Floor rim bolted to set in concrete wooden piers

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Old 08-25-12, 09:07 PM
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Floor rim bolted to set in concrete wooden piers

Hello, I've been "selected" to build my wife a studio with 16'x16' dimensions. The idea is that I set 4x6 timbers into concrete into hard clay with a footing plate 16"x16" at the bottom of the hole and the rest of the hole then filled with concrete to set the 4x6's. Two questions: 1) I am using (2) 2x8's 16' bolted together to create a 4x8 16' for each of the four sides floor rim. 2x6 8' approx length joists will be hung at 16" o.c. to the floor rim and a 4x8 16' beam down the center of the floor rim. Is this strong enough to support 2x4 walls and 2x6 rafters at 16" and 24" on center respectively (as well as a couple of people, windows, drywall, insulation, etc.?
Question 2: What does my pier spacing need to be for 16 foot sides? I was thinking of using grade 8 bolts to fasten the sistered 4x8's 16' to the 4x6 set posts. Is 8 feet too far apart for a sistered 4x8 16' rim and rest of the building? Preliminary plan is 9 36" deep holes for the concrete and PT 4x6's with 3" concrete footings 16"x16" with concrete filling and setting the PT treated for the rest of the hole.

To sum up: Will (2)2x8's 16' long bolted to 3 piers each side and down center at 8' intervals be strong enough to support a glorified shed with 2x6 floor joists.
 
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Old 08-26-12, 04:34 AM
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Welcome to the forums! OK, permit time. Be sure to ask the building people these same questions so you will have local issues solved beforehand. Is this studio to be wired? Heated/cooled, water supply/drain system??
Need this out of the way before you pour your footing. No wood sunk in concrete. All wood attached to top of concrete, whether it be sonotubes, or continuous footing. Will there be a crawl space below? How high will this be off the ground? How far apart do you plan on your posts? That will determine the lumber size to use for the rim. I would probably go every 4' with the posts and bolt the rim to them using HDG bolts. Grade 8 would be overkill and doubt you will find them in HDG.
 
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Old 08-26-12, 11:10 AM
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Per Building inspector our county is based on the IRC code so no structures can be set on top of piers. He did make it clear that setting PT posts into concrete was OK. All floor joists and rim boards also will be PT as the floor will range from 6" to 18" off the ground with a heat reflective foil for a vapor barrier beneath the subfloor. My big questions are: How many piers will I need and at what spacing; Will sistered 2x8's bolted and 16d nailed together provide enough support? (I found out 2x8's sistered provide 318 lbs per linear foot of support which adds up to 5088 lbs per wall) Our building inspector referred me the IRC code for Indiana and I found it an absolute mess to read with no glossary and no index piled on with every single revision, amendment and retraction making it a nightmare of a reading job--and I test at a 22nd grade reading level!
 
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Old 08-26-12, 06:22 PM
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Well, I only got to the 16th grade, so you got me there If you set PT posts in concrete what will you have? Piers. If he is OK with wood in contact with ground/concrete, and you don't mind it rotting out, he rules. I would put my vertical support at 4', giving you 4 per side or a total of 14. Sistered 2x8 bolted to your vertical suppports will give adequate support, and spacing your joists at 16"oc with joist hangers will work. NOW to your center supports. Unless you have "piers" or posts and beams you can't span 16', and it the inspector won't allow piers, then whatcha gonna do?
 
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Old 09-13-12, 06:40 PM
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Question

Code does not allow buildings to be on top of piers though you can bolt into piers from the side per the inspector. Also, PT treated lumber is what is being used for the piers and I've been told that this is OK, though I am hearing from some places that means diddle. Pole buildings use PT poles set in concrete as do decks. A contractor friend of mine swears you can not do this while another contractor friend tells me to make sure I don't hire the other guy if he doesn't understand the utility of PT lumber re ground and concrete contact. Thanks for answering my question on the 2x8's sistered and pier spacing. The information available to me, quite sparse mind you, confirms that sistered 2x8's at 16' supports 337#/linear foot and ups that to 1100 @ 4' spacing. Next question: can I put fiberglass insulation beneath the floor kraft side up and not have to worry about moisture issues or would it just be better to use Reflectix refelective foil insulation between the floor joists and create a thermal gap of a couple of inches?
 
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Old 09-27-12, 07:44 PM
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poles set in concrete as do decks
Nope. But since you aren't building a deck I won't go into it.

Insulation will be installed with the kraft facing the warm area (up) with metal "stay" rods. To ensure you don't have a depleting supply of fiberglas from squirrels and other rodentia making it into their homes, I would cover it with 3/8" plywood and framing over the seams and outer parts with 1x3 lumber.
 
 

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