# Deck Joist Spacing



## udlooz (Oct 24, 2008)

I built a 14'x14' deck, the frame is 4x6 footers and a pair of 2x6's are the outside joists (around the perimeter)

The floor joists I put at 34" OC, on the advice of a local shadetree carpenter who said 36" OC would be ok for floor joists on a deck. The purlins are at 48" OC. 

each floor joist has 3 footers, all connections are done with Simpson Strong Tie 90* joist hangers.

The decking is all 2x6 PT #2, the framing is all #2 

I am concerned about the floor strength, with joists at 34" because my father-in-law told me I should have them at 16"... when I walk on the deck I feel no give anywhere - how can I gauge the strength of the decking? Can I put furniture on it? 

I don't think I can get under there to add joists, plus all the purlins would have to be removed. This would require removal of all decking...

What should I do?


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## my5sons (Oct 29, 2008)

udlooz said:


> I built a 14'x14' deck, the frame is 4x6 footers and a pair of 2x6's are the outside joists (around the perimeter)
> 
> The floor joists I put at 34" OC, on the advice of a local shadetree carpenter who said 36" OC would be ok for floor joists on a deck. The purlins are at 48" OC.
> 
> ...


34" on center? I can't say I have ever heard of that. 12", 16" or 24" max. This shadetree guy you talked to wouldn't happen to be named Shannon Davidson?

When you say you can't get under there...how far off the ground are you?

As for the purlin? I'm lost, I thought those were used in roofs.


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## James Con (Aug 29, 2007)

This thread is useless without pics. LOL. I would like to see this. Either you have your terms mixed up or you have a liability on your hands. Either way pics please.


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## super carpenter Rob (Oct 28, 2008)

udlooz said:


> I built a 14'x14' deck, the frame is 4x6 footers and a pair of 2x6's are the outside joists (around the perimeter)
> 
> The floor joists I put at 34" OC, on the advice of a local shadetree carpenter who said 36" OC would be ok for floor joists on a deck. The purlins are at 48" OC.
> 
> ...


 take it apart save your lumber and rebuild to code.The joist should be 16 on center. Heres how you start the layout the first measurement should 15 1/4 and 16"after that which will give you 16 OC.The 5/4 is better to use than the 2x4s or 2x6s it will hold up better I think it's planed smoother.But if you have the 2x6 you can use them, I would say treat it as soon as possible.Use joist hangers and harricane ties is your jiost rest on a beam if you have a beam use 2 1/2" carriage where it attaches to your 4x4s or whatever you are using for colums regards Rob


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## Marvin Gardens (Sep 30, 2008)

Decks have to meet the same weight bearing specs as any floor in the house. This includes spans and sq ft loads.

There is no such thing as 34" centers. Even at 24" centers I would be concerned about stability if there were a lot of people on the deck. And 24" centers are used sometimes for floors.


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## udlooz (Oct 24, 2008)

here are pics of the perimeter before I hung the joists


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## udlooz (Oct 24, 2008)

Here are pics of the frame after hanging joists/cross braces (thought they were called purlins) and after laying decking...

Did this all myself, no help so I am dreading pulling it all apart.

You can see all connections to posts/footer use 3/8x6 Lag screws, no carriage bolts. Also all decking uses 2.5" stainless screws, no nails.

I could put beams under the joists fairly easily I think, but that wouldn't help the 33-1/4" span between joists. If I hadn't put crossbraces I could probably get under there and add more joists. would be tight though.

BTW - I used 2x6 over 5/4 because it is cheaper (I had a $1000 budget which is blown now that I am roofing it) and 1.5 inch logically would offer more rigidity than 1.25 inch, I would think. I know they are planed smoother but these are not bad at all.


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## James Con (Aug 29, 2007)

This might be a silly question but are the joist treated wood. It's kinda hard to see the color. Also if you are not putting any kind of lateral bracing like Rated sheating or let in braces you might want to reconsider the roofing. On second thought I would not put a roof over this. You might get away with the deck the way it is, being it is low to the ground (not far to fall) which is why you probably didn't need an inspection from your town. But nix the roof. Maybe get a portable popup canopy to cover it. But make no mistake about it this is not the right way to do a deck, even at the bare min. code. Take the roof warning serious!!!!!!!
Here's a good website for plans and different ways to build. http://www.decks.com/


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## Marvin Gardens (Sep 30, 2008)

Well, interesting is all I can say.

Don't get me wrong, you have a nice looking deck and did a good job for what you know and were told.

Here is where the deck falls short.

The joist spacing is too far apart. The joists are spanning too far for their size. They should be at least 2x8's or 2x10's at 16 inch centers.

The good news is that you have lots of 4x4 supports, just not in the right places.

From where I sit you can save your deck without tearing it down.

The first thing is that I would add some more joists to fill in the gaps. Use joist hangers to secure them. You will have to knock out the cross pieces in the way now.

Then get a 4x6 pt and run it down the middle perpendicular to the joists and use pier blocks to rest it on and make sure it is up tight against the joists.

While this may not look pretty from underneath and is far from accepted building practices it will hold up your deck and make it safe for years to come.

You can do this all from underneath without tearing it down.


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## udlooz (Oct 24, 2008)

Thanks for the compliment, this is the first time I have even built something like this.

I will pull the decking this weekend and add the joists/4x6 beam. Do I need to put cross braces back in? Also, no the joists are not PT, just #2

Also, the roof will be PolyCarb sheets from Suntuf, what kind of bracing do I need for that? Suntuf recommends max 36" center on the rafters, I was going to go 30"


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## my5sons (Oct 29, 2008)

That looks great. However, it is all bittersweet. Your deck isn't built with pressure treated lumber. I'd be surprised if it lasts more than 3 years - 5 years before it falls in.

You are wasting your time and money now. I would leave the deck the way it is, don't install a roof, and wait for it to rot and start all over again with pressure treated in 2 years. If you get some more money again, I'd start tearing it up and do it all over again.

I'm no expert, but just wanted to comment.


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## Marvin Gardens (Sep 30, 2008)

udlooz said:


> Thanks for the compliment, this is the first time I have even built something like this.
> 
> I will pull the decking this weekend and add the joists/4x6 beam. Do I need to put cross braces back in? Also, no the joists are not PT, just #2
> 
> Also, the roof will be PolyCarb sheets from Suntuf, what kind of bracing do I need for that? Suntuf recommends max 36" center on the rafters, I was going to go 30"


Go with what they recommend. The reason is that they are sized so they will fit exactly on 36" centers.

Is there danger of snow load? Or high winds?

If so then there needs to be some consideration for that.


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## udlooz (Oct 24, 2008)

my5sons said:


> That looks great. However, it is all bittersweet. Your deck isn't built with pressure treated lumber. I'd be surprised if it lasts more than 3 years - 5 years before it falls in.
> 
> You are wasting your time and money now. I would leave the deck the way it is, don't install a roof, and wait for it to rot and start all over again with pressure treated in 2 years. If you get some more money again, I'd start tearing it up and do it all over again.
> 
> I'm no expert, but just wanted to comment.


Thanks for the comment, I wish everone were as helpful as you... Wait for it to rot? After all the hard work? untreated wood lasts many years here, and I coat it with linseed oil. That fence in the background, 15 years old according to my neighbor who has been there that long, no rot, just discoloring.


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## udlooz (Oct 24, 2008)

Marvin Gardens said:


> Go with what they recommend. The reason is that they are sized so they will fit exactly on 36" centers.
> 
> Is there danger of snow load? Or high winds?
> 
> If so then there needs to be some consideration for that.


They recommend 24" for vinyl sheets and 36" for polycarb

We rarely get 2" of snow per year here, so snow load is not likely

We do get 60 mph winds occasionally


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## my5sons (Oct 29, 2008)

I'm just guessing, but you won't be able to coat the wood underneath the deck will you? That will be your problem. There was a study done at a college that listed pine as about 10 years for cross bracing, 5 years for L-joints and post rails.

If you used Douglas Fir, the estimates are much better.

So I'm just guessing here, but I wouldn't feel comfortable with it. Not to mention, every code I know of lists PT only!


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## Marvin Gardens (Sep 30, 2008)

udlooz said:


> They recommend 24" for vinyl sheets and 36" for polycarb
> 
> We rarely get 2" of snow per year here, so snow load is not likely
> 
> We do get 60 mph winds occasionally


Well 2 inches of snow can weigh a lot especially if it is high water content. Average is 15-20 pounds per sq ft. While there is little danger of the polycarb breaking it can rip out the nails holding it in.

High winds will get under your roofing and act as a kite. It could rip that up if you don't have it secured enough.

I would call the manufacturer and ask them what they recommend.

Maybe just putting in enough nails would do the job for both wind and snow.

The problem with snow is the support holding the panels on. Even though you don't get a lot of snow and it sounds like it is rare all it takes is one good snow to have your roof on the deck.

At the very least if it does snow be at home so your can shovel off the snow.


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## James Con (Aug 29, 2007)

If you had sunk those 4x4's into the concrete 2 feet or so like a pole barn then I might think about putting a roof on, Maybe. But being you didn't you just used wood to concrete connectors. This deck is not safe for a roof. Snow load or not. A small gust of wind will level it. If you don't understand what bracing is for and how it will prevent the roof and post from falling sideways someone will need to show you because it is a little difficult to explain over a computer in laymans terms. See if you understand from this drawing.


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## udlooz (Oct 24, 2008)

James Con said:


> If you had sunk those 4x4's into the concrete 2 feet or so like a pole barn then I might think about putting a roof on, Maybe. But being you didn't you just used wood to concrete connectors. This deck is not safe for a roof. Snow load or not. A small gust of wind will level it. If you don't understand what bracing is for and how it will prevent the roof and post from falling sideways someone will need to show you because it is a little difficult to explain over a computer in laymans terms. See if you understand from this drawing.


I wasnt going to do a peaked roof, I was going to do a pitched flat roof with polycarb sheets, I assumed the rigidity of the 4x6 corner posts, which are anchored to 80 lbs. of concrete would support that. The 4x4's were more for load bearing, as they are sitting on dek-blocks anchored with simpson connectors.

Should I use lattice instead?


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## James Con (Aug 29, 2007)

udlooz said:


> I wasnt going to do a peaked roof, I was going to do a pitched flat roof with polycarb sheets, I assumed the rigidity of the 4x6 corner posts, which are anchored to 80 lbs. of concrete would support that. The 4x4's were more for load bearing, as they are sitting on dek-blocks anchored with simpson connectors.
> 
> Should I use lattice instead?


Flat roof, pitched roof it really doesn't matter. You are creating a sail with the roof. It probably sounds like I'm picking on your deck but I'm just trying to give you some advice I edited one of your pics about the concrete anchored 4x6 post. The concrete anchored 4x6 would be fine for the deck but your now putting weight up in the air above which is gonna create leverage on the concrete mounted 4x6. ( side to side movement) The only thing I could say is finish it the way you were and see if it's stable. If not, You might want to put some braces along the back.


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## udlooz (Oct 24, 2008)

James, I see what you are saying now, it just didn't make sense before. All construction has stopped until this weekend when I can add some additional floor joists.

I have some 2" well pipe in 10 ft. sticks, I am thinking about setting one of those on each side in concrete and attaching the 4x6 post to it or the roof frame. It may be a bit unsightly but I don't want this thing flying away like you said. 

This is well pipe (irrigation) not thin tubing, I would compare it to black pipe or rigid conduit.

Could you point me towards the braces? Also, I was going to use knee joints on each 4x6 and 4x4 to support the roof, does that help prevent lateral movement?

Thanks for all the advice, sometimes here I feel like people expect me to hire a pro for everything, and not DIY - I don't feel like you are picking on me


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