Main beam construction question...

NM_Shooter · April 13, 2009, 02:24:35 PM

(Note to self.. don't hit page refresh before posting

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Okay.. I know I have only been back one day and I am already asking for help. Go figure.

I am interested in pre-cutting my boards for my main beams. I am doing a triple 2x10 with 1/2" spacers, nailed and liberal amounts of construction glue. BTW... length of cabin = 20'

See pier locations dwg below, obv. not to scale. Spacing (inches) would have been more uniform if the I had not been working with rocks and under the influence of nasty weather and beer. I'm just glad the piers are all in a line and pretty much on level. It is what it is

I'm trying to figure out the best way to cut the boards such that I get best structural integrity. I think the blue cut diagram is probably best, but I'd like your input.

I'm going to cut these a bit long for the ends, and trim off after squaring up the floor joists.

What should I use for the 1/2 spacer material? OSB or plywood? Do the 1/2" spacer joints need to be staggered too?

Thanks for any suggestions, jeers, encouragement. Whatever. I like it all!

MountainDon · April 13, 2009, 02:52:23 PM

The spacing is all over the place, Frank! Tsk, tsk. How untidy!

I never told you when you were up at the cabin but mine are a little off as well.

Your diagram looks fine to me. I also cut the ends a little long and then trimmed them off once everything was nailed together and secured to the piers. I built them on the piers with the aid of several bar clamps.

If you're going to glue something like this I prefer a glue that will be able to be compressed more easily than construction adhesive. Personally I like the polyurethanes and the Resorcinol two part glues. Both will squeeze out the excess when the planks are nailed together and produce a nice tight strong joint. The polyurethanes tend to be messier to clean up as the overflow is very sticky.

If there's any danger of the beam getting wet I would use plywood, not OSB. Getting wet up there is probably a given. Or do like I did and forgo the spacers altogether. I did 4 layers; of course I was fastening to true 6x6 rough posts and that worked out dimensionally for me.

Full length plywood spacers may impart some additional stiffness but the bulk of the strength is coming from the 2x10 material. So the spacers really more or less just add material to get to a 5.5" width. I do have an odd ball idea. I have wondered about nailing/gluing the three layers of 2x10 together and then using small plywood scabs on the outside where the metal hardware will fasten.

April 13, 2009, 03:26:57 PM

I dont see the point of adding the spacer, I always assumed it was for making the header or beam a certain width. But with beam to post connecters the beam doesnt need to be the same width as your post. I think it might be overkill.

Redoverfarm · April 13, 2009, 03:36:12 PM

OK Frank this is my $.02 worth since Don gave you a dollars worth. I would alternate the splices to opposite ends rather than them all falling at one end. If it is going to give then let it be uniform throughout.

If my memory is correct for beam lamination the experts say OSB but a lot is done with ply. Oriented
Strand Board is suppose to be superior to regular lumber when stood on it's edge like this application. On the horizontal not as much. I think it is suppose to unify the two lumber portions as one when adhered together.

The glue I would say Poly glue. But pick you up a can of acetone as it is the only thing to remove it from your skin. Better yet a pair of disposable gloves. If not it will just have to wear off sort of like walnut haul stain. Ask me how I know this.

. In fact the manufacturer of Advantex recommends Poly glue vs. construction adhesive. I recently put 1/2 ply on the cabin kitchen floor as a basis for cement board (tile). It took me two days and where I had dry fitted the next days pieces it had adhered to the edges from the previous day and I had to pry to remove. Good stuff, messy but good IMO.

ScottA · April 13, 2009, 03:46:25 PM

I'd skip the glue and the spacers. How much are you trying to hold up? I'd put 2 rows of 20 penny nails about 1 1/2: from the top and bottom spaced about 16" apart. That's how I did mine and it worked fine. So long as the spices fall over a pier you should be good.

April 13, 2009, 05:47:08 PM

Frank, you've got the metal pier to beam bases installed in the concrete already, yes? That's why I suggested scabs. Maybe I'm wrong.

OldDog · April 13, 2009, 06:25:32 PM

as usual, I would glue it and screw it!

the spacers are up to you.

MountainDon · April 13, 2009, 06:50:03 PM

No screws for this, IMO.

Screws shear off much more easily than common nails.

Maybe, that's just me.

NM_Shooter · April 13, 2009, 07:21:27 PM

I have the Simpson clips already poured into the tops of the piers. They are 6" wide if I remember right. For some reason I have a gut feel that the ply or OSB actually will increase the stiffness a bit. But I guess with a span of about 6' between adjacent piers, stiffness will not be a problem.

Thanks for the replies!

-f-

July 06, 2009, 07:14:29 PM

I'm heading out tomorrow night to buy material for the beams. Heading up to BLOK Ranch for building this weekend with my youngest daughter, who will probably be fishing more than she works.

As usual, I am struggling with a decision.

I'm not sure whether or not to buy PT wood for this. Low side of the beams will only be about 16" above grade. It increases pretty quick after that.

1) If I go with PT wood, my simpson clips are not the hot dip galvanized type, so I'll need some sort of isolation from the wood. I could use tar paper or some heavy plastic to achieve this. I also thought about using stainless flashing for the isolation between beam and clip, but am concerned about any sort of galvanic reaction because of dissimilar metals.

Do critters eat tar paper at all?
How well does glue stick to the PT wood? Most of what I see here is very, very wet.

2) If I go with non-PT wood, fasteners / contact issues go away. Glue probably sticks better too. Am I setting myself up for rot issues on the low end of the beam? Also worried about porcupines gnawing on the non-PT wood. Should probably wrap them in shop cloth. Also, they will get rained on. Probably should wrap them in heavy plastic sheets until floor is built.

Comments appreciated!

rwanders · July 06, 2009, 07:38:45 PM

1) If you choose PT, I would use a double layer of tar paper for isolation at pier.

2) I don't think porqupines will chew on sawn beams (unless you salt them)----they chew on trees/branches for the layers just under the bark. Rain will not harm your beams after they are placed unless it is going to be a LONG time before you lay your joists and subfloor. I vote for OSB and poly glue----but why not just use 6x10 timbers? Actually for 6' spans I believe 4x10s would have been sufficient but, too late for that now

I have a bias in favor of PT for all foundation wood though the usual dividing line is said to be within 12" of the ground.

Don_P · July 06, 2009, 09:15:25 PM

Stainless and galvy is a no-no, I'd opt for something like flashing tape or something totally impervious over tarpaper if you wrap the connector. So my bias is showing, I'd use treated. 12" or closer to grade is the breakline for girders 18" for joists requiring treated. The glue and filler don't make enough of a difference in my book to avoid the treated. If you use untreated I'd find some kind of nasty unappetizing stain so they'd at least get heartburn.

NM_Shooter · July 06, 2009, 10:44:46 PM

Hmmm... flashing tape is an idea. I have some Henry AP Patch too. I wonder if the beam would mash through something like that over time?

You know what else might work? That rubber shower pan liner stuff. The thin PVC sheeting. Pretty cheap too. Now that I think of it, I may also have some left over pond liner.