Quick answer. Delaware adopted the 2024 energy code for new homes, effective April 11, 2026. Counties and towns have 12 months to bring their own codes into line, so enforcement dates vary; Sussex County requires it from April 11, 2027. A new home must pass a blower door test at 3.0 ACH50 or lower on the prescriptive path. Under the 2024 code every duct system is leak tested, including ducts inside conditioned space. Delaware also specifies who may test: a certified Duct and Envelope Tightness (DET) verifier.
Local Energy Audits tests for builders in Delaware. Book a test online or call (888) 213-3975.
Which code applies in your county
| County | Status |
|---|---|
| Sussex | 2024 code required from April 11, 2027. Plans submitted after April 10, 2026 must already be designed to the 2024 code and include a REScheck or COMcheck worksheet. |
| New Castle | No date published yet. The county’s code page still lists the 2018 energy code (checked November 13, 2026). State rules require the 2024 code by April 2027. |
| Kent | No date published yet. The county’s adopted-codes page still lists the 2018 energy code as enforceable (checked November 13, 2026). State rules require the 2024 code by April 2027. |
Under the state regulation, county and municipal codes must meet the 2024 code within 12 months of its adoption. Any project may use the 2024 code now, as long as that choice is stated on the construction documents.
What changed from the 2018 code to the 2024 code
| Requirement | 2018 code | 2024 code |
|---|---|---|
| Blower door limit, prescriptive path | 3 ACH50 | 3.0 ACH50 (unchanged) |
| Duct test when ducts are entirely inside the envelope | Not required | Required, with a higher allowance |
| Duct leakage limit | 4 CFM25 per 100 sq ft (3 without the air handler) | A table based on number of returns and stage of installation (3 to 12) |
| Additional efficiency credits | None | Required |
| Electric vehicle charging readiness | None | One EV-ready space per new home with a garage or adjacent parking |
Delaware adopted the testing sections of the 2024 code without changes.
Blower door test requirements (2024 code)
A blower door test measures how much air leaks through the shell of the house. The result is reported in ACH50: air changes per hour at a test pressure of 50 pascals. Lower is tighter.
| Compliance path | Maximum air leakage |
|---|---|
| Prescriptive | 3.0 ACH50 |
| Performance or Energy Rating Index | 4.0 ACH50, or 0.22 CFM per sq ft of building envelope area |
| Attached units tested individually, and buildings of 1,500 sq ft or less | May instead meet 0.27 CFM per sq ft |
- Tested to ANSI/RESNET/ICC 380, ASTM E779, ASTM E1827 or ASTM E3158.
- Run after all penetrations of the building envelope are sealed.
- Written up in a report signed by the tester and given to the code official.
Duct leakage test requirements (2024 code)
Every duct system is tested, at rough-in or after construction, to ANSI/RESNET/ICC 380 or ASTM E1554. Ducts inside conditioned space are no longer exempt; they get a higher allowance.
Maximum total duct leakage
| Equipment and duct configuration | Fewer than 3 ducted returns | 3 or more ducted returns | System serving 1,000 sq ft or less |
|---|---|---|---|
| Space conditioning equipment not installed | 3 CFM25 per 100 sq ft | 4 CFM25 per 100 sq ft | 30 CFM25 total |
| All duct system components installed | 4 | 6 | 40 |
| Equipment not installed, ductwork entirely in conditioned space | 6 | 8 | 60 |
| All components installed and entirely in conditioned space | 8 | 12 | 80 |
Points builders miss:
- A “ducted return” has to be an actual duct. Sheet metal or flex duct from a return grille to the air handler counts. Any other way of moving return air to the air handler does not.
- Ducts in a vented attic are not “in conditioned space” unless they are buried in the ceiling insulation and meet a separate leakage-to-outside limit.
- If the air handler’s location in conditioned space can’t be verified before the certificate of occupancy, the system has to be retested.
The only exception from testing is for ducts that serve a ventilation system and are not tied into the heating or cooling ducts.
Who can perform the tests: DET verifiers
Delaware is specific. Its regulation says testing for duct and building envelope tightness must be done by a certified Duct and Envelope Tightness (DET) verifier. A DET verifier is one of the following:
| Credential | Qualifies for |
|---|---|
| Certified Home Energy Rating System (HERS) rater | Duct and envelope testing |
| Certified Home Performance with ENERGY STAR contractor | Duct and envelope testing |
| BPI Heating Professional | Duct tightness testing |
| BPI Building Analyst or BPI Envelope Professional | Building (envelope) tightness testing |
| Completion of a course approved by DNREC | As approved |
Before you book any tester, confirm that they hold one of the credentials above. Call (888) 213-3975 to discuss your Delaware project.
Planning a project in Delaware?
Call us to talk through the testing your project needs.
What your code official needs
- A signed blower door report showing the ACH50 result.
- A signed duct leakage report.
- An energy compliance worksheet such as REScheck with your plans (Sussex County states this in its notice).
Ask about report timing when you book.
Tips for passing the first time
General guidance, drawn from the code’s own air barrier and testing requirements.
- Seal before you cover. Air sealing is cheapest while framing is open. Work through the code’s air barrier checklist before insulation and drywall go in.
- Check the places the code’s air barrier table names. Top plates and attic penetrations, the attic hatch, recessed lights, rim joists, the wall between house and garage, tubs and showers on exterior walls, electrical boxes, and duct boots.
- Call for the test at the right time. The blower door test is run after every penetration of the building envelope is made and sealed. Leave time before final inspection for a re-test.
- Have the house ready. Windows and exterior doors installed and closed, interior doors open, and heating and cooling equipment off.
- Seal ducts while you can reach them. Seal joints, seams and boots before they are covered. A rough-in test finds leaks while they are still easy to fix.
- Plan for a duct test even with ducts inside. Under the 2018 code, ducts and air handlers entirely inside the envelope were not tested. Under the 2024 code every system is tested, with a higher allowance for that layout.
- Count your ducted returns. Under the 2024 code the duct leakage target depends on whether the system has fewer than three ducted returns or three or more.
Frequently asked questions
What ACH50 do I need to pass a blower door test in Delaware?
3.0 ACH50 or lower on the prescriptive path. On the performance or Energy Rating Index path the cap is 4.0 ACH50 under the 2024 code.
Which energy code applies in Delaware right now?
The state adopted the 2024 code effective April 11, 2026. Counties and towns have 12 months to enforce it, so check your county. Sussex County requires it from April 11, 2027 and already requires new plans to be designed to it.
Who is allowed to do blower door and duct testing in Delaware?
A certified DET verifier: a HERS rater, a Home Performance with ENERGY STAR contractor, a BPI Building Analyst or Envelope Professional for envelope testing, a BPI Heating Professional for duct testing, or someone who has completed a DNREC-approved course.
Is a BPI Building Analyst allowed to do the duct leakage test?
The regulation lists BPI Building Analyst for building tightness testing and BPI Heating Professional for duct tightness testing. HERS raters and Home Performance with ENERGY STAR contractors are listed for both.
Is a duct leakage test required in Delaware if my ducts are inside conditioned space?
Under the 2024 code, yes. Ducts and equipment entirely in conditioned space get a higher allowance: 8 CFM25 per 100 square feet, or 12 with three or more ducted returns.
Can I use the 2024 code before my county requires it?
Yes. The state regulation allows any project to use it, provided that choice is stated on the construction documents.
Does my new home need to be EV-ready?
Delaware’s version of the 2024 code requires one EV-ready or EV-charging space for each new one- or two-family home or townhouse that has a garage or adjacent on-site parking.
What happens if the house fails?
The leaks are found and sealed, and the house is tested again. Call (888) 213-3975 to arrange a re-test.
Sources
- Delaware Regulations: 7 DE Admin. Code 2101, State Energy Conservation Code
- DNREC Secretary’s Order 2026-CCE-0002
- DNREC: Building Energy Codes
- Sussex County: Delaware Energy Code Adoption Update (Aug 20, 2026)
- Kent County: Permitting Requirements and Adopted Codes
- New Castle County: County Laws and Code
- 2024 International Energy Conservation Code, Chapter 4 (Residential)
- 2018 International Energy Conservation Code, Chapter 4 (Residential)
- US Department of Energy: Delaware energy code status
Delaware’s energy code technical hotline: 877-610-9099.
This page summarizes the code for builders and is not legal advice. Enforcement dates differ by county and town. Confirm the details of your project with your local permit office.
Code requirements elsewhere: Pennsylvania · Philadelphia · New Jersey
Our services: Blower door testing · Duct leakage testing