had to have made those calculations.  But since the columns have been in place and standing for 28 years now and they WORK then I should only have to replace them with the same load bearing capacity or better. 



"The right answer requires an engineer to make that calculation. But out  of curiosity, what is above the columns? A roof over the porch? No  second floor? What are the dimensions? How did you determine that  they're hollow? What kind of support is under the columns? There is a  lot involved in that calculation."

I disagree that an engineer is required to determine the load capacity of materials.  I have found tables online that show the load capacity of solid wood broken down by the type of wood and size but I have not found the load capacity of a 1 x 6 box.  That is all I am looking for.

As to your questions slownsteady...
above the columns is a small roof over the front porch where the rafters are cantilevered over a block wall from the front of the house (so it has support from the structure of the house).  NO second floor above the porch.  The dimensions of the porch?? of the boxed column?? why should it matter (either one).  The box column is 6 x 6 by 7.2 feet tall and there are 6 columns across the front of the porch.  I determined they are hollow by removing one side of the box and looking inside.  Under the column is a common plate (aluminum?) that holds the bottom off the concrete underneath of the column.  That plate alone should show that the column is not holding that much weigh as those plates should not be used under a heavy weight bearing structure (I believe).  

No you all are trying to make this thing too difficult...the only calculation needed is the load bearing capacity of a yellow pine box made of 1 bys (1 x 6) that is all that SHOULD be needed to determine the load bearing capacity of the box!


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## nealtw (Sep 24, 2015)

The galvinized steel plate is there to hold the post in placeand to seperate wood from concrete.

You said the rafters are cantilevered over the wall, perhaps the post are just decritive.
Is the beam under the roof that the posts are holding up?
Did you open an end one or one of the middle ones?
I have installed hundreds of posts, never a box, I have built posts out of 2x4s or 2x6s but they always get losts of nails so they become one with each other.
But like you said, they have been doing the job they were put there for so it is a good question.


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## 1HandyWoman (Sep 24, 2015)

"The galvinized steel plate is there to hold the post in placeand to seperate wood from concrete."

the bottom plate is made of aluminum not steel which by my understanding is a soft metal.  It is called an "Aluminum Plinth".  I found a similar one here at homedepot to show what it looks like - http://www.homedepot.com/catalog/pdfImages/0d/0d77a15d-4080-4e57-964b-45244fe21d77.pdf

the fact that the columns are standing on aluminum plates makes me think they can't be holding a whole lotta weight but that is just a guess.



"You said the rafters are cantilevered over the wall, perhaps the post are just decritive."

I think they are not decorative since they are holding up a beam made of 2 - 2x10 nailed together (the rafters are resting on this beam and the columns are holding up this beam).  So that looks structural to me.


"Is the beam under the roof that the posts are holding up? "  yes

"Did you open an end one or one of the middle ones?"  Both.  Over the years I have replace many individual boards on these columns because of rot.  I am done replacing individual boards and want the whole darn column replaced with something that will not keep rotting out ever couple years.


"I have installed hundreds of posts, never a box, "  I agree Its the damnedest thing I have ever seen also (I am in south carolina after all, they do crazy *** construction down here).  My 3 car carport was also supported by these stupid box columns and those columns on that structure were holding up some serious weight (until they rotted).  I replaced those columns with treated 6x6s and it hasn't fallen down yet! (crossing my fingers).


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## nealtw (Sep 24, 2015)

Replace them with 4x4 treated posts and wrap them in a post cover.
http://www.homedepot.com/p/Veranda-4-in-x-4-in-x-100-in-Vinyl-Post-Jacket-White-73002149/100029112
If you do change out the al. for galvinized. Al. does not work with treated lumber. That will solve the rot problem and be stronger thatt the box.


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## 1HandyWoman (Sep 24, 2015)

Nealtw

that is exactly what I want to do BUT how do you know it will be stronger than the box ???  THAT is what I have been trying to determine!!!


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## beachguy005 (Sep 24, 2015)

I don't believe that anyone ever calculated the loads on those existing post when they were built or installed.  If you look at porch columns for sale in stores, they are designed for that.  Use on porches to support the roof above it.
I think you're making this way too complicated.


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## nealtw (Sep 24, 2015)

1HandyWoman said:


> Nealtw
> 
> that is exactly what I want to do BUT how do you know it will be stronger than the box ???  THAT is what I have been trying to determine!!!



The load on your posts are minimal or they boxes would have just pulled apart and buckled under the load.

For years we installed 4x4 posts for porches like yours and they worked fine but lately those in power have said they need to be 6x6.. There is a calculator because once in a while some engineer will ask for 8x8s but we just do as we are told, never calculate anything. So just from experience I think a solid 4x4 or 2 2x4 nailed together would be stronger. We install huge beams inside some houses and most often ,two studs on each end.

Just look at the square inches or the end of your box 2x 1x6 and 2x 1x4.
Your posts have 20 sq inches as appossed to a 4x4 that has 16 square inches but your posts arn't nailed together in a way that would make them structural and they didn't over load when you had some rot. So I am sure.


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## bud16415 (Sep 24, 2015)

The fact that your roof and post have stood the test of time means they have a safety factor in the design of 1.00 or greater. That means they could just be strong enough and nothing more or they could be 50 times as strong as needed also. Reverse engineering is not the proper method and not one that will pass any building code. 

It would be much easier to count up the lengths and sizes of what is above and calculate the weight of what&#8217;s above and then do a column calculation of different size timbers and select one suitable for the job. I could explain how to calculate a complex box structure but it has many variables in it that need assigned numbers like method of attachments etc. in the end we would have to assume loads and try and back figure what safety factor we were needing and at some point we would need to know the weight of the roof anyway. 

Put in a 6x6 and wrap it in decorative finish of your choosing. You know a built up 6x6 box worked so a solid will work.


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## Snoonyb (Sep 27, 2015)

1HandyWoman said:


> Nealtw
> 
> that is exactly what I want to do BUT how do you know it will be stronger than the box ???  THAT is what I have been trying to determine!!!



Despite your supposition that the posts are load bering, they are more decorative than load bering, by your description.

The roof is supported at the wall and the 2x beam is a simple method of addressing the volume of the posts used, which have only the value of supporting the 2x beam, not the roof.

You say that you want a vinyl material, I presume for maintenance purposes.

OK, purchase a 6" sq. tubular vinyl post, which will accept a 4x4 post inside, which addresses both problems.

These are available from a vinyl fence vendor.


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## bud16415 (Sep 27, 2015)

I don&#8217;t know how it is done around the country or world, but around here old porch roofs are supported by these hollow columns. A lot of them are round and hollow and others are square as described. I have never seen them replaced without putting in temporary supports of some kind. We have had lots of them fail and they are load bearing  as the roof  or deck above will start coming down and if removed it will come down. This is a case where photos would help a lot as the description hasn&#8217;t been the best. The cost of putting in the largest post you can is going to be insignificant compared to labor or bringing in someone to figure it out.


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## Snoonyb (Sep 27, 2015)

bud16415 said:


> I dont know how it is done around the country or world, but around here old porch roofs are supported by these hollow columns. A lot of them are round and hollow and others are square as described. I have never seen them replaced without putting in temporary supports of some kind. We have had lots of them fail and they are load bearing  as the roof  or deck above will start coming down and if removed it will come down. This is a case where photos would help a lot as the description hasnt been the best. The cost of putting in the largest post you can is going to be insignificant compared to labor or bringing in someone to figure it out.



What's interesting to me is that she hasn't been asked the size of the rafters, their spacing, the roofing material, yet seems to think that the projection is insignificant.

Many municipalities have published on line details for wood patio covers that tell you the size of headers and the post spacing as well as the size and projection of the rafters.

None offer a hollow column as a support alternative.

Yet those are the only charts that I know of that would be generally available to fit her needs, of self determination.


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## beachguy005 (Sep 28, 2015)

I think the issue has been about the compression strength of the box column and finding an equal, not about using them.  The problem is that it's pretty much an irrelevant quest because the compression strength of wood, even pine, is such that you could support that roof with 1"x1" posts. 
Even a 4" turned colonial style post has sections that are only about 2" in diameter yet support large porch roofs even with 4 feet of snow and ice on top of them.


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## bud16415 (Sep 28, 2015)

It is only partly about the compression strength of wood. There are more complex calculations to be made concerning column strength. The length plays and important role as does the compression strength and also the section modules that is a function of the shape of the member. A pipe with a given cross section will be much stronger than a solid rod with the same cross sectional area for example. Metals are much more controllable and thus can be applied with a lesser margin of safety than wood. Wood has all kinds of imperfections in it and that&#8217;s why the manufactured beams are so much stronger it&#8217;s not that the wood is all that much better but the process controls the product so it is safe to use it closer to its yield point. 

For the OP to focus on such a singular goal in the question without trying to look at the larger picture kind of put me off to the question. Sometimes the world just doesn&#8217;t work the way we think it does and in those cases we need to refocus and come at a problem from a different direction.


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## beachguy005 (Sep 28, 2015)

It's not brain surgery.  There is no need to re-engineer it.  People...including us, have a tendency to make things too complicated.  It's usually because the simplest method just seems too simple.  
The OP said it was a small roof. While her intent to find the exact equivalent as a replacement is, to a degree, admirable, one should also be able to accept the fact that what was existing may not be correct or best.  Even if it's been working as applied for years.
Anyone can post here that there are 100s of calculations that go into determining a support column, but for a small porch roof, anything over a 4"x4" post is more than you probably need.


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## bud16415 (Sep 28, 2015)

That was my comment in post 13. They had a 6x6 built up post , for the cost of all that pine you could buy a 6x6 PT post and it will be the right size and will surely be strong enough. Paint it, cover it, or leave it raw. 

The first half of the thread was about the OP insisting on information on how to calculate a column. Someone else might stumble on this thread that really does need to figure this out and I was just pointing out that a 1x1x 10&#8217; long was not going to hold a roof up even if it did have a high enough compressive stress number for the type of wood.


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## beachguy005 (Sep 28, 2015)

Depends on the bending strength of the wood and the weight of the roof.  I've propped up a roof with a piece of 3/4 strapping and I've had a house raised without supporting the porch roof at all and it wasn't an issue.


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## bud16415 (Sep 28, 2015)

beachguy005 said:


> Depends on the bending strength of the wood and the weight of the roof.  I've propped up a roof with a piece of 3/4 strapping and I've had a house raised without supporting the porch roof at all and it wasn't an issue.



Thats also a good way to Raze a house.


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