Interior Millwork

Summary

Interior millwork is the milled and finished woodwork applied to walls, ceilings, and openings, including base, casing, crown, wainscot, and paneling. Choose paint-grade or stain-grade material, the quality grade, and the finish early, since species, jointing, and moisture content decide how the trim looks and moves.

Cols

Image

Stain grade: clear or stained finish; needs matched color and grain
Paint grade (P-grade): opaque finish; may be finger-jointed or edge-glued
Finger-jointed: short pieces joined end to end with interlocking joints
Profile: the cross-section shape of a moulding
NAAWS grades: Economy, Custom, and Premium aesthetic grades for architectural woodwork

Standards

ANSI/AWI 0641 and the North American Architectural Woodwork Standards (NAAWS): grades and quality of architectural woodwork
ANSI A208.2: MDF, including formaldehyde emissions; specify the current edition
Woodwork Institute and AWI quality certification programs for millwork shops

Materials

Solid wood (hardwood or softwood): stain-grade and species-matched trim
Finger-jointed wood: paint-grade base and casing; acclimate to the room before installing, commonly 72 hours
MDF: paint-grade trim with no finger joints, so paint finishes more evenly
Hardwood plywood and veneer: paneling and wainscot

Detailing

Pick one material and grade per room so joints and seams read the same
Specify the finish system and whether it is shop or field applied
Acclimate trim at the site and keep it away from wetting before installation
Align trim joints with studs or blocking and fasten to solid backing
Give long runs, miters, and scarfed joints a consistent layout

Uses

Specific uses

Base, casing, and crown in residential and commercial rooms
Window and door trim
Wainscot and wall paneling
Stair parts and handrails
Reveals and shadow lines at ceiling and wall junctions

Pros and cons

Pros

Hides gaps at floor, wall, and opening edges
Wide range of profiles and species

Cons

Solid wood moves with humidity
Finger joints can telegraph through paint
Stain grade needs color and grain matching

Manufacturing and cost

Construction

Lumber or panels are milled to profile, sanded, and often primed or finished
Pieces are cut and mitered on site, fastened to blocking, and filled and sealed

Main manufacturers and suppliers

Trade associations: Architectural Woodwork Institute, Woodwork Institute, and Composite Panel Association.

Sources

Composite Panel Association: MDF mouldings technical bulletin, https://www.compositepanel.org/wp-content/uploads/24-CPA-0087_Print_Technical-Bulletin_MDF-Mouldings_F.pdf
Composite Panel Association: medium density fiberboard, https://www.compositepanel.org/products/medium-density-fiberboard/
Empire: 2016 profile guide (P-grade and finger-joint acclimation), https://issuu.com/doordepot/docs/empire_2016_e1_profile_guide_5-18-1
Woodworking Network: AWI releases new architectural wood casework standard, https://www.woodworkingnetwork.com/architectural-products/awi-releases-new-architectural-wood-casework-standard