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Giles 04-01-2011 11:28 AM

Deck Beam Question
I am in the planning stage of building a new deck. I plan to use the underside of the deck for storage of tractor and equipment and I need all the headroom possible.
I have a good understanding of building a deck and appreciate the built in safety factors of design.
On the center beam, which will span 24', I would like to attach the Joists to both sides of the double 2"x12" Beam. This would give me the needed headroom. There will be a distance of 14' between Beams.
According to some Deck building instructions, it is stated that in this joist to beam attachment, joists shall not be attached to opposite sides of beam.
Top mounting of joists to beam construction will not be a problem with outside beam as the headroom will be sufficient.
Top mounting of the center joist to beam will require additional excivation and will create a drainage problem.
My question is---Why is this a code requirement, in some places, and is there a particular way that I can attach to both sides?

dvatt 04-01-2011 12:34 PM

You could notch the post on both sides and then thru bolt

Giles 04-01-2011 01:12 PM


Originally Posted by dvatt (Post 621336)
You could notch the post on both sides and then thru bolt

So are saying is that I could notch both sides of the post and sandwich a third (center) beam between them, and then I can mount joist on both sides?

dvatt 04-01-2011 04:15 PM

No third. Just notch both sides and leave the middle

Clutchcargo 04-01-2011 05:50 PM

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Hang on,
Giles I think you are correct, you cannot attach joists the way that dvatt indicated. You will be attaching the joists using joist hangers, correct?
In essence, if you attach a 2x to each side of the post, the beam is only 1 ply. You need to build a double 2x beam and then attach to the posts. The posts will need to be notched by 3" on one side only so that you can get a double 2x attached.
Someone else will pipe in if I'm off target.

Edit: here's a good resource.

dvatt 04-04-2011 09:32 AM

Why can't u notch 1.5 on both sides? I've done hundreds of decks that way. It's a great way to prevent the double ply beam from rotting.

Clutchcargo 04-04-2011 07:31 PM

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Good point about the rot. I don't think that we have enough info. That single 2x12 that he'll be hanging on might be overloaded.

Giles 04-04-2011 07:46 PM

What I don't understand is that all homes I have owned have floor joist connected to both sides of the beams. I assume it is forbidden because of exposure to weather.

Clutchcargo 04-04-2011 08:29 PM

63 Attachment(s)
Typically a beam is 2 ply glued and nailed together. The issue I have by attaching to different sides of the post is that this beam cannot be nailed together to act as a single unit.

dvatt 04-04-2011 08:50 PM


Originally Posted by Clutchcargo
Typically a beam is 2 ply glued and nailed together. The issue I have by attaching to different sides of the post is that this beam cannot be nailed together to act as a single unit.

Glued? No. Why would you glue pt? If your going to notch 3 in then you should flash the top of the 2 2 x's

A lot of times I get my girder/dropbeam whatever you want to call it together the boards vary up to a 3/16 of an in difference in width and notching on both sides of the 6 x 6 allows this. I have seen countless girders where only one 2 by is supporting the joist due to the diff widths.

Clutchcargo 04-04-2011 09:56 PM

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No you wouldn't glue an exterior beam, but I do for all interior sawn headers.

If the 2x's are nailed together it doesn't really matter if the joists are only bearing on one of the plys of beam.

Gary in WA 04-04-2011 10:20 PM

Giles, top bearing joists in a house or on a deck is fine. Side-mounted joists in hangers on both sides in a house is fine, but not on a deck because the plywood/OSB sub-floor ties the two separate joists together from each side to hold it together in shear flow. On a deck, it is allowed on one side only. At the rim outboard or at the house ledger, inboard. This from a building code; "Floor systems having joists framing from opposite sides over a bearing support shall be tied together by lapping joists a minimum of 3 inches or with a wood or metal splice, or by continuity of floor sheathing overlapping the ends of joists at least 3 inches, or by other approved methods. Face nail overlapping joists together with 3-10 D nails."
The tie is the nails in overlapping joists. Plywood ties interior.

Ask your local B.D. for verification when you get a permit for your project.


Clutchcargo 04-05-2011 09:56 AM

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GBR, could you add strapping across the tops of the opposite joists to tie them together?
Lateral hold downs run right through the beam would be another option that sounds like it satisfies this requirement.

Gary in WA 04-05-2011 10:01 PM

The local AHJ would have final say. Another odd example, pp5;


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