One Option for Meeting the 2019 California Energy Code (Title 24, Part 6)

Frustrated by the complexity of the new requirements of the Energy Code? 

Are you looking for ways to reliably meet the California Energy Code? 

Are you looking for potential trade offs for greater flexibility and cost savings? 

Then look no further!  This article will discuss the potential of using the air sealing and balanced ventilation credit to get your projects into compliance or to substitute out other materials and requirements.

The Code Requirements

There are two sections of the code that address air sealing, one general and one specific:

All Buildings SECTION 110.7 – MANDATORY REQUIREMENTS TO LIMIT AIR LEAKAGE

All joints, penetrations and other openings in the building envelope that are potential sources of air leakage shall be caulked, gasketed, weather stripped, or otherwise sealed to limit infiltration and exfiltration (pg. 115).

Non-Residential Buildings / High Rise Residential / Hotels SECTION 120.1 – REQUIREMENTS FOR VENTILATION AND INDOOR
AIR QUALITY

b.The mechanical ventilation system shall comply with one of the following subsections 1 or 2 below. When subsection 2 is utilized for compliance, all dwelling units in the multifamily building shall use the same ventilation system type.

1) A balanced mechanical ventilation system shall provide the required dwelling-unit ventilation airflow OR

2) Continuously operating supply ventilation systems or continuous operating exhaust ventilation systems shall be allowed to be used to provide the required dwelling unit ventilation airflow if the dwelling-unit envelope leakage is less than or equal to 0.3 cubic feet per minute at 50 Pa (0.2 in. of water) per ft2 of dwelling unit envelope surface area as confirmed by field verification and diagnostic testing in accordance with Reference Nonresidential Appendix NA7.18.2. (pg. 132).

Explanation

The All Buildings part is pretty easy…it simply states that all builders need to seal potential sources of air leakage.  Beyond that it gives no specific guidance or requirements.

Something to note is that the compliance software used to calculate 2019 Energy Code Compliance for residential buildings, CBECC-RES, assumes a default 5 ACH50 (translated: 5 air changes per hour at 50 pascals pressure) if a house does not perform a blower door test.  Therefore, anything tested at better than 5 ACH50 gives you credit towards compliance.  There will be more on this later.

The Non-Residential Buildings / High Rise Residential / Hotels part is a little more complicated so let’s break that down.

These types of properties have two options for compliance:

1)  One is to use a “balanced” ventilation system (such as an HRV system), which simultaneously “pushes” fresh air into the space and “pulls” stale air out.  As long as these air flows are roughly equal the system is considered “balanced”.

2)  The other is to use supply or exhaust only ventilation (supply = blowing outside air into a space, exhaust = pulling inside air out of a space).  HOWEVER, in order to utilize this option, specific air leakage requirements come into play:

Air leakage for a dwelling unit must be less than 0.3 cubic feet per minute (CFM) at 50 Pascals of pressure per square foot of dwelling unit envelope surface area.  It is important to note that dwelling unit envelope surface area is NOT the same as floor area; it includes all “six sides” of a dwelling unit, including the floor/ceiling/wall square footage.  In apartments and hotels, this includes dividing walls between units.  Let’s look at an example apartment unit to see how this calculation works:

Dwelling unit envelope surface area — add all surface areas:  270 + 270 + 360 + 360 + 1,200 + 1,200 = 3,660 square feet

0.3 cubic feet per minute X 3,660 square feet = 1,098 cubic feet per minute maximum allowable air leakage for given dwelling unit.

What Should I Choose?  What Is The Best Option?

Worst:  No air sealing and exhaust or supply only ventilation (no longer allowed by code)

-Would result in extremely poor energy efficiency, uncomfortable indoor conditions, and no guaranteed ventilation

Better:  Good quality air sealing and exhaust or supply only ventilation

-Air sealing will dramatically improve energy efficiency and also help separate adjacent units (preventing cigarette smoke, CO2, odors, etc from flowing through the shared walls).  The exhaust or supply ventilation displaces a large amount of heated or cooled air, reducing HVAC efficiency as the furnace or air conditioner has to continuously heat or cool air.

Best:  Great air sealing and balanced ventilation (by far the best comfort and energy efficiency)

-The building is no longer leaking heated or cooled air.  Incoming air is filtered and run through a heat exchanger, greatly improving indoor air quality and HVAC efficiency.  The indoor environment is much more comfortable, energy efficient, and clean.

The Opportunity

Air sealing a home and installing balanced ventilation (both need to go together) can boost your energy compliance score by as much as 9.5-11%.  How much is that, and what can be replaced as a result?  Let’s look at an example home and run a few energy calculations to find out:

First off, we are starting with a fairly standard house.  We use a 2,100 square feet and 3 bedroom house in Sacramento with Quality Insulation Inspection (QII), 80 AFUE furnace, 14 SEER air conditioner, cool roof, R19 below deck roof insulation, R21 2×6 walls with R5 exterior insulation and stucco siding.  No credit has been taken for air sealing and balanced ventilation.  Let’s try a few different options with the energy code compliance program (CBECC-RES) and see what happens (please note that the energy calculation is very complicated and results may vary based on design and location).

This is our default home with no modifications.  The important number to look at here is the Efficiency EDR, which tracks the compliance of the home against California minimum requirements (the Total EDR adds solar so we will ignore it for now).  As long as the Efficiency EDR and Total EDR are positive (above zero) the house complies with the code.

Now we decided to get some credit for air sealing and ventilation (remember that they need to go together).  We change the default air leakage of 5 ACH50 down to 2 ACH50 and add an HRV system (heat recovery ventilator – learn more here)  that has 100 CFM of airflow.  Some folks that are familiar with air leakage standards may think that 2 ACH50 is too difficult to achieve, but we will address that down below.   We gain 5.6 points in our compliance margin…this may not sound like much, but let’s compare it to some other energy efficiency measures.

Now we remove QII – Quality Insulation Inspection, which requires a HERS rater to come out and verify the installation of insulation throughout the house.  Based on the score reduction, we can see that QII is worth 2.5 points at this particular house.

Next we remove the R19 insulation under the roof deck.  Based on the score reduction, we can see that the R19 insulation under the roof deck is worth 4.1 points at this particular house.

Next we remove R5 exterior insulation.  Based on the score reduction, we can see that the R5 exterior insulation is worth 1.3 points at this particular house.  At this point the Efficiency EDR has gone negative, meaning that this house would not be in compliance will the California Energy Code and would need to be corrected.

What Can We Draw From This?

Based on the results above for this particular house in the Sacramento climate zone, we can deduce the following.

5.6 Points–The value of reducing air leakage from 5 ACH50 to 2ACH50 and installing an HRV system.  This is roughly equal to:

2.5 + 1.3 = 3.8 Points–Eliminating QII and R5 exterior insulation

1.3 + 4.1 = 5.4 Points–Eliminating R5 exterior insulation and R19 under roof deck insulation

This basic analysis did not look at other factors such as larger windows or other trade offs that could be made, but I think it is safe to say that adding an HRV and reducing air leakage down to 2 ACH50 or less opens up a lot of options.

How to Do It

It is important to remember that the air sealing and balanced ventilation credit requires both components to get an effective result.  Efficiency First Solutions provides both air sealing via Aerobarrier and balanced ventilation with HRV installations.

Additionally, we can help train your installation crews to improve their baseline air seal work before coming in and significantly reducing leakage (50-90% less) with Aerobarrier.

To learn more about Aerobarrier, you can read more here.

To learn more about HRVs, you can read more here.

Thank you and please do not hesitate to reach out with questions.  We would be happy to help you on your path to cost effective code compliance, client satisfaction, and improved energy efficiency!