How to do a site climate analysis for architecture

What the climate part of a site analysis covers

A full architectural site analysis has several layers: the physical site (topography, ground, vegetation, water), its context (neighbouring buildings, streets, views, noise), access and movement, planning rules and zoning, utilities, and climate. This guide covers the climate layer: the conditions a building on the site will face hour by hour through a typical year, and over its working life.

Climate data describes conditions at a weather station or across a grid cell kilometres wide. The site then modifies them: neighbours cast shade, slopes and buildings shelter or channel the wind, and water and planting change temperature and humidity nearby. Record those local effects from the site visit and the context layers, and read the climate data as the background they act on.

Step 1: get representative climate data

Most climate analysis for buildings starts from a typical meteorological year: one year of hourly weather built from typical months of a longer record. Climate.OneBuilding.Org publishes typical-year files for building simulation, mainly in the EPW format. Its TMYx files are derived from hourly data in NOAA's Integrated Surface Database using the TMY and ISO 15927-4 methods, and it currently lists 17,315 TMYx locations.

Before using a station file, check how far the station is from the site and how different its elevation and setting are. An open airfield, a hillside, a valley floor and a dense city block can have noticeably different conditions. Where the nearest station is far away or unlike the site, reanalysis is the usual alternative: ERA5, the fifth-generation ECMWF reanalysis, combines model data with observations from around the world into hourly estimates on a 0.25-degree grid from 1940 onwards, and a typical year can be compiled from it at the site's coordinates.

Write the data source, the station or grid location and the period on the sheet. Reviewers and consultants need to know what the charts are based on.

Step 2: classify the climate

A climate classification tells you in one line which factors will dominate. The Köppen-Geiger system divides land climates into five major classes (tropical, arid, temperate, cold and polar) and 30 sub-classes, using thresholds and the seasonality of monthly temperature and precipitation. A code such as Csa (temperate, dry summer, hot summer) already points to summer shading and cooling, and to rain that falls mostly in winter.

Add the climate zone your energy code uses (for example an ANSI/ASHRAE Standard 169 zone, or a national zone) and the heating and cooling degree days, which show whether heating or cooling will dominate the energy balance.

Steps 3 to 8: read each factor and note the design move

Read every factor by season and time of day. Annual averages hide the conditions that shape the design, such as a hot afternoon wind or a cold, sunny winter morning.

• Sun (step 3): read a sun path diagram for the site's latitude, together with cloud cover and solar radiation. The sun is highest at solar noon, and that height depends on latitude and date: at 40° N it is about 73° at the June solstice, 50° at the equinoxes and 27° at the December solstice. In most of the northern hemisphere the noon sun is to the south, and in most of the southern hemisphere to the north; between the tropics it can come from either side depending on the season. Design moves: orient the main glazing to the equator side where winter sun is wanted, size overhangs for the high summer sun, and treat low east and west sun with vertical shading or fewer openings.
• Wind (step 4): a wind rose shows the direction the wind blows from, how often it blows from each direction and at what speeds. Read seasonal and daily roses as well as the annual one, because a cooling summer breeze and a cold winter wind can come from different directions. Design moves: place openings for cross-ventilation towards useful summer winds, and shelter entrances and outdoor spaces from cold or strong winds with the building form, walls or planting.
• Temperature and humidity (step 5): plot monthly and daily ranges against a comfort band and look closely at the diurnal range, the difference between day and night. Givoni notes that the daily range grows as humidity falls, and that the cooling a heavy building can gain from night ventilation is proportional to that range. Design moves: heavy, shaded construction closed by day and ventilated at night where the range is large; shade and air movement where it is humid and the range is small; solar gain and a well-insulated envelope where heating dominates.
• Precipitation (step 6): note monthly totals, the wet and dry seasons, snow, and how intense rain events get. Design moves: roof form and overhangs, drainage and water storage, protected entrances and snow loads. Drainage design needs rainfall intensity-duration-frequency data from the national meteorological or hydrological agency; a typical-year weather file is built from typical months, not extreme storms.
• Comfort (step 7): indoors, compare conditions with an adaptive comfort band for naturally ventilated spaces, and plot the hours on a psychrometric chart to see which passive strategies cover them. Outdoors, a thermal comfort index such as UTCI shows when terraces, playgrounds and streets are comfortable, by season and hour.
• Future climate (step 8): Beck and colleagues (2023) estimate that about 5% of the global land surface moved to a different major Köppen-Geiger class between 1901–1930 and 1991–2020, and project that 5% to 13% will change class between 1991–2020 and 2071–2099, from the low-emissions SSP1-2.6 to the high-emissions SSP5-8.5 scenario. Check whether the site's zone is projected to change within the building's life, and test shading and ventilation against a future weather file as well as the typical one.

The site climate analysis sheet: a template

A site climate analysis sheet works best as a set of small charts, each with one line saying what it means for the design. A typical sheet includes:

• Location, elevation, data source and period, and the climate classification: Köppen-Geiger code, code climate zone, heating and cooling degree days.
• A sun path diagram, ideally overlaid on the site plan with north marked, and the noon sun angles at the solstices.
• Annual and seasonal wind roses, with the useful and the unwanted winds labelled.
• Monthly temperature ranges and relative humidity against the comfort band.
• Monthly rainfall and snowfall, with the wet season marked.
• A psychrometric or bioclimatic chart showing the share of hours each passive strategy covers.
• Outdoor comfort by season and time of day, for the outdoor spaces.
• A short list of the design moves that follow. This becomes the climate brief for the concept design.

Doing the climate part in C4B

C4B produces the climate layer of a site analysis from a location: type an address or click the map. It does not cover topography, context, access or zoning, so those layers still need mapping, CAD and GIS tools.

Every search, including on the Free plan, analyses the nearest OneBuilding.org weather station file (usually TMYx): Köppen-Geiger and ANSI/ASHRAE 169 climate zones with heating and cooling degree days, hourly temperature and humidity against an adaptive comfort band, precipitation from NOAA GHCN records, annual and daily wind roses, 2D and 3D sun paths, cloud cover, UTCI outdoor comfort, a psychrometric chart and solar radiation.

Paid plans add projects. In a project C4B also compiles a typical year from reanalysis at the site's exact coordinates (Open-Meteo's blend of ERA5-Land, ERA5 and ECMWF IFS worldwide, CERRA in Europe, NORA3 in northern Europe), corrected to the site's elevation; this describes a grid cell, from 3 km for NORA3 to 0.25° (about 25 to 31 km) for ERA5, not the microclimate of the plot. Projects add written readings on most charts, passive design and outdoor comfort strategies, future climate under five SSP scenarios and a PDF report. Individual charts cannot be exported as images or CSV.