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Girders for open porches

Rick18071

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1. The IRC does not have a definition of porch or deck. Can you use 2015 IRC table R602.7(3) Girder and Headers Spans for Open Porches for covered decks?
2. This table also has beams for the floor for porches that are a little longer spans then for decks. Why the difference?
3. Does this mean the codes treats porches different than decks and porches (which also could mean a covered deck), porches do not need the tension devices and all the other things required for decks in section R507?
 

Glenn

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Okay. Here goes. First, I have to mention that I teach the following in much greater detail and with visuals, graphics and photos in my on-demand courses at www.buildingcodecollege.com (Porch Roof Framing and Decks, Down the Load Path)

1) Gravity does not care what we call things, but what we call things sure makes it confusing for us to address gravity. Table R602.7(3) is primarily to size roof beams for a "porch roof". This could be over a deck, concrete, flagstone, or a mud-wrestling arena.

2) This table also has a little tidbit about floors (which I will propose to remove in 2024, to eliminate this exact confusion.). The beam sizing for the floor in Table R602.7(3) assumes NO JOIST CANTILEVER beyond the beam. It also assumes the floor is completely sheltered from snow loads (based only on 40 psf). However, Table R507.5 for beam span assumes the JOIST CANTILEVERS THE MAXIMUM ALLOWABLE BEYOND THE BEAM. This why in table 602.7(3) you see a (2) 2x10 can span 10-4 with an 8 ft. joist span (only 4 feet is assumed to be loaded on the beam). However, go to table 507.5 and a (2) 2x10 beam supporting an 8 ft. joist span is limited to 9-0. This is because this table is designed to assume that joist cantilevers 2 feet beyond the beam, thus loading the beam with 6 feet of joist as opposed to 4.

3) No, the code does not treat these differently. It's just the evolution of the codes and the result of many people collectively creating the one code.

And as loud as I can scream it in all caps. TENSION DEVICES ARE NOT REQUIRED ON DECKS AND NEVER HAVE BEEN. (not by the model IRC)

I also have education that reveals the facts behind my above statement, but you can go to youtube for it.
 

tmurray

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Okay. Here goes. First, I have to mention that I teach the following in much greater detail and with visuals, graphics and photos in my on-demand courses at www.buildingcodecollege.com (Porch Roof Framing and Decks, Down the Load Path)

1) Gravity does not care what we call things, but what we call things sure makes it confusing for us to address gravity. Table R602.7(3) is primarily to size roof beams for a "porch roof". This could be over a deck, concrete, flagstone, or a mud-wrestling arena.

2) This table also has a little tidbit about floors (which I will propose to remove in 2024, to eliminate this exact confusion.). The beam sizing for the floor in Table R602.7(3) assumes NO JOIST CANTILEVER beyond the beam. It also assumes the floor is completely sheltered from snow loads (based only on 40 psf). However, Table R507.5 for beam span assumes the JOIST CANTILEVERS THE MAXIMUM ALLOWABLE BEYOND THE BEAM. This why in table 602.7(3) you see a (2) 2x10 can span 10-4 with an 8 ft. joist span (only 4 feet is assumed to be loaded on the beam). However, go to table 507.5 and a (2) 2x10 beam supporting an 8 ft. joist span is limited to 9-0. This is because this table is designed to assume that joist cantilevers 2 feet beyond the beam, thus loading the beam with 6 feet of joist as opposed to 4.

3) No, the code does not treat these differently. It's just the evolution of the codes and the result of many people collectively creating the one code.

And as loud as I can scream it in all caps. TENSION DEVICES ARE NOT REQUIRED ON DECKS AND NEVER HAVE BEEN. (not by the model IRC)

I also have education that reveals the facts behind my above statement, but you can go to youtube for it.
"Gravity does not care what we call things. " this is the best statement I've heard in a while.
 

Rick18071

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The code requires a design for lateral loads. Most plans we get already specify that they are using hold-down tension devices. When new plans for a plan review and do not specify a design for lateral loads review we automatically add the hold-down tension devices to the plan. If they do not want to use them we allow them design a different design for lateral loads but it would need to be designed by an professional with a stamp since the code does not have any other prescriptive way in it. This is also required by my boss.

We do use the AWC "Prescriptive Residential Wood Deck Construction Guide"

I just mostly wanted to know if the code treats porches different than decks. Or even a Category 1 sunroom (screened-in)
 

Glenn

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The code requires a design for lateral loads. Most plans we get already specify that they are using hold-down tension devices. When new plans for a plan review and do not specify a design for lateral loads review we automatically add the hold-down tension devices to the plan. If they do not want to use them we allow them design a different design for lateral loads but it would need to be designed by an professional with a stamp since the code does not have any other prescriptive way in it. This is also required by my boss.
The code does not treat the structural design of an elevated, wood-framed, exterior, floor surface differently based on whether it is called a deck, porch, or balcony.

As for the quote above, I'm sorry, I just can't bite my tongue, as your statement is precisely why I have screamed against these lateral load anchors since they were first put in the code. NOTE: this rant is not an angry rant, just frustrated.

They are false solutions that ended the vital conversation, research, and work needed to provide a real "design for lateral loads". I was in the deck industry long before these connectors and as a lowly young deck builder I knew decks were missing overall lateral load design with every deck I tore down that was swaying in the wind, loose and rickety. Lateral loads are not just a ledger issue.

As a way to soothe a concerned code committee (see my video) ten years ago about a ledger pulling a band joist from a house, we got a picture of a connector.

These two connectors are now being considered "a lateral load design" for any and all deck shapes and sizes, simply because they are in the code. As if they are some magical device and to do anything else a builder needs a fully licensed engineered design.

It is irresponsible and reckless of the IRC to have a universal, seemingly prescriptive, structural design for a major loading direction that makes no reference what-so-ever to the overall shape of the structure. Compare this to over 20 pages of braced wall design...

This would be like approving a house of any shape or size with zero braced wall panels, but plenty of hold down anchors in the corners. Then comparing that house to a fully engineered house.

I am very aware of the DCA-6 from AWC and work closely with those folks at times. They also do not provide a complete lateral load design for decks. This is a big deal that needs to be fixed, but its hard to get attention to fix it when folks for a decade have just pointed to a connector and said "we're good".

I have to add, the research in my video reveals that the greatest lateral load on a deck is a "live lateral load". Okay, what's the magnitude of that load? Without a standardized design load magnitude for an engineer to design against, how are we even asking for legitimate engineering? They would have to literally make up their own loads to design for. ASCE 7 has no "lateral live load" magnitude to design for, unless something recent was approved. I know that the researches that conducted the research I referenced were at one point submitting that criteria to ASCE. There has been little other research to "lateral live load", and I've explained why, but here it is again.

People think two connectors solved the problem ten years ago.
 

ADAguy

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Live load on decks (both new & old) with uncontrolled access by multiple individuals continues to be the cause of deaths and injuries, how many? Need to ask and provide stats to get their attention.
 

Rick18071

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Thank you Glenn for all your research on the subject. I saw your video a few years ago and agree with you but I still need to inforce using the hold-down tension devices. It makes me wonder how many requirements in the code were really tested and researched or just made up.

PA took out the over 20 pages of braced wall design because they said there was no proof of a house in PA of ever having damage because it lacked wall bracing. (I don't mind, it looks too complicated anyway) And also the housing industry has a lot of political power. But that is another story and left us with a hodgepodge of a code from 3 different editions of the IRC put together, and some things made up without a PA edition of the IRC to put it all together in one book.

What ticks me off is when there is no consistency of terms. There shouldn't be many words that mean the same thing. If a porch, deck, landing, category 1 sunroom is the same thing then it should have the same name with a definition. I think balcony is treated different but still no definition..
 

Glenn

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I agree with everything you stated Rick, and I understand that you have to do the job you have to do. The IRC is definitely one hell of a mess before you even get it to the government.

I am working a lot of proposals to "clean up" things like this in the IRC for 2024. Thanks for the conversation.
 

Rick18071

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Stringers are joists and use the joist span tables.

R311.5.1 Attachment. Exterior landings, decks, balconies,
stairs and similar facilities shall be positively
anchored to the primary structure to resist both vertical
and lateral forces or shall be designed to be self-supporting.
Attachment shall not be accomplished by use of toenails
or nails subject to withdrawal.


R502.6 Bearing. The ends of each joist, beam or girder shall
have not less than 11/2 inches (38 mm) of bearing on wood or
metal and not less than 3 inches (76 mm) on masonry or concrete
except where supported on a 1-inch by 4-inch (25 mm
by 102 mm) ribbon strip and nailed to the adjacent stud or by
the use of approved joist hangers. The bearing on masonry or
concrete shall be direct, or a sill plate of 2-inch-minimum (51
mm) nominal thickness shall be provided under the joist,
beam or girder. The sill plate shall provide a minimum nominal
bearing area of 48 square inches (30 865 square mm).

R502.6.2 Joist framing. Joists framing into the side of a
wood girder shall be supported by approved framing
anchors or on ledger strips not less than nominal 2 inches
by 2 inches (51 mm by 51 mm)
 

steveray

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No.....Because you can't notch a joist enough to make it a stringer....And I don't know that I would buy joist bearing being the same as a stringer which is more like a R802.3 rafter connection...Not really knocking what you guys do, just maybe pushing the envelope of "accepted engineering practice" vs. sealed by an engineer....
 

Rick18071

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If they just need a 2x6 per the span tables but they use a 2x12 and notch it for a stringer there is still enough wood left that is not notched to be a 2x6. i wouldn't be any different then nailing triangle shapes of wood onto the edge of a 2x6. This is what I was taught in IRC classes long ago.
You measure the span horizontally like you do rafters.

For something we see in every house and deck I wish the code book would be more specific about stringer construction.
 
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steveray

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Absolutely a hole in the code, ripping structural lumber is also not allowed by most if not all grading/ wood manufacturers..So it is not really just like a 2x6:

1610737972651.png

"American Softwoods Standard" DOC PS 20-99
Section 7.3.7:
"Remanufacture (ripped, resawn, or surfaced) of graded or grade marked lumber negates the grade or grade mark and the design values of the original product"
 

Glenn

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This is an incredibly difficult subject to tackle, as there are many of us that have been trying to figure it out for a long time. The problem tops out at the modification of graded lumber. There is no way to field cut graded lumber for structural use without an evaluation of the remaining lumber. That evaluation is very difficult to "simplify" in the IRC without undercutting the long-established grading process.

Sistering a 2x6 alongside the notched stringer is one way to pirate off the rafter span table for stairs. However, for all of time, notched stringers have been accepted, so this is a very difficult change for people to accept. "finding a problem for a solution" is a common response.

More often than anything, notched stringers don't fail in shear or bending from the remaining solid portion. They fail in the triangle pieces that fall off by breaking along the short lengths of grain.

Though that and lateral bracing (sway of the stairs) are actually the two biggest issues in stairs visible in existing structures, the talk is always about the span of the cut material.

Fun stuff. I look forward to other responses.
 
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