Pier and Beam Foundation - Strong Enough?

[Kodakjello]

Hey Everyone,

Well, it's been a while but I've finally managed to get my butt in gear and the building inspector is reviewing the plans as we speak. However, I now have some doubts about the Beam foundation. I've modified the beam to be 8x12 built-up from 4 Pressure Treated 2x12's and 1/2" Pressure Treated plywood in between each 2x12. The beam will sit in CB88 brackets from Simpson StrongTie which in turn will sit on 12" concrete piers.




My plans call for a wrap-around porch on all three sides and a deck on the fouth side, so the beam will be at least 8 feet from "the elements" and a minimum of 30" above the ground. My question is are, How long can I expect this beam to last? Will it last as long as a standard concrete foundation?

I mean, while the beams are covered and protected from direct moisture, and I will seal them with a breathable latex sealant, they are still exposed to the outside air. The house will be skirted with metal mesh and lattice but nothing will stop the wind from blowing beneath the house.

My father, who has been in the construction business forever, has planted a few seeds of doubt as to the longevity/solidity of the beam foundation I have described.

Any help would be greatly appreciated!!! Thanks,

Shaun

[bartholomew]

I would think a PT beam should last as long as the house provided you don't let moisture build up below. Keeping the crawlspace area well-ventilated and sloping the ground so water drains away from the house should prevent that. And if the beam doesn't last as long as expected, it's not all that difficult to replace as long as your joists sit on top of the beam rather that hanging off the side. My question is, why did you decide to use a sandwich with plywood rather than 4 2x12s?

[Kodakjello]

To answer your question, I have actually decided to use 4 2x12s AND sandwich plywood in between each 2x12 to increase the beam's strength. The beefy brackets are 7 1/2" wide so 4 2x12 and three 1/2" plywood should fill it perfectly. I was just hoping someone with experience using the beam foundation could speak to its performance in the field.

As for replacing the beam...that's the problem. I have the joists hanging off the side of the beam because I'm using TJI360 14" deep joists. I guess I could have them placed on top. I just thought it would be easier and more secure to hang them from the beam rather than nail them down onto the beam.

Any suggestions?

Thanks again!

Shaun

[PEG688]

Shawn what size beam did John spec.? To me your MTL wasting money with this bigger beam , if  4 x12 is big enought a 8x 12 isn't neccesally better just bigger.

 Your post would be the issue if rot is your concern , unless your setting your post brackets right on the money and will have no post.

The TJI's would be of more concern to me solid wood kept dry and vented as you described should be fine .

If it was me , I'd set my beams in and under at least 12" and put a rim joist on the end of those joist , hung TJI's can be squeakie as heck , especally the top flange type hangers . You'll also have issues if your beam is treated ACQ lumber , no "I" joist hangers are made in ZMAXto my knowledge , so you'll have to Vycor wrap the beam where the hanger goes another PITB that could be avoided by setting the joist on top of the beam.

So in closing I'd not worry about the beam /post use treated ACQ lumber , ZMAX hardware or stainless , make sure the crawler stay's well vented and you should have no problems for 50  years or more . Settling of posts might occur if the footing are not done right , IE under sized ,not deep enought to get to solid ground , poor concrete mixing if done on site .

There are many other variables but those are general issues .

G/L PEG  

[PEG688]

Another issue you'll might run into if you put the beam right under the exterior walls will be any plumbing / wiring ,etc  that might need to go down thru that beam/space . If you have no wiring or plumbing , no problems .

[Kodakjello]

Thanks for the feedback PEG. John has spec'ed out the beam as built-up from 3 2x12's but I figured adding another 2x12 would only cost me another $200 and would give me some extra protection.

The comments about squeaky top-flange hung I-Joists are news to me ...I'm starting to seriously lean towards placing the I-Joists on top of the beam rather than hanging them from the side :-/. It's a good point that the plumbing and electrical would be much easier to route if the joists were on top of the beam.

As for the piers, I'm leaning towards 12" sonotubes with bigfoot footings. Do you guys have any experience with these?

Also, has anyone sealed their beam with any type of latex or acrylic sealant? Would this be a good thing or bad thing? I'm thinking that it would keep water for getting in but does that mean it woudl also keep moisture from escaping to prevent rot?

Thanks!

[glenn kangiser]

If you have water getting into that beam, the rest of your house will already be gone.  Wood in the air doesn't have much problem if it has proper ventilation- it can last hundreds of years.

When wood has a problem is when untreated wood touches the ground - fungus starts - sends out tendrils into the soil to collect and bring in water to break down the wood ( can be as little as a few months).  Termites love the damp wood so come in and lunch out.

[Kodakjello]

So what I'm hearing is that as long as the beam isn't in contact with the ground, and doesn't get directly rained on or get wet for long periods of time, it is permanent. That's a big relief   because I've never dealt with Pressure Treated wood before!

[John Raabe]

The bigfoot would make a great footing/pier. Your foundation beams should easily outlast the lifetime of the building itself.

Putting the joists on top of the beams makes for better insulation and avoids the sticky problem of having a plumbing waste stack coming down the wall and having to dive under the floor. The downside is that the floor is higher off the ground.

[Kodakjello]

Your comments have settled the discussion I'll go ahead with the beam foundation and place the joists above the beam. I'm also going to start up a thread in the owner-builder section to give everyone a look at what we're up to  8-)

Thanks John!