Beam Help?

[mudcat]

What size lumber should I use to span a 17' span? It basically will carry very little load. It will carry a doubled 2x6 in the center and 6" in from each end. The 2x6's will attach to a free span truss, they will not be supporting the truss. They will hold purlins 2' OC. I will attemp to attach a sketch to aid in my poor description. I thinkmy sketch is as poor as my description

 

[ovrszd]

I used a 2x10 with a 2x8 nailed to the bottom of it to form an L across the top of my 16' door. As you said, it's supporting very little weight and is more used to create stability to the wall above the door. That's why I created the L shape for strength both directions. I put the 2x10 on the outside of my door poles to also create a purlin to fasten my sheeting to. Then ran a 2x8 down each side door pole to cap the ends of the remaining purlins on the side of the building as well as give the header something to sit on. This created a nice smooth surface all around the door opening to cover with finish trim. Probably used more material than needed but it's bull strong.

 

[Timber]

It’s hard to tell if that is a hip roof because if it is all 4 walls are load bearing. If it is an A frame the gable is suspended. You have several options. You can use steel I beam that personal I like because it gives you the ability hang a chain fall on it but the option I think your looking for is a laminated I beam. It is basically a plywood construction, There very light and very strong and very easy to work with. I would recommend this over 2x? Construction. Speak to your lumber retailer and they can bring you up to speed on this product.

 

[EddieWalker]

First choice would be a Glu-Lam beam. It's what they are made for and when you order it, they will size it for your needs.

Since it looks like a garage door opening, or something similar, you can do what builders have done for decades. Take two 2x12's and put a rip a piece of half inch plywood inbetween them. You can add some liquid nails to really beaf it up if you like. Then nail and screw it together. I usually hit if a couple dozen times with the nail gun from both sides, then for overkill, I like to put a few dozen screws in from each side too.

The plywood in the middle is the key. Without it, you will get sag over time, with the plywood, it will never sag on you.

If the bottom of the beam will be exposed, you can make it pretty by adding a 2x4 across the bottom. It won't add much strength, but it does give you a nice finish to a paint.

Have fun,
Eddie

 

[bugstruck]

Glad Eddie figured that sketch out for me. I was wondering for a few moments.

If an inspector is looking at it I'd go the glulam route as they virtually never differentiate between bearing and non-load bearing walls if they are exterior. All exterior walls are assumed as load bearing to them. Don't ask why because the answer parallels the thought that goes into that decision.

If it's not being inspected Eddie's double 2 x 12 with plywood sandwiched in between is a good solution. All that assumes we are looking at a gable end wall beneath a scissor truss that has all the end loading picked up at two walls perpendicular to your sketch. You have to size the beam with enough integrity to carry itself and a few to perhaps several hundred pounds of of wall load. Not much. The only other loading that beam will get is wind load and proper wind bracing can take that up. Frankly, the wind loading on that beam would far exceed any dead load from above.

If you were in 30lb. plus snow load zone I'd go glulam. Those scissor trusses are prone to some limited deflection under heavy snows and would then impart/transfer some live load to the beam. In that instance you want to limit the beam deflection IMO, although even that suggestion is a little overkill on design. The beam would never deflect more than the truss, little. Not a consideration in Florida though. Just the big breezes.

Don't take my reply as engineering advice. I'm not that qualified.

 

[LarryD]

The hay strorage I built 3 years ago has a 2x6 header 14' long like Eddie described. It is a bearing wall although the rafters are only 8'. My double sliding doors also hang on this wall. It may have lost a little of the crown that was originally in it but is still holding strong. Of course 2" of snow shuts the town down so that's not an issue here, as it souldn't be in FL.

I'd be comfortable with a 2x12 header like Eddie said.

 

[ovrszd]

Wow, after reading the other suggestions, I had to go back and read the original post and revisit the picture thinking I must have missed something. Nope, a simple gable roof design that just needs a simple door header which is carrying very little vertical weight because the door poles are fastened to the end rafter. Will probably have more horizontal stress from wind than anything. If he doesn't suffer from high winds, I think I could adjust my suggestion and only use a 2x8 rather than a 2x10. Mine has been standing for 15 years with no sag, in snow country, on top of an open hill with frequent winds. Hmmmm,,, I must have got lucky!!!

 

[Paddy]

Generally, gable ends are not load bearing and no header is required. If that is the case, your 2x6 set will be fine. If it is load bearing, the 2x12 set is not even close to holding the load and a tall lamo-beam is required.

 

[bugstruck]

Generally, gable ends are not load bearing and no header is required. If that is the case, your 2x6 set will be fine. If it is load bearing, the 2x12 set is not even close to holding the load and a tall lamo-beam is required.

Paddy, Can't really argue with that statement for dead load bearing assuming structural sheathing (OSB or Ply).

I can tell you that virtually every 16' clear span header installed in a home within a hundred miles of me (prior to about 1980), whether it carries just a rafter or truss system or a second floor deck, walls, and roof, was the double 2 x 12 with plywood sandwich variety. They didn't have glulam readily available and seldom thought of flitch plates on middle-class residential work during that period. I've only seen two of those with some limited sag (maybe 1/2") and those had a roof immediately over (no second floor deck). That will confound most engineers at first blush (bigger loads), but not framing carpenters. So why doesn't the two story with more load move that header more than the simple roof system does? What happens as you add second floor deck and roof load above? Assuming the second floor wall above does not contain expansive window or door openings, the wall system and the band or ring joist sitting on top of (2) 2x4 top plates, on top of that double 2 x 12 header create a very deep (albeit poorly engineered) ganglam of sorts. The sheathed second floor wall has some spanning and load transferring capability too. If that second floor exterior wall sheathing is 1/2" plywood (often 5 ply fir through the mid 70's) and well fastened, it's assembled/combined strength is vastly greater than nearly any engineer could calculate conventionally. Unless, of course, they read this and think about it awhile. They are plenty sharp enough to see what I'm talking about. I don't suggest doing it that way on a load bearing wall today. No need to and it really is both required and desired to go glumlam on a bearing span that long, rather shorter even. However, I've never seen one of those 16 foot clear span 2 x 12 sandwich type headers deflected anywhere near failure with 30 lb snow loads. Somewhere a few poorly constructed ones have certainly failed but it's exceedingly rare. There are probably tens of millions of those headers in service today (at that crazy span) in the US all the way to Canada. Most for several decades. They sure don't calculate and they sure do work. Go figure.

 

[Paddy]

This engineer is not confounded
Beams are rated by deflection not by breaking. A 1/2" sag means doors and windows stop working normally. No doubt, a wall above sheeted with 1/2" ply is a beam of sorts, if glued/nailed and run 90 deg to the studs The issue is, ply/osb is not required by code in most places, in the corners only. Celitex, (tar coated mush) ruled for most of the '60 and '70s out of the corners.

Codes are minimum. We used to have a saying when fixing old houses, "They don't build them like they use to...Because it'd illegal and dangerus". Ele systems had no ground years ago too, worked greate..untill you were the ground.

An engineers job is to use the minimum amount of material to do the task safely. That is why I started my statment with "is it load bearing?" At a glance I don't think so. The boys at Lowes/Home depot have the tables to reccomend the right(minimum material)