Florida runs its own residential energy code framework under the Florida Building Code, Energy Conservation — and for contractors and designers working in the state, R405 is one of the most important sections to understand. It's the performance-based compliance path, and it's the option most custom homes and design-flexible projects end up using instead of the more rigid prescriptive route.
Florida's residential energy code offers multiple compliance approaches, but the two most commonly used are:
R402 (Prescriptive) — similar in concept to REScheck's prescriptive method, this path requires every envelope component (walls, ceiling, windows, etc.) to individually meet fixed minimum requirements for the applicable climate zone within Florida. It's straightforward but inflexible — no trade-offs allowed.
R405 (Performance) — this path uses whole-house energy simulation software to demonstrate that a proposed home's total annual energy performance meets or exceeds a code-defined baseline "reference home" with the same geometry but built to prescriptive minimums. Because it's based on total performance rather than component-by-component minimums, R405 gives designers much more flexibility — a larger window package, an unconventional layout, or non-standard assemblies can all still comply as long as the overall energy performance measures up.
R405 compliance is determined by running an approved energy simulation program that models the proposed home's actual specifications — envelope assemblies, HVAC equipment efficiency, duct location and leakage, water heating system, and other energy-relevant details — against a reference home baseline. The proposed home's estimated energy use has to be at or below the reference home's, factoring in required credits and specific mandatory requirements that apply regardless of which path is used.
The output is a compliance report (the R405 form) showing the comparison, the inputs used, and confirmation that the project meets the total energy performance requirement. This is the documentation submitted with the building permit application.
The 9th Edition (2026) Florida Building Code, Energy Conservation is based on the 8th Edition (2023), incorporating updates from the 2024 IECC along with Florida Building Commission approved modifications — meaning the specific credits, baseline assumptions, and mandatory requirements referenced in R405 do get updated with each code cycle, and staying current on the applicable edition for a given project matters.
For projects with larger window-to-wall ratios, open floor plans with extensive glazing, or unconventional envelope designs, the R402 prescriptive path can be genuinely difficult or impossible to meet on individual components. R405's whole-house approach lets those design choices get offset by improvements elsewhere — better HVAC efficiency, tighter duct sealing, improved water heating — without forcing a redesign of the envelope itself.
One documentation detail that trips up a lot of first-time R405 submissions: if the compliance form doesn't indicate "default leakage" assumptions, a completed duct leakage test report is required as part of the performance method documentation. This means duct leakage testing (typically performed once ductwork is installed but before drywall, or as a final test) needs to be planned into the project schedule, not treated as an afterthought — a home that was modeled assuming tested (verified low) duct leakage but never actually gets tested creates a documentation gap that can hold up final inspection.
Even under the performance method, certain requirements are mandatory and can't be traded off through energy modeling — things like minimum equipment efficiency thresholds, specific insulation requirements in certain assemblies, and air sealing requirements. R405 gives flexibility on the overall performance target, not a blanket exemption from every individual code requirement.
For simple, conventional home designs that comfortably meet prescriptive minimums on every component, R402 can be the faster, simpler path — no energy modeling software required, just a component checklist. For anything with more design ambition — larger glazing areas, complex geometry, or a desire to offset one weaker assembly with strength elsewhere — R405 is usually the more practical route, even though it requires approved simulation software and more detailed input data.
Is R405 more expensive or time-consuming than the prescriptive path?
It typically requires more detailed data collection and approved simulation software, so it can take more upfront work, but it often saves money and design flexibility overall by avoiding costly envelope redesigns to meet prescriptive minimums.
Does R405 replace the need for a Manual J load calculation?
No — R405 is an energy code compliance demonstration, not an HVAC load calculation. Manual J is still required separately for correct equipment sizing.
What happens if duct leakage testing isn't completed after an R405 submission assumed tested leakage?
This creates a documentation mismatch that can delay final inspection approval — the as-built performance needs to match what was submitted and modeled.
Do R405 requirements change with each Florida Building Code cycle?
Yes — each edition (roughly every three years, with interim updates) can adjust reference home assumptions, credits, and mandatory requirements, so confirming the current applicable edition for a project's permit date matters.
Psychro.Pro supports Florida R405 performance path documentation alongside Manual J, S, and D — keeping your energy code compliance and HVAC sizing aligned on the same project data. Learn more.
