Footings and stem walls

[bill1952]

Just can't find in 2018 IRC but: where is requirement - seismic A, B, or C - for dowels or keyway between footing and stem wall? Certainly not shown in illustrations, Figure R403.1(1) for example, and not finding in text.

 

[mtlogcabin]

I think you should be in R404 foundation walls and look at the various tables. Depending on the unbalanced backfill and width of the foundation wall (masonry or concrete) will determine if vertical reinforcement is required. Also top and bottom lateral support will determine if the wall needs to be connected to the footing not just the seismic zone.

 

[Mark K]

Typically the footing and the stem wall are poured together.

 

[Msradell]

Typically the footing and the stem wall are poured together.

Maybe where you are from but around here they are seldom poured together. The footing is normally poured first and then the stem off poured separately with the forms for it set on top of the footing. This also allowed for the additional verticals required for the stem wall and the horizontals to be tied in place after the footing of poured.

 

[Mark K]

When the stem an footing are poured together the vertical and horizontal stem reinforcement is still provided and tied off. The one disadvantage is that you only need to pour concrete once.

ACI 318 referenced from the IBC has provisions relevant to construction joints.

The IRC was sold as a simpler code but then everybody expects it to address an almost unlimited number of issues. I sense that there is a conflict.

 

[bill1952]

And I'm only asking about what is required by the IRC, not what is often done, specifically seismically inactive areas. I am certain no reinforcing is required in the footing. Just trying to find if and where in the code and when dowels or a key is required between footing and stem wall. Any foundation on gravel footings, including wood and precast, of course is not required to be pinned. Just looking at poured and specifically block foundation prescriptive requirements.

 

[steveray]

Not spelled out in IRC....Which technically means you don't need it....The foundation wall is typically braced at the top by the floor system and at the bottom, by the concrete floor....Granted that doesn't cover it moving outward...

 

[bill1952]

mt - Thanks. I have been studying chapter 4 and concluded for my building - minimum footing at 48", cmu stem wall, slab on ground, and a portion of walls above slab will be cmu because grade rises 30", but no rebar or grouting is required by code.

I probably will add 2 no. 4s in footing and 1 no. 4 vertically and grout in 8" block wall every 4', but not dowel footer to wall. Seems much easier to lay block and set rebar after than lay block over vertical rebar stuck in footing. And 3 1/2 ft below grade, will fill on both sides, how in an area with no seismic activity could they move at all, let alone differentially? (If NYS hadn't amended out crushed stone footings, it wouldn't be a question even.) I'm thinking of grouting every cell and a bond beam on top course but that's definitely overbuild.

Having used IBC and legacy codes before that for almost 40 years, which seem fairly clear, this IRC really could use a major rewrite for clarity. The the predecessor CABO OTFDC was just as poorly written.

 

[mtlogcabin]

Maybe this will help

R404.1.3.3.7.8 Construction joint reinforcement.
Construction joints in foundation walls shall be made and located to not impair the strength of the wall. Construction joints in plain concrete walls, including walls required to have not less than No. 4 bars at 48 inches (1219 mm) on center by Sections R404.1.3.2 and R404.1.4.2, shall be located at points of lateral support, and not fewer than one No. 4 bar shall extend across the construction joint at a spacing not to exceed 24 inches (610 mm) on center. Construction joint reinforcement shall have not less than 12 inches (305 mm) embedment on both sides of the joint. Construction joints in reinforced concrete walls shall be located in the middle third of the span between lateral supports, or located and constructed as required for joints in plain concrete walls.

Exception: Use of vertical wall reinforcement required by this code is permitted in lieu of construction joint reinforcement provided that the spacing does not exceed 24 inches (610 mm), or the combination of wall reinforcement and No. 4 bars described in this section does not exceed 24 inches (610 mm).

 

[bill1952]

I had read that but believe its intended for a vertical joint - like one wall butting into another or an addition to an existing wall? The fact that the diagrams show no rebar in footing or stem wall for non-seismic and very deliberately show it in the seismic versions seems clear as to intent. (are illustrations "code" in ICC? I know in NFPA no requirements in illustrations or in definitions.)

 

[Paul Sweet]

R404.1.1 requires engineered design for walls supporting more than 4 ft. of unbalanced backfill that do not have permanent lateral support at the top or bottom.

A key wouldn't be required for a wall wall with less than 4 ft. of unbalanced fill.

 

[bill1952]

That was my conclusion. Thanks.

 

[my250r11]

ACI 318 referenced from the IBC has provisions relevant to construction joints.

This is where I go. Footing in the IRC do require reinforcement.

Construction joints are generally addressed as common practice or pointed out in ACI 318 or the Concrete manual. If not in IRC move to IBC wihich will put you back in ACI.

 

[bill1952]

I'll stick with IRC.

I think IRC very clearly does not require rebar in footings in Seismic A B and C areas, at least not the 2018 ICC version nor the NYS version based on it.

 

[bill1952]

Similar division here a decade ago.

2009 IRC Rebar in Footings

Most cities in Oklahoma the inspectors are requiring four #4 horizontal rebars in the footing, or two #5 stacked. I find that no rebar is required in the 2009 IRC except that foundation with stemwall one 12 inches from top of stemwall and one within 3 or 4 inches of bottom of footing...

www.thebuildingcodeforum.com

Discussions at FHB and JLC similar.

 

[Mark K]

Regardless of how you interpret the IRC there is a need for horizontal and vertical reinforcing in footings. Concrete cracks and without reinforcing to hold the pieces together the cracks will grow during the life of the building.. This is not unique to seismic areas. Even in non-seismic regions the vertical loads are not uniform and the ground does not settle uniformly.

If you use block for the stem wall there is more need for reinforcement to hold the pieces of block together. The verticals need to be embedded in the concrete footing. For most stem walls placing the block units over vertical bars is not a problem since many of these walls are relatively short. When dealing with tall walls speed block, open ended block, can be used without requiring the block be lifted over the top of the bars.

 

[bill1952]

I'm surprised the people who vote on the code don't seem to agree.

Having lived most of my adult life in 100+ year old houses, both as straight, level, and plumb as any well built new house, I was not uncomfortable without a stitch of rebar in the foundations.

 

[Robert]

I've seen leaks at the cold joint in 2 pour systems. If you go this route, maybe add a waterstop on the footing before the stem is added.

 

[Mark K]

So many problems created by two pours that would be solved if it was cast monolithically.

water stops create problems because it is difficult to consolidate the concrete near the water stop. This allows water to flow around the water stop.

When engineers want the equivalent of a monolithic joint the existing concrete is sandblasted and roughened. This allows the new concrete to bond to the existing. In addition reinforcing is cast in the first pour perpendicular to the joint to prevent slippage at the joint. If there is a concern about water leakage waterproofing is installed on the wet side.

 

[tmurray]

Interesting. In thousands of foundation jobs here, only one was done monolithically and it was a complete disaster. The guy was an engineer from Israel and had no clue about construction in our climate. We had to explain that the foundation needed to be below frost to him. I would like to see a professional do it.

I have not heard of an epidemic of leaks in 2 pour method.

 

[bill1952]

I assume this concern about leaks is for a basement or crawl space? Just clarifying as my project is just a stem wall for a garage, with footer 48+ inches below a slab on ground. Not to mention incredibly well draining soil.

I have to wonder if some of these things are so basic and critical, why they are not required by the IRC.

 

[bill1952]

Rereading this reminds me why I became involved with code development in 1980s - inconsistent interpretation working nationwide of what is now IBC section 4.10 the Assembly section of chapter 10 and now 11 (and assembly chapters of NFPA 101 and 5000). I think the IRC needs a lot more help.

 

[Paul Sweet]

Keys are usually used only for concrete walls, and are usually more for waterstopping than structural. Dowels are usually specified when the wall height exceeds the maximum unbalanced fill height.

Oklahoma might have required rebar in footings because of severe shrink-swell soil issues.

 

[redeyedfly]

So many problems created by two pours that would be solved if it was cast monolithically.

water stops create problems because it is difficult to consolidate the concrete near the water stop. This allows water to flow around the water stop.

When engineers want the equivalent of a monolithic joint the existing concrete is sandblasted and roughened. This allows the new concrete to bond to the existing. In addition reinforcing is cast in the first pour perpendicular to the joint to prevent slippage at the joint. If there is a concern about water leakage waterproofing is installed on the wet side.

You've never poured a concrete wall. Pouring monolithically is 10x more difficult. Waterstops are much, much easier. Typically it's a bentonite waterstop at that location which is very easy to consolidate around and very effective. If the soil is well draining, they won't even use a waterstop and rely on the exterior waterproofing.

Just because it looks good on paper does not mean it will work in the field.