Siding Installations in High-Wind Regions
Hurricane Ike Recovery Advisory
FEMA
January 2009


Purpose: To provide basic design and installation tips for various types of 
siding that will enhance wind resistance in high-wind regions (i.e., greater 
than 90-mph gust design wind speed).

Key Issues

	Siding is frequently blown off walls of residential and non-residential 
buildings during hurricanes. Also, wind-driven rain is frequently blown into 
wall cavities (even when the siding itself is not blown off). Guidance for 
achieving successful wind performance is presented below.

	To avoid wind-driven rain penetration into wall cavities, an effective 
moisture barrier (housewrap or building paper) is needed. For further 
information on moisture barriers, see Technical Fact Sheet No. 9 in FEMA 499, 
Home Builders Guide to Coastal Construction, Technical Fact Sheet Series 
(available online at: http://www.fema.gov/library/viewRecord.do?id=1570). For 
further information on housewrap, see Technical Fact Sheet No. 23.

[Begin text box]
Moisture barrier (also known as a water-resistive barrier): In the context of 
residential walls, the moisture barrier is either housewrap or building paper 
(felt). The moisture barrier occurs between the wall sheathing and the siding. 
The moisture barrier is a dual-purpose layer: it sheds water that gets through 
the siding and it limits air flow through the wall. When properly sealed, 
housewrap is considered an air barrier. Although building paper provides some 
resistance to air flow, it is not considered an air barrier. Moisture barriers 
shed water, but they allow water vapor to pass through them.
[End text box]

	Always follow manufacturers installation instructions and local 
building code requirements.

[Begin text box]
For further guidance on principles, materials, and procedures for the design 
and construction of walls to make them resistant to water intrusion, see ASTM 
E 2266, Standard Guide for Design and Construction of Low-Rise Frame Building 
Wall Systems to Resist Water Intrusion.
[End text box]

	Use products that are suitable for a coastal environment. Many 
manufacturers do not rate their products in a way that makes it easy to 
determine whether the product will be adequate for the coastal environment. 
Use only siding products where the supplier can provide specific information 
on product performance in coastal or high wind environments.

	For buildings located within 3,000 feet of the ocean line, stainless 
steel fasteners are recommended. 

	Avoid using dissimilar metals together.

	The installation details for starting the first (lowest) course of lap 
siding can be critical. Loss of siding often begins at the lowest course and 
proceeds up the wall (Figures 4 and 12). This is particularly important for 
elevated buildings, where the wind blows under the building as well as against 
the sides.

	When applying new siding over existing siding, use shims or install a 
solid backing to create a uniform, flat surface on which to apply the siding, 
and avoid creating gaps or projections that could catch the wind.

	Coastal buildings require more maintenance than inland buildings. This 
maintenance requirement needs to be considered in both the selection and 
installation of siding.

Vinyl Siding

Vinyl siding can be used successfully in a coastal environment if properly 
designed and installed.

	Windload resistance: 

	Vinyl siding is required by the International Building Code (IBC) and 
the International Residential Code (IRC) to comply with ASTM D 3679, 
Standard Specification for Rigid Poly(Vinyl Chloride) (PVC) Siding, which 
requires the siding to withstand wind pressures equivalent to 110 mph on a 
building up to 30' in height in Exposure B. Most vinyl siding has also been 
tested for higher wind pressures, and can be used in locations with a higher 
basic wind speed, greater building height, more open exposure, or some 
combination of those. The design wind pressure or wind speed for which these 
products are rated is available from product literature, installation 
instructions, or listings of agencies such as the International Code Council 
(ICC) Evaluation Service.

	For design wind speeds greater than 110 mph, or building heights greater 
than 30', or Exposure C, choose a model of siding rated for those conditions 
or higher. The manufacturers product literature or installation instructions 
should specify the fastener type, size and spacing, and any other installation 
details needed to achieve this rating.

[Begin text box]
Definition of Wind Exposure Zones
Exposure B: Urban, suburban, wooded areas.
Exposure C: Open terrain, flat open country, grasslands, all water surfaces in 
hurricane-prone regions.
[End text box]

	Products that have been rated for high winds typically have an enhanced 
nailing hem and are sometimes made from thicker vinyl (Figure 1). Thick, rigid 
panels provide greater wind resistance, withstand dents, and lie flatter and 
straighter against the wall. Optimum panel thickness should be 0.040" to 
0.048", depending on style and design. Thinner gauge vinyl works well for 
stable climates; thicker gauge vinyl is recommended for areas with high winds 
and high temperature changes.

[Begin figure]
Figure 1 is an illustration showing features of typical high-wind siding and 
standard siding. 
[End figure]

	Position nails in the center of the nailing slot (Figure 2).
[Begin figure]
Figure 2 is an illustration of proper and improper fastener locations.
[End figure]

	To allow for thermal movement of the siding, do not drive the head of 
the nail tight against the nail hem (unless the hem has been specifically 
designed for this). Allow approximately 1/32" (which is about the thickness of 
a dime) clearance between the fastener head and the siding panel (Figure 3).

[Begin figure]
Figure 3 is an illustration showing you should allow 1/32 clearance between 
the fastener head and the siding panel.
[End figure]

	Drive nails straight and level to prevent distortion and buckling in the 
panel.

	Do not caulk the panels where they meet the receiver of inside corners, 
outside corners, or J-trim. Do not caulk the overlap joints.
	Do not face-nail or staple through the siding. 

	Use aluminum, galvanized steel, or other corrosion-resistant nails when 
installing vinyl siding. Aluminum trim pieces require aluminum or stainless 
steel fasteners.

	Nail heads should be 5/16" minimum in diameter. Shank should be 1/8" in 
diameter.

	Use the manufacturer-specified starter strip to lock in the first 
course; do not substitute other accessories such as a J-channel or utility 
trim (Figure 4) unless specified by the manufacturer. If the manufacturer 
specifies a particular strip for high-wind applications, use it. Make sure 
that the starter strip is designed to positively lock the panel, rather than 
just hooking over a bulge in the strip; field test the interlock before 
proceeding with the installation.

[Begin figure]
Figure 4 is a photo showing how utility trim was substituted for the starter 
strip and the bottom lock was cut off the siding. Siding was able to pull 
loose under wind pressure. 
[End figure]

	Make sure that every course of siding is positively locked into the 
previous course (Figure 5). Push the panel up into the lock from the bottom 
before nailing rather than pulling from the top. Do not attempt to align 
siding courses with adjacent walls by installing some courses loosely.

[Begin figure]
Figure 5 is a photo showing that the siding panel was not properly locked into 
the panel below. 
[End figure]

	Make sure that adjacent panels overlap properly, about half the length 
of the notch at the end of the panel, or approximately 1". Make sure the 
overlap is not cupped or gapped, which is caused by pulling up or pushing down 
on the siding while nailing. Reinstall any panels that have this problem.

	Use utility trim under windows or anywhere the top nail hem needs to be 
cut from siding to fit around an obstacle. Be sure to punch snap-locks into 
the siding to lock into the utility trim. Do not overlap siding panels 
directly beneath a window (Figure 6).

[Begin figure]
Figure 6 is a photo showing that proper detailing around windows and other 
obstacles is important. Use utility trim, punch snap-locks into siding, and 
dont overlap directly beneath a window. 
[End figure]

	At gable end walls, it is recommended that vinyl siding be installed 
over wood sheathing rather than over plastic foam sheathing, as was done at 
the house shown in Figure 7. 

[Begin figure]
Figure 7 is a photo showing that the vinyl siding at this gable was installed 
over plastic foam insulation. Without wood sheathing, the wind pressures on 
the vinyl are increased. Also, if the siding blows away, the foam insulation 
is very vulnerable to blow off. With loss of the foam insulation, wind-driven 
rain can freely enter the attic, saturate the ceiling insulation, and cause 
collapse of the ceiling.
[End figure]

	Install vinyl siding in accordance with manufacturers installation 
instructions and local building code requirements. 

	It is recommended that vinyl siding installers be certified under the 
VSI Certified Installer Program sponsored by the Vinyl Siding Institute. For 
more information, go to 
http://www.vinylsiding.org/aboutsiding/installation/certinstaller. 

Wood Siding

	Use decay-resistant wood such as redwood, cedar, or cypress. See the 
Sustainable Design section regarding certified wood.

	To improve longevity of paint, back-prime wood siding before 
installation.

	Carefully follow manufacturers detailing instructions to prevent 
excessive water intrusion behind the siding.

	For attachment recommendations, see Natural Wood Siding: Selection, 
Installation and Finishing, published by the Western Wood Products Association 
(http://www.wwpa.org).

	This publication recommends an air gap between the moisture barrier and 
the backside of the siding to promote drainage and ventilation. Such a wall 
configuration is referred to as a rain screen wall. See the text box on page 
5.

	Follow the installation details shown in Figure 8. (Note: Although these 
details do not show a rain screen, inclusion of vertical furring strips to 
create a rain screen is recommended.) 

[Begin figure]
Figure 8 is an illustration showing various wood siding installation details.
[End figure]

[Begin text box]
Pressure-equalized rain screen wall system
In areas that experience frequent wind-driven rain and areas susceptible to 
high winds, it is recommended that a rain screen design be considered when 
specifying wood or fiber cement siding. (Typical vinyl siding products 
inherently provide air cavities behind the siding that facilitate drainage. 
Therefore, incorporation of vertical furring strips is normally not applicable 
to this type of wall covering.) A rain screen design is accomplished by 
installing suitable vertical furring strips between the moisture barrier and 
siding material (see Figure 9). The cavity facilitates drainage of water from 
the space between the moisture barrier and backside of the siding and it 
facilitates drying of the siding and moisture barrier.

[Begin figure]
Figure 9 is an illustration a pressure-equalized rain screen system.
[End figure]

Furring strip attachment: For 1" x 2" furring strips, tack strips in place and 
use siding nails that are " longer than would be required if there were no 
strips (thereby maintaining the minimally required siding nail penetration 
into the studs). For thicker furring strips, an engineered attachment is 
recommended.

At the bottom of the wall, the cavity should be open to allow water drainage. 
However, the opening should be screened to avoid insect entry. 

At the wall/soffit juncture, the top of the cavity can open into the attic 
space to provide inlet air ventilation, thereby eliminating soffit vents and 
their susceptibility to wind-driven rain entry. If the rain screen cavity vent 
path is used in lieu of soffit vents, the depth of the cavity needs to be 
engineered to ensure that it provides sufficient air flow to ventilate the 
attic.
[End text box]

Fiber Cement Siding

Installation procedures are similar to those for wood siding, but require 
specialized cutting blades and safety precautions because of the dust produced 
during cutting with power tools. Manufacturers installation recommendations 
should be strictly adhered to, and particular attention paid to the painting 
and finishing recommendations for a high-quality installation.

	Always seal field-cut ends according to the manufacturers instructions. 
Properly gap the intersection between siding edges and other building 
components and fill the gap with sealant.

	Always consult and follow the manufacturers installation requirements 
for the needed wind speed rating or design pressure (refer to the 
manufacturers building code compliance evaluation report). Observe the 
manufacturers fastener specifications, including fastener type and size, 
spacing, and penetration requirements. Do not over drive or under drive.

	At gable end walls, it is recommended that fiber cement siding be 
installed over wood sheathing rather than over plastic foam sheathing.

	Keep blind nails between " and 1" from the top edge of the panel 
(Figure 10). Be sure to drive nails at least 3/8" from butt ends, or use 
manufacturer-specified joiners.

[Begin figure]
Figure 10 is an illustration showing blind nailing. 
[End figure]

	Face nailing (Figure 11) instead of blind nailing is recommended where 
the basic (design) wind speed is 100 miles per hour or greater. If the local 
building code or manufacturer specifies face nailing at a lower wind speed, 
install accordingly.

[Begin figure]
Figure 11 is an illustration showing Face nailing. 
[End figure]

	Do not leave the underside of the first course exposed or extending 
beyond the underlying material (Figure 12). Consider the use of a trim board 
to close off the underside of the first course.

[Begin figure]
Figure 12 is a photo blind nailed siding installed with exposed gap at bottom 
(red circle) is vulnerable to failure.
[End figure]

Sustainable Design

Material selection for sustainable sources and durability

For wood products, select a Forest Stewardship Council (FSC) certified 
product. The FSC seeks to ensure that wood is harvested in a more responsible 
fashion, including protecting forest ecosystems, and avoids the use of 
chemicals and genetic engineering. While redwood, cedar, and cypress are 
decay-resistant and recommended for durability, they are generally cut from 
old growth timber. You can determine if the manufacturer is FSC certified by 
going to http://www.fsc-info.org.

For other siding products, consider long-term life-spans for coastal 
environments, recycled content, and post-consumer use.

The following publications discuss sustainable aspects of vinyl siding:

A Dozen Things You Might Not Know That Make Vinyl Siding Green (available 
online at 
http://www.vinylsiding.org/aboutsiding/greenpaper/080919_VSI_Green_Paper_for_w
eb.pdf).

Siding with the Environment (available online at 
http://www.vinylsiding.org/publications/final_Enviro_single_pg.pdf).

Energy Conservation and Air Barriers: Uncontrolled air leakage through the 
building envelope is often overlooked. The U.S. Department of Energy estimates 
that 40 percent of the cost of heating or cooling the average American home is 
lost to uncontrolled air leakage. In warmer climates, it is a lower percentage 
of loss. An air barrier system can reduce the HVAC system size, resulting in 
reduced energy use and demand.

Uncontrolled air leakage can also contribute to premature deterioration of 
building materials, mold and moisture problems, poor indoor air quality, and 
compromised occupant comfort. When uncontrolled air flows through the building 
envelope, water vapor moves with it. Controlling the movement of moisture by 
air infiltration requires controlling the air pathways and/or the driving 
force. 

To effectively control air leakage through the building envelope, an effective 
air barrier is required. To be effective, it needs to be continuous; 
therefore, air barrier joints need to be sealed and the barrier needs to be 
sealed at penetrations through it. The Air Barrier Association of America 
recommends that materials used as a component of a building envelope air 
barrier be tested to have an air infiltration rate of less than 0.004 
cfm/square foot, assemblies of materials that form the air barrier be tested 
to have an air infiltration rate of less than 0.04 cfm/square foot, and the 
whole building exterior enclosure have an air infiltration rate of less than 
0.4 cfm/square foot.

Air barrier systems installed behind siding:

Housewrap is the most common air barrier material for residential walls. To be 
effective, it is critical that the joints between sheets of housewrap be 
sealed as recommended by the manufacturer, and penetrations (other than 
fasteners) should also be sealed. At transitions between the housewrap and 
door and window frame, use of self-adhering modified bitumen flashing tape is 
recommended. 

An air barrier should be installed over a rigid material, or it will not 
function properly. It also needs to be restrained from pulling off of the wall 
under negative wind pressures. For walls, wood sheathing serves as a suitable 
substrate, and the siding (or furring strips in a rain screen wall system) 
provide sufficient restraint for the air barrier.  

At the base of the wall, the wall air barrier should be sealed to the 
foundation wall. If the house is elevated on piles, the wall barrier should be 
sealed to an air barrier installed at the plane of the floor. 

If the building has a ventilated attic, at the top of the wall, the wall air 
barrier should be sealed to an air barrier that is installed at the plane of 
the ceiling. 

If the building has an unventilated attic or no attic, at the top of the wall, 
the wall air barrier should be sealed to an air barrier that is installed at 
the plane of the roof (the roof air barrier may the roof membrane itself, or a 
separate air barrier element). 

[Begin text box]
Air barrier: A component installed to provide a continuous barrier to the 
movement of air through the building envelope. Housewrap is a common air 
barrier material for residential walls. Although very resistant to airflow, 
housewrap is very vapor permeable and therefore is not suitable for use as a 
vapor retarder.
Vapor retarder: A component installed to resist diffusion of water vapor and 
provide a continuous barrier to movement of air through the building envelope. 
Polyethylene is a common vapor retarder material for residential walls. To 
determine whether or not a vapor retarder is needed, refer to the Moisture 
Control section of the NRCA Roofing and Waterproofing Manual, published by the 
National Roofing Contractors Association (NRCA).
[End text box]

[Begin text box]
ASTM E 1677, Standard Specification for an Air Retarder (AR) Material or 
System for Low-Rise Framed Building Walls: This specification covers the 
minimum performance and acceptance criteria for an air barrier material or 
system for framed walls of low-rise buildings with the service life of the 
building wall in mind. The provisions contained in this specification are 
intended to allow the user to design the wall performance criteria and 
increase air barrier specifications to accommodate a particular climate 
location, function, or design of the intended building.
[End text box]

Siding maintenance:

For all siding products, it is very important to periodically inspect and 
maintain the product especially in a coastal environment. This includes 
recoating on a scheduled maintenance plan that is necessary according to the 
manufacturers instructions and a periodic check of the sealant to ensure its 
durability. Check the sealant for its proper resiliency and that it is still 
in place. Sealant should be replaced before it reaches the end of its service 
life.