Hey all,
Can someone explain the circumstances that require a structural ridge beam. I often hear framers discussing this issue, and would like to understand more (I butcher trim for a living). Most houses that I have been in seem to have non-structural ridges ie 1×8. What is different about a roof that needs a structural ridge.
Thanks
matt
Replies
When the roof frame is a structurally sound triangle, like a simple truss or a pair of rafters combined with a rafter tie/ceiling joist, the entire load of the roof is transfered to the exterior walls, or sometimes to them and an interior bearing wall or two.
But in the case of a cathedral roof, there is no rafter tie or ceiling joist to prevent the roof load from pushing the walls out away from the ridge. If you driver along the highway and notice old houses and barns with a pronounced sag in the ridge and lean out in the exterior load bearing walls, you know that the ridge beam was under designed or that someone later removed the ceiling joists htat formed the base of that triangle.
In a cathedral ceiling, the ridge must be sized to handle one half of the total load of the roof, including both live load and dead load.
this is the simplistic answer. complex roof design gets more complicated answers.
Excellence is its own reward!
Matt,
Basically a structural ridge carries the load of the roof and holds the rafters up, instead of in a non-structural ridge where the ridge is there only for a convienent nailing base for the rafters and the walls bear the brunt of the roof load. You typically find SR's in cathedral or vaulted ceilings, where there are no ceiling joists to keep the walls from spreading. SR's are usually composed of large dimension lumber or LVLs that sit atop large bearing posts at either end (and sometimes in the middle if there is a bearing wall) that transfer the loads to the foundation.
Please note that I am a framing carpenter, not an engineer or architect, and this is what I know to be true. I could be wrong on a few points and I hope others more knowledgeable in this subject will add to this or correct me if I'm wrong.
Quality before Quantity
Cap,
Thanks for the explanation.
Matt