We are planning a two story addition to the back of our house, which has a basement. Addition will be on crawl space, frost depth here in Cincinnati is 30″. Architect acquaintance said he heard it is possible to start new footer, at frost depth, and somehow join to existing basement wall. Nothing in Ohio Building Code referring to this, no idea how to do so. Construction friend said he usually starts footer at same depth as basement footer, gradually steps up to frost depth. Wouldn’t this latter approach still require that new footer be tied to existing basement footer and wall? Any info greatly appreciated. Thanks.
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Is existing wall block or reinforced concrete?
And, do you know any details about the type of soils and perimeter drain you have?
Either method will work. Drill into existing foundation and epoxy dowels into it. I would use two 15M in the footings and probably a couple into the wall. Make sure that you are building on a a good foundation base. How are you going to gain access to the crawl space.?
March 2002 issue of FHB has a "How to" article about an addition foundation. Joe H
Pin it. Jeff She's exotic ,but not foreign, like an old Cadillac......she's a knockout!
Sorry I omitted details. Basement wall is concrete. Soil here basically yellow clay. Future access to crawl space will be via shallow opening cut into top of basement wall that is parallel to floor joists. Thanks for all the input. Plan to take drawings to structural engineer this week, don't know how long to get answer back. Hope his solution something as simple as pinning with pieces of rebar and epoxy.
It should be that simple as long as your excavator doesn't disturb soil any deeper than bottom of footer. You should give thought to protecting existing perimeter drain and how or whether you will tie to it with new.Excellence is its own reward!
ICF distributor/contractor said he typically uses (3) 12" #4 rebar pins across crawl space footer to tie to existing basement wall (rather than excavate down to wall footer)and 3 more of the same to tie crawl space wall to existing wall. If inspector complains, he offers to use #5 rebar instead. If still complains, offers to use #5 and epoxy in existing wall. Said that has never been turned down.
Don - "soil here is basically clay" -
The problem is that when the excavation for the basement was originally done, the area next to the foundation wall was also dug out. Therefore, the soil between the basement wall and the originally-unexcavated area is basically backfill meaning generally unsuitable for footing bearing, or of questionable bearing. The approach of stepping up from the footing to crawl space frost depth is therefore correct. That being said, it is possible to 'span' the old backfill area if the new footing 1) is reinforced to act as a grade beam (spanning 3' or so is no problem) 2) has a poured concrete base below it extending to the footing and 3) is pinned to the foundation wall/concrete base/existing footing below.
T. Jeffery Clarke
Like the idea of your "concrete base" extending to the original footer. Stepping footer seems like a nasty alternative. I'm sure the pinning as stated is used because saves time and is relatively easy, although there is no doubt the soil below is fill.
Can you expand on the concrete base concept? Sounds like it would involve a footer pad, perhaps 24" square by 12" high, with 8" column to bottom of crawl space footer? (Just realized, that would require backfilling under the new crawl space footer, which would be REALLY dumb. Is your post a constant diameter concrete column down to the original footer? Diameter?) Relatively small increase in time and cost for reduced likelihood of settling problems down the road. Thanks for the tip.
Edited 6/28/2002 10:01:23 AM ET by Don Stephan
Edited 6/28/2002 10:54:45 AM ET by Don Stephan
Get a bid on having a full basement under the addition and cutting a door for access. Most of the fixed costs - footers, equipment transportation, sills etc. etc. are the same for full and crawl. Presumptively the reason for building the addition is the need for extra space. The marginal difference in price of basement vs. crawl makes that space the most affordable.
I've never heard anyone complain that their basement was too large; so much more room for keeping tools.