Before beginning to frame, decide what you will do; will there be a ridge board, or a ridge beam? A ridge board is simply a narrow piece of lumber running between the top edges of rafters to align them, without bearing any weight.
It relies on the triangular form created by the ceiling joists and rafters to hold walls together; therefore a ridge board depends on a flat-ceilinged attic, where removing the joist to create a cathedral look won’t work. If the joists is removed, the rafters push out, causing wall bow-out and cracking of the drywall.
Choosing Between a Ridge Board and a Ridge Beam
In such circumstances a structural ridge beam are required because it catches the vertical load at the top and transmits it downward to walls or posts. Instead of pushing against it, the rafters dangle from the beam so they change entire structure’s physics.
The beam has to be sized properly for the job. That means you can’t just pick any old lumber dimension and say it will work. Depending off the width of the building and the snow load, the span limitations changes. In other words, a Florida roof is different than that of a Minnesota one. Not only do the spans depend on the snow load, but also the width of the building.
Snow is considered a live load, which are added to the dead loads of framing and shingles to calculate total weight. In areas of heavier snow, the allowed span become greatly reduced. A double 2×12 might span fourteen feet in a light snow area, but that span drops to less than twelve feet when the snow load doubles. It’s not a linear relationship. A little more weight demands a far stronger beam. I see many folks undersizing their beam due to this element.
The size isn’t all that counts: The type of material used also play a big role. Most builders use standard dimensional lumber such as SPF (Spruce, Pine and Fir) or Douglas Fir. However, engineered LVL beams are stronger and more consistant. These can typically go farther while using less depth than built-up wood. This makes them ideal for longer spans on open ridge lines without mid-point support posts. Unlike conventional wood which will tend to bow and bend over time, LVL holds its shape much better, though it must be nailed according to the specs provided by the manufacturer, down to the last detail. With multi-ply beams, the joints needs to be staggered, this is what gives the structure its integrity.
If you don’t support the ends of the beam, they’re the weak link. You can’t hang a structural beam on nothing; the beam must have solid bearing on posts that extend all the way to foundation.
Collar ties are not proper rafter ties: Don’t make this mistake. A low-slope roof holds more snow, while a steep roof sheds snow but also creates more horizontal thrust. Order from a chart value that’s appropriate for your zone (check your local snow map), or it will fail if you use a chart value for light snow in a heavy snow region. In summer the roof looks fine, but come February it sags. You should of checked the loads first.
Consider the ridge as the spine of your home. When this part is weak, the rest of the house suffer for it. Use the right material and figure out the loads. Make sure the supports are in place and secure. Spend an hour learning what’s required rather than a year straightening bowing walls. Pay attention to these details and ceiling won’t budge.
