Whether you are closing in a garage, conditioning a back porch, or pushing out a wall for more living space, modeling additions is bound to raise some questions. This article is here to help answer some of these questions and some you may not have considered.

To start, what is an addition? Per the Florida Energy Code* an addition is “an extension or increase in the conditioned space floor area or height of a building or structure.” This means that it does not have to necessarily be a brand new extension constructed onto an existing house. Conditioning an existing garage or closing in and conditioning a porch increases the conditioned space floor area, so these would be additions as well. If in doubt it is always best to speak with your local building department or plans reviewer and see what they expect to see on the final forms before starting your project.

Does the Code require that additions comply alone, or together with the existing building? Section R502 of the Florida Energy Code clarifies that 1) an addition alone can comply, or 2) the addition together with the existing building can comply as a single building, or 3) compliance can be shown where the building with the addition does not use any more energy than the existing building. 

Are there special calculations in Florida Code for additions? As touched on above, the main Florida Energy Code section addressing residential additions specifically is Section R502, which we’d recommend reviewing. The Florida Code does however generally stipulate the same calculation methods and compliance criteria when it comes to modeling additions as it does for whole building new construction. One notable exception states that air leakage testing “is not required for additions, alterations, renovations or repairs of the building thermal envelope of existing buildings in which the new construction is less than 85 percent of the building thermal envelope” (see Section R402.4.1.2 Testing). Another exception, this one specifically for the performance (R405) compliance method, allows the area of a window in an existing exterior wall that is enclosed by an addition to be subtracted from the glazing area for the addition, for that overhang and orientation (see Section R405.5.3.1 Glass areas).

EnergyGauge USA does however have a special status classification entry for additions as compared to new construction whole buildings. This building status type, entered on the Project page, does not change any code compliance criteria or calculation methods but does allow for certain anomalies for additions that should not exist in whole buildings. For example, whole building new construction cannot be modeled in EnergyGauge USA without windows. If windows do not exist a warning will appear for this to be corrected prior to running code compliance calculations. Under the “addition” building status however, it is perfectly acceptable to have no windows as there are circumstances where this may be the case. So be sure to use the addition status when entering additions as a number of later EnergyGauge entries will rely on this when modeling additions.

Do I use the original year of construction or the year of the addition's construction? The year of construction field on the Project page refers to the work that is being described in the EnergyGauge project, so for additions it will be the year that the new conditioned space is being added. That being said, year of construction does not have any effect on code compliance and does not appear on any of the code forms. It is a field used for ENERGY STAR calculations.

How do I model the existing space or walls? If entering the addition alone…you don't! Only the new conditioned space is modeled for additions complying alone; all components (walls, windows, doors, floors, and ceilings) that separate the addition from the outdoors or from unconditioned space such as a garage or attic are entered, but any walls or other components separating the addition from existing conditioned space are not entered. If an addition is adjacent to an unconditioned garage, a garage will also need to be added to the project on the Garage page to account for the associated load. Alterations and repairs to existing buildings are handled separately (see Energy Code sections R503 and R504). If in doubt check with your plans reviewer to see what will be expected for compliance purposes.  

What infiltration values should I propose? Do I have to do blower door testing? As mentioned previously there is an exception to the Code which states that additions do not have to be tested for air leakage if they are less than 85% of the building thermal envelope. If this exception applies and no testing is being performed we suggest that a proposed ACH(50) of 7 be entered. This is the maximum air leakage rate allowed by code and even though it may not be tested it still must be entered. If a lower ACH(50) is entered and the performance method is used for code compliance, the project will receive credit for the lower leakage value so testing will be required to verify that the level entered is actually achieved. This is another situation where when in doubt, ask your local officials what they expect to see.

We are keeping the existing/replacing the existing/adding new HVAC equipment. How do we model that? Once the project status has been entered as “Addition” on the Project page (as discussed above), the Heating and Cooling pages will include an additional “Florida Addition” entry. As illustrated below, EnergyGauge has four Florida Addition heating and cooling system entry options:

  1. “Replacement for wholehouse”: select this option when replacing the existing air conditioning and heating equipment with new equipment that will serve both the existing space and the addition.
  2. “Supplemental for addition”: select this option when adding new equipment that will only serve the addition.
  3.  “Existing/confirmed efficiency”: select this option if the existing equipment will be used to condition the addition (new equipment is not being installed) and the existing system has a documented efficiency that is better than base efficiency.
  4.  “None (Baseline assumed)”: select this option if the existing equipment will be used to condition the addition but the equipment’s efficiency is uncertain or lower than base efficiency.

We had to run new ducts to the addition from the existing duct system. How much duct do we model? Just like with the various envelope components, you will need to model all new ducts that are part of the addition.

Do we need to have the addition’s ducts air leakage tested? With one exception for prescriptive compliance, the same duct air leakage testing requirements apply to additions that apply to whole building new construction:

For performance compliance, ducts do not need to be tested if on the Ducts page “Default Leakage” is selected as the duct leakage type

For prescriptive compliance, with one exception, per Energy Code Section R403.3.3, ducts need to be tested unless the ducts and air handler(s) are entirely within the building thermal envelope.  The exception in Section R502.1.1.2 relaxes the testing requirement for ducts extended from an existing heating and cooling system to an addition that are less than 40 linear feet.

We are not adding or changing the hot water system, do we enter anything? No! If no changes are being made with the water heating system then no water heating needs to be modeled. Simply leave it out. You will receive a warning from the software prior to calculating performance method compliance however, as for the performance method simulation a water heating system must exist. EnergyGauge will take care of that system for you in these cases, so you can just click “OK” on the warning message and the calculation will continue. EnergyGauge adds a default water heater that will match the baseline and the effect will wash out and not change the project results.

Note that once the Project page “Addition” status has been selected, a “No. of Bedrooms in Addition” entry field is added to the Project page.  This entry must be made even in addition cases where the hot water system is not being changed, as EnergyGauge still uses the number of bedrooms in the addition to calculate hot water and other loads.

*Florida Energy Code and references to code calculation, code compliance, and compliance criteria refer to the 2017 Florida Building Code - Energy Conservation, Sixth Edition.