Ridge beam and rafter sizing?

[Jim Andrew]

Larry, I was talking about the LVL's that are manufactured plywood beams. You are talking about box beams built on site. I can build a better beam using lumber and plywood than these LVL's. I call them plywood beams because they are layered like plywood and available practically any length, because they made in plys. As for engineering, the beam companys will size their beams for you if you take a plan to the lumber yard where you plan to purchase them.

[Brett Nelson]

Larry, I was talking about the LVL's that are manufactured plywood beams. You are talking about box beams built on site. I can build a better beam using lumber and plywood than these LVL's. I call them plywood beams because they are layered like plywood and available practically any length, because they made in plys. As for engineering, the beam companys will size their beams for you if you take a plan to the lumber yard where you plan to purchase them.

Really, you've seen an LVL beam bend under its own weight? Maybe you should get a different manufacturer, because LVLs are by far the stiffest and most structurally sound beams I've ever used, excluding steel.

[Jerry Olexa]

Wow...thanks guys. Good and thorough responses... I've been out of town for several days (w/o my laptop) @ this country property we are discussing. Sorry to get back to you all so slowly.
More detail now :The addition would be 19X 20 (possibly 22'). The ridge beam would be approx: 24' or 26' allowing for a 2' overhang on both ends. The roof pitch would be 1/1 or a 45 degree slant. (this permits a small loft on the 2nd floor). We would use a few cross ties in area not included in the loft.
I met with 3 contractors while there to get their plans, estimates to do the foundation, framing, roof , windows, siding, etc..I plan to do all the interior work myself including wiring ,some plumbing, etc. Each of the bidders is checking further the local building engineer, inspector and plan to get back to me in a few days (in the country that means a few weeks). 2 of them are talking prelaminates and the 3rd, lacing together 2 2X10's.
The site itself is on a hillside with some slope so foundation will be piers driven 4 to 5 ' topped with 6X6 posts and a strong system of beams and joist.
Your advice is very helpful to me. Thanks... I'll continue to follow this thread..

[Jerry Olexa]

Jerry, is this what you mean (with 2' overhangs instead of the 1' I drew)? In this case, 2x8's will work, but you might want to use 2x10's for added insulation. I'd need to know how far the ridge will be spanning to say whether 2x10's would work, or you'd need an L.V.L. As for the wall ties at 4' o.c., they would probably be overkill, since the ridge is resisting the outward pressure of the roof on the walls.

Brian, yes as you drew it but 19 ft across and 20 feet deep where the ridge beam spans. Thanks and roof pitch/rise would be 1/1.

[Jerry Olexa]

Forgot to mention: I'm avoiding trusses as I want to incorporate a 2nd floor loft and want it to blend and match the interior of the existing structure,
Yes, we spoke today and will get necessary permits, inspection, etc. All 3 builders with be meeting with the local engineer, inspector for verifying code.. Just wanted your general input guidelines prior to start. I usually overkill on my rafter, joist, beam, etc sizes Thanks guys

[Brett Nelson]

Wow...thanks guys. Good and thorough responses... I've been out of town for several days (w/o my laptop) @ this country property we are discussing. Sorry to get back to you all so slowly.
More detail now :The addition would be 19X 20 (possibly 22'). The ridge beam would be approx: 24' or 26' allowing for a 2' overhang on both ends. The roof pitch would be 1/1 or a 45 degree slant. (this permits a small loft on the 2nd floor). We would use a few cross ties in area not included in the loft.
I met with 3 contractors while there to get their plans, estimates to do the foundation, framing, roof , windows, siding, etc..I plan to do all the interior work myself including wiring ,some plumbing, etc. Each of the bidders is checking further the local building engineer, inspector and plan to get back to me in a few days (in the country that means a few weeks). 2 of them are talking prelaminates and the 3rd, lacing together 2 2X10's.
The site itself is on a hillside with some slope so foundation will be piers driven 4 to 5 ' topped with 6X6 posts and a strong system of beams and joist.
Your advice is very helpful to me. Thanks... I'll continue to follow this thread..

The 2' extra on each end of the beam doesn't really come into play. What really matters is the span between bearing walls and the length of nailing surface where the beam sits on the wall. Sounds like you'll have drywall directly on the rafters which means you don't want any more deflection than l/240 or your drywall flexes too much. I would stick with l/360 personally.

The 2x10s will certainly be cheaper, but not strong enough in my estimation. I'll check my span tables later, but I really think that 2 ganged 2X10s isn't enough for this application. By size, LVL beams can span the greatest distances and they still call for a 3.5x14" beam. Again, I'll have to check my span tables, but If using dimensional lumber, I think you'll actually need to go with 2x10s for the rafters with a pitch that steep. If your lumber yards are like mine, you'll be looking at No.2&btr for your lumber. I really have to be picky if I want select lumber. But if you can get select lumber, then 2x8s shouldn't be problem for the rafters. You have to remember that your 12:12 pitch results in a surface area 41.4% larger than the floor space underneath it. Conversely, if the roof were only 6:12 pitch (half as steep as your roof) then the surface areas would only be 11% greater than the floor space beneath it. IOW, by doing a really steep roof, you're gonna have 30% more snow on it. Given that you have a steep roof, and you're suggesting that the room width might actually be closer to 22', I would count on needing to use 2x10 lumber, or 9 1/2" TJIs for the rafters. In that case you would need to use at least 2x12" for the ridge beam anyway, to have a large enough nailing surface for the angled rafters to nail to.

All this changes if you are planning to install collar ties. Without the collar ties, the load of the roof rest mainly on the ridge beam without much lateral stress on the walls. Conversely, when using collar ties, you can shift some of the load to the walls to get it off the ridge beam. This is similar in concept to trusses. That is why they don't need ridge beams.

[Jerry Olexa]

All this changes if you are planning to install collar ties. Without the collar ties, the load of the roof rest mainly on the ridge beam without much lateral stress on the walls. Conversely, when using collar ties, you can shift some of the load to the walls to get it off the ridge beam. This is similar in concept to trusses. That is why they don't need ridge beams.[/QUOTE]

I plan to do collar ties on 4' centers on the open ceiling. It'll be covered with 1X6" car siding. The loft area will have joist to serve same purpose as collar ties. Thanks

[Brett Nelson]

Alright, that will help to transfer some of the stress to the exterior walls and take some off the ridge beam. This is where things actually start to get tricky to calculate though. You will be able to get away with 2x8 rafters if there is a collar tie, but you'll need an engineer to size the ridge beam for you. Personally I would still use the 12"TJI for the rafters so that you can blow it full of insulation. That will give you an R35 ceiling vs just an R25.

I was checking my span tables and if you wanted to go with dimensional lumber for the ridge beam, you'd really be looking at 2x12s ganged about 5 thick. I don't know if you've ever made a beam out of 2x12s, but it isn't fun. They aren't dimensionally stable, and there will always be warping and cupping. I would still recommend going with an LVL ridge beam. You'd only need two 14" for your span and you can lift them into place easily and lag them together. They are perfectly straight every time with no cupping. But for the application you will be spending an extra $100 or so to use the LVL.

BTW, I wouldn't hire the guy who said he would use 2 2x10s for the beam.