Deck joist blocking/bridging

[Jason C. Bancroft]

I need some advice regarding blocking or bridging to prevent the deck joists from "racking".

Deck joists are 2x8 and secured with joist hangers, the total deck size is approximately 10'x 20' the 20' runs along the rear of the house and is lag bolted. There is no blocking or bridging between the joists. Is there a structural concern or safety issue not having this blocking present??? Should this even be mentioned in the report?

thanks,

Jason

[Larry D. Kage]

Originally Posted by jbancroft

I need some advice regarding blocking or bridging to prevent the deck joists from "racking".

Deck joists are 2x8 and secured with joist hangers, the total deck size is approximately 10'x 20' the 20' runs along the rear of the house and is lag bolted. There is no blocking or bridging between the joists. Is there a structural concern or safety issue not having this blocking present??? Should this even be mentioned in the report?

thanks,

Jason

Probably not but possibly, without seeing it, hard to say for sure.

The ledger against the house was the 20 foot length?...and was bolted to the house and had proper joist hangers installed? How were the other end of the floor joists framed?

Here's a nice reference:
Ooops...it's too big of a file...I'll see if I can find a link instead.

[Jason C. Bancroft]

Ledger board ran the entire 20' length and was actualy two pieces both were attached with lag bolts and joist hangers. The other end is on a support beam that is bolted to vertical support posts.

[Larry D. Kage]

Yes, here it is: http://buildingcodes.jocogov.org/doc...eck%20Book.pdf

[Larry D. Kage]

It looks like solid blocking above the beam, as is shown in figure 15, or hangers at the rim joist could be helpful for the cantilevered joists...Oh, I see, the deck boards attached to the house on the ends keep it from racking.

The flashing of the ledger looks strange in your pics...was the ledger flashed on top?...I can't see that...only see what appears to be flashing on the bottom.

One of the most common areas of water infiltration and rot I find is where the deck attachment is not flashed properly.

[Brian R. Paull]

Looks like 2x6 joist hangers on 2x8 lumber.

[Kenton H. Shepard, CMI]

Mid-span blocking (and bridging) is supposed to address joist rotation. It's seldom used anymore and works best for providing squeaks to floors which would have otherwise have been nice and quiet. Joists are fastened at each end by nails or hangers (2x6 hangers on 2x8 is OK) and are fastened along the length of their top where the planking fastens to them, or in the case of a floor where the subfloor is nailed to them. They won't rotate and blocks/bridging are a waste of time. I would never call them if I didn't see them unless I knew they'd been spec'ed by an engineer.

[Richard A. Hetzel]

There has been debate for decades about whether joist bridging actually does anything or not. Its stated purpose is to help distribute any unusual concentrated load to adjacent joists. Whether it actually does so has never been fully established. I still specify it, because many code enforcement officials will expect it, and it saves my clients expensive "extras" if it was not specified but was required by the code official. The manufacturers of composite joists actually state in their literature that cross-bridging is not required for their product. It's just one of those little construction issues that linger on without proof of function, much like the 2x4 key that is often shown where a wall meets a footing. It isn't really required, because the mortar joint has sufficient strength to prevent lateral movement, but even when I don't show it on my drawings, I notice that contractors sometimes do it anyway.