But my buildign inspector required that I replace my double 2x6 porch
support beam with double 2x8 with a 1/2" ply well glued.
Of course it is the old "what the inspector wants, is what he
gets" :). I did talk him out of some of his other complaints. Built
his way I could have parked a D6 dozer on it.
I agree. The ply is mostly just to make the two other boards conform
to the 3 1/2" wall thickness. I've seen all sorts of scraps used in
that application. If 2x8 was marginal then maybe the inspector was
doing you a favor. What did the span tables call for? What's your
span? Double 2x6 as beam is not a lot of beam. The ability to resist
deflection goes up a lot as you increase the height of the beam. Not
because of the increased strength but because of the increased
distance between the top and the bottom. That's how they make I beams
out of 2x4 and osb.
Any time you have a composite structural member the parts should be
well attached. A simple window header doesn't really benefit from
attaching the parts with more than the usual attention. Unless there
is a great disparity in the strength/stiffness between the two 2x
layers, the header parts will naturally work together.
There's an old saying - stiffness attracts load. The weaker layer will
deflect more/sooner than the stronger layer. The stronger (read
stiffer) 2x will take more of the load until it deflects to the point
where the weaker layer starts picking up the load.
Bonding the layers together makes the composite header's layers work
in unison immediately, which would tend to reduce the deflection by a
little bit. But the header span is usually relatively short and the
absolute deflection is small - much, much smaller than a floor joist
Window headers do move, but most of the movement - at least for solid
sawn lumber headers - is shrinkage from drying. That's one of the
reasons that there shouldn't be any shims between the header and the
top of the window.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.