Attached Buildings

Attached Buildings

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Buildings with Zero Lot Line Construction will need to establish protocols for the design and constructing of their attached buildings, which are given here.  A lot line may be modified by the pattern Street Mutation, and then the owners will wish to develop Attached Buildings, given here.  …etc

As the plots in a block are built out, there is often a need to create attached buildings incrementally.  But this requires that many problems be solved. These include fire protection, water intrusion, and protection of each side in the event the other is modified or demolished.

Let us suppose that two adjacent plot owners have agreed that they would prefer to build attached buildings, but their plans are not necessarily standardized.  One unit may be taller than another, or wider than another.  Furthermore, one party may make changes later that will expose parts of the other’s wall.  In each case, care must be taken to protect the separate buildings from damage by water, fire and other dangers.

This requires that a number of steps be taken to protect each side.

  • First, each wall must be built as a fully insulated, weather-protected enclosure, of a type that allows flashing to be installed (see below).
  • Second, flashing must be introduced at the top edge where the two buildings abut.
  • Third, an air space of approx. 1” must be maintained between the two walls.  This gap can be enclosed by a method agreed upon by the parties and the building official, such as caulking with a backer rod at the exposed edges, or covering with a piece of trim.
  • Fourth, any elements of one structure that project beyond the surface of another must be built with fire-resistive structure, as required by local building codes.


Where attached buildings are desired, build each building as a free-standing structure, with full sound insulation, moisture protection, and all other engineering requirements.  Make sure that the party wall is set up to admit flashing for an adjoining construction, and to maintain a minimum 1-inch air space (i.e. 1/2 inch to the property line on each side).  When both structures are complete, the remaining exposed areas and gaps can receive an exterior finish that is agreed by both parties.

Maintain an agreement between the neighbors that specifies how many times modifications may be made, and the relative responsibilities of each for incurred costs.  Record this agreement with your local property deed authority.

A portion of a residential yard may need to accommodate a side yard, given in the pattern Side Yard House.

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