In the building industry, historic preservation is a term that describes the preservation, restoration, or rehabilitation of a property that is (typically) at least 50 years old and (debatably) possesses some aspect of historic importance.  The general rules for historic preservation have been established by the National Park Service (NPS), and treatment guidelines have been published through their "Preservation Briefs" series. 

However, the practice of historic preservation is not just reserved to those buildings on the National Register.  Rather, the techniques and recommendations established by the NPS are excellent guidelines to consider in the renovation of any building, regardless of its age.  However, for projects on the National Register or eligible public facilities, the guidelines are mandatory.

One example of the application and importance of this knowledge is a project that involves the "re-pointing" of existing brick masonry - the process of carefully removing the worn surface of mortar and replacing with new mortar.  We have observed a number of older buildings where this has been previously done incorrectly.  If the mason uses a power tool to aggressively remove the surface mortar, irreparable damage can occur to the edges of the brick.  Normally, it is best practice to use manual tools to "dig out" the old mortar, being careful to protect the brick.  Another problem we have observed is the inappropriate use of modern mortar mixes.  Older brick walls were originally set with a lime/cement/sand mortar mix, which is much softer than the more modern pre-mixed mortars available today.  Because these modern mortars set harder than the clay brick they contain, any movement in the wall will result in hairline cracking in the historic brick (rather than the mortar).

Restoration projects should involve a design professional that has a good track record in the practice of historic preservation to avoid irreparable damage to the building, and to ensure a healthy extended life for the property.