Oversizing Deck Beams - 2021 IRC FIX

[Glenn]

I have been representing the North American Deck and Railing Association (NADRA) in work with many others in the Deck Code Coalition to improve the prescriptive codes for deck construction in the IRC. We have a number of proposals in for the 2021. I would like to make you aware of them, answer your questions, listen to your concerns, and earn your support. The text below is from my social media. There are two links. One to a written blog that explains two of our proposals. The other is to a portion of one of my class videos from 2015 that explains the problem we are trying to fix and the mathematical analysis I created.

FYI: NADRA is an industry association with builders, manufacturers, home inspectors, and retailers among their membership. They are not trying to benefit only one sector of membership. I am no "hired gun". The Deck Code Coalition includes the AWC, NAHB, CLMA, SMA, multiple engineering firms, product manufacturers and code officials. We have honestly done very well bringing together a wide diversity of interested parties to share, learn and compromise on our proposals.

Please watch the video and read the blog. I will be writing a blog each week that discusses our proposals.

THANK YOU.

Are you OVERsizing your deck beams? You probably are, so let's fix that in the 2021 International Residential Code! North American Deck & Railing Association and the Deck Code Coaltion (DCC) have submitted proposal RB190-19 and it was approved at the International Code Council Committee Action Hearing. In 2015 the first deck beam sizing table was published in the IRC, but it sizes every beam as if supporting maximum cantilevered joists, whether they do or don't cantilever. So I came up with a "fix" and began teaching it in my deck classes as "unofficial code" (see video snippet from my online course: https://youtu.be/SROAZgyhXQI ). Through my work for NADRA, I took this idea to the DCC for support and got it. The American Wood Council engineer in our coalition polished it up and we submitted it to the 2021 IRC. Take a read of my explanation of this proposal on the NADRA blog. I'll be highlighting all of our proposals each week. Please contact me if you have any questions. If you believe in appropriate minimum standards for deck construction, please share this.

BLOG LINK FOR ARTICLE: http://www.nadrablog.com/?p=5126

 

[e hilton]

Im not sure i understand why its wrong to over build ...

 

[jar546]

Im not sure i understand why its wrong to over build ...

There is nothing wrong with it at all. I think the minimum codes have a built in safety factor and building to the codes can make a contractor's bid more competitive. No reason to exceed the code. It is like suggesting that wherever you have #14 or #12 wire in your house, you build it with all #10 instead. It might make you feel good but it is not necessary and the #14 & #12 will work just fine for decades to come.

 

[e hilton]

True. I guess im thinking that so many builders cut corners, that over-spec is good.

 

[TheCommish]

put a decent note for the saying if the beam is supporting a cantilever use the next size up.

 

[Mr. Inspector]

I wish the IRC had provisions for self supporting decks. We all herd over and over again about deck ledger failures is the most common problem in construction and get the most people hurt. I would think that the code would encourage self supporting decks, maybe even require them and not allow ledger support unless engineered.

 

[Sifu]

Glen,
Is it stated in the code that the beam spans automatically assume the cantilever or is that something you know from being an insider? For me the code says cantilevers are permitted but I don't see the assumption. When I have a deck with a cantilever I add the proposed cantilever distance to my span. So the 10' span in your video would be a 12 1/2' span if they used the entire allowable distance. I agree that may be overly conservative if the table assumes it already. If so, it seems like a pretty easy fix with a footnote.

As an aside, while I GREATLY appreciate the clarity of the footing tables, most people in our neck of the woods use caissons, not true footings, and those tables are awfully conservative for caissons. For my part I am OK with a little overbuilding, but I feel a little hypocritical when I complain about the high cost of building while at the same time I might be requiring more money be spent when it is not needed.

Appreciate all your work.

 

[Glenn]

I wish the IRC had provisions for self supporting decks. We all herd over and over again about deck ledger failures is the most common problem in construction and get the most people hurt. I would think that the code would encourage self supporting decks, maybe even require them and not allow ledger support unless engineered.

Freestanding is definitely getting more attention, but it creates a new host of problems. We are working to address them, but it's not easy:
1) A deck doesn't have braced walls. It is essentially an un-defined method of construction (not platform, balloon, or post-frame). When you are no longer connected to a braced house, the deck must be braced on it's own. When people propose to me freestanding deck designs, I always remind them to imagine the deck is standing alone in the center of the yard. That helps folks realize the missing bracing. The AWC and their DCA-6 document does address some methods of bracing freestanding decks.
2) The beam adjacent the house ends up with footers or caisions in the backfill area of the foundation. This is not "undisturbed soil". If there is a basement, this means very deep excavation, helical piers or other alternatives.

 

[Glenn]

Glen,
Is it stated in the code that the beam spans automatically assume the cantilever or is that something you know from being an insider? For me the code says cantilevers are permitted but I don't see the assumption. When I have a deck with a cantilever I add the proposed cantilever distance to my span. So the 10' span in your video would be a 12 1/2' span if they used the entire allowable distance. I agree that may be overly conservative if the table assumes it already. If so, it seems like a pretty easy fix with a footnote.

As an aside, while I GREATLY appreciate the clarity of the footing tables, most people in our neck of the woods use caissons, not true footings, and those tables are awfully conservative for caissons. For my part I am OK with a little overbuilding, but I feel a little hypocritical when I complain about the high cost of building while at the same time I might be requiring more money be spent when it is not needed.

Appreciate all your work.

That is a really, really good point. I know the beam span table assumes the joist cantilever because I am part of the group that developed the table and continues to work on it. This is something that should be mentioned in the commentary or a footnote. Of course, if our proposal is approved for 2021 it will make it clear and provide the modification method for when the joists don't cantilever.

You are absolutely correct about the footing table, and I am working on it. The problem is that the IRC prescriptive foundation designs ONLY account for bearing area. So whether a footing or a caision/pier, the only prescriptive way to size them is the bearing area at the bottom. Basically a caision is just a really tall footing. I am in Colorado and we have seen success with 36" deep, 8" round pier for decks for all of time. I have exclaimed this until I am blue in the face to the group I work with, but I get no where. The proof of performance is completely empirical ("we've been doing it this way and have no problems"). That argument gets me NO WHERE with engineers. We have to have funding for new research regarding shallow piers and skin friction for lightly loaded flexible structures. We have tons of homes built on piers and grade beams, but when you read the soil report and foundation design, they discredit the upper 15 ft. for having any skin friction. This hurts my argument again for narrow, 36" deep piers.

HOWEVER, we also have a proposal to modify the footing table. Right now the smallest pier is 14 inch diameter, which NO ONE will adopt in my region. There is no need. The smallest tributary area in the table is 20 square feet. We have proposed a new 5 square feet area to cover small stair landings. We have also reduced the minimum size of 14 inch. That is proposal RB184 and it was not approved at the committee action hearing. We have a public comment and hope for the government member vote to approve it.

 

[Glenn]

Im not sure i understand why its wrong to over build ...

The code minimum is there so that safety is balanced with affordability. If a beam will perform, why make the deck more expensive or have more obstructive posts than necessary. Most everyone shares the dream of home ownership. Minimum code makes that more possible for people.

Also consider that decks are MUCH more expensive than they used to be. That has a lot to do with that we used to build them like garbage. Decks don't last forever. They become very unsafe, but are very expensive to replace. Yet, they are often the only access to the front or back yard. If the minimum code is more expensive due to unnecessarily large beams (among other things), then maybe someone can't afford to replace their rotting deck. Now they are more unsafe with the old deck than if they could build a minimum code deck. I feel a lot of people forget that as they strive for a "better" code. They forget that a "lesser" code for new construction is probably still much better than existing construction.

Here's a way of looking at it. You are starving to death (rotting deck, old house, etc). You would be better off if you could eat some green bean casserole (bare minimum code), than not being able to afford the organic, farm-raised, five course meal (excessive code). I always remember that when folks are trying to fix or repair their homes.

 

[TheCommish]

For a free standing deck, you can still attach to the building for lateral resistance

 

[e hilton]

Glenn ... question about footings and columns/posts. Going from bad memory here ... code requires a 24x24x8” footing 30” below grade to get below frost depth. What is the preferred method of dealing with the post? Have the last 2 ft be below grade to attach to the footing? Or use a sonotube 30” tall so the post sits on a connector above grade?

 

[Mr. Inspector]

Freestanding is definitely getting more attention, but it creates a new host of problems. We are working to address them, but it's not easy:
1) A deck doesn't have braced walls. It is essentially an un-defined method of construction (not platform, balloon, or post-frame). When you are no longer connected to a braced house, the deck must be braced on it's own. When people propose to me freestanding deck designs, I always remind them to imagine the deck is standing alone in the center of the yard. That helps folks realize the missing bracing. The AWC and their DCA-6 document does address some methods of bracing freestanding decks.
2) The beam adjacent the house ends up with footers or caisions in the backfill area of the foundation. This is not "undisturbed soil". If there is a basement, this means very deep excavation, helical piers or other alternatives.

I had a lot of decks that they attached the ledger to rim joist of a cantilever on a house. The deck plans never indicate a cantilever on the house. So now it must be free standing (after they messed up the house siding). Also have a lot of free-standing above-ground pool decks.

 

[steveray]

Freestanding is definitely getting more attention, but it creates a new host of problems. We are working to address them, but it's not easy:
1) A deck doesn't have braced walls. It is essentially an un-defined method of construction (not platform, balloon, or post-frame). When you are no longer connected to a braced house, the deck must be braced on it's own. When people propose to me freestanding deck designs, I always remind them to imagine the deck is standing alone in the center of the yard. That helps folks realize the missing bracing. The AWC and their DCA-6 document does address some methods of bracing freestanding decks.
2) The beam adjacent the house ends up with footers or caisions in the backfill area of the foundation. This is not "undisturbed soil". If there is a basement, this means very deep excavation, helical piers or other alternatives.

I have no problems with freestanding, as Rick says we do it all the time for pools....While we are on the "fill" topic, does anyone not allow a crawlspace addition or deck for that matter adjacent to a 30yr old backfilled house? We do it all the time here and never heard of a failure...

 

[Glenn]

I have no problems with freestanding, as Rick says we do it all the time for pools....While we are on the "fill" topic, does anyone not allow a crawlspace addition or deck for that matter adjacent to a 30yr old backfilled house? We do it all the time here and never heard of a failure...

When I wrote my deck code book for ICC on the 2009 IRC I tried to state that the building official could approve deck piers/footers on older backfill that had long settled. The technical editors struck it out and responded to me with, and I quote, "If T-Rex didn't walk on that earth in its natural state then it is NOT 'undisturbed soil'". Every time this subject comes up and I try to argue this, I am beat up by academia. Empirical observations are very hard to argue in the code development arena.
It is absolutely fact that backfill settles and is not suitable (originally) for a foundation. I have torn out dozens of old, original, ground-level decks to find large sink holes in the backfill. However, I do believe for a deck, at some point, the backfill has probably settled enough. Other agree with me...and then say an engineer has to approve it with a compaction test. So...yeah... I go in circles.

 

[steveray]

Thanks Glenn!

 

[Mr. Inspector]

Deck piers within 5' of a house foundation should be as deep as the house footing.

 

[Glenn]

Deck piers within 5' of a house foundation should be as deep as the house footing.

Indeed... this blanket statement is the problem for freestanding decks. By the written words of the IRC, you are correct...

I live in a 1950's home with a full basement. I have a deck framed with 2x6 that is sitting an inch above grade and supported on piers. It is nearly as innocent as a flagstone patio, but as a deck builder 16 years ago when I built it, I wasn't going to be using flagstone! I have many piers within 3 feet of my foundation and definitely in the backfill. You would never have known if you had been the one digging the three-foot deep holes. Very tough digging.

So... The building department tells someone coming to get a permit like this that they need to dig those piers 9 feet deep to the bottom of their foundation. Ok... so I tear down my fence, ruin my yard, and rent heavy equipment to perform this excavation? Or I pay for a helical pier company? NO. That is not what an average American does.

What happens is that building department never sees that homeowner again. EVER. He never looks for a permit from his "crazy" building department ever again. He tells all his friends and neighbors the story. They agree. Then they build the deck over an egress window, they block a dryer vent, they build to close to overhead service cables, they build their stairs wrong, etc, etc. The BO never gets to help protect them from real hazards... they fell on their sword of backfill...

This is everything wrong with how some code administrators choose to be enforcers. My deck is 16 years in service and as level as the day I built it. I cannot deny that truth.

I also cannot not deny the truth that currently the code says you can't bear on undisturbed soil. This is a problem.

 

[Sifu]

I must point out that in a recent AWC webinar it was stated that free-standing decks are not supported by the 2018 IRC by R311.5 which says the deck shall be designed to be self-supporting. In the past I tended to ignore the word designed when it came to this subject whereas most other times I do not. I think that section is a little weak, however the AWC rep pointed it out so I figured I would pass it along. As I recall, one of the reasons for this was the disturbed fill at the foundation. I do agree that they can work, especially in cases of long term consolidation but there would shirley be times when they would not. I actually carried a probe back in the day and would do me best to try and make a case by case determination instead of a blanket approval or denial.

 

[jar546]

The issue of a foundation next to an existing structure where there is a basement or crawlspace has been around for a while. Especially when there is a basement and they want to put on an addition with just a crawlspace. The first 5 feet can be problematic.

 

[my250r11]

What happens is that building department never sees that homeowner again. EVER.

This happens on many subjects!!!

As for undisturbed that is up to the local AHJ's interpretation. Here that means match the existing footing level.

 

[nw matt]

I have a couple of questions regarding pressure treated beam sizing for exterior decks: In the 2021 irc, table R507.5, I see multiple plies of 2x, but don't see single ply of 4x. I think I remember that the irc used to support the use of 4x beams; what is the reason for no longer allowing this? If I'm building up (3) 2x10, would I be allowed to place spacers between the plies to build the beam out to a 5.5" width to better fit the top of my 6x6 post? Thanks.

 

[Joe.B]

I see multiple plies of 2x, but don't see single ply of 4x. I think I remember that the irc used to support the use of 4x beams; what is the reason for no longer allowing this? If I'm building up (3) 2x10, would I be allowed to place spacers between the plies to build the beam out to a 5.5" width to better fit the top of my 6x6 post? Thanks.

I believe that if you want to use 4x then technically speaking you would be required to have it "engineered". Whether your local AHJ would hold you to that or not I can't say.

I believe the reason for this is that there is less likely to be a "fatal" flaw in two individual pieces. Meaning that if you install a 4x there could be a flaw that would cause the entire beam to fail. The odds of two 2x's having the same flaw in the same place is a lot lower.

When I have seen two 2x's used to build a header they would add a piece of 1/2" ply to bring it out to the correct depth to sit flush on the trimmer. I guess if you used PT plywood then it should hold up too the elements, but I've never seen it done.

 

[Paul Sweet]

I expect that 4-bys aren't included is because they are harder to find than 2-bys. A 4-by is 3 1/2" wide while two 2-bys add up to 3", so a 4-by of the same grade is stronger.