# Keyway in top of footing?



## Tubafore (Feb 27, 2013)

I am about to begin forming footings for a foundation wall and I have found conflicting information online about the importance of a keyway in the top of the footing. 
Some sources say it is an important feature to lock the stem wall into the footing and prevent lateral movement. 
Others say it is unnecessary and even discouraged now days. The rebar and simple friction between the two pours will stop movement. 

What's the deal?


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## Willie T (Jan 29, 2009)

Frankly, just think about it. Ever seen a block wall that was bumped by a truck? What immediately happens to the blocks that are "held in place by friction"?

Well, that is about all the connection your stem wall has to the footer. New concrete pours do not bond to old pours.

A running keyway is one of the simplest things to do. Why wouldn't you?


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## Tubafore (Feb 27, 2013)

I agree a keyway makes sense and shouldn't be too difficult to form. 
The talk I have found is that vertical rebar plus a roughened surface on top of the footing resists shear better than a keyway and makes it an unnecessary step. My engineer already spec'd #4 bar at 32" o.c. but made no mention of a keyway.


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## Tscarborough (Mar 31, 2006)

It is also there as a waterproofing measure. Use something like a rubber waterstop poured into slab in the keyway or a product like Synko-flex instead.


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## jomama45 (Nov 13, 2008)

Depends greatly on what the foundation is for (full basement, garage with balanced fill on each side, crwal space, etc...) but with dowels on 32" centers, I don't think the keyway will do much at all. As a matter of fact, there's scenario's where a keyway in the footing will actually create more problems in a block foundation IMO...........


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## Gary in WA (Mar 11, 2009)

IMO, the keyway is mute point. That is the purpose of the verticals tied to the horizontal footing rebar. Detached garage and addition says "or"; http://www.google.com/url?sa=t&rct=...sg=AFQjCNE7OwJiaySRCVp1nzgY-zOSSLRngQ&cad=rja

Page 3; http://www.google.com/url?sa=t&rct=...sg=AFQjCNGWT1HV6rOSB-psCfZXa4iTDDd_WQ&cad=rja

If basement living space, waterproof top of footing as said already or with membrane between, Fig.6, 9-14; http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems Be sure at add a thermal break at slab/concrete wall as pictured, second biggest heat loss next to above grade areas.

Gary


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## Tscarborough (Mar 31, 2006)

In the commercial work I have done the keyway was for waterproofing, not structural enhancement.


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## stadry (Jun 20, 2009)

typically 1 finds a keyway more in commercial rather than residential,,, IF you promise ( no crissed finners behind your back, neither ) to properly waterproof the structure's foundation & bsmt walls, pass on the keyway,,, IF a schoolbus does hit the home, no keyway is going to save it :no:


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## Tubafore (Feb 27, 2013)

Ok then, no keyway it is and I will properly waterproof. This will be a 36" tall crawlspace wall that will be partially backfilled. 
I don't anticipate any schoolbuses crashing into it but just to be sure I will put up a sign in the yard forbidding it. 

Thanks


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## GBrackins (Apr 26, 2012)

are you planning on leaving exposed soil in the crawl space or placing a concrete slab with vapor barrier?


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## stadry (Jun 20, 2009)

IF you leave soil rather than conc in the crawl space, use MINIMUM 15mm vapor barrier w/overlapp'd seams ( 12" ) secured by dble face tape,,, plan on 1st running it up the walls to your sill plate, too


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## Tubafore (Feb 27, 2013)

GBrackins said:


> are you planning on leaving exposed soil in the crawl space or placing a concrete slab with vapor barrier?


No slab but I am going to use a vapor barrier over the soil and going up the sides.


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## Gary in WA (Mar 11, 2009)

IMO, leave the poly 2" down from the sill for annual termite inspection; http://termites101.org/termite-basics/termites-by-region

Gary


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