Calculating the Conditioned Space Volume and Why it Matters

To conduct a Blower door test the overall volume of the home is needed. The higher the volume, the better chance the property passes the test.

How do you calculate a homes volume?

RESNET specifies the standards and methods permitted for calculating this volume. Link: ANSI/RESNET/ICC 301-2022

Here are the three main measurement options:

1.) Measuring the interior space of the building

2.) Building Plans and Blueprints - MUST BE PROVIDED

3.) Exterior of the home subtracting all doors and windows sq ft.

When measuring conditioned space volume for building performance assessments, it's can be extremely helpful for homes that are close to passing to employ various calculation methods to determine the allowable option that provides the maximum volume. Unfortunately, there is no calculation method that will yield the highest volume calculation every time.

Doctor Air’s Approach

We always start with the fastest option to first to reduce the time the test takes. If that doesn't pass the code requirements, we will calculate the volume for the other options to hopefully get a higher total volume.

Here's why using multiple measurement methods is crucial:

1. Comprehensive Assessment: Different buildings have diverse designs, layouts, and architectural features. Using a single measurement method may not capture all the nuances of a building's conditioned space. Employing multiple methods allows for a more comprehensive assessment that considers variations in ceiling heights, architectural features, and interior structures.

2. Maximizing Volume: By using multiple measurement techniques, you can identify the option that yields the maximum conditioned space volume. This maximization is essential for accurately assessing the building's energy efficiency, thermal comfort, and ventilation needs. It ensures that no potential volume is overlooked.

3. Compliance with Standards: Some building performance assessment standards or regulations, like those set by organizations such as RESNET, may allow for different options to measure conditioned space volume. Using multiple methods helps in choosing the option that aligns best with these standards while optimizing the volume measurement within their specified guidelines.

4. Consistency and Fair Comparison: Using a single measurement method for all buildings might not be fair or consistent, especially when dealing with diverse structures. Employing multiple measurement techniques allows for fair comparisons between different buildings and ensures that each is evaluated in a manner that best reflects its design and layout.

In summary, using multiple measurement methods when determining conditioned space volume is crucial for ensuring that the most appropriate and voluminous option is chosen. This approach results in a more comprehensive and accurate assessment, aligns with industry standards, promotes fair comparisons, and ultimately provides a more realistic representation of a building's interior space for building performance evaluations.

Which areas are classified as Condition Space Volume?

1. If both the space above and below a floor assembly meet this definition and are part of the subject Dwelling Unit, then the volume of the floor assembly should also be included. Otherwise, exclude the volume of the floor assembly.

   • Exception: For non-top floor level Dwelling Units, the wall height extends from the finished floor to the bottom side of the floor decking above the subject Dwelling Unit. For top floor level Dwelling Units, it extends to the exterior enclosure air barrier.

2. If at least one of the horizontally adjacent spaces to a wall assembly meets this definition and is part of the subject Dwelling Unit, include the volume of the wall assembly. Otherwise, exclude the volume of the wall assembly.

   • Exception: If one of the horizontally adjacent spaces to a wall assembly is a different Dwelling Unit, divide the volume of that wall assembly evenly between both adjacent Dwelling Units.

3. Exclude the volume of an attic that is not both air-sealed and insulated at the roof deck.

4. Exclude the volume of a vented crawlspace.

5. Exclude the volume of a conditioned garage.

6. Exclude the volume of a thermally isolated sunroom.

7. Include the volume of an attic that is both air-sealed and insulated at the roof deck, an unvented crawlspace, and a basement only if it is contiguous with the subject Dwelling Unit and:

   • Either an ACCA Manual J, S, and either B or D report confirms that the heating and cooling equipment and distribution system can offset the entire design load of the volume.

   • Or, a visual inspection verifies that the heating and cooling equipment and distribution system serve the volume and can maintain the specified heating and cooling temperatures.

8. Include the volume of a mechanical closet contiguous with the subject Dwelling Unit if it is serviced by a space heating or cooling system designed to maintain space conditions at 78 °F (26 °C) for cooling and 68 °F (20 °C) for heating, only includes equipment for the subject Dwelling Unit, and is not intentionally air-sealed from the subject Dwelling Unit.