Dimensional Stability Test reports from
Certified Kiln Dried the USDA Forest Products Laboratory
show that redwood has less volumetric
Siding Patterns and and tangential shrinkage than any other
domestic softwood. This means that The CRA trademark is on products of
Applications redwood siding will lay flat and straight member mills of the California Redwood
throughout the life of the structure with Association only and is an additional
minimal warping, cupping, checking and assurance of quality.
Redwood is synonymous with quality
nail popping. With tighter joints, redwood
Redwood grades are established by the
architecture. No other siding material
provides better siding performance
Redwood Inspection Service in the
adds value to a home or commercial
than other woods.
Standard Specifications for Grades of
building like redwood. The value of
California Redwood Lumber. Properly
redwood’s beauty is immediately appar- Finish Retention
grademarked lumber will bear the RIS
ent and the value of its long-lasting Redwood has an open cellular structure
mark. The RIS is the exclusive rules-
performance is appreciated for decades. and contains relatively little pitch or
writing agency for redwood lumber.
resins. This enables redwood to absorb
Architects and builders specify redwood
and retain all types of finishes better than Quality redwood siding is available in
with confidence, knowing that exceptional
most other woods. As a result, projects the architectural grades: Clear All Heart,
performance is grown into every board
look better over a longer period of time. Clear, Heart B and B Grade.
and that redwood will add value and
Protective finishes last longer and work
sales appeal to their projects. Clear All Heart is a superior grade for
better. Refinishing is required less often.
fine sidings and architectural uses. It is
Redwood’s Total Performance
Resistance to Decay and Insects all heartwood and the graded face of
Redwood’s performance characteristics
Redwood heartwood has grown-in each piece is free of knots.
are unique among American softwoods.
resistance to decay and insects that is
Its superior stability is especially suited to Clear is similar in quality to Clear All
present throughout the lumber, not just
the demands of siding applications. Its Heart, except that it includes sapwood
on the surface. Wood exposed through
finish retention, weatherability, flame in varying amounts. Some boards may
sawing, boring or nailing is as decay-
resistance and insulation properties have one or two small, tight knots on
resistant as the surface.
make it ideal for virtually any project and the graded face.
even the most extreme climate.
Heart B is an economical all-heartwood
grade containing a limited number of
tight knots and characteristics not
permitted in Clear or Clear All Heart. It
is graded on one face and one edge.
B Grade is an economical grade con-
taining a limited number of tight knots
with sapwood accenting the heartwood.
Specifying Redwood Siding
To ensure delivery of the proper siding
product, the specifications should
Storage & Handling include: use, grade, grain, seasoning, General Application Information
pattern description and number, and Careful attention to construction detailing
surface texture. is necessary to prevent moisture pene-
tration into the siding and the wall cavity.
Redwood lumber has either flat or vertical For Example
Flashing over window and door headers
grain. Siding Is considered vertical grain Redwood lumber for 1exterior siding shall
and at other horizontal siding breaks
when the annual growth rings form an be CRA-RIS grademarked redwood,
should be sufficiently sized, well placed,
angle of 45 degrees or more with the Heart B grade, 3mixed grain. 4Certified
tightly anchored and sealed with caulk-
surface of the siding. If the angle is less Kiln Dried, 51x8 channel V shiplap,
ing. Thorough caulking of all joints with a
than 45 degrees, the siding is known pattern 785R, 7saw-textured face to
non-hardening compound is important,
as flat grain. Vertical grain siding pos- be exposed.
particularly at the butt joints of short
sesses enhanced dimensional stability Use Pattern
length siding laid vertically. High per-
and will hold paints and finishes better Grade Pattern Number
formance caulks such as polyurethane,
than flat grain. Grain Texture
polysulfide or acrylic latex are recom-
Vertical Grain Flat Grain mended for best results.
In addition, the Installation section of the The lowest edge of siding should be at
specification should specify: non-corro- least 6 inches off the ground to prevent
sive fastener materials, type and size; moisture problems. It is particularly
bearing and fastener spacing require- important that end grain at the bottom
ments; water repellent application as ap- of vertical siding be coated with water
Annual rings Bark side Pith side
propriate, and field priming of cut edges. repellent. The use of a drip cap at the
Seasoning lower edge of the siding is recommended.
Storage and Handling
Clear All Heart, Clear, Heart B and B
Redwood siding and trim are quality A water repellent building paper, with a
Grade sidings are available Certified Kiln
finish products and should be handled permeability rating of at least 5 perms,
Dried for applications requiring minimal
with care. At the job site, redwood siding should be applied over sheathing. This will
shrinkage and top performance.
should be kept completely under cover help reduce water and wind penetration.
Redwood kiln dried to accepted stan-
and off the ground. Water-proof cover-
dards will include the words “Certified Note: There have been reports of prob-
ings should allow air to circulate between
Kiln Dried” or the initials “CKD” in the lems arising from the combination of
the covering and the siding. Keeping the
grademark on each piece or package of wood siding and rigid plastic foam
siding clean and dry will help to eliminate
siding or be so specified on the invoice. sheathings. CRA advises caution.
the possibility of finish problems. For
Request Redwood Technical Data Sheet
Patterns protection, redwood siding is now avail-
Using Redwood Siding Over Rigid
Standard redwood siding patterns able wrapped in moisture-proof paper at
include: bevel, rabbeted bevel, tongue the sawmill and it should not be un-
and groove, shiplap, channel shiplap and wrapped until installation begins.
V shiplap. Board and batten siding is
laid up using standard size boards.
It is recommended that a water repellent
Pattern Numbers containing mildewcide be applied to all
Each siding pattern has a pattern num- surfaces of redwood siding before
ber. To ensure delivery of the proper construction begins. This will inhibit the
product, the pattern number should be movement of moisture as well as mildew
included on specifications and invoices. growth, two conditions which can
Pattern details are given in CRA’s severely damage a finish coating. When
Architectural Guide and Redwood a clear, bleached or semitransparent
Pattern Book. finish is to be applied later, a preliminary
coat of water repellent will protect
Textures against weathering and construction
Surfaced sidings have a smooth, planed staining prior to final finishing. For best
face, emphasizing the wood’s grain performance, special care should be
and color. given to end grain; cut ends should be
Saw-textured sidings have resawn faces coated before installation. Redwood
providing a rough textured appearance siding should always be back-primed.
that holds finishes extremely well. Factory priming or pre-finishing is
Preventing Moisture Problems
Measuring and Cutting causes of structural and finish failures. It
All butt joints must occur over a stud or moves as invisible moisture vapor from
solid blocking. Be sure that siding fits the warm interior of the house toward the
snugly against corner strips and trim. cold exterior. Vapor travels through
Mitered corners, sometimes used with plaster, insulation and wood and may
thicker patterns, should be cut in a miter condense into water as it approaches the
box. Plain bevel siding requires a com- colder exterior surfaces of the sidewall.
pound miter. Predrill nail holes for all This can sometimes result in structural
ends, especially mitered ends. damage as well as siding cupping and
Surfaces nail popping. Water entering the siding
Using bevel cuts at a 45° angle (see
can also cause finishes to blister, peel
illustration) can minimize the appearance Insulation and discolor.
of gaps if end shrinkage does occur.
Vapor barriers are necessary to prevent
Bevel Cut Siding migration of moisture vapor. They must
be applied to the warm side of the stud
Paper wall, directly under the finish material.
There are several types; the most fre-
quently used are either plastic or alu-
Stud minum sheet material with a rating of
one perm or less. Those sheets should
overlap at least 2 inches at their edges.
Ordinary building felt is not a vapor barrier.
Do not reduce CRA lap recommenda-
Proper interior and exterior wall construction When residing an existing house without
tions as this can result in damage from
prevents moisture problems. Building paper a vapor barrier, an effective solution can
wind-driven water. Carefully observe
should have a permeability rating of 5 perms,
be to paint the inner side of the exterior
expansion clearance requirements for the vapor barrier, a maximum of 1 perm.
walls with a vapor barrier paint.
the siding pattern selected.
Attic areas should be adequately vented
Moisture is the largest cause of siding to prevent vapor from condensing on
Nailing recommendations refer to nailing
and finish problems. Most problems can cold surfaces or penetrating through the
siding to every stud or (for vertical cours-
be avoided if precautions are taken ceiling. Critical sources of humidity, such
ing) each 2x4 blocking line, at not more
during construction. Understanding the as kitchens, baths and laundries, are
than 24 inches on center.
dynamics of wood’s reaction with mois- best ventilated by fans that exhaust out-
Selection of proper nails is important. ture will be the builder’s best protection doors. Crawl spaces should be well
Siding nails with annular-ringed shanks against callbacks. ventilated all around the house; the vent
provide the best holding power. All nails area should equal about 1/50th of total
New energy-efficient construction tech-
must be either stainless steel, aluminum floor space. Keep vents free of obstruc-
niques increase the amount of humidity
or top-quality, domestic, hot-dipped gal- tions. Movement of vapor into stud
within homes and commercial buildings.
vanized. Electroplated galvanized nails spaces from crawl spaces may take
Efficient insulation, storm windows,
are not recommended. Poor quality place as water evaporates from the
weatherstripping, as well as heating
nails will react with redwood’s natural ground under the house, and can be
equipment and appliances that retain
decay-resisting extractives, and will cause retarded by laying polyethylene film
warmth add to the build-up of interior
unsightly stains. over the ground. Basements may be a
source of considerable dampness and
Nails can be countersunk (not more than
This invisible moisture is one of the least require effective ventilation.
1/16 inch) or driven flush with wood sur-
understood and most troublesome
faces. Unfilled nail holes may not be par-
ticularly noticeable where natural finishes
are used as long as proper quality nails
have been used. At mitered corners, or
near the edge or end of a piece, pre-drill
the nail hole to avoid splitting the wood.
Nails must be long enough to penetrate
into studs (or stud and wood sheathing
combined) at least 1-1/2 inches. Do not
fasten siding to only composition or
pressed fiber sheathing as those materi-
als provide no nail-holding power.
Do not use staples for redwood siding.
Staples do not provide adequate
holding power and most are not
Plain Bevel Rabbeted Bevel
Bevel & Rabbeted Horizontal Siding (Side View) Horizontal Siding (Side View)
Bevel Patterns Overlap
Redwood bevel siding, also known as lap 1⁄8''
or clapboard siding, has the timeless clearance
appeal of a strong traditional style and Sheathing
provides the deepest horizontal shadow Beware of
line of all siding patterns. driving nail Sheathing
Bevel siding is produced in both plain too heavy
a final blow.
and rabbeted patterns. Each is available penetrate
in two different butt thicknesses for solid wood
split due to
variation in depth of shadow line and non-support
Plain bevel patterns produce a bolder
shadow line than rabbeted bevel pat-
Nail clears tip
terns of the same thickness. Rabbeted of undercourse
bevel, with its 1/2-inch rabbet milled
to fit over the thin edge of the preced- penetrate
ing course, allows the siding to lay solid wood 1-1⁄2''
flat against the studs or sheathing.
Face nail with one nail only per bearing. Face nail with one nail only per bearing.
Rabbeted patterns provide a weather-
Drive nail so shank just clears the tip of the Position material to allow expansion
tight lap and lay up with greater coverage preceding undercourse. The space between clearance of 1/8 inch. Drive nail about one
than plain patterns. the nail shank and the tip of the preceding inch above lower edge of course.
course should not exceed 1/8 inch.
Bevel and rabbeted bevel sidings are
edge of the pattern. Nail bevel siding at Surface Feet of Bevel Siding to Cover
available in all architectural grades.
every stud, which should not exceed 24 1 Square (100 sq. ft.)
Plain bevel siding has a smooth surface
inches on center. Nominal
on one face and a saw-textured surface
Width Plain Rabbeted
For plain bevel siding, a lap of one inch is
on the other face. Either face may be
required to ensure weather-tightness.
exposed. Rabbeted bevel siding is 4 inch 160 128
available with either a smooth or saw- Note: With CKD rabbeted bevel patterns, 5 inch 143
textured face. Saw-textured faces are an expansion clearance of 1/8 inch is
more even in color and appearance and 6 inch 134 117
required in the rabbet.
they hold finishes better.
8 inch 124 117
Installation Exterior siding shall be CRA-RIS grade- 10 inch 122 113
With plain bevel patterns, use a furring marked redwood Clear grade, mixed
strip to support the lower edge of the grain, Certified Kiln Dried, 3/4x8
starting course. With rabbeted patterns, Rabbeted Bevel, pattern 372, with a Size Availability
the bottom course should be supported saw-textured face. Bevel & Rabbeted Bevel
by a nailing strip sawn from the thin
4'' 5'' 6'' 8'' 10''
1/2 inch • • • •
3/4 inch • • •
Rabbeted Bevel S1S-2E smooth
4'' 5'' 6'' 8'' 10''
1/2 inch • • •
3/4 inch • • •
Rabbeted Bevel S1S-2E saw-textured
4'' 5'' 6'' 8'' 10''
3/4 inch • • •
Tongue & Groove Tongue and Groove Tongue and Groove
Horizontal Siding (Side View) Horizontal Siding (Side View)
Redwood tongue and groove siding is
versatile and weathertight. Its variety Stud
of refined patterns has established a
permanent place in residential and
commercial architecture. Tongue and
groove siding can be laid up vertically, Stud
horizontally or diagonally and is ideal for
matched interior-exterior combinations.
Tongue and groove patterns are pro- Blind nailed
duced in square edge, eased (slightly
rounded) edge and various widths of
V groove edges. The latter create a Nail must
shadow line emphasizing the direction penetrate
Nail must solid wood
of the courses. Various design effects penetrate 1-1/2''
are achievable by alternating patterns
and board widths.
Tongue and groove sidings are available
in all architectural grades.
Standard tongue and groove patterns For 4-and 6-inch widths of tongue and groove Tongue and groove siding 8 inches or wider
come from the mill with a smooth surface siding over solid wood sheathing, blind nailing should be face-nailed, using two 8-penny
is possible using one 8-penny finishing nail nails per bearing.
on both faces. Reversible patterns are
saw-textured on one face and surfaced
smooth on the other. All tongue and
groove siding patterns can be special
installed between the studs at not more Surface Feet of Tongue & Groove
ordered saw-textured. Saw-textured
than 24 inches on center. As an alterna- Siding to Cover 1 Square (100 sq. ft.)
faces are more even in color and
tive, vertical siding may be nailed to 1x3
appearance and they hold finishes better. Nominal Width Coverage Factor
furring strips and solid wood sheathing at
Tongue and groove redwood is also 4 inch 128
24 inches on center.
available in thinner patterns commonly
6 inch 118
used for interior paneling. Sample Specification
8 inch 117
Exterior siding shall be CRA-RIS grade-
marked redwood Clear grade, vertical 10 inch 113
Tongue and groove siding is properly
grain, Certified Kiln Dried, 1x8 Tongue
applied with the groove edge down; this
and Groove, pattern 712R, saw-textured
assures a weathertight wall.
face to be exposed.
Horizontally-applied tongue and groove
siding should be nailed at every stud,
Tongue & Groove
not exceeding 24 inches on center.
Eased Edge S2S-CM
Siding applied vertically should be nailed
to 2x4 horizontal blocking that is 4'' 6'' 8'' 10''
1 inch • • •
4'' 6'' 8'' 10''
1 inch • • • •
V2S-S1S Saw Textured 1S
4'' 6'' 8'' 10''
1 inch • • • •
Shiplap & Channel Shiplap V Shiplap
Vertical Siding (Overhead View) Horizontal Siding (Side View)
Channel Shiplap Stud Stud
Redwood shiplap patterns are widely Sheathing
used for siding and paneling because
of the varied visual effects that can be
achieved. The boards are self-aligning, 1⁄8''
which makes installation easy. Shiplap expansion
patterns form strong, deliberate
Shiplap siding in V channel, Cove and
Boston shiplap patterns can be applied
either horizontally or vertically. Square- Nail must penetrate
edged channel shiplap patterns should penetrate solid wood
solid wood 1-1/2'' 1-1/2''
only be applied vertically.
Shiplap sidings are available in all archi-
Standard shiplap siding has a smooth
finish on both sides, except those pat-
For 6-inch V Shiplap patterns, use one nail
Use one nail an inch from the lap for 6-inch
terns designated with the suffix R, which
per bearing with the nailing point one inch
Channel Shiplap. Face nail with two nails per
are reversible. Those have a saw-textured
from the overlapping edge. For patterns 8
bearing for 8-inch and wider patterns. Space
channel pattern on one side and a smooth
inches and wider, face nail with two siding
nails 1-1/2 inches from edge of overlap and
finish V pattern on the other. Shiplap nails per bearing. Position nails one quarter
two inches from edge of underlap for 8-inch
siding patterns can be special ordered the width of the material in from each edge.
boards. Nail wider patterns proportionately.
with a saw-textured face. Saw-textured
faces are more even in color and
appearance and they hold finishes better.
Shiplap sidings applied horizontally start
with the bottom course and are nailed at
each stud, which should not exceed 24
inches on center. Channel shiplap pat-
tern sidings require a 1/8-inch expansion
clearance in each joint.
Shiplap siding applied in vertical courses
should be nailed to 2x4 horizontal
blocking that is installed between the
studs at not more than 24 inches on
center. As an alternative, vertical siding
may be nailed to horizontal 1x3 furring
strips and solid wood sheathing at 24
inches on center.
Exterior siding shall be CRA-RIS grade-
marked redwood Clear All Heart grade,
mixed grain, Certified Kiln Dried, 1x8
V Shiplap, pattern 794, smooth face.
Surface Feet of Shiplap Siding to
Cover 1 Square (100 sq.ft.)
Nominal Width Coverage Factor
6 inch 124
8 inch 121
10 inch 116
6'' 8'' 10''
1 inch • • •
Board & Batten Board and Batten
Vertical Siding (Overhead View)
The popular board and batten siding
styles are not, strictly speaking, siding
patterns but are created using standard
size lumber. Any number of interesting
treatments can be created, including
various width battens over wide board,
even spaced board and batten, and
reverse board and batten.
Any clear or tight-knot grade of redwood
lumber may be used, either with smooth
or saw-textured face. Clear All Heart,
Clear, Heart B and B Grade lumber is
available Certified Kiln Dried. penetrate
Board and batten patterns should only be
applied vertically. Boards should be
nailed to horizontal blocking placed not
more than 24 inches on center. As an
Space underboards at least 1/2 inch apart Board and batten siding can have a variety
alternative, 1x3 or greater horizontal and nail with one nail per bearing through the of appearances depending on the width of
furring strips may be applied over solid center of the material. For boards wider than boards and battens. A reverse board and
wood sheathing. 8'', use two face nails evenly spaced. Wider batten pattern is achieved by placing wide
spacing may be used with wider battens. boards over the narrow battens.
Sample Specification Nail batten strips through the center so the
Exterior siding shall be CRA-RIS grade- nail shank passes through the space. Make
marked redwood, B grade, mixed grain, certain the batten laps the underboard at
Certified Kiln Dried, 1x10 saw-textured least 1/2 inch on both sides.
and 1x2 saw-textured battens.
Board and Batten Siding
Nominal Surfaced Nominal Surfaced
1 11/16 3 2-1/2
1-1/4 1 4 3-1/2
2 1-1/2 6 5-1/2
Apply finishes to clean, dry surfaces only.
The optimum temperature range is
between 50 and 70 degrees Fahrenheit.
Saw-textured redwood holds finishes up
to twice as long as smooth-surfaced wood.
Siding Finishes for Redwood
Description Application Maintenance
Clear Water Repellents with Apply with brush or roller. Two coats Reapplication required after old finish
Mildewcide recommended for new wood. Coat sawn has lost its effectiveness. Reapplication
Stabilize color at a buckskin tan and let ends, backs and edges before nailing may be required every 18-24 months.
the grain and texture show through. siding in place.
Minimize the effect of weathering and
redwood’s natural darkening.
Bleaching or Weathering Stains Apply with brush or roller. Use one or Bleaching stains provide low mainte-
Provide a gray, natural weathered two coats according to directions. nance. Periodic reapplication of clear
appearance. Bleaches accelerate the Bleaching action may be aided by water repellent with mildewcide is
natural color changes of wood. periodically spraying surfaces with water. recommended.
Semitransparent Stains Apply with brush for best results, roller Color may wear away after weathering.
Variety of colors are available in these next best applicator. Two coats usually Refinishing may be necessary every
finishes that let the wood grain show required for new wood; follow manu- 2-4 years. Remove loose dirt and old
through. Oil-based stains are recom- facturer’s directions. finish with bristle brush before refinishing.
mended for best performance.
Solid Body Stains For best results apply with brush. Avoid Color may wear away with age.
Available in a variety of opaque colors. drips and lapmarks. Two coats usually Refinishing may be necessary every
These finishes obscure the grain and required for new wood; follow manu- 3-5 years. Remove loose dirt and old
have an appearance similar to paint. facturer’s directions. finish with bristle brush before refinishing.
Latex stains should be applied over a
compatible stain-blocking primer.
Paints Apply with brush for best results. Roller Repaint one coat after most of old coat
Durable attractive finishes for traditional is next best applicator. One prime coat and has weathered. Avoid creating an ex-
exteriors. Paints obscure the grain and two finish coats are recommended. Back- cessively thick paint film. Sand or scrub
the texture of the wood. priming required. Use oil- or alkyd-resin with bristle brush to remove old finish
base primer and acrylic latex top coat. and dirt. Countersink nails if sanding.
Caution: Varnishes, lacquers and clear
film-forming finishes deteriorate rapidly
in moisture and sunlight, so they should
not be used.
405 Enfrente Drive, Suite 200 Redwood—our renewable resource
Novato, California 94949 Additional Literature
Telephone 415 382-0662 Architectural Guide
Toll Free 888 CAL-REDWOOD Redwood Pattern Book
Fax 415 382-8531 Grades and Uses
www.calredwood.org Exterior Finishes 10/97