It is not at all uncommon that the continuing viability of many historic properties demands expansion of habitable space into the attic or basement, or requires the construction of an addition. When confronting this issue, it is important to know that the governance of the State Historical Building Code (SHBC) extends to all work undertaken on the historic site (SHBC 8-102,8-103).
"New work" within an historic property is routinely expected to conform to the requirements of current codes and regulations. However, that new work is also governed by the SHBC, so that whenever the historic character or the historic geometry interface with new work, the new work is expected to accommodate existing historic conditions.
- For example, the daylight and ventilation requirements of current code are frequently impossible within the historic geometry of former industrial loft buildings. In these instances, a reasonable level of equivalency is permitted by means of artificial substitutes, generated on a case-by-case basis.
- Another common example is the reclamation of "high basement" spaces in victorian residences built, initially, to defend from the frequent flooding of many California communities during the last half of the nineteenth century. Those who have seen the result of raising the main floor an additional foot or more off the ground, in order to accommodate headroom downstairs, recognize that this solution generates an awkwardness in the geometry of the building facades, their porches and stairways, creating an unacceptable disservice to the building's historic character. Here, an acceptable solution is to excavate in order to achieve—on a case-by-case basis, a reasonable headroom clearance.
- Within new space, whether basement or attic, one would expect construction to reflect current code; however, ceiling heights, head clearance, light, ventilation, and other issues may still be subject to reasonable compromises dictated by the new work's interface with the historic.
For additions which extend the footprint of the historic structure, the mandates of the regular code properly take greater precedence, although the project remains under the SHBC's governance. The reason for this is to again insure—on a case-by-case basis—that the new work does not interact unfavorably, either practically or aesthetically, with the historic property.