The building can be modeled either as a single space or multiple spaces. The decision as to whether multiple spaces are necessary depends on many factors. If two spaces are operated at different temperatures (have different thermostat set points, overheated or under-heated due to distribution loss, imbalance or internal gains), different heating or cooling schedule, have different mechanical ventilation loads, or one space (perhaps an attic, basement or garage) is unconditioned, then use of multiple spaces may be necessary. If you plan to use TREAT for sizing a heating or cooling system, then each area for which the design load is of interest should be modeled as a separate space. A little experimentation will soon reveal the cases in which a more complex multi-space description is needed.

Note: If each room in the building is modeled as a separate space, the input may be very time consuming. In most single-family houses all rooms that belong to one heating/cooling zone and are serviced by one thermostat may be modeled as a single space. Be sure to consider the following pieces of information.

  • If an unheated space is vented (for example if this is a vented crawl space) you may choose not to model it as a separate unconditioned space. Instead you may enter the surfaces that are adjacent to this space (floor of the first level) as adjacent to exterior.
  • An un-vented roof cavity that will be filled with insulation may be modeled as unconditioned space.


This window has several inputs that must be made. These include: Space Type, Space Name, Ceiling Height Ft, Elevation Ft, Conditioned, Occupied Hrs./Day, and Persons.

Space Type:

Sets the defaults for all other input fields on this screen except for floor area. It also defines the occupancy schedule used by TREAT to calculate internal heat gains and default infiltration of unheated spaces.

Space Name:

Allows the user to assign a custom name to the space. Be as descriptive as possible, because this name will be used on many screens to define the location of walls, lighting, appliances, etc. The space name must be unique for the project.

Ceiling height:

Allows the user to enter the height of the ceiling in feet. If the space has a varying ceiling heights as in the case for a sloped ceiling then enter the average height for that space. Ceiling height is used in infiltration calculations to calculate building volume.

Floor Sq. Ft:

Requires inputting the area of the space in square feet. For each space the product of the ceiling height and floor area should be equal to the actual volume of the space. Floor area is used to calculate defaults for the distribution system and in many reports that display area-normalized outputs.

Note: The total floor area of all floors must be entered for a multi-story building that is modeled as a single space. Ceiling height in this case must be equal to the ceiling height of one floor. Floor area is not the footprint of the building. For example, to model a three story building with 4000 SqFt area per floor and 8 Ft ceiling height as a single space, you would enter 12,000 SqFt in Floor Area field and 8 in the Ceiling Height field. You would NOT enter 4000 Sq.Ft. in the Floor Area field and 24 in the Ceiling Height field.

Elevation ft.:

This number is the height of the space floor above the floor of the lowest level. For example if the building has a basement then elevation of a space is equal to the height of the floor of this space above the basement floor. Basement elevation is equal to zero. The elevation is used to calculate stack effect.


This field should be set to Yes if the space is part of the conditioned area (if it is heated and/or cooled).

Occupied Hrs./Day: 

Use this field to enter the number of hours each day that the space is occupied


Two three-hour meetings are held in a meeting room on an average weekday. Occupied [Hr/Day] =2[meetings per day] × 3[hours per meeting] × 5[week days per week]/7[days per week]


This input represents the number of people that are typically in this space when it is occupied. TREAT accounts for internal gains in calculations of heating and cooling annual energy consumption by generating hourly occupancy schedule based on number of persons, hours occupied and space type. The following logic was used:

  1. Sleeping Quarters: center hours on 2 am.
  2. Living Space: first 10 hours – center on 8 pm; next 8 hours center on 11 am; last 6 hours will be distributed between 12 am and 6 am as follows: start from 1 am, next 6 am, next 2 am, then 5 am, then 3 am, then 4 am.
  3. Office: center hours on 1 pm.
  4. All other spaces: half is centered on 7 am; the other half centered on 7 pm.

Note: For heating load sizing, no credit is given for internal heat gains from occupants; however, occupancy affects cooling load sizing.

If you enter an unheated space after you have entered surfaces for other spaces in the project, remember that you need to go back to the Surfaces screen and add surfaces not just for the new space, but also to the existing heated spaces that are adjacent to it. Otherwise your new unheated spaces will appear disconnected from the heated building envelope.

The Advanced button brings up a window with optional inputs for the selected space.

Is the Space Furnished:

This box allows accounting for the thermal mass of furniture and light interior partitions. By default, the value is set to Yes for conditioned spaces and to No for unconditioned spaces. For spaces created in the versions prior to TREAT 2.5, the default value is No for all types of spaces.

Heavy (brick) interior walls:

This input allows accounting for the added thermal mass of heavy interior walls, such as a central fire place. The heavy walls may play an important role in solar gain calculations.

Use Natural Ventilation for Free Cooling During Non-Heating Months: 

This input allows for modeling the effect of opening the windows when the outdoor temperature is below 68F and the space temperature is above 70F. Natural ventilation is modeled only for the months that are not part of the heating season, which is specified on the Weather/Defaults screen. Natural ventilation will not be modeled if a 12-month heating season is specified.