Codes Changes in Davidson County - What does this mean for new construction?
Changes to the Residential Energy Code in Davidson County Tennessee
Davidson County recently adopted the 2018 residential building codes, without amendments. What does this mean for new construction projects in and around Nashville? Below is a summary of the major changes and important components that will require special attention.
What changed regarding building envelope and mechanical systems?
- Insulation levels
- Air leakage levels
- Duct leakage levels
- Mechanical ventilation now required
- Manual J and S now required
- ERI pathway
- Documentation certificates
Each section below describes the changes in more detail. Note that at this point, E3 is unaware of all the details and we encourage builders, architects, and homeowners to check with the local codes officials for specific questions.
For a full review of the 2018 code, visit EnergyCodes.gov.
Previously, Davidson Co. codes had amended R-values back to the 2009 standards. The new insulation levels for ceilings, wood framed walls, and mass walls have increased, as shown in the table below.
Air and Duct Leakage Requirements
The tables below lists the changes to air leakage rate and duct leakage rates. It is important to note that with the air leakage requirements now at 3 ACH, mechanical ventilation becomes a requirement to allow for the proper supply of fresh air to the home.
Without the proper mechanical ventilation, the house runs the risk of indoor air quality concerns include radon, humidity, VOCs, carbon monoxide, odors, and an overall sense of stuffiness and discomfort. These issues can lead to call-backs and home warranty claims. Getting the ventilation system right is very important!
How much fresh air is needed? With a tight house, one also runs the risk of over-ventilating! Too much outdoor air in a humid climate like Nashville's can lead to mold and mildew growth as well as comfort concerns and high energy bills. The right amount of fresh air can be calculated using the ASHRAE 62.2 equation (below), or referenced from Table M1507.3.3(1).
Manual J & S
The Manual J and S are the formal load and sizing calculations, respectively, used to match the heating and cooling needs of a home to the proper mechanical equipment.
In the Manual J, a room-by-room calculation used to determine the BTUs of heat lost and gained by each room (load). The heat gain is split into two parts: Sensible(temperature) and latent (humidity). The heat gained or lost in a room then determines how much conditioned air that room needs (CFM).
The Manual J calculation accounts for:
- Each surface of the building envelope; areas and insulation levels
- Wall orientation
- Location and tightness of the duct system
- Infiltration rate of the house
- Internal loads (appliances and people)
- Where the house is located
The Manual S then guides the HVAC contractor in selecting the proper equipment (or capacity). This step is important for optimizing comfort and managing humidity.
Tight homes have a much different load profile than what builders and contractors were used to in the past. This sizing exercise helps to ensure the heating and cooling system doesn't short cycle, which can lead to serious humidity issues inside the home! Properly sized systems will also have a longer life span, will provide better comfort, and can reduce energy consumption.
The ERI (or Energy Rating Index) pathway allows builders to use a HERS Index to show compliance with code standards. For the 2018 code, a HERS Score of 62 is needed in Climate Zone 4 (Nashville, TN). To obtain a HERS Index, the builder must obtain a HERS certificate from a certified HERS Rater. More information can be found at RESNET.us.
As before, a UA-trade off can also be used as a performance pathway to compliance. Note that the UA-trade off must be completed before permitting. One method for obtaining the proper documentation for the UA-trade off is to use a REScheck. More information about how to obtain a REScheck can be found enegycodes.gov. The software is available as a free download for builders.
Display of Certifications and Labels
Last but not least, the 2018 building code requires a few labels be displayed in certain areas of the house.
The first label is an Insulation Certificates (see Ceiling Section R303.1). R-values must be pruned on the batt insulation or ridge foam board in the attic. For blown cellulose, a certificate must be displayed at or near the opening of the attic and include the following information:
- Blown-in insulation must have an insulation certificate at or near the opening of the attic. Certificate should include:
- R-value of installed thickness
- Installed density
- Settled thickness/settled R-value
- Coverage area
- Number of bags installed
Additionally, insulation markers must be placed every 300 ft, be marked with the minimum installed thickness, and be affixed to the trusses or joists.
The second label is a performance certificate that can be filled out by the builder and must be visibly posted on a wall in the space where the furnace is located, a utility room, or an approved location inside the building. This certificate should include:
- R-values of insulation installed for the thermal building envelope, including ducts outside conditioned spaces.
- U-factors and SHCG for fenestration
- Results from any required duct system and building envelope air leakage testing
- HVAC efficiencies and types
- SWH equipment
- Duct sealing, duct and pipe insulation and location
- Air sealing details
Most of this information can be obtained either from the Manual J report or the HERS Index or REScheck input data.
Plan Ahead Get Ahead
E3 INNOVATE is here to help builders meet these new requirements with New Construction Design Review Consultations, Manual J and S services, RESchecks, and HERS ratings.
A Design Review Consultation will help you plan for every new home you build. This small investment in planning can say you thousands in lost time, materials, and warranty claims in the future. We can help you plan out each step of the way to ensure a high-quality product and a home that serves the owners for years to come.
Give us a call today to schedule a consultation.