HOUSE OF REPRESENTATIVES STAFF ANALYSIS
BILL #: HB 1185 Thermal Efficiency Standards for Unvented Attic and Unvented Enclosed Rafter
Assemblies
SPONSOR(S): Griffitts
TIED BILLS: IDEN./SIM. BILLS: SB 1130
REFERENCE ACTION ANALYST STAFF DIRECTOR or
BUDGET/POLICY CHIEF
1) Regulatory Reform & Economic Development 12 Y, 1 N Wright Anstead
Subcommittee
2) Commerce Committee
SUMMARY ANALYSIS
The Florida Building Code (Building Code), Energy Conservation (EC Code), regulates the design and
construction of buildings for the effective use and conservation of energy over the useful life of each building.
The EC Code is intended to provide flexibility to permit the use of innovative approaches and techniques to
achieve this objective.
The Building Code and EC code requires that unvented attics and unvented enclosed roof framing assemblies
in residential homes must meet the following requirements:
The unvented attic space is completely within the building thermal envelope.
Where only air-impermeable insulation is provided, the insulation must be applied in direct contact with
the underside of the structural roof sheathing.
The attic is built using R-30 insulation in Climate Zone 1, and R-38 insulation in Climate Zone 2.
The home is verified as having an air leakage rate not exceeding seven air changes per hour (7
ACH50) in Climate Zones 1 and 2.
If the home has an air leakage rate less than three air changes per hour (3 ACH50), the home must
have whole-house mechanical ventilation.
The bill provides that unvented attic and unvented enclosed rafter assemblies that are insulated and air sealed
with a minimum of R-20 air-impermeable insulation meet the requirements of the EC Code, if all of the
following apply:
The building has a blower door test result of less than 3 ACH50.
The building has a positive input ventilation system or a balanced or hybrid whole-house mechanical
ventilation system.
If the insulation is installed below the roof deck and the exposed portion of roof rafters is not already
covered by the R-20 air-impermeable insulation, the exposed portion of the roof rafters is insulated by a
minimum of R-3 air-impermeable insulation unless directly covered by a finished ceiling. Roof rafters
are not required to be covered by a minimum of R-3 air-impermeable insulation if continuous insulation
is installed above the roof deck.
All indoor heating, cooling, and ventilation equipment and ductwork is inside the building thermal
envelope.
The bill provides an effective date of July 1, 2024.
This docum ent does not reflect the intent or official position of the bill sponsor or House of Representatives .
STORAGE NAME: h1185a.RRS
DATE: 2/6/2024
FULL ANALYSIS
I. SUBSTANTIVE ANALYSIS
A. EFFECT OF PROPOSED CHANGES:
Current Situation
The Florida Building Code
In 1974, Florida adopted legislation requiring all local governments to adopt and enforce a minimum
building code that would ensure that Florida’s minimum building standards were met. Local
governments could choose from four separate model codes. The state’s role was limited to adopting all
or relevant parts of new editions of the four model codes. Local governments could amend and enforce
their local codes, as they desired.1
In 1992, Hurricane Andrew demonstrated that Florida’s system of local codes did not work. Hurricane
Andrew easily destroyed those structures that were allegedly built according to the strongest code. The
Governor eventually appointed a study commission to review the system of local codes and make
recommendations for modernizing the system. The 1998 Legislature adopted the commission’s
recommendations for a single state building code and enhanced the oversight role of the state over
local code enforcement. The 2000 Legislature authorized implementation of the Florida Building Code
(Building Code), and that first edition replaced all local codes on March 1, 2002.2 The current edition of
the Building Code is the seventh edition, which is referred to as the 2020 Florida Building Code. 3
Chapter 553, part IV, F.S., is known as the “Florida Building Codes Act” (Act). The purpose and intent
of the Act is to provide a mechanism for the uniform adoption, updating, interpretation, and
enforcement of a single, unified state building code. The Building Code must be applied, administered,
and enforced uniformly and consistently from jurisdiction to jurisdiction.4
The Florida Building Commission (Commission) was statutorily created to implement the Building
Code. The Commission, which is housed within the Department of Business and Professional
Regulation (DBPR), is a 19-member technical body made up of design professionals, contractors, and
government experts in various disciplines covered by the Building Code. The Commission reviews
several International Codes published by the International Code Council, 5 the National Electric Code,
and other nationally adopted model codes to determine if the Building Code needs to be updated and
adopts an updated Building Code every three years. 6 The current edition of the Building Code is the
eighth edition, which is referred to as the 2023 Florida Building Code.7
Building Thermal Envelope
The Florida Building Code, Energy Conservation (EC Code), regulates the design and construction of
buildings for the effective use and conservation of energy over the useful life of each building. The EC
Code is intended to provide flexibility to permit the use of innovative approaches and techniques to
achieve this objective.8
The EC Code defines:9
1 The Florida Building Commission Report to the 2006 Legislature, Florida Department of Community Affairs, p. 4,
http://www.floridabuilding.org/fbc/publications/2006_Legislature_Rpt_rev2.pdf (last visited Feb. 2, 2024).
2 Id.
3 Florida Building Commission Homepage, https://floridabuilding.org/c/default.aspx (last visited Feb. 2, 2024).
4 See s. 553.72(1), F.S.
5 The International Code Council (ICC) is an association that develops model codes and standards used in the design, building, and
compliance process to “construct safe, sustainable, affordable and resilient structures.” International Code Council, Ab out the ICC,
https://www.iccsafe.org/about/who-we-are/ (last visited Feb. 2, 2024).
6 S. 553.73(7)(a), F.S.
7 Florida Building Commission, Homepage, https://floridabuilding.org/c/default.aspx (last visited Feb. 2, 2024).
8 S. R101.1-101.3. FBC, Energy Conservation (8th Ed. 2023).
9 S. R202, FBC, Energy Conservation (8th Ed. 2023).
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“Building thermal envelope” as the basement walls, exterior walls, floors, ceilings, roofs and any
other building element assemblies that enclose conditioned space or provide a boundary
between conditioned space and exempt or unconditioned space.
“Conditioned space” as an area, room or space that is enclosed within the building thermal
envelope and that is directly or indirectly heated or cooled. Spaces are indirectly heated or
cooled where they communicate through openings with conditioned spaces; where they are
separated from conditioned spaces by uninsulated walls, floors or ceilings; or where they
contain uninsulated ducts, piping or other sources of heating or cooling.
The building thermal envelope for residential buildings must meet the requirements of ss. R402.1.1
through R402.1.5 of the EC Code, except the following low-energy buildings, or portions thereof,
separated from the remainder of the building by EC Code-compliant building thermal envelope
assemblies:10
Those with a peak design rate of energy usage less than 3.4 Btu/h · ft2 (10.7 W/m2) or 1.0
watt/ft2 of floor area for space-conditioning purposes.
Those that do not contain conditioned space.
Log homes designed in accordance with ICC-400.
Parts of a Roof
In general, a roof is composed of the following structures: 11
Roof sheathing, also called roof decking, are the wooden boards that make up the framing of a roof
system. These boards are what shingles and other roofing components are installed directly on. 12
Roof rafters are structural components of a roof on a building. Traditional rafters frame out the roof and
connect to the exterior walls, and land on a ridge board, which runs across the length of the building.
The result is a vaulted ceiling that can be filled with insulation and drywall to finish the space or be left
as open space in an attic.13
Unvented Attics
10 S. R402.1, FBC, Energy Conservation (8th Ed. 2023).
11 Kimberly Magerl, 21 Different Parts of a Roof, Roof Gnome, Oct. 9, 2023, https://roofgnome.com/blog/roofing/different-parts-of-a-roof/
(last visited Feb. 4, 2024).
12 Bill Ragan, What is Roof Sheathing? (What You Need to Know About It), Bill Ragan Roofing Company, Aug. 31, 2022,
https://www.billraganroofing.com/blog/what-roof-sheathing (last visited Feb. 4, 2024).
13 MT Copeland, What Are Rafters?, Dec. 22, 2021, https://mtcopeland.com/blog/what-are-rafters/ (last visited Feb. 4, 2024).
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Residences may be constructed with either a:14
Vented attic: With openings for outside air to ventilate the space underneath the roof with
insulation above the ceiling finish.
Unvented attic: Without any opening underneath the roof–creating an unvented attic space with
insulation at the roof deck. The unvented attic is completely within the building thermal
envelope.
Unvented roof assemblies, such as conditioned attics and unvented cathedral ceilings, are created by
eliminating ventilation openings and moving the thermal (or insulation), moisture, and air control
boundaries to the plane of the roof deck.15 Unvented attics are also typically built with the HVAC
system completely within the building thermal envelope. Insulation is usually a spray foam product that
also provides air sealing to create a semi-conditioned space.16
Although the rationale for attic ventilation is for moisture control, this was historically based on needs in
cold climates and to prevent ice dams. However, vented attics can introduce additional moisture loads
into Florida homes by allowing moisture laden air in the attic that may come indoors. Unvented attics
can help to reduce moisture condensation on attic mounted ducts and air handlers by reducing the
moisture level of the air around the ducts and on the back side of ceiling drywall when low thermostat
set points are used.
Unvented attics offer the following potential advantages over vented attics: 17
Energy Savings - An unvented attic is warmer in winter and cooler in summer, reducing the
HVAC load. The equipment will be more durable and more efficient, especially if ductwork is in
the attic.
Moisture Resistance - The attic will stay dry, avoiding problems with mold and wood rot, and
thus can serve as living or storage space.
Disaster Resistance - Roofs over unvented attics are less likely to be blown off in high winds
because the wind cannot readily enter the attic. In addition, a house in wildfire zones is less
likely to catch fire from floating embers since there are no soffit vents for the embers to enter. In
coastal areas, an unvented roof keeps out wind-driven rain and better protects metal connectors
in the roof assembly against salt spray and corrosion.
However, an unvented attic system can be more expensive than a vented attic, as it requires more
spray foam insulation, which means more cost.18
An example of an unvented attic is pictured below:19
14 University of Central Florida, Florida Solar Energy Center, Attic Insulation and Ventilation,
https://energyresearch.ucf.edu/research/buildings-research/roof-assembly/attic-insulation-ventilation/ (last visited Feb. 4, 2024).
15 U.S. Department of Energy, Unvented, Conditioned Attics, https://www.energy.gov/eere/buildings/articles/unvented-conditioned-
attics-building-america-top-
innovation#:~:text=Insulating%20and%20air%20sealing%20along,insulating%20along%20the%20ceiling%20deck%3A&text=Energy%
20Savings%20%2D%20An%20unvented%20attic,the%20attic%20(Rudd%202005). (last visited Feb. 4, 2024
16 UCF, supra note 14.
17 US Dept. of Energy, supra note 15.
18 Amanda Ringler, Vented vs. Unvented Attic: Which is Better?, RetroFoam of Michigan Inc., July 13, 2020,
https://www.retrofoamofmichigan.com/blog/vented-vs-unvented-attic-which-is-better (last visited Feb. 4, 2024).
19 U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Unvented Attic Insulation,
https://basc.pnnl.gov/resource-guides/unvented-attic-insulation#edit-group-description (last visited Feb. 4, 2024).
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Air-impermeable Insulation
Permeable and impermeable air barrier membranes differ in their ability to block moisture: 20
Impermeable air barriers block water vapor and air.
Permeable air barriers block air but allow water vapor to move through the membrane,
promoting diffusion out of the wall system. Permeable air barriers offer varying permeability
rates and come as either sheet or fluid-applied membranes.
Air-impermeable insulation that is installed to the underside of the roof sheathing of an unvented roof is
typically spray foam. Air-impermeable spray foam insulation for unvented attics applied under the
sheathing is typically installed as follows:21
Florida generally requires insulation to be installed under the roof sheathing, 22 but elsewhere, air-
impermeable insulating sheathing applied over the roof deck may be used for unvented attics, and is
typically installed as follows:23
20 Cory Bendokas, Impermeable vs. Permeab le Air Barriers: Main Differences, Build Meets World by Tremco CPG Inc.,
https://blog.buildmeetsworld.com/impermeable-vs-permeable-air-barriers (last visited Feb. 4, 2024).
21 US Dept. of Energy, supra note 19.
22 S. R806.5, FBC, Residential (8th Ed. 2023).
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R-Value
R-value is a measure of how much resistance insulation has to heat flow. The higher the R-value, the
more the resistance and the better the material is at insulating a home. Generally, insulation materials
with higher R-values cost more when compared to those with lower R-values.24
Blower Door Tests
Blower door tests determine to what degree a home is airtight. A temporary “blower door” equipped
with a powerful fan is fitted into the frame of an existing front or back door, and when the fan is turned
on, it sucks the air out of the house and blows it outside. Digital gauges compare the difference in air
pressure between the inside air and the outside air to determine how much air is leaking into the
house.25
The standard way to determine air tightness of a building is to measure air leakage at 50 Pascals
(ACH50) to the conditioned volume of the building. Air Change per Hour at 50 Pa (ACH50) is calculated
by dividing air flow per hour by the volume of the building. ACH50 tells us how many times per hour the
entire volume of air in the building is replaced when the building envelope is subjected to a 50 Pascal
pressure. The airtightness of existing homes can vary dramatically based on the construction style, age
and region.26
Proper, tight air sealing of unvented attics is important for proper function.27 Whole-house mechanical
ventilation is required for homes with a high air-tightness.28
23To meet durability goals in most applications, the airtightness must be provided by a continuous membrane—preferably
adhered to the top surface of the structural roof deck and under rigid insulation that provides condensation control . Id.
24 Emily Glover and Samantha Allen, What Is Insulation R Value? Everything You Need To Know, Forbes, Jan, 20, 2022,
https://www.forbes.com/home-improvement/home/what-is-insulation-r-value/ (last visited Feb. 4, 2024).
25 Glenda Taylor and Bob Vila, All You Need to Know Ab out Blower Door Tests, BobVila.com, Oct. 23, 2020,
https://www.bobvila.com/articles/blower-door-tests/ (last visited Feb. 4, 2024); Tyler Vanzo, Air Changes Per Hour (ACH): What is it &
How to Calculate it, SmartAir, Jan. 16, 2024, https://smartairfilters.com/en/blog/what-is-air-changes-per-hour-ach-how-to-calculate/ (last
visited Feb. 4, 2024).
26 The Energy Conservatory, TEST RESULTS AND SAMPLE TEST FORMS, https://energyconservatory.com/wp-
content/uploads/2017/08/Test-Results-and-Sample-Test-Forms-Guide-.pdf (last visited Feb. 4, 2024).
27 UCF, supra note 14.
28 Eric Martin and Charles Withers, Jr., Survey of Unvented Attics in Climate Zone 2A, University of Central Florida, Florida Solar
Energy Center,