# Questions about double rim joist on deck



## chandler48 (Jun 5, 2017)

2x8's are more than adequate with your span, but 2x10's are good. With the option of a double rim, I like to use 2x8 for the inner rim and raise the 2x10 outer rim 1" above the 2x8 to allow for the deck boards to sit inside and form its own breadboard. What is the short beam for, and why does it only go part of the way? Do you have plans for a hot tub or something heavy? Your earlier posts are not referred to, so we will probably be asking the same questions again.


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## jlhaslip (Dec 31, 2009)

I prefer to add the outer layer last. That allows for mitred corners which hid the end grain.


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## Nealtw (Jun 22, 2017)

We always wrap the outside with painted fascia 2x10s just for the look and they are 2x10s
But is doesn't matter where you put the extra.

As you are not attaching this to the house you want to have a 2x4 acroos under the joist on an angle to keep it square just one between the two long beams. and you want a 2x4 from high in the side of a joist to low on a post in two place between the two long beams, that will stop it from rolling.
Then mid span of the joists you want a 2x4 block between the joists


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## MTN REMODEL LLC (Sep 11, 2010)

Maybe we can get Dan to chime in from an engineering standpoint...

but I have never understood the necessity or advantage for a double rim/closure joist from a structural/ rigidity standpoint.

(I had a 2 foot cantilever, maybe 8-10 foot wide, that the engineer specked out a double rim... I did it... but never got to ask him why).

I normally on a deck will use what I call a rim joist and a 2" wider member that I call a facia to close my decking end cuts.... but acts, I guess as a double rim.

But .... I do wonder the structural advantage of a double rim.

Just curious.... anybody know...????


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## chandler48 (Jun 5, 2017)

In the OP's situation a double rim joist has no advantage due to the short distances between supports. This is the case normally. Doubling the rims will give more support, but if it is not needed, then why go to the trouble except for a breadboard effect, which I like.


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## RETALS (Sep 27, 2016)

chandler48 said:


> 2x8's are more than adequate with your span, but 2x10's are good. With the option of a double rim, I like to use 2x8 for the inner rim and raise the 2x10 outer rim 1" above the 2x8 to allow for the deck boards to sit inside and form its own breadboard. What is the short beam for, and why does it only go part of the way? Do you have plans for a hot tub or something heavy? Your earlier posts are not referred to, so we will probably be asking the same questions again.


Well when I started my plans I used the Lowes deck designer to get a rough outline. That notch is where the deck wraps around my chimney. If it weren't for that corner I wouldn't even need the short beam. Its sole purpose is to add support under that corner. That's why it wasn't needed to make it a full length beam.


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## RETALS (Sep 27, 2016)

chandler48 said:


> In the OP's situation a double rim joist has no advantage due to the short distances between supports. This is the case normally. Doubling the rims will give more support, but if it is not needed, then why go to the trouble except for a breadboard effect, which I like.


If I were going to go the breadboard route, I would only need to double the rim on 3 sides right? It would be pointless to double it against the house.


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## RETALS (Sep 27, 2016)

jlhaslip said:


> I prefer to add the outer layer last. That allows for mitred corners which hid the end grain.


Wouldn't I want to have both plys of a double rim resting on the beams rather than the outer ply just hanging?


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## jlhaslip (Dec 31, 2009)

RETALS said:


> Wouldn't I want to have both plys of a double rim resting on the beams rather than the outer ply just hanging?


Size and position the Beams to suit the double rim.


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## chandler48 (Jun 5, 2017)

RETALS said:


> If I were going to go the breadboard route, I would only need to double the rim on 3 sides right? It would be pointless to double it against the house.


You are correct.


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## ktmrider (Apr 3, 2017)

the only time you need a double rim joist is if you are not using a beam,if you're joists are running the entire span


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## Californiadecks (Aug 30, 2012)

Double rims are great for picture frame backing. You can alternate the corners of the rimboards in a "woven" pattern. We call it "log cabin corners." 

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## ront02769 (Nov 28, 2008)

Nice thought. But not necessarily correct in all circumstances. Ron


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## Californiadecks (Aug 30, 2012)

I just wrote a 6 page article in next month's Professional Deck Builder magazine that includes this exact same topic. The double rim is great for strengthening any posts you may have and gives solid backing for your borders. In fact it's almost always called out for by my engineers. Like this.









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## RETALS (Sep 27, 2016)

chandler48 said:


> 2x8's are more than adequate with your span, but 2x10's are good. With the option of a double rim, I like to use 2x8 for the inner rim and raise the 2x10 outer rim 1" above the 2x8 to allow for the deck boards to sit inside and form its own breadboard. What is the short beam for, and why does it only go part of the way? Do you have plans for a hot tub or something heavy? Your earlier posts are not referred to, so we will probably be asking the same questions again.


I've already got everything spec'd and measured for 2x10. If I double the joist, and I raise the outer ply up an inch, that's going to leave a 1" gap between the end of my beams and the board? Or am I not understanding? If I were to move up to 2x12 on the outer ply I would be a half inch too tall.


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## Californiadecks (Aug 30, 2012)

I don't apply the fascia rim over the deck board ends. I run the decking past to allow for a nosing. Like this with a picture frame border.









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## Californiadecks (Aug 30, 2012)

applying the fascia over the ends allows for water intrusion and rot. 

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## RETALS (Sep 27, 2016)

Californiadecks said:


> I don't apply the fascia rim over the deck board ends. I run the decking past to allow for a nosing. Like this with a picture frame border.
> 
> 
> 
> ...


I like the look of that. Is there additional blocking to support the ends of the decking? I assume the picture frame takes up all of the rim itself.


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## chandler48 (Jun 5, 2017)

A pure breadboard as Californiadecks shows is preferred and I like it. To answer your question, the taller board on the outside would only be raised 1", leaving 1/2" below the inner board. Since you have spec'd it out at 2x10's, using a 2x12 would be quite obtrusive looking, IMO. For the breadboard, yes, you will need to use additional blocking to nail down the strips and bring your field boards to something to attach to, but it makes for a much neater design, especially something low as this deck is.


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## RETALS (Sep 27, 2016)

Decking aside, I started on the rim this weekend. My 16'-4" board against the house ended up being a little more crowned than I would like. It spans 3 of the beams (see image at beginning of thread) and is crowned over the middle beam. So it's hovering a good 3/4 of an inch off the beam. Is this a concern? Will it naturally settle? Should I just crawl under and add a hurricane tie later?


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## RETALS (Sep 27, 2016)

Actually 3/4" is probably a little on the high side. It's closer to 1/2".


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