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Krupp17
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# Posted: 5 Dec 2019 10:59am
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Howdy, new member, long time lurker learner here, thanks for some great info.
I am building a 30x30 cottage in southeast Oklahoma, Plan on constructing pier and beam foundation. Question is: reference to the built up beams, is it preferable to use built up beams all around perimeter of foundation? (all four sides) In other words, I have seen images of pier and beam construction where the beams only run parallel and I have seen where the beams are forming a square. Please see attached crude image. What are the advantages of the beams running parallel vs. running them all around perimeter. ? thanks for any help here.
Krupp
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Peewee86
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# Posted: 5 Dec 2019 11:45am
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I’m not an architect but this is my internet opinion. 
You have a square floor plan. Do you plan to use a hip roof so all four of the walls are load-bearing from the roof? If so, then I would think you would want the built up beams to be all the way around the perimeter.
Many of the designs that have beams going only one direction are using a gable roof with the roof line parallel to the foundation beams and perpendicular to the floor joists. Other than cost I don’t believe there’s any negative to running to running the beams all the way around the perimeter. -PeeWee
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Princelake
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# Posted: 5 Dec 2019 12:35pm
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Peewee is correct but I'd think you'd need atleast a beam in the center to support the floor joists
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snobdds
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# Posted: 5 Dec 2019 01:08pm
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Peewee is correct. A lot will be determined on how you build your roof.
I have a gable roof and only needed built up beams on the non gable ends. I also put a built up beam in the center.
If hip roof, all sides need built up beams.
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Krupp17
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# Posted: 5 Dec 2019 01:12pm
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Excellent replies, thank you. Yes, I failed to draw the support beams in center for the Joists. No hip roofs. Just a simple rafter or trussed roof. Good info about the gable ends. And you answered another question I had, reference the perpendicularity of the floor joists.
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Brettny
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# Posted: 5 Dec 2019 01:46pm - Edited by: Brettny
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Personally I like the second d pic better. Beams under the floor joists don't rely on hangers. Also if the beams are under the floor joists you can and prob should pull the beams in about 1' from the edge of the building. This helps protect them and makes your span shorter.
In your case being 30' wide you may need 4 beams. I would also price out engineered floor joists/trusses.
You should also notch the vertical posts to accept a good part of the beams.
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Krupp17
Member
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# Posted: 5 Dec 2019 04:26pm
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Brettny, Thank you ! wow, I hadn't considered floor joists, i-joists in particular and now that I'm looking at them, I am liking the idea.
BTW, I'm pouring concrete piers and pads using sonotubes and Squarefoot forms. And I'm not sure what I'll use to secure the built up beams to the concrete piers. some of the simpson products seem rather pricey. I was thinking of setting two heavy gauge galvinized straps into the concrete when pouring, and maybe a enough galvy sheet metal underneath the beam? And thoughts on that>? thanks again.
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ICC
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# Posted: 5 Dec 2019 06:43pm - Edited by: ICC
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What is your frost depth where the build will be? Frost depth in SE OK may not be all that deep. A rototiller can be used in many soil types to dig and loosen dirt easily enough to enable the pouring of a full perimeter footing. A footing only has to be 12" deep if the frost depth is that or less. Concrete blocks can be set and a short stem wall built. Then you can do I-joists or floor trusses, one piece side to side with no center beams. Plus you end up with a more solid foundation, one that can be built to meet codes.
Then you use a PT mudsill and install the joists or trusses on that. Use the applicable rim joist and sheath the floor with Advantec paanels.
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Krupp17
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# Posted: 5 Dec 2019 07:43pm
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Frost depth is 18" . The clay soil is more expansive than a full perimeter footing could support , I fear. Most of the small cabins/cottages built nearby are done on pier and beam with a good sized bell shaped pad. I did a precursory soil investigation using online resources. Carnasaw-Octavia-Pirum is what it's geologic name is. Not really suitable for full slabs or perimeter footing. With the pier and pad foundation, I assume i could shim the structure more easily if it needs it someday.
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Peewee86
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# Posted: 5 Dec 2019 09:10pm
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Krupp- As I pondered your post earlier today two thoughts come to mind. First, you are working with dimensions of 30 x 30. (900 ft.²). Unless there is something special about that size, switching to 28 x 32 (896 ft.²) would probably be much more cost-effective. Your exterior dimensions would be a multiple of four. There will be less lumber waste. Flooring trusses at 28 feet will be cheaper. Many times dimensional lumber is not available longer than 28’.
Second, I-joists are generally used for the flooring of upper floors. They will not survive moisture like dimensional lumber will. I’m not only think about possible flooding but even the elevated humidity from the morning dew at ground level. Clay soils hold moisture. Be cautious in using I-joists at or near the ground level. I don’t believe there is a such thing as green treated I-joists. -PeeWee
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Brettny
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# Posted: 6 Dec 2019 08:26am
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I you will have to read up on the install requirements of I joists. Moisture shouldn't really be a problem if you insulate to the bottom of them and vent the area under.
With out knowing the framing layout of a 30x30 you really can't say 28x32 will be any easier to build. In a 30x30 building you may not need lumber longer than 16'. There are a lot of people stuck on a 16x?? Building because they think they need lumber to go the full width. It's just not always true.
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Aklogcabin
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# Posted: 6 Dec 2019 10:10am
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The manufactured joist or I beam are made with waterproof glue. I would refer to the manufacturer but I believe that they would be fine . I used TJI made by Boise cascade I think. Been a few years.
You should place your support beams under your load bearing walls. Do not cantilever your walls out over your support beams. Your floor joist ends and rim joist should both sit on your beam. You have overhang on your roof to protect your building. On our cabin I have 3 feet .
I used 16’ long x almost 12†tall manufactured joist on our cabin. Sat across 3 ea. 4 x 12 beams I got from local sawmill. The cabin size is 16’ x 24’. They have been there for 5 or 6 years now and look brand new.
I used 30’ long x 16†tall for roof joists in my garage to span 24’ with 2 feet overhang on ends.
I have had no movement in my foundation. I used cedar , treated telephone poles I got that were removed from a power line company. I was able to put posts in then level and cut off was chain saw. Then cut a shoulder on post for the 4x12 to sit on . Bolted together with 1/2†galvanized bolts.
Good luck on your build.
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Brettny
Member
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# Posted: 6 Dec 2019 12:04pm - Edited by: Brettny
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Overhangs don't protect from driven rain and even in a slight wind your rim board area will get wet.
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ICC
Member
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# Posted: 6 Dec 2019 02:21pm
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FWIW, as I know there are people who who don't give codes a second thought, the IRC allows a cantilever amount equal to the height of the floor joist without any engineering. So if one uses 2x12 floor joists the cantilever can be equal to the height of 11.25 inches (the actual measurement, though inspectors around me allow a full 12 inches). There are sound engineering facts behind that limit.
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