2x4 as a beam?

Reply

  #1  
Old 11-06-13, 12:04 PM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
2x4 as a beam?

Hi Everyone,

I'm finishing up a deck build. Months ago I did extensive research on this site (maybe even posted about it), but I'm nearing the end.

Long story short, my joists are 2x4s over a concrete patio, and I spaced them 12" OC, supporting them every foot. They feel very stable, and are covered by Timbertech.

The last part will extend 4 feet into the yard. My plan is to continue the 2x4's and have them end on deck blocks. From joist span tables, it looks like a 2x4 should be able to span 4' no problem.

Right no, I would need 20 deck blocks, which is basically building a wall across my yard (under the deck). I'm considering using a beam instead, and hanging the joists off of it with joist hangers.

Think I could get away with a 2x4 beam? supported by deck blocks ever 2 or 3 feet? The deck blocks would also support the joists they intersected (no need for hangers there). So, if I did 2 feet between deck blocks, each length of 2x4beam would support one joist. If I spaced them 3 feet apart, it would support two joists.

Is the beam subjected to a twisting force, since the joists will only be hung from one side?

I also don't know how I would finish it, because the joists would terminate into the beam, which is sitting on deck blocks, meaning I couldn't screw a fascia board to it...
 
Sponsored Links
  #2  
Old 11-06-13, 03:07 PM
czizzi's Avatar
Member
Join Date: Jul 2007
Location: USA
Posts: 7,376
Received 9 Votes on 7 Posts
Don't like anything I have read so far. Here is a copy of universal revised span tables for decks - http://www.awc.org/Publications/DCA/DCA6/DCA6-09.pdf No where within this code does it mention anything about using 2x4's for joists let alone on a free floating deck. Not sure where in VA you are, but 18" is the depth for the frost line on footers where I am in SE VA. Deck block on the lawn may be stiff as a board now, but will shift and settle in due course and leave you with an unsafe structure.
 
  #3  
Old 11-06-13, 07:31 PM
BridgeMan45's Avatar
Member
Join Date: Oct 2011
Location: USA
Posts: 3,196
Received 0 Votes on 0 Posts
And exactly how does one "continue the 2 x 4s . . .4' into the yard"? You worded the post as if they are already in place (meaning cut to length and installed), and now you plan to somehow make them longer? Splicing additional, longer 2 x 4s alongside the existing is a possibility, I guess, but it doesn't sound very practical for a 4' span situation. Might have enough flexibility for a trampoline effect.
 
  #4  
Old 11-06-13, 08:26 PM
canuk's Avatar
Member
Join Date: Sep 2013
Posts: 293
Received 0 Votes on 0 Posts
Hi Everyone,

I'm finishing up a deck build. Months ago I did extensive research on this site (maybe even posted about it), but I'm nearing the end.

Long story short, my joists are 2x4s over a concrete patio, and I spaced them 12" OC, supporting them every foot. They feel very stable, and are covered by Timbertech.

The last part will extend 4 feet into the yard. My plan is to continue the 2x4's and have them end on deck blocks. From joist span tables, it looks like a 2x4 should be able to span 4' no problem.

Right no, I would need 20 deck blocks, which is basically building a wall across my yard (under the deck). I'm considering using a beam instead, and hanging the joists off of it with joist hangers.

Think I could get away with a 2x4 beam? supported by deck blocks ever 2 or 3 feet? The deck blocks would also support the joists they intersected (no need for hangers there). So, if I did 2 feet between deck blocks, each length of 2x4beam would support one joist. If I spaced them 3 feet apart, it would support two joists.

Is the beam subjected to a twisting force, since the joists will only be hung from one side?

I also don't know how I would finish it, because the joists would terminate into the beam, which is sitting on deck blocks, meaning I couldn't screw a fascia board to it...
If I read this correctly this deck is ground level. The section that is being extended sounds to be on the lawn ???
If so consider using the doubled 2X4 beam under the the joists instead of hanging them. You can dig down as much as needed to set the blocks ( on a base of crushed gravel ) at the correct height.
This way you can probably get away with only 5 or 6 blocks to support the beam and you can simply attach a rim joist to the ends of the joists.
 
  #5  
Old 11-06-13, 08:40 PM
Banned. Rule And/Or Policy Violation
Join Date: Apr 2013
Location: USA
Posts: 4,297
Received 0 Votes on 0 Posts
2X's are not direct ground (or grade) rated.
Go back and read the Timbertech install manual, if I remember right it states it needs to be at least 12" above grade and free air flow under it.
I agree, I see no way they can even sell those Deck blocks.
 
  #6  
Old 11-07-13, 05:22 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
Hi Everyone,

Thanks for all the replies. I'll go backwards, starting with Joe:

- The 2x4s are ground contact rated. I went to a local lumber shop and had him tell his supplier to throw 30 in with his next batch. He charged me $.50 extra per 2x4, so a total of $15. Easy peasy.

- Timbertech only needs a minimum of 1.5" below it. Both the manual, and their customer service agree it can be installed on sleepers (which is my installation). They have actually been very helpful.
 
  #7  
Old 11-07-13, 05:29 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
I don't know why I can't figure out how to quote. But for Canuk, I like this idea, and it was a modification to my initial idea, which was just to set a ground contact rated 4x6 on crushed gravel paver base. I can't remember offhand why I went away from that idea. Maybe something about drainage?

Let's say I do this instead. Do I even need to worry about the blocks? Basically, I'm digging a 16' wide trench across my lawn (the deck narrows from 20' wide to 16' because I have built a raised planting bed that juts into the corner). I dig down deep enough for 6" of paver base, compact with a hand tamper, level, then just set the 4x6 (or 6x6) down. Only about 2 inches or so of the 4x6 would be above the ground, the rest would be sunk to keep it in place.

The more I think about this, I think I would go with a 6x6, and treat it almost like the initial course of a retaining wall. I could even drill and throw some spikes or rebar into it.
 
  #8  
Old 11-07-13, 05:50 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
For Bridgeman, here's the link I'm basing much of this deck build off of:

DIY Steps for Building a Deck Over a Patio Slab: The Low Down on Low Decks - Extreme How To

My deck looks very much like this guy's. I had to taper my sleepers, because the pitch of the concrete patio was 2" over 8', and I only pitched the deck at 1/2" over 8' (per Timbertech's instructions). My sleepers start at a thickness of 2" and extend to the full 3.5" thickness. Each joist is shimmed every 12". The joists were tapcon'd to the patio at every shim, which I know was overkill, but helped to keep them in case, and straight (obviously, the PT lumber likes to warp).

My deck differs from this guy's in a couple of small areas:

- It looks like he didn't taper his joists, and just ripped them down to the smallest dimension, then used progressively larger shims. I wanted to keep as much of the 2x4 intact as possible, so built a sled jig, then tapered each 8' joist on a table saw.

- As a result, I have the full 3.5" of lumber at the end of my joists, not just 2.5" like this guy had. He extended his joists out to the pier blocks, with what looks like tapered 2x6's sistered to them. I had my initial joists end at the edge of the patio (a convenient 8'), and plan to just run 4' 2x4's out to the pier blocks, sitting on the same shims as the initial joists. They'll probably overlap (ie. be sistered) for a foot or so, and I was figuring I would screw them to the other joists with 3" structural screws. So just look at his pictures, and pretend he has cut off the ripped down 2x4, and the part that goes over the lawn is just the tapered 2x6 (in my case, a normal 2x4).
 
  #9  
Old 11-07-13, 06:06 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
Hi Czizzi,

You were the first to reply, and the last to get a reply! Sorry about that!

I used this span calculator:

Maximum Span Calculator for Joists & Rafters

As others have written, this is a ground level deck; at it's highest point, you're only about 6 inches off the ground. The deck is not attached to the house.

I did a lot of reading about deck blocks vs footers. The concrete pad I built over was 4" thick, and I didn't want to jackhammer it out and pour footers. If the pad is floating, I figured the deck blocks may as well too. If I go the deck block route, they will sit on 6" of compacted paver base.

I'm definitely aware that the patio could sink, and the deck blocks could sink or heave. I'm hoping this will be minimal, and I may just need to repair it. This is one of the reasons I spaced the joists 12" OC when the Timbertech can be spaced at 16". I wanted to overbuild the structure.

No one has mentioned it yet, but a paver or stone patio definitely would have been easier. However, I got 300 sq ft of Timbertech for free (20' planks), along with all the stainless steel conceal loc fasteners and screws. So I traded off a more complicated, labor intensive build for saving a couple of grand in materials.
 
  #10  
Old 11-07-13, 07:10 AM
czizzi's Avatar
Member
Join Date: Jul 2007
Location: USA
Posts: 7,376
Received 9 Votes on 7 Posts
I think you fail to see one of the disadvantages of composite decking - Expansion and contraction. Composite expands so much that you install it based on what the ambient temperature is at the time of install. A poorly constructed floating base substructure covered by material that will expand and contract as much as 1 inch over the 20 ft length of the board awaits your future. It also expands across its width. I have seen composite boards literally shear off the heads of multiple rows of composite deck screws and have two end to end boards literally stand up and float over the joists in a tent like fashion. These are on fully footed and cemented installations. The decking will push your floating deck all over the place. I just don't like the idea no matter how pretty it looks the day you finish. You will have issues. It may be fine for you, but I think of the safety of future owners of the property as well as unknowing guests you may be entertaining on a sub-par structure.

Refer to my span charts for PRESSURE TREATED LUMBER and not span tables/calculators for standard framing timbers.
 
  #11  
Old 11-07-13, 07:54 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
I thought of the pressure treated issue, ie. what it did to the span. However, I will likely be spanning it a little less than 4', with a small overhang (the deck blocks are shaped like pyramids, and I wouldn't want them to show). So let's say the actual span is 3'8". I'm only at about 60-70% of the allowable span.

Anyone know offhand what PT does to joist spans?

I followed the Timbertech installation procedures to the T. Because the boards are so long, there are no butt joints. All boards are installed with TT's concealed fastener system, which gave a 5/32 gap between boards (TT claims 1/8, but I think it's a little larger than that). According to TT, when using the concealed system, you do not gap the boards based on the temperature. Either way, I installed in 70 degree weather, so should be pretty average.

In terms of the ends of the boards, I went conservative, and left 3/8 to a half inch between them and the adjacent retaining walls (I think TT specc'd only 3/16th). The gap varies because the retaining walls are slightly angled. In hindsight, I could have cut each board at an angle, but I wasn't that organized :-).

It sounds like your bigger issue is with a sleeper installation in general. I saw a number of people, not just on this board, state their preference against that sort of installation, for a number of reasons, including heat, debris build-up, the smaller dimensions of the wood, etc.

However, TT themselves allow this installation, and claim it is common on roof decks.

I would be the first to worry about safety, but the total height, including the TT itself, is at most 6", in some places only 3 1/4". Honestly, I'm much more concerned about cosmetic issues like you cite: something popping, something sagging, etc.
 
  #12  
Old 11-17-13, 11:00 PM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
I wound up going with solid concrete blocks (rather than dek blocks), as I didn't want or need the extra height.

I basically dug a trench, just like you would for a block retaining wall, put down 3-4" of paver base, compacted it, then just laid the blocks across it like a wall. They were actually cheaper than the equivalent 6x6, and I hope more durable.

I'm laying asphalt shingles on top, then will attach with tapcons.
 
  #13  
Old 11-18-13, 05:47 AM
canuk's Avatar
Member
Join Date: Sep 2013
Posts: 293
Received 0 Votes on 0 Posts
Good stuff.

What's the shingles for and where are they being used ?
 
  #14  
Old 11-20-13, 10:25 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
The shingles are going over the blocks as very thin shims (to help with level), and to avoid wicking of moisture from the concrete blocks to the wood.

Probably overkill, but I saw it on another site (fine homebuilding?), and grabbed a couple of ripped/torn shingles from Lowes when I was there getting other stuff. I offered them a buck for a couple of them, and they took it, as they would have thrown them away anyway.
 
  #15  
Old 11-20-13, 11:41 AM
canuk's Avatar
Member
Join Date: Sep 2013
Posts: 293
Received 0 Votes on 0 Posts
I was kinda thinking that may be the case.

If you're using PT lumber the moisture shouldn't be an issue.
Just be aware that even though the shingles have a granular layer they do slip and move.
 
  #16  
Old 11-20-13, 06:04 PM
czizzi's Avatar
Member
Join Date: Jul 2007
Location: USA
Posts: 7,376
Received 9 Votes on 7 Posts
For what I'm reading, you could have dug a couple of 24" holes filled with concrete by now and had a real footer other than your paver sand with block mess. Why the insistence on the floating deck? Educate all of us. I'm not following the logic.....
 
  #17  
Old 11-20-13, 06:30 PM
canuk's Avatar
Member
Join Date: Sep 2013
Posts: 293
Received 0 Votes on 0 Posts
It's not uncommon for a ground level deck to be floating and I don't see a problem.
 
  #18  
Old 11-21-13, 08:54 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
That's a fair question, czizzi, and one I debated several times.

First, just to clarify, I did not use paver sand, but paver base. I'm sure you all already know this, but that stuff is like concrete when compacted. I figure if it's strong enough for multi-ton retaining walls, it's strong enough for a ground level deck. A lot of sites said this was not necessary, and I could simply set the block on the dirt, but, again, I probably went for overkill.

My initial decision was that the blocks and paver base were cheaper (the blocks are $1.20 each before my 10% discount), and would require less work.

Again, remembering that height is the main issue, I would have had to mostly bury any kind of beam. Basically, dig an identical trench to the one I dug, then dig footers in the trench, fill with concrete, somehow attach the beam (would I use normal connectors underground, or would that not be necessary?), then backfill around it to bring the soil up to grade.

So, I would basically be building a conventional deck, only I would be doing the whole thing underground, with literally 2" or so of the top of the beam sticking out. If I used joist hangers, I could probably get 6" above grade.

My thought process was conventional deck building is meant to build something decently above ground. Footings, posts, beams, they're all designed to transfer forces down. I didn't need all that with a floating deck, and the design could be much simpler. Effectively build a short retaining wall, lay one end of my joists on that, the other end goes on the existing concrete pad (with shims), and boom!, instant deck. Moreover, I could build in periodic gaps for ventilation and drainage. Lastly, concrete is even more weather and insect resistant than PT wood. Plus, it's cheaper, and sturdier.

The one place I think I erred was not considering how much paver base I would use (about 15 bags, or $50 worth). Plus, I had to level the trench, then level each block so that it matched the slope of the joist resting on it (remember, I'm sloping the whole deck slightly away from the house). That part has been annoying, and would be much faster with one or two long pieces of lumber, resting on a couple of contact points.
 
  #19  
Old 11-21-13, 09:03 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 44
Received 0 Votes on 0 Posts
Also, before someone mentions it, I'm going to screen the gaps to keep critters out!
 
Reply

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


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description: