What knowledge do architects need before visiting a building site?

That depends on where you are in the design and construction of the building.

If you are in a Concept phase, sometimes referred to as pre-design, a site visit is part of your own due diligence. It's easy to assume a site's context when looking at the Civil Engineering plans or flying around Google Maps or Google Earth. But to truly unlock a site's potential, you must get “boots on the ground.” This allows you to more fully understand the local context, including the area's other architectural and environmental characteristics. You will begin to understand the connections to other key elements, like transit patterns, site positioning, and local culture. You will also observe the landscape of a site, like prevailing wind patterns, area noise origins, size and scale of other nearby elements, and existing sun & shadow studies. For all of this, an Architect simply needs to be in touch with their own sensory and cognitive perceptions, while documenting every observation.

If you are in Schematic Design, Design Development, or Construction Documentation phases, you will need to understand how your building's design addresses site conditions. This must include a strong understanding of the architectural design of your building as they relate to the site. A site visit in this regard helps to keep your design honest, with real world coordination.

If you are in Construction Administration while the building is being built, your observations are meant to bridge the gap between your Client and their Builder or General Contractor. You will need a strong knowledge of constructibility as well as intimate knowledge of how your building is put together. Your task will be to observe if the construction of your building matches the design intent, with special consideration made to multiple building trades, building codes, and any zoning ordinances. These observations will be distilled into a monthly or bi-monthly Field Report that both the Client and their contractor will use to mitigate any deficiencies. A camera, tape measure, amd notebook is typically enough to document your review, but many firms also use software and digital devices to streamline the process. You may also want to have a level and calculator at your disposal. You will be required to wear your Personal Protection Equipment, such as a hard hat, hi-vis vest and closed toe shoes. Eye and ear protection may also be required.