Can a new foundation be dug alongside an existing house with a deep foundation or cellar without compromising the structural integrity of the existing house?

Subquestion: should I leave rebar or sth sticking out from the existing foundation to join it with the new foundation?

existing house (not built yet):

  • foundation 1.8m deep (wall)
  • foundation is on a pad of compacted crushed rock that creates a 1m perimeter around the house. The perimeter above that is filled with sand up to ground level
  • wood framed, some brick walls

new addition:

  • walls and pipes will be joined to the existing house
  • will have the same type of foundation and frame
  • dug into ground, that is fresh - that is never compacted or dug into before.
  • 1
    $\begingroup$ Why is your foundation 1.8m deep? Is it in order to go through poor soil to a decent load-bearing strata? Is it simply in order to have a cellar? Is it to provide horizontal capacity due to building on a slope? You state that the new addition is dug into fresh ground - is the unbuilt "existing" house also being dug into fresh ground, or was there a previous house there? The simplest solution is probably to build the foundation for the addition at the same time as the "existing" house. $\endgroup$ – AndyT Mar 16 '17 at 9:55
  • $\begingroup$ I live in Estonia (northern EU), in winters the ground can freeze solid for more than a meter here so for my soil in my county its recommended to have a foundation atleast 1.8m deep. Crazy, right? :) the whole house site is untouched, its like it was after the ice age. its level ground and mainly a random mixture of clayish limestone and gravel. based on the test holes around the house site I would guess it to be gravel with a slight clay content (~3% maybe) $\endgroup$ – allanlaal Mar 18 '17 at 1:06
  • $\begingroup$ @AndyT It would be preferable if I wouldn't have to build the foundation for future addons for budgetary considerations and also taking into account the fluidity of the design of future addons :) $\endgroup$ – allanlaal Mar 18 '17 at 1:08

From what I know, you no need to stick out or drill in the new reinforcement of new footing to your existing footing. If you do that, some of new loadings will go into your existing footing which the previous designer does not take into account in their design.


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