Which Is A Stronger Joist?

 
Thread Tools Search this Thread Display Modes
Old 03-28-2006, 10:09 AM   #1
Registered User
 
ATHC's Avatar
 
Trade: General Construction
Join Date: Mar 2006
Posts: 14
Rewards Points: 10

Which Is A Stronger Joist?


First up, I'm new to the board... great place and a wealth of info & help!

Concerning deck construction for large 6' hot tub, deck height under 3'-0".

1. Which is a stronger support joist: 4x6 or (2) 2x6

2. Advantages/Disadvantages

Thanks much.
ATHC is offline  

Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ContractorTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

   
 

Old 03-28-2006, 10:30 AM   #2
unlicensed hack
 
maj's Avatar
 
Trade: wood butcher
Join Date: Mar 2006
Location: North Pole
Posts: 1,087
Rewards Points: 500

Re: Which Is A Stronger Joist?


Depends on the span, which you don't give. Personally I would figure 1" of joist width per 1' of span. So if the span is 10', then usa 2x10 for joist. I would also space them 12" centers for the hot tub area.

maj is offline  
Old 03-28-2006, 11:36 AM   #3
Pro
 
Bob Kovacs's Avatar
 
Trade: Consultant
Join Date: May 2005
Location: Holly Springs, GA
Posts: 1,221
Rewards Points: 500

Re: Which Is A Stronger Joist?


A 4x6 will be stronger, as it's actual dimensions are 3 1/2 x 5 1/2. two 2x6's would total 3 x 5 1/2, which is approximately 15% less cross-sectional area.

However, if you're talking about supporting a hot tub, you'd better get far more design info than this to work with- 6" deep anything won't span very far supporting a hot tub.........

Bob
Bob Kovacs is offline  
Old 03-28-2006, 11:42 AM   #4
Custom Builder
 
Glasshousebltr's Avatar
 
Trade: From dirt to ridge vent
Join Date: Feb 2004
Location: South Central Illinois
Posts: 4,406
Rewards Points: 2,000
Send a message via AIM to Glasshousebltr Send a message via Yahoo to Glasshousebltr

Re: Which Is A Stronger Joist?


Some extra poles and footings under the tub would be a better route to go.

Bob
__________________
Bob
Glasshousebltr is offline  
Old 03-28-2006, 11:52 AM   #5
unlicensed hack
 
maj's Avatar
 
Trade: wood butcher
Join Date: Mar 2006
Location: North Pole
Posts: 1,087
Rewards Points: 500

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by Glasshousebltr
Some extra poles and footings under the tub would be a better route to go.

Bob
I'll second that
maj is offline  
Old 03-28-2006, 03:04 PM   #6
Pro
 
Peladu's Avatar
 
Trade: General Contractor
Join Date: Jan 2006
Location: Chicago
Posts: 1,370
Rewards Points: 500

Re: Which Is A Stronger Joist?


I would first verify with the HO if they ever plan on putting water in the tub. If not then you don't need additional support. Should they feel the need to add water, you may wish to "beef" it up.
Peladu is offline  
Old 03-28-2006, 03:44 PM   #7
Soon to be senile
 
Shamrock's Avatar
 
Trade: Remodel and repair
Join Date: Mar 2006
Location: Outer Banks
Posts: 177
Rewards Points: 150

Re: Which Is A Stronger Joist?


I've done several using 2x10's on 12" centers over a 10' span and over time there is a noticable deflection...not terrible but definitely there. Currently make it a point of adding additional girder support in the middle these days for hot tubs.
Shamrock is offline  
Old 03-28-2006, 05:53 PM   #8
Registered User
 
ATHC's Avatar
 
Trade: General Construction
Join Date: Mar 2006
Posts: 14
Rewards Points: 10

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by Bob Kovacs
A 4x6 will be stronger, as it's actual dimensions are 3 1/2 x 5 1/2. two 2x6's would total 3 x 5 1/2, which is approximately 15% less cross-sectional area.

However, if you're talking about supporting a hot tub, you'd better get far more design info than this to work with- 6" deep anything won't span very far supporting a hot tub.........

Bob
I thought the 4x6 was stronger. This will be a new deck (extension). The HO currently has the hot tub (filled & in use daily) sitting on an existing 10' W x 20' L deck, span is 8' (12" overhang front/back) with 2x6 joists sitting on top a double 2x6 beam and no center support, 5 - 4x4 post spaced 5' on front and back. I was amazed it had not collasped when I first saw it. HO want's to add a 5' x 15' extension to move the hot tub out farther. No problem building the new to meet/exceed the requirements, I was just wondering if there was any real difference between two 2x6 or one 4x6 other then dimensionally. I've used both and know there is post beam/tie caps available for each.

This forum is really great! It's nice having a diverse group of professionals to discuss ideas/concerns. Much appreciated!
ATHC is offline  
Old 03-28-2006, 08:23 PM   #9
Pro
 
RobertCDF's Avatar
 
Trade: Custom deck builder
Join Date: Aug 2005
Location: Colorado Springs, Colorado
Posts: 7,861
Rewards Points: 3,471

Re: Which Is A Stronger Joist?


You can use 2x6 for the joists if you like... but then I would put a beam every 2' under the joists... Other wise I would recomend double 2x10 at 12" O.C. and some large beam just depending upon what distance you want between the posts. But then again I just overbuild most everything.
RobertCDF is online now  
Old 03-28-2006, 10:24 PM   #10
Pro
 
old27's Avatar
 
Trade: Work
Join Date: Feb 2005
Posts: 262
Rewards Points: 250

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by RobertCDF
You can use 2x6 for the joists if you like... but then I would put a beam every 2' under the joists... Other wise I would recomend double 2x10 at 12" O.C. and some large beam just depending upon what distance you want between the posts. But then again I just overbuild most everything.

Robert-

I'm with you all the way on the beefier framing call........or he could use 2x4 for the joists...and then put a beam every 1' under the joists.

-msacras
old27 is offline  
Old 03-28-2006, 11:05 PM   #11
Pro
 
RobertCDF's Avatar
 
Trade: Custom deck builder
Join Date: Aug 2005
Location: Colorado Springs, Colorado
Posts: 7,861
Rewards Points: 3,471

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by old27
Robert-

I'm with you all the way on the beefier framing call........or he could use 2x4 for the joists...and then put a beam every 1' under the joists.

-msacras
Lol it might be cheaper... you would just have to run the numbers.... or you could just put the tub on a slab and be done with it. Then build the deck around it. Personally I think this looks better.
RobertCDF is online now  
Old 03-28-2006, 11:12 PM   #12
Pro
 
bob the builder's Avatar
 
Trade: Home Improvement
Join Date: Oct 2005
Location: Wisconsin
Posts: 302
Rewards Points: 250

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by RobertCDF
Lol it might be cheaper... you would just have to run the numbers.... or you could just put the tub on a slab and be done with it. Then build the deck around it. Personally I think this looks better.

I like the privacy also...

Bob
bob the builder is offline  
Old 03-29-2006, 03:11 PM   #13
General Contractor
 
nadonailer's Avatar
 
Trade: General Contractor
Join Date: Nov 2005
Location: Coronado, CA (Just outside San Diego)
Posts: 548
Rewards Points: 500

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by Glasshousebltr
Some extra poles and footings under the tub would be a better route to go.

Bob
Ditto - concrete tubes w/ 4x4's and post caps holding up 4x6's is what I'd do below the tub.............
__________________
"History does not long entrust the care of freedom to the weak or the timid”.
Dwight D. Eisenhower
nadonailer is offline  
Old 03-29-2006, 06:15 PM   #14
Pro
 
Joasis's Avatar
 
Trade: General Contractor
Join Date: Mar 2006
Location: Hennessey, Oklahoma
Posts: 7,365
Rewards Points: 2,456

Re: Which Is A Stronger Joist?


I guess I am missing something here, but why is 6X being considered? Just because they are already there? 6X as a joist and beam under the joist does not equal the strength of a 2X12. On the other hand, give a little thought to load distribution and exactly what weight is involved. My own hot tub weighs in at a hefty 1050# and holds 550 gallons of water @ 7# per gallon for 3850#, for a grand total of 4900lbs. It rests on a 7 ft square cabinet rim with a cross uqually dividing the tub base. Toss in a couple of adults, or more on a party night, and you have lots of weight to consider. You say you have less then 3 ft to work with, so the 2X10's or 12's may be a something to sell the HO on simply because it is better, safer, and if the deck sags even slightly under the tub, it will stress the tub and cabinet...more expense later. Just my 2 cents.
Joasis is offline  
Old 03-29-2006, 09:01 PM   #15
HouseWright
 
Riversong's Avatar
 
Trade: Designer/Builder
Join Date: Mar 2006
Posts: 65
Rewards Points: 75

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by ATHC
I thought the 4x6 was stronger.
Like most things, it's not quite that simple. A 4x6 joist is theoretically stronger than a doubled 2x6 joist because it's 1/2" thicker, but the actual strength depends upon the knots and other inherent weaknesses of any particular piece of lumber (#2 lumber can have some nasty spike knots or large not-so-tight round knots or wane).

If the doubled 2x6s are well nailed (3 10d common every 16"), then they can be stronger than a single 4x6 because both the grain and the weaknesses can be supported by the sistered member.

It sounds like there's some good sense being shared here from years of experience, but I'm surprised that no one has mentioned using span tables or the formulas required for the relatively simple engineering of such a deck.

But, using standard lumber specs and the required 60 lbs/sf live load for an outside deck, plus adding a 5000 lb hot tub load spread over 4 or 5 joists (assuming 16" oc - that's an additional 1000 lb per joist), 2-2x6 PT yellow pine joists 16" oc will just about carry the design load, but be a little over-stressed in horizontal shear. With 4x6 joists 16" oc, the shear and deflection are OK (I'm assuming the new deck will also have an 8' span).

If you want to be sure there won't be problems, then going 12" oc won't be a bad idea for the area carrying the hot tub. And make sure your pier footings can handle the extra load, too (use bigfoot pier bases).

- Robert
Riversong is offline  
Old 03-30-2006, 08:16 AM   #16
Registered User
 
ATHC's Avatar
 
Trade: General Construction
Join Date: Mar 2006
Posts: 14
Rewards Points: 10

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by Riversong
(I'm assuming the new deck will also have an 8' span).

If you want to be sure there won't be problems, then going 12" oc won't be a bad idea for the area carrying the hot tub. And make sure your pier footings can handle the extra load, too (use bigfoot pier bases).

- Robert
Thanks for all the input from everyone. Robert, your thinking was inline with what I was wondering. Both ways have their purpose, however there's numerous factors that can alter both outcomes.

The new span will only be 6' and yes bigfoot pier bases are a must. The HO called yesterday to ask more questions, I'm still trying to steer them to a concrete slab with the deck built around the tub.

Thanks much!
ATHC is offline  
Old 03-31-2006, 07:47 PM   #17
Pro
 
Joasis's Avatar
 
Trade: General Contractor
Join Date: Mar 2006
Location: Hennessey, Oklahoma
Posts: 7,365
Rewards Points: 2,456

Re: Which Is A Stronger Joist?


Maybe you could sell the HO on the idea of the tub going to concrete based on keeping the hot tub ridgid, and will help it in not cracking, ect as a selling point. Try all angles to get where you know you need to be.
Joasis is offline  
Old 03-31-2006, 08:02 PM   #18
Pro
 
Teetorbilt's Avatar
 
Trade: Residential Contractor
Join Date: Feb 2004
Location: Jensen Beach, FL
Posts: 10,474
Rewards Points: 2,000

Re: Which Is A Stronger Joist?


joasis, where are you getting the light water? Mine weighs 8.336#s at 62*F.
__________________
You can't solve you're problems with the same level of thinking that created the problems.

Albert Einstein
Teetorbilt is offline  
Old 03-31-2006, 10:48 PM   #19
Pro
 
kapena's Avatar
 
Trade: General Building Contractor
Join Date: Aug 2004
Location: Honolulu
Posts: 124
Rewards Points: 75

Re: Which Is A Stronger Joist?


Lighter water happens when you turn on the Jacuzzi jets. How light it gets depends on the "bubble factor".
kapena is offline  
Old 04-01-2006, 12:12 AM   #20
Pro
 
bob the builder's Avatar
 
Trade: Home Improvement
Join Date: Oct 2005
Location: Wisconsin
Posts: 302
Rewards Points: 250

Re: Which Is A Stronger Joist?


Quote:
Originally Posted by kapena
Lighter water happens when you turn on the Jacuzzi jets. How light it gets depends on the "bubble factor".
But you don't leave your jets on for load calcs.

bob the builder is offline  


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Floor Joist dante1 Flooring 0 02-14-2007 05:02 PM
3/4 Hardwood laid parallel to joist? pburchett Flooring 9 10-08-2006 10:37 AM
Joist Jaw Woodcrafter74 Tools & Equipment 8 08-04-2006 07:57 AM
HELP! HELP! Joist Hangers allsolutions Construction 19 05-27-2006 10:08 PM
Floor joist out to deck? irving Carpentry 18 04-15-2006 09:15 PM

Join Now... It's Fast and FREE!

I am a professional contractor
I am a DIY Homeowner
Drywall Talk is for
PROFESSIONAL CONTRACTORS ONLY!

At DrywallTalk.com we cater exlusivly to professional contractors who make their living as a contractor. Knowing that many homeowners and DIYers are looking for a community to call home, we've created www.DIYChatroom.com DIY Chatroom is full of helpful advices and perfect for DIY homeowners.

Redirecing in 10 seconds
No Thanks
terms of service

Already Have an Account?