How to Model Unconditioned Basements

Modified on Wed, 03 Oct 2018 at 12:26 PM

We get a lot of questions about how to correctly model unconditioned basements in Ekotrope so we’ve written this article to answer them.

First question: where is the thermal boundary?

If the majority of the insulation is in the framed floor over the basement, then this should indeed be modeled as an unconditioned basement. Model the framed floor in Ekotrope and say it is located above an Uninsulated Unconditioned Basement or Insulated Unconditioned Basement if the basement walls are insulated.

If the majority of the insulation is in the foundation walls not in the framed floor above the basement, then in Ekotrope this is actually considered a conditioned basement. The framed floor above the basement should not be included in the Ekotrope model. The slab and foundation walls should be included and should be marked “Encloses: Conditioned Space.”

Should the space be included in the Infiltration Volume?

If the floor above the basement is air sealed and insulated, then door(s) between the basement should be closed during the blower door test and the basement volume should not be included in the Infiltration Volume.

If the floor above the basement is not air sealed and insulated, then door(s) between the basement should be open during the blower door test and the basement volume should be included in the Infiltration Volume.

This is paraphrased from the ANSI/RESNET/ICC 380-2016 definition of Infiltration Volume and Section 3.2.5 on Basements.

Should the space be included in the Conditioned Floor Area?

If the space is outside the thermal boundary, no.

Otherwise this is a little tricky. Here’s how it’s defined in RESNET MINHERS and ANSI/RESNET/ICC 380:

The floor area of a basement shall only be included if the party conducting evaluations has either:

Obtained an ACCA Manual J, S, and either B or D report and verified that both the heating and cooling equipment and distribution system are designed to offset the entire design load of the volume, or,

Verified through visual inspection that both the heating and cooling equipment and distribution system serve the volume and, in the judgment of the party conducting evaluations, are capable of maintaining the heating and cooling temperatures specified by the Thermostat section in Table 4.2.2(1) of ANSI/RESNET/ICC 301-2104.