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Old 08-14-2019, 05:41 PM   #1
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Deck Joist Blocking


Trying to determine blocking requirements for my deck. I found one reference which said blocking over beams is required. Another said every 8’ and another said mid-span blocking is not required if you block ends at the rim joist.

My deck is attached to my house and has 2x12 joists, 16”oc supported by two beams. Total span is 20’. First beam is 9’ from ledger board and second beam is 18’ from ledger board. Deck was built with blocking over both beams. Some of the blocking is split and/or punky, not sure it is even PT material. Many pieces are loose and falling out. I think the original blocking was partially removed when the new deck boards were installed and then pushed back in place but not toe nailed.

I would like to remove old blocking and install a new PT blocking system. Do I really need a row of blocking over each beam? Thx.

Last edited by Abuc; 08-14-2019 at 05:43 PM.
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Old 08-14-2019, 07:16 PM   #2
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Re: Deck Joist Blocking


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Originally Posted by Abuc View Post
Trying to determine blocking requirements for my deck. I found one reference which said blocking over beams is required. Another said every 8’ and another said mid-span blocking is not required if you block ends at the rim joist.

My deck is attached to my house and has 2x12 joists, 16”oc supported by two beams. Total span is 20’. First beam is 9’ from ledger board and second beam is 18’ from ledger board. Deck was built with blocking over both beams. Some of the blocking is split and/or punky, not sure it is even PT material. Many pieces are loose and falling out. I think the original blocking was partially removed when the new deck boards were installed and then pushed back in place but not toe nailed.

I would like to remove old blocking and install a new PT blocking system. Do I really need a row of blocking over each beam? Thx.
Decks some times have local codes but where I am we treat it like a floor.
The rim and the ledger hold the ends up square and there should not be more that 7 ft between supports or blocks

So you have more than seven feet between beams and or ledger I would put a row of blocks in the center of each span.

We would snap a line and put the blocks on alternate sides of the line for easier nailing, for 2x12 joists the blocks would be 2x6 flush with the bottom.
But asking the city is always a good idea.
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Old 08-14-2019, 07:56 PM   #3
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Re: Deck Joist Blocking


You probably don't need the blocks on 18' beam side if the joist ends have a same 2x12 rim board. If the blocks are that bad, you should find out if rest of the deck material is treated. Taking a sample with 1" hole saw and looking for greenish color. Even drilling and looking at the chip color. Also time to check for joist to beam connections. When decking is removed, step on each joist and see if it moves away from the beam.
When redecking, check each joist, ledger and all nails, screws and bolts. Condition of the joists around the fastener holes.
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Old 08-15-2019, 05:08 AM   #4
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Re: Deck Joist Blocking


Thx. Here is one of the references I used. It suggests I need blocking over the outboard beam because I do have a short cantilever. It also says blocking must be at 60% of joist depth which means I would need at least 2x8. Perhaps this code has been updated or I do not understand how to interpret it. I will call my local code inspector.

https://www.deckmagazine.com/design-...he-2015-code_o
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Old 08-15-2019, 09:28 AM   #5
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Re: Deck Joist Blocking


Local codes can select and follow whatever rules they want and add or subtract from them, makes it tough to help from long distance, so indeed talk to them.

Verify all material used which should have been done when deck boards were replaced.

Double check what you can around/behind that ledger as the majority of time there is moisture damage.

IMO, 2x12's with those spans should be rather solid but follow codes.

Bud
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Old 08-15-2019, 09:55 AM   #6
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Re: Deck Joist Blocking


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Local codes can select and follow whatever rules they want and add or subtract from them, makes it tough to help from long distance, so indeed talk to them.

Verify all material used which should have been done when deck boards were replaced.

Double check what you can around/behind that ledger as the majority of time there is moisture damage.

IMO, 2x12's with those spans should be rather solid but follow codes.

Bud
One of my first projects in this 16 yo new to me house was replacing two sliders over the deck. Had substantial rot in subfloor but rim joist and ledger looked good. It appears that the entire deck was reframed with PT when the new deck boards were installed but they reused the original blocking. Not sure if that is what they did, but it looks that way. Will let you know what my inspector says. I got to know him pretty well when I converted my garage from two door to one door.
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Old 08-15-2019, 03:22 PM   #7
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Re: Deck Joist Blocking


Pulled out a tape to make sure I had straight scoop for inspector. Turns out joists are 2x10, not 2x12. Total span is only 14’ with beams at 6’ and 12’ from ledger. Hopefully I can do one row of 2x6 or 2x8 blocking 7’ from ledger.
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Old 08-15-2019, 03:25 PM   #8
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Re: Deck Joist Blocking


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Pulled out a tape to make sure I had straight scoop for inspector. Turns out joists are 2x10, not 2x12. Total span is only 14’ with beams at 6’ and 12’ from ledger. Hopefully I can do one row of 2x6 or 2x8 blocking 7’ from ledger.
6 and 12 ft you would not need them here.
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Old 08-15-2019, 04:17 PM   #9
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Re: Deck Joist Blocking


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6 and 12 ft you would not need them here.
So I only count the span between ledger and first beam and between beams? Is the connection (toe nail) between the joist and beam sufficient to keep joists from twisting or rolling over? Why does the code call for blocking over beams?

Last edited by Abuc; 08-15-2019 at 04:21 PM.
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Old 08-15-2019, 04:21 PM   #10
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Re: Deck Joist Blocking


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So I only count the span between ledger and first beam and between beams? Is the connection (toe nail) between the joist and beam sufficient to keep joists from twisting or rolling over?
That is the way it is here.
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Old 08-16-2019, 05:47 AM   #11
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Re: Deck Joist Blocking


Inspector returned my call last night. He said no blocking required on my deck. I asked him why not and what were the local requirements. He did not know off the top of his head but said you almost never see blocking on decks around here anymore and he did not seem concerned about it. I asked him specifically about blocking over beams and he said he sees that mostly when load bearing wall is directly above beam. So, I am planning to remove the old unsightly blocking and not replace it with blocking in any configuration. Thx for your help.
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Old 08-16-2019, 06:16 AM   #12
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Re: Deck Joist Blocking


Being on good terms with your inspector just makes life a whole lot easier.

Bud
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Old 08-16-2019, 07:50 AM   #13
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Re: Deck Joist Blocking


Blocks add some stiffness to somewhat over-spanned joists as well as physical bracing so the lumbers stay straight. There is also the old saying, monkey see monkey do. I would, example, skip asking the inspector or any pro if I thought I can fix the problem just replacing parts. Although I'm learning not to on my cars. Your deck lumbers are also over engineered in a way with only 6' joist spans between beams. I think your deck was built by somebody who over engineers, which is a good thing. Still, check all of the parts, flashing, ledger, fasteners, foundation to post connections, etc.
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Old 08-16-2019, 08:18 AM   #14
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Re: Deck Joist Blocking


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Blocks add some stiffness to somewhat over-spanned joists as well as physical bracing so the lumbers stay straight. There is also the old saying, monkey see monkey do. I would, example, skip asking the inspector or any pro if I thought I can fix the problem just replacing parts. Although I'm learning not to on my cars. Your deck lumbers are also over engineered in a way with only 6' joist spans between beams. I think your deck was built by somebody who over engineers, which is a good thing. Still, check all of the parts, flashing, ledger, fasteners, foundation to post connections, etc.
Agree, no need to ask inspector to repair/replace in kind. However, the old blocking was in bad shape and unsightly. Replacing a few of the worst offenders would make it look even worse. My deck is elevated and you can see the underneath from my finished basement window. I already decided to remove all of the old blocking and I definitely did not want to install blocking under both beams unless it was required.
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