DIY Foundation Advice

[TexasRedNeck]

I know some of you may be more experienced in construction than me.

I'm wanting to build a 16x24 wood framed building on my weekend place to use inititally as a dedicated reloading/gun smithing room.  I want to build it well so that later, if I decide to convert it to a Casita ( mexican word for little house) with an efficiency kitchen and bath with a loft for guests, I can.

For that reason I want to make sure I build a decent foundation.  I've been researching on the webz and can't quite decide how to go.

I don't want a slab - makes adding plumbing later too hard and any settling would require too much work.

Looking for design help.

I thought about 3 glue lam beams the long way on 4x6 treated posts sunk in concrete, with a 2x6x16 footers over the top leaving 8ft span, which could be on 24 inch centers to give me 20psf load rating for #2 yellow pine.  I would then use 1 1/4 subfloor plywood.

Keep in mind this is South Texas so there is no freeze/thaw concern with depth of footings.

1.  Is this a good plan?  If so, what size glu lam and spacing on the footings for a 24ft beam to support this building.
2. Is there a simpler cheaper way to acheive the same result?

The building will have either 10 or 12 ft stud walls, 6/12 pitch roof.  Metal roof and hardiplank finish with a loft area in the back 8 ft of the building.

[Dawg25385]

How bout concrete footing and blocks around the perimeter, then run a beam down the middle on posts And instead of 16' joists, just do 8's since they'll terminate at the beam anyway


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[TexasRedNeck]

Thought about that.  That's the way houses are built.  I'm not sure I like laying concrete block that much.  Never was much of a mason.

[Dawg25385]

Then do columns of concrete piers, with steel beam saddles set in them (or bug all thread so you can tweak height). You can get those cardboard "form" tubes. Then 3 main beams, with beams saddled on the long ends to tie into the 3 long beams, obviously with one down the center. Then 2x8x8 or 2x6x8 joists in between with joist hangers (depending on how strong you need), to achieve flush top to sheet over with your TG plywood subfloor. You can clad the perimeter with fascia or tin or something to protect from weather when siding.

I would prefer closer OC with smaller lumber, via bigger OC and larger lumber, that's just me tho. I.e. 16" OC with 2x6 vs 24" OC with 2x8, but again that's just me. More joists and more hangers, vs marginally more expensive 2x8s... Again, just how my brain works.

Btw, I assume this is off grid style. I'm not a contractor obviously lol


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[Dawg25385]

Edit: 2x6 is prob too small to span 8' even with smaller OC... Dunno


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[Wilbur]

I am no engineer so won't pretend to know the psf ratings but I have worked a lot of construction and built a lot over the years. I think you CAN use 2x6's but they will be more springy on the floor than 2x8's. And standard would be 16 oc not 24. I agree with the sonotube for the footings. They are easy and work well.

http://www.homedepot.com/p/SAKRETE-10-in-x-48-in-Concrete-Form-Tube-65470006/100350260

One question though before you go there though....does it make a difference in your area if you have footings versus putting this on some concrete block from a tax perspective? A lot of places if you just put it on blocks it is not a permanent structure so you are either not taxed or taxed very differently. If you use footings etc. then it becomes permanent and adds to the tax rolls. While you use it as a gun shed no real worries if it moves slightly etc. Its only when you decide to plumb it would you need the structure to be mounted more permanent and then you could pour the footings, etc. And even if you wanted it on the same spot you could make "rollers" of logs.....roll it off to one side, pour the footings and then roll it back on.

But assuming you have a well drained area you can put the cinderblocks down and then build your 2x8 frame on top of that. If you really wanted to save construction costs you could make two 8x24 sections bolted/framed together. Then you are buying 8' 2x8's as opposed to 16' 2x8's.

If the site is not that well drained I would start with a frame of Pressure Treated 2x8 or 2x10 in something like an 18 x 26 shape. Then fill that with gravel, peastone etc. for drainage then put your cinderblocks down and build the frame on it. While there are no freeze thaw issues you don't want a hard rain washing away dirt for the cinderblocks and then causing your shed to shift.

And you can do either 2x6 or 2x4 stud walls. Although if you are putting in a "loft" that may become a bedroom at some point it might make more sense to do 2x6 walls. Or at least 2x6 walls on that "half" of the structure. Especially if you are storing lots of sardine cans up there.  ;) 

[rasimmo]

Edit: 2x6 is prob too small to span 8' even with smaller OC... Dunno


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Good rule of thumb is span 1.5 x thickness on floor joists and 2x thickness on rafters. That's assuming 16" OC. Using that 2x6 would be good up to 9' and 2x8 up to 12' for floor joists.

[Dawg25385]

Edit: 2x6 is prob too small to span 8' even with smaller OC... Dunno


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Good rule of thumb is span 1.5 x thickness on floor joists and 2x thickness on rafters. That's assuming 16" OC. Using that 2x6 would be good up to 9' and 2x8 up to 12' for floor joists.

Great to know!


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[Dawg25385]

Kind of like this Charles


Looking mainly at the beams and piers


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[TexasRedNeck]

Thanks guys.  Here's the table I've been referencing http://www.awc.org/Publications/update/WFCM2001FullPage.pdf



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[KensAuto]

x3 on the concrete tubes. Super strong, pretty easy with a post hole digger. Setting the brackets/allthread  in the right spots is a bit important but not hard. A laser makes it a bit easier. You can tint the concrete to blend with the surroundings (because I know how picky you are)....and like Kyle said (?) you can chop up the subfloor into smaller sections by adding more columns, allowing you to use 'smaller' wood. If you did it right, glue lam wouldn't be needed.

[TexasRedNeck]

Thanks Ken. I guess I need to price the lumber to decide. The glue lam I saw didn't seem that cost prohibitive but I have to weigh the cost of footings to the extra expense of glu lam. Glu lam means fewer footings.  With 16 feet I don't want to try to clear span that distance. The lumber costs and load on the outside perimeter would be huge. Most of the weight would be on the outside long walls anyway. The center support would carry a lot of the live floor load.


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[Flyin6]

I'm late to the game here...been reading this since inception

RN one thing I would add to the opinions is not to sink any treated posts directly in concrete if you can do otherwise. Concrete reacts with the concrete, blah, blah, blah...

Sonotubes with a bolt and fixture to fasten to the base of the 6X6 tube (And make sure the base of the 6X6 has drainage), is a lifetime support system