I’m back with another design question re: a front porch that I will be hiring out the framing on. In designing the roof I’ve arrived at the outboard carrying beam that will rest on 6×6 posts spaced 19’8″ OC. The roof will be a simple shed type with a total load of 30 and a 12/3 pitch. In your opinion what would be the best way to design a beam such as this? I’m thinking box beam or doubled up 2x material with 1/2″ply in between and 2×4 at top and bottom.
I’ve seen Boss’ rule of thumb of 1″ beam depth per foot of span but am not sure if that is intended for heavier loads. For a 19′ span do you think I need a 19″ beam? If you were framing this how would you prefer to handle it?
Replies
19' 8" is a big span. You may want to consider an engineered wood beam.
Plenty of other options, but this is the easy (and low labor cost) way out.
Hard to find a straight 20' board these days,
I figured for a built up beam that staggered splices with a plywood core would over come the length problem. I thought about an LVL or such, but are they applicable to what would essentially be an exterior application even though it would probably be wrapped?
Some are rated for more moisture resistance than others. Some have a thick waxy coating.
It really should not see much water, unless there is a leak.
Laminated beams can be built, like you say. They are derated compared to solid members. I'm sure the tables can be had somewhere. I've built a couple of these. You can also build a 'flitch beam', with a steel-in-wood sandwich.
By the time you do out the labor, my guess is that an engineered beam off the shelf would be a better deal.
Thanks for the input. It sounds like the LVL may be the way to go. I'll go to the GP site to see what I can find out. Do you have a preference as to LVL manufacturers?