Engineered Wood Siding & Trim

Engineered Wood Siding and Trim (EWST) are categories of composite panels that have been designed and manufactured to perform in interior and exterior exposure applications with the appearance of traditional wood. These advanced composites can be engineered with enhanced resistance to moisture, dimensional stability and protection against fungal decay and termites.

The engineered properties translate into long-lasting durability allowing for decades of service life while maintaining their attractive appearance. Today’s engineered wood siding and trim products are highly versatile and come in many forms including sophisticated woodgrains and embossed surfaces.

Because engineered wood siding and trim are a types of composite panels made from residual wood fiber, such as chips and shavings, they are carefully value engineered for each application. This results in product solutions which are substantially less expensive than alternatives.

Please visit the Product Locator to find more detailed information and search CPA's manufacturers.

Common Uses

  • Siding
  • Interior Trim
  • Exterior Trim


Today's siding and trim products are offered in a wide range of textures, widths and profiles that can create endless styles and themes.

Product Standards and Certification

The American National Standard for Hardboard Siding (ANSI A135.6), now referred to as the Engineered Wood Siding Standard, covers requirements and methods of testing for exterior durability, dimensions, straightness, squareness, physical properties and surface characteristics. It also includes trade terms and methods of identifying engineered wood siding. Third-party certification to the ANSI Standards is required for many applications of siding panels. Many building code jurisdictions require the physical properties of engineered wood siding to be third-party certified. CPA’s accredited certification program is recognized and approved by building code officials to evaluate siding products for code compliance.

The ANSI Engineered Wood Trim Standard was completed in 2012.  The new standard covers requirements and methods of testing for exterior durability and interior applications including physical and mechanical properties.  This consensus-based standard is sponsored by CPA.

Recommended Reading

Available from the association bookstore:

ANSI Engineered Wood Siding Standard

ANSI Engineered Wood Trim Standard

Available for download:

Buyers Guide

Maintenance Tips for Engineered Wood Siding Technical Bulletin [PDF]




The page you are requesting is on CPA’s main site,, which will open in a new window. Most of the site content is shared with

Return Continue