Author Topic: Joist Spacing/Decking Thickness (Read 1090 times)

TexasTimbers · « **on:** February 28, 2007, 10:16:33 am »

For ERC and woods similiar in characteristic (loosely similiar) what do you prefer?

8/4 on 24" OC

5/4 on 16" OC

Other

Jeff · « **Reply #1 on:** February 28, 2007, 10:24:00 am »

I think you would need to factor in joist size as well. Personally I think any floor I would build would be 16" center irregardless of the decking material.

tcsmpsi · « **Reply #2 on:** February 28, 2007, 10:24:25 am »

What kind of application?

TexasTimbers · « **Reply #3 on:** February 28, 2007, 10:32:32 am »

2x6 joists on a wrap-around porch.

isawlogs · « **Reply #4 on:** February 28, 2007, 11:04:49 am »

Personnaly , I prefer the 8/4 on 24 "center ... Is this porch going to be covered or not .

tcsmpsi · « **Reply #5 on:** February 28, 2007, 11:17:45 am »

I've never been quite satisfied with any of the 4/4 decks/porches I've had to do. The 2X flooring always been more satisfactory.

Not that you have not already probably thought about it, but don't be light on your foundation because it's 'just a porch'. Most all the time those things (porches/decks) are asked to hold all sorts of paraphernalia.

TexasTimbers · « **Reply #6 on:** February 28, 2007, 01:04:01 pm »

Yes I actually have plenty of building experience and have always used treated nominal 2Xs but I wanted to know what others have done with ERC. I don't have much experience with it as decking. I figured I would use 8/4 on 2x6 24" OC. It is a covered porch.

beenthere · « **Reply #7 on:** February 28, 2007, 01:17:53 pm »

What ya think the quality of the ERC would be? knot free? straight grain?

I'd go with 16" center, per Jeff's idea. Otherwise, it'll be a bit springy, and cause extra nausia after some bleu's.

More stiffness needed for a good feeling when walking on a deck. But I see no problem with just strength, as I doubt you will break through 5/4 on 24" centers.

TexasTimbers · « **Reply #8 on:** February 28, 2007, 01:22:36 pm »

I just have one question. What is a "bleu"

Tom · « **Reply #9 on:** February 28, 2007, 01:26:21 pm »

That's a Canadian Grass seed wine that Isawlogs and Chet like a bunch.

TexasTimbers · « **Reply #10 on:** February 28, 2007, 01:36:20 pm »

Man there's no end to what can be learned on the FF

tcsmpsi · « **Reply #11 on:** February 28, 2007, 01:54:41 pm »

Quote from: kevjay on February 28, 2007, 01:04:01 pm

Yes I actually have plenty of building experience and have always used treated nominal 2Xs but I wanted to know what others have done with ERC. I don't have much experience with it as decking. I figured I would use 8/4 on 2x6 24" OC. It is a covered porch.

Oh. OK. Man, sometimes I wish I had plenty.

Raphael · « **Reply #12 on:** March 02, 2007, 07:22:16 pm »

Quote from: Tom on February 28, 2007, 01:26:21 pm

That's a Canadian Grass seed wine that Isawlogs and Chet like a bunch.

I won't go into the potential gastric side effect's of Bleu, and have been fortunate to avoid them myself.
Set out some real Brador and I'll be there.

I like a little spring in my floors, I'd be tempted to go 19.3" OC (one less joist every 8') w/ 5/4" decking.

isawlogs · « **Reply #13 on:** March 02, 2007, 09:01:06 pm »

Quote from: Raphael on March 02, 2007, 07:22:16 pm

I won't go into the potential gastric side effect's of Bleu, and have been fortunate to avoid them myself.
Set out some real Brador and I'll be there.

Careful what one wishes for .... ya might have to make plans , mon ami .....

Don P · « **Reply #14 on:** March 02, 2007, 09:27:57 pm »

I have a feeling y'all will be more needing a quality handrail

Just doing the deflection math on sections of equal strength material;

If a 1" thick board on 16" centers deflects .0028"
A 1.5" thick board of the same material will deflect .0043" at 24" centers
A 1" thick a 19.3" will deflect .006"
A 1.5" thick at 19.3" will deflect .0017"

I adjusted the load for the spacings.

Sooo, 1.5" at 19.2, 1" at 16, 1.5" at 24, 1" at 19.2 is the order of least to most bouncy.

Jim_Rogers · « **Reply #15 on:** March 03, 2007, 06:56:59 am »

Don:
What floor load per sqft are you using?

Jim Rogers

Don P · « **Reply #16 on:** March 03, 2007, 08:10:20 am »

I used 40 psf on a 6" wide plank, the 24" spacing had a 40 pound total load on the plank and I treated it as a simple beam. Not real accurate but I figured it would show the order of bounciness. Try it with different combos. If I was right, load and species don't matter other than keep the design values the same to compare apples and adjust the load to reflect the joist spacing.

I've had joists spaced >36" it just takes heavy decking.

Jim_Rogers · « **Reply #17 on:** March 04, 2007, 02:22:24 pm »

The reason why I asked, is I though decks and porches had a higher value like 60 lbs....

Jim Rogers

TexasTimbers · « **Reply #18 on:** March 04, 2007, 02:59:08 pm »

I don't care for any spring at all. I built a test porch in my shop with full 2" X 6" on 2" X 6" joists, 8' long to give an accurate accounting; there was no appreciable bounce or spring on the deck. I think 2X8 joists are overkill since they are supported mid span by another girder. I think I will use the 2X6 joists.
Don you mind running your model using 2X6 decking on 2X6 jiosts? See how close the numbers jibe with the actual test.

Don P · « **Reply #19 on:** March 04, 2007, 10:58:02 pm »

Well first off ERC doesn't appear in the official lumber numbers. So I went to the Wood Handbook. Just finished writing a post about why you aren't supposed to do that

.

Stiffness (E) which is what you checked for, is a true average number, unadjusted from the handbook to the codebook, so its easy. ERC ~800,000 psi

At 60 psf design load, 480 lbs on the joist on a 4' span it deflects .024"
The plank has 60 lbs on 24" span, .003"

For your mockup, I called you 200 lbs. The joist should deflect under your weight 5 thousandths of an inch, double that under a good heeldrop. The one plank under your foot is loaded more than design, it should have bowed about .011 underfoot... about a third of 1/32".

I then ran it with you on one 5/4 (1.25" full) x 6 plank on 16's, .013". So they are mighty close.

And really with decking continuously spanning over several joists it will be lower deflection than my calc or a 1 bay mockup.

Anywhere close to the test result?

TexasTimbers · « **Reply #20 on:** March 05, 2007, 12:00:54 am »

Quote from: Don P on March 04, 2007, 10:58:02 pm

Anywhere close to the test result?

If you can't predict deflection any closer than thousandths of an inch, I guess we'll call it close anyway

Yes, I'd say it was very, very close. Thanks for running all those numbers!

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Author Topic: Joist Spacing/Decking Thickness (Read 1090 times)