CS79 Energy Code Feasibility Study in Ocean View, Delaware

Goal

To find the most cost-effective compliance path, this report isolates energy code related costs from total construction. We use real bid data from vendors & clients to create a reliable framework for aligning incentives and design, with all recommendations confirmed by detailed energy modeling.

Project

• Ocean View, DE 19970
• 6 Buildings | 126 Units | 195,462 SF Conditioned
• New Construction | Lowrise | 3-story 21 unit lowrise multifamily building (x6).
• All-Electric | 2024 IECC with DE Amendments | HERS/ERI ≤ 53 or REScheck

Overview

Read This: This report compares different ways you can build the project and meet energy code, looking at both cost and incentives, with the ultimate goal as finding the most affordable path.

• The overview outlines the key differences between each of the paths we show in this report and why we recommend the one we picked over the others.
• The recommended design section is where we share the requirements and incentives for the path we think is best based on affordability.
• The path comparison section shows the detailed requirements and incentives for each path we compared, basically showing our work if you want to dig in.

Path Summaries

Both paths meet the Delaware energy code and are modeled to pass on a lean margin, so the choice between them is a matter of cost and process rather than compliance.

REScheck (All-Electric): Recommended

This is the path to build, at approximately $28.19/sf net. It is the lowest net cost route and the simpler process to run because nothing has to be graded or certified. The physical building is essentially the same on either path, so the decision is whether third party verification and a utility rebate are worth roughly $1.17/sf on a project this size, and on the numbers alone they are not.

HERS (All-Electric): Alternative (Certified / Rebate-Eligible)

This path costs approximately $29.36/sf net, about $1.17/sf above the recommended route, and what that premium buys is a certified, third party verified building rather than a checklist. It is also the only path that qualifies for the Delmarva ENERGY STAR New Homes rebate at $350 per unit, or $44,100 on this project. Choose it when that rebate or the verified rating genuinely matters to financing, marketing or asset value.

What Changes Between Paths

Multifamily Low-Rise, 3 stories

2024 IECC with DE Amendments | HERS/ERI ≤ 53 or REScheck

The project is governed by the Delaware Energy Code 2024, which adopts the 2024 International Energy Conservation Code with Delaware amendments. The whole state is in climate zone 4A, and a Group R-2 building of three stories or less above grade plane follows the residential provisions. Two compliance options are open to this building, and this study prices both.

Option A, REScheck (the prescriptive option, R401.2.1 and R401.2.2). Every assembly and every piece of equipment meets the prescriptive tables directly: envelope R-values and U-factors per Table R402.1.2, fenestration U-factor and SHGC, the Section R403 systems requirements, and the Section R408 additional-efficiency credits the prescriptive option carries. No energy model is needed. Compliance is documented with a REScheck report and the 2024 IECC checklist.

Option B, the Energy Rating Index (R401.2.3, Section R406). Each dwelling unit is rated to an ERI or HERS Index of 53 or lower, the Table R406.5 value for climate zone 4 with no credit taken for on-site generation. Compliance is documented by HERS modelling with third-party verification by an approved agency under Section R406.6. The Section R408 credits belong to the prescriptive option and are not triggered here. Where a project instead takes Index credit for an on-site array, the ceiling tightens to 40.

Both options carry the same mandatory items: envelope air-leakage (blower door) testing, duct-leakage testing where ducts are present, the Appendix RE electric vehicle charging infrastructure, and the permanent certificate posted in each dwelling unit under Section R401.3.

Permit / Certificate of Occupancy Requirements

At permitting, the energy-code compliance report is submitted with the building permit application.

On the REScheck option that is the REScheck report and the 2024 IECC checklist, backed by the component specifications on the drawings: assembly R-values and U-factors, fenestration U-factor and SHGC, equipment types and rated efficiencies, and the Section R408 credits claimed.

On the Energy Rating Index option that is the Section R406.7.2.1 proposed compliance report for each unit type: the Index achieved, the compliance software name and version, the modelling inputs behind the reference and rated designs, and the same component specifications, with the Index declared on the drawings.

Either way the construction documents show the Appendix RE electric vehicle charging infrastructure.

At certificate of occupancy on the REScheck path, the built work is confirmed against what was permitted with envelope air-leakage (blower door) testing at 4.0 air changes per hour or 0.22 CFM50 per square foot of enclosure, with the 0.27 CFM50 per square foot alternative available for attached units and units in an R-2 tested without simultaneously testing their neighbours, plus duct-leakage testing where ducts are present, ventilation airflow verification, and the permanent certificate posted in each dwelling unit.

On the Energy Rating Index option, each unit type is additionally confirmed at or below an Index of 53 through the Section R406.7.2.2 confirmed compliance report, made site and address specific, verified by an approved third party under Section R406.6, with the final Home Energy Rating Certificate issued through the rater's provider. Both options close out with blower door testing; the REScheck path does not require a HERS Index certificate.

Recommended Design

This section outlines the design requirements, product recommendations, and incentives for the design that we believe will be the most affordable path to meeting energy code.

Recommended Design - Incentives

Incentives Available: $0

• No Delmarva Rebate On The REScheck Path ($0) : The Delmarva Power ENERGY STAR New Homes rebate is paid for dwelling units that earn ENERGY STAR certification. The REScheck path demonstrates code compliance with a prescriptive checklist and never enrolls for certification, so it earns nothing from this program however the building performs. Delaware has no separate rebate that pays per dwelling unit for a code-only design, so this path carries no incentive at all.
  • IMPORTANT: There is no partial credit. The rebate is all or nothing on whether the units are certified, so the choice of compliance path is the choice of whether this money exists.

HVAC Design Loads

Sussex County, DE · heating 18.0°F/70.0°F · cooling 91.0°F/75.0°F · loads include a bad-install allowance (UA +8%, infiltration +25%, recovery held to 60%) · all values kBtuh

Design heat loss · components

Design heat gain · components

Selection

Recommended Design - Units

Recommended Design - Common Areas

Exterior Wall (HERS, REScheck)

Slab on Grade (HERS)

Slab on Grade (REScheck)

Rim Joist (HERS, REScheck)

Roof / Ceiling (HERS, REScheck)

Path Comparison

This section shows the detailed requirements and incentives for each path we compared, basically showing our work of how we determined the recommended path is the most affordable way of meeting energy code compliance.

Path Comparison - Incentives

REScheck: $0

• No Delmarva Rebate On The REScheck Path ($0) : The Delmarva Power ENERGY STAR New Homes rebate is paid for dwelling units that earn ENERGY STAR certification. The REScheck path demonstrates code compliance with a prescriptive checklist and never enrolls for certification, so it earns nothing from this program however the building performs. Delaware has no separate rebate that pays per dwelling unit for a code-only design, so this path carries no incentive at all.
  • IMPORTANT: There is no partial credit. The rebate is all or nothing on whether the units are certified, so the choice of compliance path is the choice of whether this money exists.

HERS: $44,100

• Delmarva Power ENERGY STAR New Homes Rebate - Multifamily ($44,100) : Delmarva Power pays this builder rebate for dwelling units that earn ENERGY STAR certification, at $350 per unit on the Multifamily version 3.1 line of its ENERGY STAR New Homes Builder Benefits schedule. The project enrolls with the program before construction starts and carries a certified rater through completion, and payment goes to the enrolled builder once the certification documentation is submitted and approved. This is the one Delaware program that pays per dwelling unit on a new multifamily building, and certification is what earns it.
  • IMPORTANT: The rebate turns on ENERGY STAR certification, not on the rating alone. A design that beats code but never completes certification earns nothing here, which is the whole difference between the two paths in this study.
  • IMPORTANT: Enrollment happens during design, before construction starts. A building that mobilizes before it enrolls has lost the rebate, so this is a timing decision as much as a design decision.
  • IMPORTANT: Delmarva Power customers only. Delaware Electric Cooperative members and customers of the nine municipal electric utilities cannot apply, and Delaware electric territory does not follow town lines, so confirm the account from the meter or the bill rather than the address.
  • NOTE: The amount quoted here is the multifamily version 3.1 line of the current builder rebate schedule, which is the rate this project qualifies for. Delmarva publishes higher amounts for other certification tiers and separate bonuses for specific equipment, and those are confirmed against the schedule in force at enrollment rather than assumed at feasibility.

Path Comparison - Net Cost Summary

Path Comparison - Envelope

Path Comparison - Mechanical

Path Comparison - Plumbing & Appliances

Path Comparison - Electrical

Path Comparison - Soft Costs & Whole-Building Incentives

Additional Design Considerations Not Represented In This Study

• NEXTGen Multifamily (MFNC v1.2) Path: A third design path was modeled in Ekotrope under the ENERGY STAR NextGen Multifamily framework with heat pump water heating and higher-performance measures. The worst-case unit landed at an Energy Rating Index of 53 with no margin against the Delaware limit of 53 and did not satisfy the NextGen requirements, so the path is excluded from this study.
• Heat Pump Water Heater: Heat pump water heaters were reviewed as part of the excluded NextGen package. Both study paths keep in-unit electric resistance tank water heaters at UEF 0.93 or better inside conditioned space. The heat pump units improved modeled performance but added equipment and closet space cost, and neither path needs them to clear the Delaware Energy Rating Index limit of 53.
• Ducted Air-Source Heat Pump With a Standalone ERV: A ducted air-source heat pump at higher rated efficiency paired with a separate in-unit ERV was considered for both paths. Both paths instead carry a vertical terminal heat pump with the ERV integrated into the same package, which puts heating, cooling and ventilation in one factory-built unit and removes a second piece of equipment to install, balance and commission in every apartment. The ducted alternative did not change compliance on either path.
• Alternative Roof Assemblies: Two other ways of reaching R-49 at the roof were considered and set aside. A sealed unvented attic insulated at the roof deck is not needed because the ductwork stays in conditioned space or below the attic insulation, so there is no reason to bring the attic inside the thermal boundary. Splitting the roof into an R-38 cavity layer plus a separate R-11 continuous layer above the deck reaches the same total with an extra layer to fasten and detail, so the roof is specified as one R-49 depth at the ceiling plane in a vented attic.
• Corridor Wall Insulation: Insulating the walls between apartments and the interior corridors was reviewed and is not applicable on this project. The corridors are conditioned, so a corridor wall is not part of the thermal boundary and carries no envelope requirement. Corridor walls are listed as N/A on both paths and no corridor assembly is drawn.
• Committed Design Energy Rating Index of 51: The client's design goal was an index of 51. The recommended HERS path is modeled at a worst-case index of 52, which clears the Delaware limit of 53 by one point but sits one point above the design goal. Tightening the envelope or the mechanical package further to reach 51 adds cost for no compliance benefit, so it is not carried into the costed paths.
• Non-Ducted Equipment for the ENERGY STAR Cooling Sizing Limit: The three-bedroom worst case needs at least 26.0 kBtuh of heating at the 18F design temperature, and the smallest purchasable size that delivers it is 30 kBtuh, which is 174% of that unit's 17.2 kBtuh cooling load and above the ENERGY STAR Condition A cooling ceiling. Taking the heads off the ducts would exempt the equipment under Footnote 30, and dropping to a smaller size would leave the unit short on heating. Heating governs the selection, so the 30 kBtuh capacity stands and this is reported as a design finding for the mechanical engineer rather than resolved by changing the equipment family.