I'm trying to decide whether to go with inexpensive pressure-treated
evergreen wood decking or low cost 1" thick (approx.), radius edge, cedar
(which is must less expensive than standard patio grade cedar decking). I
kind of prefer the cedar option, but I'm unsure about whether it's wise to
go with cedar that is only half the thickness (hence, half the strength) as
standard patio grade cedar. My concern is not about safety per se so much
as it is about structural rigidity, solidness, etc. I don't want it to feel
like I'm 'bouncing on planks' when walking on the deck. Any suggestions,
advice, experiences? Thanks...
How thick exactly is this cedar, and (very importantly) what's your
joist spacing? There is stuff called 5/4 ("five-quarters") which is
very close to 1.25" thick and meant especially for decking on standard
(16"?) joist spacing. It is radius edge. If this is what you've got,
you should be fine. Nominal 1" planks will be probably 3/4 and probably
unsuitable, but I have not seem them in radius edge. I'm not sure what
you mean by "regular patio grade cedar", as the 5/4 stuff seems to be
"the" boards for decking. But it's been a while since I built a deck
and availability of lumber varies regionally.
On bouncy decks a lot of the problem is the substructure, so the
decking may be the least of your worries.
Some folks think that pressure-treated wood is death at 100 yds and
some think you can make tea with the sawdust from it. I figure that if
there's one place it's nice to avoid it it's where your kids might be
walking barefoot on it.
I used the 5/4 cedar on mine with 16" spacing and it was fine. 12"
joist spacing should give an exceptionally solid feel, at least as far
as the planking is concerned. You also need to consider the rest of
the substructure: joist spans, posts, and what the posts rest on.
There are plenty of books with guidelines on that if you're not already
familiar. The cedar is nice to work with and you can let it weather or
stain it, either way it should last a long time. You don't have to
worry if it's toxic when you kids drop their gummy bears on it then
pick'em up and eat'em.
Cedar is a splintery wood. Try that on the SO and or small humans. I have
a friend that has to stain his redwood deck every year to keep it looking
nice. He says forget about the 4-10 year stain guarantees in Phoenix.
If I was to look into a exterior deck I would look at the reclaimed wood and
plastic lumber being sold now. Once installed you should have 10-20 years
of no maintenance. http://www.trex.com/products/whatistrex.asp ?
I like not doing outside maintenance when at all possible.
I have never seen a raised deck with "1 inch" material. Since I weight more
than 250 lbs I am not into taking a step and getting that springy feeling.
I guess if you increased the stringers, ( structure below the "1 inch"
material it would be ok. Except for the yearly maintenance.
The reclaimed stuff is NOT cheaper.
What is your joist spacing (16", 12")? What exactly is the thickness of
the cedar (5/4, 4/4?)? Is there a snow load? Does your roof line slope
onto the deck? For example, my deck has doug fir tubaten joists on 12"
centers with sixbasix supports holding up tubasix redwood decking. Even
though the roof slopes to the side of the deck, we had from two to six
feet of snow on it for several months this year. Until this year, I had
thought that that deck was way overdesigned. A LOT of decks in my town
ended up on the ground.
jo4hn wrote on Mon, 13 Jun 2005 21:09:25 GMT:
j> What is your joist spacing (16", 12")? What exactly is the thickness
j> the cedar (5/4, 4/4?)?
12" and 5/4, respectively.
j> Is there a snow load?
This being Vancouver (the rain capital of so called, "Great White North"),
snow fall during the winter is usually negligible.
But as far as the kind of loads that the deck might someday need to hold, I
have visions of the deck being packed by people visiting for a family
reunion, or some such other large family event. :)
Actually it has much less than half the bending strength. Resistance to
bending is proportional to the cube of the depth.
So, if the normal stuff is 1.5 inches (which is what a 2 by ... measures)
then 1 inch would be about 30% of that stiffness.
Take a few pieces in the yard and lay them out at the joist spacing you
want. Stand on them. See if you like it.
Personally I think 1" is too thin.
Admittedly it was 30 years ago and things change, but when I took mechanical
engineering it was proportional to the square. You integrated the material
multiplied by it's distance from the center; that means squared, no?
Perhaps you didn't do that well in mechanical engineering... :-)
Moment of inertia (I) for a rectangular beam with width b and height h has
I = bh^3/12
for as long as I can recall.
And for deflection (d) of a simply supported beam we use the formula
d = PL^3/48EI
Other formulas for bending (canteliever, multiple supports ...) vary, but
all the ones I can recall off the top of my head include I in the
Therefore I am certain that I did mean cubed and did not mean squared.
>>You integrated the material multiplied by it's distance from the
>>center; that means squared, no?
Well - you're confusing bending strength and deflection. In your first
post you said:
Quote: Actually it has much less than half the bending strength.
Resistance to bending is proportional to the cube of the depth.
This is incorrect - bending strength is governed by stress, which is
derived from bh^2/6 - the square of depth, as "toller" noted.
But in your second post you introduced deflection:
Quote: Moment of inertia (I) for a rectangular beam with width b and
height h has been I = bh^3/12 for as long as I can recall.
This is correct - for deflection.
My deck out at cabin has that cedar decking. Smooth round edge like
flooring material. Used deck screws for fastening. Over 5 years, yet
no problem. I think your joist strength and spacing is more important.
I finished my deck last night. :-) I built it with 5/4 radiased cedar
decking on base of pressure treated wood. The construction style is
floating dekblok with 2x8, 16" centers and I used deck screws to attach the
cedar to the frame. I'm confident for anything less than a mosh pit type
party that the structural integrity will be fine. I'm over 200lbs and the
cedar feels plenty rigid.
I'm considering covering a concrete slab I dislike. I was going to use painted
spf 1x4s on 12" centers on treated 2x4 joists.
Should the 1x4s be fine on twelve in centers? The 2x4 joists are going right on
the slab so no bounce.
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