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Bolting a built up beam together

RobKress's picture

Hi all,

Quick question for the masses about bolting a beam together.

I am building up a 3 ply 2x12 beam and need to bolt it together.

How many bolts?  Spacing?  Pattern?

The beam is 16' long.

Any advice greatly appreciated.


Rob Kress

(post #58812, reply #1 of 25)

You could use the Simpson SDS 1/4x3 wood screws found in their catalog "Effective: 1/1/2003" Catalog C-2003, page 10. I can't see that there is a fastening schedule, but I would drive three across 16" o.c. IMO

(post #58812, reply #2 of 25)

why you bolting them? I only bolt every 8" when I use a flitch plate sandwhiched tween em'.

Otherwise its nails and PL Premium.

BE well


My life is my practice!


(post #58812, reply #3 of 25)

You don't really say what the load and installation location is for this beam and how you determined that it was sufficient. In some loacations the glue and nails or a structural screw will do the job and other times nothing but an agressive bolt pattern will work.

This is an engineering question so more facts are needed before we say that this or that will or won't work - and even then we won't agree.



Excellence is its own reward!



Oh Well,

We did the best we could...

(post #58812, reply #4 of 25)

Kind of funny.... right after I hit the post button on that question I knew what kind of answers I would get.  I guess I know the forum pretty well now.

Ok, here's more info....

This is a beam sitting on top of 2 6x6 posts.  This beam holds up my breakfast room (12x16).  Three people looked at the size of this beam and all agreed that 2ea 2x12 treated boards nailed together would be enough to support the load.

But because this is my house and most everything that I am doing is overbuilt, I decided to build it with 3ea. 2x12's and one piece of 1/2" plywood.  It worked out that this was the best combination of lumber on site to get the width to come out very close to 5 1/2" (same as the posts).  This was intentional.  But of course, the beam is not perfectly tight along its entire length (slightly crooked and cupped boards....not real bad though).

So, to make it look better, make it stronger (pull all boards tightly together), give me more piece of mind (on an already over built situation), and to please the inspectors who have been very surly up to now, I would like to bolt it together in some select places.  I have not asked the city how they feel about this because this is the sort of question they would not give me a ruling on.  They would only say to go get it checked out by an engineer and give them a letter.  This has already been sized (and is currently oversized).  They would however, come out to the site, look up at the beam, not be happy, stop production, and tell me to go get a signed letter from an engineer.  If it looks like a serious situation when they get there to take a look, it will just pass without any words.

Thanks for the help

Rob Kress

(post #58812, reply #5 of 25)

If the load is sitting on top of the beam, no bolting is necessary. That's not to say your building inspector won't want to see some. But there's no real reason for it structurally.

Doesn't matter how many people have looked at it - You may still have to come up with some supporting documentation on whether or not it will work.

Every great advance in natural knowledge has involved the absolute rejection of authority. [Thomas Huxley]

(post #58812, reply #6 of 25)

If you are already over-building and you just want to draw the members together for your own peace of mind then put in as many as it takes!

Use 3/8" bolts one 3" from top, one 3" from bottom every 2',add more to satisfy your anus.

You may consider using hex head bolts if you think carraige bolts will spin out before they dray your members tight.


Mr T

Do not try this at home!

I am an Experienced Professional!

. .

(post #58812, reply #7 of 25)



Using 3/8" grade 5 hex head bolts with fender washers.

1 1/2" down from top, starting 1 1/2" from end, 16" OC.

1 1/2" from bottom, starting 9 1/2" from end, 16" OC.

In middle, starting 5 1/2" from end, 16" OC.

Gives a "W" pattern.

If last bolt in top and bottom rows are more than 8" from end, add bolt 1 1/2" from end.

Pre-assemble beam, clamp, drill holes. Disassemble and apply glue in a triangle inside every  /\  and  \/  formed by bolt holes and along each edge. End edges too.

Use 2 pieces 1/4" 1/2" ply for symmetry.

On outer 2 2X's set bark side to outside, use 2 2X's with most similar ring curvature.

Don't clean excess glue 'til after inspector sees.

Print these instructions and show to inspector.


Technically you don't need the middle row 'cuz there's no stress down the middle of a beam. It does help prevent delamination from cupping stresses, IMHO.

Edit: for ply sizeing.

"You will do me the justice to remember that I have always strenuously supported the right of every man to his opinion, however different that opinion may be to mine. He who denies to another this right, makes a slave of himself to his present opinion, because he precludes himself the right of changing it."   Thomas Paine

Edited 11/2/2003 7:06:20 AM ET by SamT

A Pragmatic Classical Liberal, aka Libertarian.

I'm always right!
Except when I'm not.

(post #58812, reply #8 of 25)

Ya, what Sam says!  LOL.

Oh, but put the 1/4" ply on the out side of the 2x12's so as to be able to recess teh bolt heads in holes cut in the 1/4" ply.  Keep it pretty.

(post #58812, reply #9 of 25)

 Three people looked at the size of this beam and all agreed that 2ea 2x12 treated boards nailed together would be enough to support the load.

Who are these three people and what do they know about construction are they architects? If not what qualifies them to tell you that it's  ok?

This has already been sized (and is currently oversized). 

Who has it been oversized by?

I guess you don't have Architectual plans, do you?

Since this is your own house your probably allowed to do your own drawings. In NJ you can do this.

Joe Carola

Joe Carola

(post #58812, reply #10 of 25)


I do have plans.  They were done by an architect.  The plans call out 2 ea. 2x12's.  No real detail on the drawings but I did have subsequent conversations with the architect who said he intended the beam to be placed on top of the posts and that it was plenty beefy.  But if I wanted to do more I could add another 2x or even a flitch plate.  He is guy number one.

Guy number two was an engineer that I had a conversation with.  He was doing some other work for the house and I asked him about this situation.  He said no problem.

Guy three is a combination of 3 separate lumber yard "guys-in-the-know" who quoted my project.  I asked all three specifically about sizing issues all over the house.  One of them caught a mistake by the architect on another situation and it was corrected early on.  They all said no problem with the 2 ea. 2x12's setting on top of the posts.

The reason this question even came up is because the 35 year master carpenter who is helping frame questioned it.  So I in turn questioned it.  He's really good at what he does and I trust him.  So we ended up over building it.

I guess I am just being a little overly cautious about things since it is my own house... you should see the concrete piers that I had poured for the 2 6x6 posts (the concrete guys were pissed)!

My guess is that the city probably would have let me draw my own plans but while I am an advanced AutoCAD user, I am totally unqualified to make my own house plans.  The only thing I could have done is make meaningless pretty pictures.

Thanks for chiming in.

Rob Kress

(post #58812, reply #11 of 25)

Thanks everyone for the advice.   I see that this is going to just be a matter of prefernce more than anything.

Thanks again,

Rob Kress

(post #58812, reply #12 of 25)

Joe is a master framer too, so that's probably why he was online with your framer questioning the beam sizing.

There is still information missing but there is now way that I would use a double and possibly not even be satisfyed with a triple spanning sixteen feet if the floor and the roof loads onto it. But maybe the span is only twelve feet with a two foot cantilever on the posts. I would like that. Or maybe the floor loads to it ands the roof loads elsewhere...

Personally, it this werre mine, I would be using LVLs or adding a flitchplate. But I'm no engineer and the information is still short.

Anyways - back to the original question and followup answers - IF the beam is sized right and is already in place, all you need to do is pull it together tight to make all that lumber function as one. a typical pattern i see often is placement at 1-1/2" from edges, place 1/2" carriage bolts on a diagonal pattern every 16" with two vertically aligned at ends of beam.

take it and run with it....your ball now


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #58812, reply #13 of 25)


It's hard to participate in this forum sometimes because there are so many qualified posters that it's a little intimidating.  One cannot post with the preconceived notion of getting advice and then doing it half assed.  And posters with questions really have to be prepared to step up to the plate and swing the bat in the big league.  I think that's the thing I like the best about this forum.

Rob Kress

(post #58812, reply #14 of 25)


I think you have touched on something that is Quite relevant here.

DIY types often have a lot of preconcieved notions about how easy a construction project may be.

But when they come here they are forced to think thing through a bit and really understand what is involved.

One of the biggest problems with the residential construction industry is consumer education.

There is always someone that knows how to do it better, cheaper or faster.

But that person does not always have the experience to really make a qualified judgement about any given situtation.

By coming here an amateur can get a broad spectrum of experienced advice that will hopefully help them sift through and make an informed decision.

Sure there are alot of people out there who have the ability and intelligence to work on thier own house, but for every one of those there are dozens who would be better of hiring a pro.

Sure this aint rocket science or brain surgery, but if rocket scientists and brain surgeon built houses, a lot of us would still be living in caves.


Mr T

Do not try this at home!

I am an Experienced Professional!

. .

(post #58812, reply #15 of 25)

* my breakfast room 12x16 * sounds like youve got enough room to have breakfast with Tony the tiger...  bolting a bunch of 2xs together is usually for flush beams ...meaning a beam that is raised to the hight of the rest of the jiosts and they in turn are hung with hangers.These bolts would be staggard and spaced at 32inch intervals. In your case you want to use the bolts to counter the poor instalation and may need to use a tighter interval.You may consider useing a clamp and hoist macgiverin them up to sqeeze the 3 ply back together. In my opinion when faced with a repair I aim for the end result to look as it was never an issue. eg remove the beam remove the nails and then asemble it together without the gaps.this way when looking at the structure when finished  you dont see a bunch of uncalled for carrage bolts at ilregular spacings

(post #58812, reply #16 of 25)

I agree with piffin that 16' does seem a little far to span. According to ICC 2000 code a triple 2x12 supporting a single floor and roof can only span 8'10". four 2x12 can span 10'2. FYI it is table R502(1). I would first fire the architect and consult someone who knows what they are doing. Good luck. A 5-1/4"x16" parallam beam will handle the load.

(post #58812, reply #17 of 25)

One more thing we did a house a while back for a civil engineer. He spec'd a triple 2x12 beam with 1/2 OSB between the 2x12's. it was only spanning about 10' and was only supporting a floor. We did not question him on his own house, but when we were finished the beam deflected so bad (+- 3/4") that it cracked his sheetrock. And this was before his furniture was in. FYI we glued, screwed and bolted the beam.

Laminated beams are cheap enough that I don't spec. 2X12 for any beam any more. I have framers change my design to 2x12's all the time, but whenever the contractor comes and asks me why his roof is sagging, my butt is covered.

P.S. We found out later that the Engineer had no experience with wood and was working with the DOT building highways. He spec'd the 2x12's because a friend told him that was enough.

(post #58812, reply #18 of 25)

This example paoints out the fallacy of the held forth myth that Architects are gods. No offense meant to thoise of you who are here reading and who do all things well - but there are archys who practice art and those who practice engineering and those who still need some more practice.

Few there are who do it all well and as there are schlocks in any profession who pass off carelessness as performance so it is with archs. Hopefully, this was only a single oversight in an otherwise good design.

This is the same one with the window wall, right???

Any way to post drawings for critique of the whole thing? Or would that be stepping on his toes too much?


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #58812, reply #19 of 25)

I agree with piffin that 16' does seem a little far to span.  I wonder if the clear span is 16 ft, or maybe that's the total length of the beam with one or two intermediate supports.

Do it right, or do it twice.

I'm sorry, I thought you wanted it done the right way.

(post #58812, reply #21 of 25)

I raised theat Q earlier but I guess we won't know until Bob gets back in. I bet he'll be muttering sweet nothings sprinkled with four letter words in the general direction of his archy when he reads all this.



Excellence is its own reward!



Oh Well,

We did the best we could...

(post #58812, reply #23 of 25)

Man, hanging out with you guys could give even the most calm and cool headed person a heart attack!  Now I'm afraid that my great view out back is going to be littered with the scattered rubble of my formerly great breakfast room (piled up of course in front of my really sweet walk out basement door).

A little more detail....

Excuse me for being not so clear in the beginning.  The situation is indeed not as bad as 16' clear span.  It is 14 ft.  16ft total beam length.  Whoo Hoo!!

But from all of the conversation here about this beam, one thing is most clear.... it definitely needs more attention!  I will be getting on that first thing in the morning.  Luckily I am not at the point of no return.  Here are options for me I think.....

I could flitch plate the sucker.  A little difficult but definitely effective.  I'll if this is what I do I'll have that sized and done by an engineer.

I could very easily put another post in and cut the span down to 7 ft.  The bummer of this is that the post would be smack dab in the middle of my sweet walk out basement door.  I would rather not do that.

Put in some other beam situation that is just right if this is not.

Pif, you mentioned something about being surly with the architect.....  I'm not really too upset (and don't usually get that way) about this.  Everyone makes mistakes and misses things.  I figure that it's partly everyone's responsibility (including in large part mine) to check things over after it has been passed on.  This is me checking things over.  And in fact, I think that the fault is really all mine for addressing this situation so late in the game.  Late is relative, but for sure this should have been wrapped up long ago.

Of course, the city plan review committee said nothing about several things on my plan that should have been at least a mention.  To me it just makes sense that things will slip through the cracks.  Heck, I've already caught some of my mistakes (after the fact and after they couldn't be reversed) and wish there had been someone there to check me.  And I think a lot of it like this..... it would be way worse if my post started out "I have this great breakfast room and the floor seems to be sagging and the drywall is cracking, and the roof is leaking.  What should I do?"  I have all the power to make this right.  Being an engineer has given me the insight to realize that nothing is perfect and things need to be checked multiple times.  Working as a carpenter for the past 2 years has given just enough courage and the right amount of insanity to attempt the crazy feat of building my own house.  Every day that goes on, I think that I loose a bit of courage and gain of bit of insanity.

Thank you all for the advice.  I will be checking back in with updates.  Hopefully, it will turn out to be a non-dire situation!

Rob Kress

(post #58812, reply #24 of 25)

Of course the comment about muttering at the archy was my attempt to introduce a little bit of levity to what could have been a serious oversight problem. It was his job after all.

A way of transfering some of that load in the center of the beam to the tops of the posts would be to run strapps from the bottom middle of beam up to the top of the top plate over the studing that is over the post at end of beam. Then add corbels or diagonal kickers from the post waist up to the beam from under. I won't attempt to engineer it but there's somethig to throw at the engineer or archy.

Let me also compliment you on your thoroughness. One of the complaint often leveled at engineers as a group is that they have a tendency to over analyse the details. In this case, it is proven to be a good quality to behave that way - and it seems you are able to do it with good will, humour and patience!

Good luck and glad to know you.


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #58812, reply #25 of 25)

" hanging out with you guys could give even the most calm and cool headed person a heart attack! "

We cure heart problems here too!

We report - you decide



Excellence is its own reward!



Oh Well,

We did the best we could...

(post #58812, reply #20 of 25)

Go to the library, take a copy of the U.S span book and calculate the load sitting on top of the beam, then reference the book and calculate the beam needed using species, length, width available or required.  You can also find the book online for like a mere $12 bucks.  I personally would glue all parts of the beam, then drill the beam every 8"alternating the top and bottom, staying away from the top and bottom 25% of the beams, because the bottom is what is under the most load and is in tension, the top is in contraction and is under least load. 

The beam DOES need to be "solid" though and to say that as long as it is supported it does not need to be solid is ridiculous, because if the individual members weren't properly secured than the beam would be three individual members and not one big one which is where the strength comes from.  Strength in numbers, aye.  Remember also that when a beam of any size or material is notched the effective beam size and strength is only that of the left over material being supported, whether the notch is in a vertical column or horizontal beam.  Good Luck.

Edited 11/2/2003 3:47:11 PM ET by vineyrdbuilt

(post #58812, reply #22 of 25)

The National Design Standard for Wood Construction covers the design and bolting of such beams. I would suggest you find a copy.

Since no one here knows what is being suported by the beam, you should find a local engineer nd pay him.