TONGUE AND GROOVE DECKING

Transco Mills Decking provides a solid permanent roof deck with good insulating properties and a
handsome, ready-to-finish interior ceiling. Roof decking is especially suited for use with post and
beam timbers or glue laminated beams where application is quick and easy.It Serves as an ex-
cellent base for any roofing material. It is available in species, grade and sizes suitable for both
residential and commercial construction. Transco Mills Select decking is ideally suited for exposed
ceiling areas in homes, schools, churches, motels and restaurants, wherever attractive surface ap-
pearance is important. Transco Mills Commercial decking is suitable for use in warehouses, service
stations and other structures where appearance is not a prime factor. Transco Mills Roof Decking may
also be used in solid wall construction and is especially popular for summer cabins.


GRADES:
SELECT: Lumber of this grade is recommended for high class construction where strength and
fine appearance is required. Knots and other characteristics which add to the decorative
character of the piece are permitted. Transco Mills Select Decking is graded under
para. 127b of National Lumber Grades Authority (NLGA) rules (equivalent to WCLB 16 Rules) and
conforms to the requirements of the Canadian National Building Code for heavy timber decking as
well as the AlTC “Standards for Tongue and Groove Heavy Timber Roof Decking”.
The following characteristics and limiting provisions may apply to the exposed face (except
where noted) although all of the permissible characteristics of the grade are never present in
maximum size or number in any one piece. Any piece with an unusual combination of
characteristics which seriously affects normal serviceability is excluded from the grade.
Bark pockets: Medium
Checks: Medium
Crook: Light, occasional piece
Holes: Equivalent to chipped knots
Pitch: Light or equivalent, very small streak
Pitch pockets: Very small, dry
Rate of growth: Medium grain, Douglas Fir only
Skips: Very light, maximum 10% of face in occasional pieces
Slope of grain: 1 in 10
Splits: Short, occasional piece
Stained wood: Medium
Torn or raised grain: Medium
Tongue: 1/16” scant, occasional piece
Twist: Very light, occasional piece
Knots: Sound and tight on exposed face, well spaced.
2x6 3&4x6

WIDTH KNOT SIZE KNOT SIZE
6" 2-3/8" 2-1/2"
Both Faces Both Faces
Spike and narrow face knots equivalent. In occasional pieces, firm and tight knots not exceeding
1 1/2” in diameter are permitted if not through the piece and limited to 2 per 12 lineal feet or
equivalent smaller.
Knots may contain chipped or unsound spots approximately 3/4" in diameter not through, 2 per 12
lineal feet or equivalent smaller.
Back and unexposed edges - hit and miss skips. Wane approximately 1/3 face and other
characteristics which do not affect the end use. In cedar peck is permitted on back and unexposed
edges in narrow streaks well scattered which do not affect the strength more than other
characteristics allowed.

COMMERCIAL: Decking of this grade is recommended and customarily used for the same pur-
poses as the higher (Select) grade when appearance and strength requirements are not as
critical.

Transco Mills Commercial Decking is graded under para 127c of National Lumber Grades
Authority (NLGA) rules (equivalent to WCLIB 16 Rules) and conforms to the requirements of the
Canadian National Building Code for heavy timber decking as well as to AlTC “Standards for Tongue
and Groove Heavy Timber Roof Decking”. 
The characteristics and limiting provisions are listed below. Any piece with an unusual combina-
tion of characteristics which seriously affects normal serviceability is excluded from the grade.

Checks
Crook: Medium, occasional piece
Holes: 1
Pitch: Streaks
Pockets: Bark or pitch
Rate of Growth: Medium grain in Douglas Fir
Shake: Not serious
Skips: Hit and miss
Slope of grain: 1 in 8
Splits: 1/6 length
Torn grain
Tongue: 1/16” scant
Twist: Very light, occasional piece

Unsound wood: In small spots or streaks up to 1" wide on any face. In cedar spots or streaks of
peck 1/3 of any face
Wane: 1/16 face width
White speck: 1/3 width or equivalent
Knots: Well Spaced
2x6 3&4x6

WIDTH KNOT SIZE KNOT SIZE
6" 2-7/8" 3"
Both Faces Both Faces
Spike or narrow face knots: Equivalent

Chipped and/or broken out knots approximately 1 1/2” in diameter not through
Back and unexposed edges: Wane approximately 1/3 face and other characteristics not affecting
intended end use.

PATTERNS

All patterns illustrated are as specified in NLGA Rules.

 Nominal Size 2"x6"
 Finished Size 1 7/16" x 5" (plus 3/8" tongue)

SINGLE TONGUE AND GROOVE

Nominal Size 3" x 6"
Finished Size 2 1/2" x 5 1/4" (plus 3/8" tongue)

DOUBLE TONGUE AND GROOVE DRILLED 30" O/C 



Nominal Size 4"x6"
Finished Size 3 1/2" x 5 1/4" (Plus 3/8" tongue)

DOUBLE TONGUE AND GROOVE DRILLED 30" O/C 



A rougher head face can be put on all patterns and grades. This makes a rough face which gives a
rustic appearance.

LENGTHS
Transco Mills Select Roof Decking is normally shipped in random lengths of 6' to 14' or longer
(odd and even).
Length specifications shall be as follows: For orders 5,000 FBM or over:
2" Select Decking:
Approximately 85% 10' and longer
Approximately 25% 14' and longer
3" and 4" Select Decking:
Approximately 40% 14' and longer
Approximately 85% 10' and longer
Not over 5% 6' - 7'
Transco Mills Commercial Roof Decking is normally shipped in random lengths of 6' to 14' or
longer (odd and even).
Specified lengths may be supplied by negotiation.

INSULATION FACTOR
Transco Mills Roof Decking has excellent insulating properties. Decking itself, especially if 3"
or 4" thick, may be sufficient insulation in many areas. Where there is a combination of warmth
and high humidity inside and low temperature outside a building, the moisture vapour inside tends
to move outward through walls and ceilings. Under these conditions a vapour barrier should be
placed on the deck followed by appropriate insulation. (See U values, Table 4). Accumulation of con-
densation is minimized because of a gradual temperature gradient.
Table 2. Conductance and Resistance of Western Red Cedar Decking


Table 3: Conductance and Resistance of Douglas Fir Decking


Table 4: U Values for Typical Roof Assemblies


HANDLING
Transco Mills Roof Decking is air dried to an average 19% moisture content before being
carefully machined. It is then inventoried in our large covered warehouse facilities. Roof Decking
requires dry storage and careful handling en route to and at the job site.

APPLICATION
Transco Mills Roof Decking in 3” and 4” thickness is supplied pre-drilled 30”on centre for conceal-
ed lateral nailing. These starter holes are 1/4" in diameter and are drilled in the centre of the piece
from the tongue side. They are designed to speed lay-up time, guide proper nailing procedures and
prevent splitting of the piece.Application principles for 2” Tongue and Groove
Decking are the same as for 3” and 4” decking except that 2” decking is not pre-drilled, the lateral
nailing of one piece to another is replaced by toenailing approximately every 30” through the backs
of the pieces with 2 1/2” common nails. Each piece should also be fastened directly to the supporting
beams or purlins with 3” or 31/2” nails.
On sloping roofs install decking with tongues toward the peak of the roof; on flat roofs install
with tongues away from the applicator. For nailing to supports, bright common nails may be used but hot
dipped galvanized common nails have better holding power and reduce the hazard of rust streaks.
If there are three or more supports for the decking a “Controlled Random” laying pattern may be us-
ed, This is an economical pattern because it makes use of the random length planks, but the
following rules must be observed.
1.Stagger end joints in adjacent planks as widely as possible and not less than two feet.
2.Separate joints in the same general line by at least two intervening courses.
3.Minimize joints in the middle third of all spans.
4.Make each plank bear on at least one support.
5.Minimize joints in the end span.
For better alignment, appearance and strength where 3” and 4” material is used, metal splines are required.
Fasten decking at each support with common nails twice as long as nominal plank thicknesses
using one toe-nail and one face nail. Side nail 3” and 4” decking through the pre-drilled holes with
8” spiral decking spikes. (At end joints not over a support a side nail should be within 10” of each plank end.)
Transco Mills inventories all the spikes and splines required for proper application.


MAXIMUM SPANS FOR WESTERN RED CEDAR DECKING
Table 5. Simple Span — Deflection / Span Ratio 1/240


MAXIMUM SPANS FOR DOUGLAS FIR DECKING
Table 6. Simple Span — Deflection / Span Ratio 1/240

MAXIMUM SPANS FOR SPF DECKING
Table 7. Simple Span — Deflection / Span Ratio 1/240



CALCULATING QUANTITIES
To calculate the quantities in foot board measure (FBM) multiply the square footage to be covered
by the approximate factors as follows. Please note that these factors make no allowance for waste.
For 2"x 6" Decking multiply by 2.40
For 3"x 6" Decking multiply by 3.43
For 4"x 6" Decking multiply by 4.57
STANDARDS AND APPROVALS
Transco Mills Roof Decking is graded according to rules published by the National Lumber
Grading Authority (NLGA) and West Coast Lumber Inspection Bureau (WCLIB)
These grading rules are approved by the Canadian Lumber Standards Administrative Board (CLS),
the Council of Forest Industries of British Columbia (COFI) and the American lnsitute of Timber
Construction (AITC).