AC90-0611-R1
#18
8385 White Oak Avenue
Rancho Cucamonga, CA 91730
909.483.0250 ph. | 909.483.0336 fx.
May 27, 2011
Michael Merrigan, P.E.
ICC Evaluation Service
5360 Workman Mill Road
Whittier, CA 90601
RE: Proposed Revisions to AC90
Dear Mr. Merrigan,
QAI submits the following comments regarding the proposed revisions to AC90, Proposed Revisions to the
Acceptance Criteria for Fiber Cement Siding Used as Exterior Wall Siding, Subject AC90-0611-R1 (MM/MB),
dated May 4, 2011 as posted on the ICC-ES website.
We have 3 points to comment in reference to the rewording of Section 4.1.
1. The first sentence reads that the air pressure difference is to be “applied to the back of the siding.” In
reading further in the paragraph it stipulates that the air pressure be applied by a plastic film installed in
between the siding and the sheathing and/or framing. This test set up will apply a pressure to the siding in only
one direction, which we would describe as the negative pressure direction (meaning the direction of a negative
wind pressure). A positive pressure applied in this manner would exert no load on the siding material as the
film would be pulled in to the sheathing and/or framing, leaving the siding untouched. The positive pressure
application requires the film to be applied on the front of the siding. We recommend that the test set-up for
positive and negative loading be described separately in the criteria, with language presented further on in this
letter.
2. The second sentence reads to apply a “2-mil (0.058 mm) maximum thickness” plastic film in accordance
with ASTM E330. As the plastic film is already described in the E330 standard, it is not necessary to repeat this
in the criteria. We recommend striking the specifics of the film thickness.
3. The third sentence describes holes that are to be cut in the sheathing to allow pressure through to the
plastic film. There are several conflicts with this requirement: a) This would apply only in negative pressure
loading when the film is between the sheathing and siding, b) The holes are only necessary in the negative
wind pressure loading direction if you are pushing the air pressure through the film on to the siding, many test
chambers would align the test specimen so that the film is pulling against the siding, in which case the holes
would be facing in to the open air and serving no purpose, c) The vertical spacing of the holes of the holes is
not specified, which leaves out instruction to ensure the pressure is distributed all the way across the test
specimen in both directions.
The following page includes our recommended language for section 4.1.
WWW.QAI.ORG
[email protected]
Recommendation on AC90
May 27, 2011
Page 2 of 2
4.1 Transverse Load Tests: Transverse load tests of the siding material shall be in accordance with ASTM E
330, Procedure B. For negative load direction tests, the air pressure difference shall be applied to the back of
the siding through a plastic film, in accordance with Section 11.1.1 of ASTM E 330, installed between the
siding and the studs or sheathing and sealed to the perimeter of the test frame. If sheathing is applied to the
exterior of the studs and the test chamber applies air pressure from the back of the sheathing through to the
siding, 2-inch (50.8 mm) minimum diameter holes shall be cut through the sheathing, centered horizontally
between studs and spaced 24-inches (610 mm) vertically from each end and through the center, to allow an
even pressure application to the plastic film. For positive load direction tests, the plastic film is to be applied on
the outer face of the siding and sealed to the perimeter of the test frame. At least three positive and three
negative load tests shall be conducted with the siding material fastened to the framing system in accordance
with the published installation instructions. Test assemblies shall be a minimum of 4 feet by 8 feet (1219 mm
by 2438 mm). Test assemblies of the siding material shall include vertical joints. Test assemblies of panel
products shall include at least one vertical joint and one horizontal joint. Application of loads to failure shall be
in at least six increments with a 10-second load duration for each increment. Test assemblies shall be mounted
according to ASTM E 330. Relative movement between the siding material and any part of the test assembly
or test apparatus shall not be restricted during testing. Framing supporting the panel shall be located at the
maximum spacing on which recognition is desired. ICC-ES shall approve any variations from these spans prior
to commencement of tests. Load deflection readings at the midpoint of panel spans shall be reported.
Conditions of acceptance shall be based on the following:
1. Allowable loading shall be based on a factor of a safety of 3.0 applied to the ultimate load, if all of the
following are satisfied:
a. No single test result varies by more than 15 percent from the average of three tests. Variations exceeding
this limit will result in larger safety factors.
b. Allowable load does not exceed established values for mechanical connectors such as nails,
screws and staples.
2. Other factors of safety can be considered based on unique conditions of installation or material used.
If there are any questions or comments on this recommendation, please feel free to contact me at (909) 4830250 or [email protected].
Sincerely,
QAI Laboratories, Inc.
Chris Bowness, P.E.
General Manager
WWW.QAI.ORG
[email protected]