On 12-Oct-17 2:46 PM, notbob wrote:
On 2017-10-12, wrote:

Not so bad with deck railings with typically shorter spans and
intermediary supports as with fences, but every one of the synthetic
fences I've seen in town has serious sag from loss of rigidity over a
couple summers...

I saw a neigbor install a entire Trex deck. As a geezer with some
wood framing experience, I was shocked. Not only by the screws used to
assemble everything (first time), but the extra support needed to
install things like steps, etc. That "serious sag" can even be seen
at the lumber yard. I saw Trex long boards that couldn't even support their
own weight.

No doubt Trex requires a different technique.

Indeed, comparatively it's a wet noodle even without the temperature
issues...

Modulus of Elasticity is 400 kpsi (ultimate) for Trex while SYP in
lengthwise bending is about 1.8E6 psi or 1800 kpsi. In deflection
calculations, E shows up linearly in the numerator so for a given span,
loading and material dimensions being the same, the Trex will have a
deflection roughly 4X that of SYP.

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