Energy Efficiency

Building Thermal Envelope

Residential energy efficiency requirements per 2018 IECC as adopted by Delaware. All of Delaware is Climate Zone 4A (Mixed-Humid). Three compliance paths available: (1) Prescriptive (Section R402.1), (2) Total UA Alternative (Section R402.1.5), (3) Energy Rating Index (Section R406). Zone 4A: R-49 ceiling, R-20 or R-13+5ci walls, R-19 floor, U-0.35 windows, SHGC 0.40, 3 ACH50 air leakage.

Scope — Energy Code

Covers the energy efficiency provisions for residential buildings. Prescribes thermal envelope requirements, HVAC efficiency, water heating, and lighting based on IECC climate zone. Applies to new construction and alterations that affect the building thermal envelope.

Climate Zones

Establishes climate zone map based on county location. Climate zones 1-8 with marine (C) subtype. Zone determines all insulation R-values, fenestration U-factors, and SHGC requirements. Cross-reference Table N1101.3 or ASHRAE 169 for county-to-zone mapping.

Building Thermal Envelope — General

The building thermal envelope shall meet prescriptive requirements of Table N1102.1.2 or the total UA alternative of N1102.1.4. This is the master section that drives insulation and fenestration requirements.

Insulation and Fenestration Criteria Table

Key prescriptive table specifying R-values and U-factors by climate zone. Example: CZ4 requires ceiling R-49, wall R-20 or 13+5ci, floor R-19, basement wall R-10/13, slab R-10, windows U-0.32, skylight U-0.55, SHGC varies by zone. This table is the most-referenced energy code reference.

Ceilings with Attic Spaces — Insulation

Where insulation is installed in a vented attic, the insulation shall extend over the top plate of the exterior wall to the full required R-value. When blown or batt insulation is used, an insulation marker showing installed R-value shall be placed in the attic.

Air Leakage — Thermal Envelope

Building thermal envelope shall be sealed to limit infiltration. Testing option: max 3 ACH50 in climate zones 3-8, 5 ACH50 in zones 1-2. Prescriptive option: seal all envelope joints and penetrations per approved methods. Blower door testing increasingly required by local jurisdictions.

Fenestration — Air Leakage

Windows, skylights, and sliding glass doors shall have an air infiltration rate not exceeding 0.3 cfm/ft² (NFRC 400 or AAMA/WDMA/CSA 101/I.S.2/A440). Swinging doors: max 0.5 cfm/ft². Relevant for window and door replacement scopes.

Fenestration U-Factor and SHGC

Maximum fenestration U-factor and SHGC values per Table N1102.1.2. NFRC rating required. U-factor affects heating energy; SHGC affects cooling energy. Both must be listed on the NFRC label of replacement windows. Critical for window replacement documentation.

HVAC Controls

Programmable thermostat required in new installations. Heat pump supplemental heat lockout control required. Ducts in unconditioned spaces require R-8 insulation. HVAC system sizing per ACCA Manual J.

Duct Sealing and Insulation

Supply and return ducts outside the building thermal envelope shall be insulated to minimum R-8. Duct sealing required with mastic, tape, or approved methods. Duct leakage testing may be required: max 4 cfm25/100 sq ft conditioned floor area.