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FatherofTime
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# Posted: 21 Feb 2022 16:39
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Hi all,
I am building a 16x24 cabin, with a loft, and I need help with the layout of my footers. I am planning on using 2x12' floor joists that should span the 16'. On the 16' side of the building (gable end,) I was planning on having 1 footer in the middle at the 8' point. My ceiling is going to be supported by a ridge beam and that weight will be placed on this footer, on each side.
On my 24' side, I could do the same, with roughly 8' footers OC. This would be 10 altogether for the whole building.
I am planning on having treated 6x6 posts tied into the concrete footers.
Will the 8' spacing work? Or should I go down to 5-6'? My understanding is that it depends on the load of the building and the width of the footer. It is extremely hard for me to find this info online, so hopefully this will help a lot of future cabin builders. My question is: how does one calculate the # and distance between footers?
More info:
In VA we sometimes get a lot of snow. Once or twice a year, we will get between 6" and 2' in extreme cases. I calculated that if there was a foot of wet snow (highly unlikely) on the roof, there would be 20,000lbs of live load that would be split between the ridge beam (50%?) and the 24' walls (25% each?). That amount of load blows away the dead load.
The building has to pass code.
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happilyretired
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# Posted: 21 Feb 2022 17:50 - Edited by: happilyretired
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My opinion has always been that it never hurts to exceed code for structure. After all, code is really "minimum allowed". Look it up for your area and go slightly stronger. If it says 8' then I would space them 6', the additional cost is negligible.
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ICC
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# Posted: 21 Feb 2022 18:22 - Edited by: ICC
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Quoting: FatherofTime The building has to pass code.
If that is the case, it will be a full perimeter foundation, would it not? Or the two 24 ft sides at least would be continuous strips, probably 12" wide x 6" thick at frost depth. VA uses the 2018 IRC.
IRC does not allow piers for habitable buildings unless the plans are stamped by a state-licensed engineer.
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ICC
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# Posted: 21 Feb 2022 18:29 - Edited by: ICC
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Footer width depends on the soil load-bearing capability as well as the design load.
The ground snow load for the area you will build in should be available from the county or state. That is what would be used for design work. You can always go better for more peace of mind.
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Brettny
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# Posted: 22 Feb 2022 11:26
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Why use 12ft joists to span 16ft? Just get 16ft lumber for the floor joists. Use 12' for the girter in the 24' direction. If you want to get a bit more fancy get a few 24' for the girters.
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FatherofTime
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# Posted: 22 Feb 2022 11:38
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I meant 2"x12"x16'***
@brett To clarify, you're advising me to run my boards 24' longways (from gable end to gable end) across the building instead of 16' from side to side? I wasn't planning on putting footers in the center of the building, just the perimeter
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BRADISH
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# Posted: 22 Feb 2022 12:31
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Quoting: FatherofTime @brett To clarify, you're advising me to run my boards 24' longways (from gable end to gable end) across the building instead of 16' from side to side? I wasn't planning on putting footers in the center of the building, just the perimeter
To interject here - I think he is just saying to use 12' boards to split the 24' 'Beam' run in half. Then stack your 16' joists on those (perpendicular).
I would not recommend running 24' joists. I had to on mine due to some other constrictions and am now having to go back and beef them up.
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FatherofTime
Member
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# Posted: 22 Feb 2022 12:55
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Okay so then he is saying to put one footer in the very center of the building. A girder would then be built on top of that with 12' boards to support the center of the floor.
I'm not planning on running joists along the building lengthwise. I am planning on running 16' joists from side to side. I am running a 24' ridge beam for the cathedral roof, which I mentioned because of the increased weight on the gable end footers, which I was planning on spacing 8' apart. 2 on the corners and 1 in between on the 16' side.
Basically, I am trying to calculate how far apart my footers should be. It doesn't seem practical to have five in the 16' span. Simply cannot find the answer to that question. Soil is rocky, with sand and clay. It's on top of a ridge and the ground percs. Perhaps there's a cheatsheet people use to help plan their footer layout?
Building has to pass code as an ag building. Thank you guys.
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BRADISH
Member
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# Posted: 22 Feb 2022 14:56
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I think we are all saying the same thing, but it's getting lost in verbiage.
From my non-engineering brain, I think you would be very safe to space your footers at 8 ft based on using 2"*12" lumber as floor joists.
Personally I used an engineered product, but the span values are similar in many applications. I used an I-joist similar to the BCI (different brand, same dimensions available locally). BCI makes a very handy and mostly easy to read (lots of pictures!) Western Specifier Guide that gives spans values/ratings which is what I based my build off of. Conversely, if you are in the eastern side of North America, they make a Eastern Specifier guide.
Here is a link to the Western Guide as it is what I am familiar with: (Google search will provide the Eastern Guide)
https://www.bc.com/wp-content/uploads/2018/09/W-spec-guide-BCI-and-VL.pdf
For my main floor, I was very set on meeting their 4 Star deflection rating as I wanted it to be sturdy and comfortable. We visit many friends cabins that are very bouncy/reactive and I loathe the experience.
For my upstairs floor - which is strictly bedrooms - I barely met their 3 star span calcs. But I was willing to accept that being that its just sleeping space and that the 3-star is generally accepted building practice. My building constrictions led me here as well (didn't want to mess with a beam supporting the second floor).
So for your build, I think you would be very satisfactory to have a total of 3 appropriately sized footers along the 16ft spans, and a total of 4 appropriately sized footers along the 24ft foot span. This would be a total of 12 footers for the building.
That design would not lend itself to splitting the 24 foot girder span into 12 foot pieces, however there is certainly tradeoffs to adding additional footers. Having 5 footers along the 24' wall certainly seems like overkill to me, and doesn't add a ton of value in deflection terms.
Personally I would go with 12 total footers, and sister 16' boards to make your girders that would then support your floor joists.
But again, I caution that I am no engineer and have no building codes to meet where I am located. I hope this helps.
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Brettny
Member
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# Posted: 23 Feb 2022 08:43
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Quoting: FatherofTime I'm not planning on running joists along the building lengthwise. I am planning on running 16' joists from side to side. I am running a 24' ridge beam for the cathedral roof, which I mentioned because of the increased weight on the gable end footers, which I was planning on spacing 8' apart. 2 on the corners and 1 in between on the 16' side.
Can you draw this out?
You dont want to use girters (basically like shed skids but bigger) and want to use a ridge beam?
A ridge beam needs to have a footing/block under it for support all the way to the ground. The best way to accomplish this is with 3 girders. Since the building is on blocks you more than likely will need to relevel it at some point unless a hell of alot of site prep is done or your on bed rock. If you skip the ridge beam and do 2 girders it will make releveling alot easier.
Also to board length. Buy the longest they sell to not have any joints in the run you need. For the 16ft width get 16ft boards. For 24ft girders get 24ft boards. The cost savings in splitting up a 24ft run with say 8ft and 16ft board is very very minimal and you need s block under each joint.
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spencerin
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# Posted: 25 Feb 2022 00:30 - Edited by: spencerin
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I did some research and couldn't find anything specific, either. Just that things like soil/ground composition and structure design were factors, which was already mentioned.
I was in your shoes 3 years ago. I didn't have to worry about meeting code, but I wanted to make sure the structure was still sound in this regards. My piers are 8' apart, and I went with two 2x10s married together for the rim joist. I found tables that showed how much weight a vertical 2 by ? could handle over an 8' span and estimated how much weight would be on that span, and that's how I arrived at what I did. I probably went overkill.....
But, since you have to pass ag code, why don't you call some ag structure builders in the area for their opinion? If you have to meet ag code, they probably have to meet ag code and so should know.
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