Ridge Beam and Rafters

Started by VannL, March 12, 2018, 10:35:30 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

VannL

Building a 16 x 20 workshop. I want to use a ridge beam and rafter set up. Looking at pictures, it looks like folks have used two or more pieces for the ridge beam, which makes sense. When you do that, what do you do to connect the two pieces together?
If you build it, it will be yours!

Don_P

Usually nails, sometimes bolting or structural screws. The design phase involves determining the load on the beam and providing a beam of sufficient strength and stiffness to carry the load at that span. To determine load you need to know your design snow load in lbs/square foot, the live load, plus the weight of materials, the dead load. A 20' span is pretty healthy, you'll probably be into LVL's.


VannL

No snow here in central Alabama, no live load, and the only dead load is the plywood and the metal roofing. I did look at the IRC and it said that 2x8 was good for my rafters. I can, and likely will, leave a few braces helping to hold things up between the ridge beam and the ceiling joist. The joists aren't holding up a ceiling. I just put them in to keep the walls from flexing out. Also, no storage above the ceiling joists. Straightforward and simple design.

I was thinking about joining the beam pieces with some metal plates and nailing it through the plates.
If you build it, it will be yours!

Don_P

We're mixing things up here. What you are describing is a ridgeboard rather than a ridgebeam . A ridgebeam is designed to carry half of the roof load, spans unbroken for the entire 20' span and does not require ceiling joists, no joints in that beam. If the ridge cannot sag the rafters cannot spread the walls, or to put it another way the rafters hang from the ridge.

A ridgeboard by contrast is simply a framing convenience, something to align and nail the rafters to, it is not structural. The triangle formed by the rafters and ceiling joist is what keeps the walls from being bowed out. This sounds more like what you are proposing. In this case I would simply make sure the single ridgeboard is deep enough to fully support the plumb cut on the top of the rafter at that pitch. I usually nail 2x cleats on each side of any joints in the ridge, the blocks fit in between rafters and are below the rafter top edge. You must use ceiling joists with this type of roof. They may be raised up no more than 1/3 of overall roof height.

When there is no snow load the minimum design live load is 20 psf for wind, check the wind chart in chapter 3, and I would use 10 psf dead load minimum.

VannL

Ah, thanks. And yes, the second scenario is what I am doing. I already have the ceiling joists in place.
If you build it, it will be yours!