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Existing house with 48" crawlspace, 8" CMU on 8h x 16w continuous footing, will get an addition.

Addition will have crawlspace foundation of formed and poured 'crete, 8" walls on footing same size as existing. At two places, we'll tee the new to the old.

What do you recommend for the structural tie of new walls to existing, at these tees?

I thought of a couple.

Mark out the junction on the existing wall, drill away and hammer out the face to expose as much core as possible. Place hooked rebar horizontally so hooks go into cores. Hooks cannot be very long, but the embedded long ends in the new wall should be 40d long. Pour with soupy mix so 'crete enters cavities. A little shear resistance, not much tension.

Drill 3/4" holes clear through existing wall, one per block course bottom to top. Run 1/2" long threaded rods through, with minimum 40 diameters embedment in new wall, use piece of flat steel bar as a large washer on inside of existing wall, then fix with nuts and fender washers when 'crete is cured. Some shear, pretty good tension.

BTW, it is being done in a soil that is extremely stable gravel. Existing foundation has been there for over 25 years and is free of any cracking or settlement issues.
 

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As a rule, subject to what the structural engineer specifies, you will not want a hard connect between the old and new. It should be a flexible joint, and there are anchors designed specifically for this application.
 

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I probably do twenty of these a year. Rarely do any more than a head joint. Once in a while if the side pressure seems to be high I will pin truss wire into existing, but that is rare.

I have not seen engineer specs for this type of junction. Not saying they don't exist, just haven't seen them myself. If you have enough side pressure to blow the wall out at the junction, block is the wrong material for your wall anyway.

Another option to strengthen the junction is to make a corner and run new block parallel to exixting bloc for a few feet to give the new corner additional strength, but I doubt you will have any issues either way.
 

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tied the footings with rebar to prevent vertical movement and then just use a head joint for the wall portion since the concrete wall is fresh and will shrink as it slowly cures. Wire across the joint will do little. If a crack occurs it can be opened and repaired or sealed.

If concrete block were used, it would be more compatible, especially since the block are essentionaly 100% cured when you lay them so the curing shrinkage is minimized.
 

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Eater of sins.
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I have speced. this out here a couple times and it always flies with tbuilding departments. 5/8" drill holes at a 30-45 deg. angle down min. 6" long two in the footings and up the foundation wall about 12" o.c. All for 1/2" rebar and Simpson set epoxy. Sometimes the city wants a deputy inspector for this sometimes not.

Andy.
 
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