Thread: decking issues

Originally Posted by grease monkey

I plan to use [...] with a Aus. mixed hardwood deck.

Beware of "mixed" hardwood! It tends to mean a mix of
class-2 and class-3 timbers (e.g: blackbutt and stringybark).
Blackbutt is ok outside, but stringybark is not. Go for a
specific timber species and research its properties carefully.
E.g: tallowwood and ironbark are both class-1.

2. The posts are to continue past the deck level to become the handrail supports. I plan to use s/s cabling under the handrail (@125mm or less spacing). Is my post size adequate for the force that these generate if I am using the 88 x 88?

Beware again. The required tension on such s/s cabling is quite enormous,
if you want to meet regulations. If I recall correctly, for a 1.5m post
spacing, and 80mm cable spacing, 3mm (1x19) cable, you have to be able
to hang a 2kg weight at the middle of a cable span, and it must not deflect by more than 5mm! Larger spacings require even higher tension.

I haven't done the experiment with pine posts, but I can tell you 65x65
blackbutt is not even close (and blackbutt is far more rigid than pine).
Most people use 100x100 blackbutt (or other hardwood), but
when I walk up and press my hand against a cable, I seriously doubt
whether it's tight enough. There's a reason why people use 50mm diam
stainless steel posts for this. And even those can bow inwards by 1-2mm
at the centre if spaced too wide apart.

Try doing an experiment: make up one section of the ballustrade as a
stand-alone frame. Then put in your s/s cabling and tighten it up to
spec (using something which is measured to weigh 2kg). How much
does the wire deflect at the middle? Do the posts start to bow inwards
under the tension.

To meet current standards the way i get it ...

you can't use horizontal cable with floor heights greater than 4m
for a 1500mm post spacing using 3mm 1 x 19 stainless cable you must be able to tension 1330 N with a 5mm allowable deflection.......
There are ways of minimising the timber post flex that most guys get but thats a secret LOL if you want to put your posts wider or are unable to get the required tension you can buy 40mm x 6mm fat stainless bar with a bend at either end to attach the the floor and under side of top rail (they come predrilled)this will break the span without visually adding another post and cuts down the cable flex.....

cheers Ute Mad