Energy Code FAQ's

Topics: Lighting, Section 405, Slab Insulation, Duct Testing, Knee Walls

Q1. What does high-efficacy mean?
A. Efficacy is the rating given in lumens per watt. The International Codes Council (ICC) defines high-efficacy as: 60 lumens/W for lamps over 40W; 50 lumens/W for lamps over 15W to 40W; and 40 lumens/W for lamps 15W or less. In general, LED and Compact Fluorescent bulbs are high-efficacy. Halogen bulbs are not high-efficacy (nor are incandescents if you find any that are still out there).

Q2. Does the fixture itself have to be high-efficacy or is just the bulb?
A. Only the bulb must be high-efficacy.

Q3. When would a home use section 405, Simulated Performance Alternative, for compliance?
A. When the home doesn’t meet some of the required provisions of the code and doesn’t comply via RESCheck. An example would be a home in Raleigh without slab insulation. If the home does not comply via RESCheck, it might be able to comply using section 405 if measures such as window Solar Heat Gain Coefficient, air leakage rate, and duct leakage rate are substantially better than the code requires.

Q4. What strategies can be used to trade off slab insulation in Zone 4 for other energy efficiency measures?
A. RESCheck, available as a free download here, is an approved method for conducting such trade offs. Examples of measures that might substitute for slab insulation are R-19 insulation in Zone 4 or higher insulation levels in Zone 5, lower U-factors for windows, and additional slab insulation. Such a tradeoff usually requires several measures to garner enough energy savings to substitute for slab insulation.

Q5. Is there a way to install slab insulation that will protect it from being damaged during construction and/or by homeowners using weed eaters, etc.?
A. Yes, use stem wall construction, the insulation will be on the interior and be protected by the masonry wall and concrete slab. If stem wall construction is not preferred, install stone or mulch beds around the perimeter. It will protect the insulation from weed eaters and other lawn maintenance devices.

Q6. If heat rises, then how can slab insulation be effective in eliminating heat loss?
A. Actually, heat doesn’t rise, but warm or hot air rises over cooler air. Heat is thermal energy that moves through objects from warmer areas to cooler areas. Thus, in a heated house with a slab floor, thermal energy moves from the house through the slab to the cooler exterior soil and air around the base of the home. Uninsulated slabs lose a substantial amount of heat during the winter.

Q7. For duct leakage testing, the code allows a leakage to the outside test or a total duct leakage test.  What is the difference?
A. Leakage to the outside measures only the air lost to the outside of the building envelope and total duct leakage measures all of the leakage occurring within the duct system.

Q8. Which is the better of the two tests?
A. Total duct leakage is a better measure of overall duct performance, and ensures a more comfortable home.

Q9. What are the advantages/disadvantages of each test?
A. Total duct leakage

  • Advantages: by measuring all of the leakage of the ducts, you are ensuring a more comfortable home- delivering the air where it is intended to go; shorter/easier test; only requires a duct blaster
  • Disadvantages: in older homes where ducts have been replaced and must be tested, it can be hard to seal supply lines and difficult to get an accurate test; often results in larger leakage measurement

Leakage to the outside

  • Advantages: it allows you to test an older home
  • Disadvantages: it allows leakage to the inside which means the air may be leaking to the floor systems and not be delivered to the living space, effecting the comfort of the home; requires more equipment (blower door)

Q10. What is the best product for sealing ductwork?
A. Duct sealing mastic is the best way to seal duct connections. Unfortunately, other products have been shown to lose their adhesion over time, often due to installation errors.

Q11. How do you properly frame a knee wall when roof trusses are being used?
A. Code requires insulation to be encapsulated on all 6 sides. Truss knee walls are missing bottom plates and top plates. To properly frame a truss knee wall, install a bottom and top plate between each truss member, then install a backer as previously mentioned. Click here to watch an animation that shows how to install the frames properly.


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