lainhateslife wrote:i need to design a building with a roof with the following specification:
Truss framed - 2x4 members, trusses at 24" on center
Vaulted ceilings: 2x8 roof joist
What on earth is a 2x4 members? is 2x4 a length or an area? or is it some kind of cubic with a certain volume?
and what about 2x8 roof joist? how long & wide will that joist have to be? (in inches plz)
thank u so much.
These are "nominal" lumber dimensions, based on rough cut. After planing, the actual dimensions are around 1/2" less, i.e. a 2 x 4 is closer to 1.5" x 3.5" cross section, by whatever length.
2" x 8" rafters and joists would support a reasonable load across a reasonable span. 2" x 4" lumber would not (as a simple roof). However, the basic triangle is braced by many shorter pieces to form a truss which is quite strong. These trusses are usually prebuilt in a factory. One disadvantage is that the numerous braces eliminate any possibility of attic storage space, but it can be cheaper and stronger than a simple vaulted 2x8 roof structure.