• Uses
  • Grades
  • Coverage
  • Specs

Lap Siding

Lap sidings are normally supplied in a variety of patterns either green (unseasoned) or dry in clear or knotty grades and with a smooth or saw textured face.

LA00175118Channel Siding

Channel siding is a popular type of lap siding and is used whenever a rustic appearance is desired. A versatile siding, it can be installed vertically, horizontally or diagonally. In channel siding the profile of each board partially overlaps that of the board next to it creating a channel that gives shadow line effects, provides excellent weather protection and allows for dimensional movement.


Channel siding is normally supplied in unseasoned knotty grades. The face side is saw textured. Commonly available sizes are 1″x6″, 1″x8″, and 1″x10″. Clear grades are manufactured to order.

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Clear Grades

Clear Heart
The highest grade. Includes only pieces with heartwood on the exposed face. Many pieces completely clear, others have minor imperfections that do not detract from their fine appearance.

Grading Rule Paragraph
NLGA 200a
WCLIB 102-b
WWPA 20.11

A Clear
Permits somewhat more imperfections than Clear Heart but the grade is still restricted to pieces with excellent appearance.

Common specifications are A and Better and A and Better with a percentage of B clear allowed (NLGA 200c/WCLIB 102-d/WWPA 20.13).

Grading Rule Paragraph
NLGA 200b
WCLIB 102-c
WWPA 20.12

Knotty Grades

Select Knotty
Available kiln dried or unseasoned. Knots are sound and tight.

*Common specification is select Knotty with a percentage of quality knotty allowed.

Grading Rule Paragraph
NLGA 204a
WCLIB 111-e

Proprietary Grades
Designed to meet appearance requirements for cedar sidings and trim. Ask your WRCLA distributor for details.

Manufacturers may market their own proprietary grades.

Grading Rule Paragraph

Standard and Better
Suitable for exterior construction. Occasional pieces may require trimming to yield suitable quality for the intended end use.

Grading Rule Paragraph
NLGA 114a, b, c
WCLIB 118-a, b, c


NLGA – National Lumber Grades Authority
WCLIB – West Coast Lumber Inspection Bureau

Lap Siding Coverage Table for Green (Unseasoned) Siding

Nominal Width (inches)Dressed Width (inches)Exposed Face Width (inches)Linear Feet FactorBoard Feet Factor


The following information is required when specifying lap siding products:

Specification Information RequiredSample Specification
Western Red Cedar
WRCLA Western Red Cedar
Product Pattern and Intended Use:
Siding is used as an exterior cladding to provide both weather protection and architectural style. The designer may choose from a variety of lap siding patterns specified by name or pattern number.
Lap Siding Pattern WP11
Specify the nominal size of the product.
1 x 6″
The grade of the product governs its overall quality. Refer to WRCLA specification literature or grading agency rule books for available grades.
Select Knotty
Grading Agency Paragraph:
To ensure that the product meets a written standard, an agency grade paragraph should be referenced.
NLGA para. 204a
Moisture Content:
Specify whether the product is to be green (unseasoned) or kiln-dried.
Surface to be exposed:
Specify the application orientation to assist the supplier in shipping the right product for the job.
Sawn face
Express in linearĀ feet the quantity required.
2,000 linearĀ feet