I am looking for feedback about not using sheetrock (drywall) on my ceiling.  Can I put wood slats directly on the bottom sides of my panels without causing code problems. I have asked three different inspectors and have three different answers. I know the answer to that statement( if they don't know how should we.) All ceilings are vaulted. Thanks, Sam

Sammy,

Here are the code references related to your question:

R314.1.2 Thermal barrier. Foam plastic, except where
otherwise noted, shall be separated from the interior of a
building by minimum 1/2-inch (12.7 mm) gypsum board or
an approved finish material equivalent to a thermal barrier to
limit the average temperature rise of the unexposed surface
to no more than 250°F(121°C) after 15 minutes of fire expo-
sure to the ASTM E 119 standard time temperature curve.
The gypsum board shall be installed using a mechanical fas-
tening system in accordance with Section R702.3.5. Re-
liance on adhesives to ensure that the gypsum board will re-
main in place when exposed to fire shall be prohibited.

R314.2.2 Roofing. Foam plastic may be used in a roof cov-
ering assembly without the thermal barrier when the foam is
separated from the interior of the building by wood structural
panel sheathing in accordance with Section R803, not less
than 15/32 inch (11.9 mm) in thickness bonded with exterior
glue and identified as Exposure 1, with edge supported
by blocking or tongue-and-groove joints. The smoke-
developed rating shall not be limited.

Show the code official these paragraphs and see if you can get something in writing for your desired application.

Sorry my brother and I are boring you with code references, but sometimes that's all building inspectors want to see. Below is the section of the IBC (International Building Code) that relates to your question.

2603.4.1.5 Roofing. Foam plastic insulation under a roof
assembly or roof covering that is installed in accordance
with the code and the manufacturer’s instructions shall
be separated from the interior of the building by wood
structural panel sheathing not less than 0.47 inch (11.9
mm) in thickness bonded with exterior glue, with edges
supported by blocking, tongue-and-groove joints or
other approved type of edge support, or an equivalent
material. A thermal barrier is not required for foam plastic
insulation that is a part of a Class A, BorC roof-covering
assembly, provided the assembly with the foam
plastic insulation satisfactorily passes FM 4450 or UL
1256.

So, basically your 'Wood Slats' need to conform to the above, which typically means 3/4" solid wood tongue and groove decking, but 1/2" T111 Plywood would also qualify.

Jeff D and Simon D,
You two always give good answers! Thank you!

Do you know what the code says about metal skin SIPs for walls and roof?
Thanks!
Richm

richm,

The International Building Code (IBC) has more information on metal SIPs than it does wood SIPs. Although the information is mostly about cooler and freezer structures. For example:

2603.4.1.2 Cooler and freezer walls. Foam plastic
installed in a maximum thickness of 10 inches (254 mm)
in cooler and freezer walls shall:
1. Have a flame spread index of 25 or less and a
smoke-developed index of not more than 450,
where tested in a minimum 4 inch (102 mm) thickness.
2. Have flash ignition and self-ignition temperatures
of not less than 600°F and 800°F (316°C and
427°C), respectively.
3. Have a covering of not less than 0.032-inch (0.8
mm) aluminum or corrosion-resistant steel having
a base metal thickness not less than 0.0160 inch
(0.4 mm) at any point.
4. Be protected by an automatic sprinkler system in
accordance with Section 903.3.1.1. Where the
cooler or freezer is within a building, both the
cooler or freezer and that part of the building in
which it is located shall be sprinklered.
2603.4.1.3 Walk-in coolers. In nonsprinklered buildings,
foam plastic having a thickness that does not
exceed 4 inches (102 mm) and a maximum flame spread
index of 75 is permitted in walk-in coolers or freezer
units where the aggregate floor area does not exceed 400
square feet (37 m2) and the foam plastic is covered by a
metal facing not less than 0.032-inch-thick (0.81 mm)
aluminum or corrosion-resistant steel having a minimum
base metal thickness of 0.016 inch (0.41 mm). A thickness
of up to 10 inches (254 mm) is permitted where protected
by a thermal barrier.
536

Here is another excerpt from the IBC chapter 26 Plastics again under Foam Plastic for one story buildings, but it is limited to one story buildings that have fire sprinklers.

2603.4.1.4 Exterior walls-one-story buildings. For
one-story buildings, foam plastic having a flame spread
index of 25 or less, and a smoke-developed index of not
more than 450, shall be permitted without thermal barriers
in or on exterior walls in a thickness not more than 4
inches (102 mm) where the foam plastic is covered by a
thickness of not less than 0.032-inch-thick (0.81 mm)
aluminum or corrosion-resistant steel having a base
metal thickness of 0.0160 inch (0.41 mm) and the building
is equipped throughout with an automatic sprinkler
system in accordance with Section 903.3.1.1.

IBC Chapter 1407 talks about metal composite materials used as an exterior finish as follows:

SECTION 1407
METAL COMPOSITE MATERIALS (MCM)
1407.1 General. The provisions ofthis section shall govern the
materials, construction and quality of metal composite materials
(MCM) for use as exterior wall coverings in addition to
other applicable requirements of Chapters 14 and 16.
1407.1.1 Plastic core. The plastic core of the MCM shall
not contain foam plastic insulation as defined in Section
2602.1.
1407.2 Exterior wall finish. MCM used as exterior wallfinish
or as elements of balconies and similar projections and bay and
oriel windows to provide cladding or weather resistance shall
comply with Sections 1407.4 through 1407.14.
1407.3 Architectural trim and embellishments. MCM used
as architectural trim or embellishments shall comply with Sections
1407.7 through 1407.14.
1407.4 Structural design. MCM systems shall be designed
and constructed to resist wind loads as required by Chapter 16
for components and cladding.
1407.5 Approval. Results of approved tests or an engineering
analysis shall be submitted to the building official to verify
compliance with the requirements of Chapter 16 for wind
loads.
1407.6 Weather resistance. MCM systems shall comply with
Section 1403 and shall be designed and constructed to resist
wind and rain in accordance with this section and the manufacturer's
installation instructions.
1407.7 Durability. MCM systems shall be constructed of
approvedmaterials that maintain the performance characteristics
required in Section 1407 for the duration of use.
1407.8 Fire-resistance rating. Where MCM systems are used
on exterior walls required to have a fire-resistance rating in
accordance with Section 705, evidence shall be submitted to
284
the building official that the required fire-resistance rating is
maintained.
Exception: MCM systems not containing foam plastic
insulation, which are installed on the outer surface of a
fire-resistance-rated exterior wall in a manner such that the
attachments do not penetrate through the entire exterior
wallassembly, shall not be required to comply with this section.
1407.9 Surface-burning characteristics. Unless otherwise
specified, MCM shall have a flame spread index of 75 or less
and a smoke-developed index of 450 or less when tested in the
maximum thickness intended for use in accordance with
ASTM E 84 or UL 723.
1407.10 Type I, II, III and IV construction. Where installed
on buildings of Type I, II, III and IV construction, MCM systems
shall comply with Sections 1407.10.1 through 1407.10.4,
or Section1407.11.
1407.10.1 Surface-burning characteristics. MCM shall
have a flame spreadindexof not more than 25 and a smokedeveloped
index of not more than 450 when tested as an
assembly in the maximum thickness intended for use in
accordance with ASTM E 84 or UL 723.
1407.10.2 Thermal barriers. MCM shall be separated
from the interior of a building by an approved thermal barrier
consisting of 1/2-inch (12.7 mm) gypsum wallboard or
equivalent thermal barrier material that will limit the average
temperature rise of the unexposed surface to not more
than 250°F (121°C) after 15 minutes of fire exposure in
accordance with the standard time-temperature curve of
ASTM E 119 or UL 263. The thermal barrier shall be
installed in such a manner that it will remain in place for not
less than 15 minutes based on a test conducted in accordance
with UL 1715.

The way one needs to approach the use of SIPs in the building code is to apply the code to the individual parts of the SIP. If there are wood skins look under the chapters regarding building with wood. If there are metal skins look under the chapters regarding building with metal. If there is a plastic foam core look under the chapters regarding building with foam plastic. After reading these chapters one will have a list of performance tests that the SIP component materials have to meet. Now make sure the manufacturer of the SIP has tested their SIP to these performance requirements. Also all SIPs have to meet the requirements of chapter 16 Structural Design. After reading this chapter make sure the SIP manufacturer has the required structural test results needed to meet chapter 16.

One day soon SIPs will be described by the code until then this is the process we have to go by. I have designed, permited and have seen completed over 100 Metal SIP buildings in many states and have never been denied the use of a load bearing metal SIP for roof and wall applications from a reputable manufacturer.

Simon,

I'm a little confused with"So, basically your 'Wood Slats' need to conform to the above, which typically means 3/4" solid wood tongue and groove decking, but 1/2" T111 Plywood would also qualify.

Seems to me that the specified fire retarder is the OSB itself as long as the edges are splined.  Thereby any subsequent covering could be anything.  Why do you say it needs to be 3/4" and also tongue and groove?  The only mention of T&G was as one of the options around edges of the sheathing.

LarryT,

"provided the assembly with the foam plastic insulation satisfactorily passes FM 4450 or UL 1256."

If the OSB SIPs you have installed have passed the tests listed above then no additional thermal barrier is required. Check with the manufacturer.

I mentioned the 3/4" dimension with regard to the decking because that is typically the least thick material that is readily available in a solid wood product. Plywood (Engineered Wood Products) can be less thick and still remain stable.

In addition most OSB SIPs have 7/16" thick OSB panel skins and if you divide 7 by 16 it equals .4375", which doesn't meet the minimum thickness requirement in the code of .47".