Installation — Drafting Millwork

Install is where the drawing meets the building. The published standard expects a wall to be out by up to 1/4" over twelve feet and a floor by up to 1/2". Add a pipe where the back panel goes, and the installer finds every assumption your drawing made, one at a time, with a level in one hand.

This chapter covers what a set must say so the install goes to plan: the tolerances the building owes you, how to absorb the rest with scribes and shims, where the fixings go and what they go into, service penetrations, and what arrives in one piece. The rules come from the Architectural Woodwork Standards (AWS), 2nd Edition, Section 10, Casework, and Section 2, Care and Storage. Moisture figures come from the USDA Wood Handbook.

Which edition

The AWS 2nd Edition (2014) is published in full, free, by the Woodwork Institute. Jobs bid later may fall under NAAWS or the AWI Standards. Chapter 19 explains how to tell. The standard named in your spec sets the value.

The building's tolerance, and yours

The AWS sets out what the building owes the woodwork before install begins. Wall, ceiling and opening variations above 1/4" (6.4 mm) in 144" (3658 mm), or floors above 1/2" (12.7 mm) in 144", from plumb, level, flat, straight, square or correct size "are not acceptable for the installation of architectural woodwork, nor is it the responsibility of the installer to scribe or fit to tolerances in excess of such". The contractor provides the substrate. The installer may inspect it and "accept or reject for cause" before starting.

Then it sets what the woodwork owes once installed: "plumb, level, square, flat and in plane within 1/8" (3.2 mm) in 96" (2438 mm)".

Who	Tolerance	Over
Walls, ceilings, openings (building)	1/4" (6.4 mm)	144" (3658 mm)
Floors (building)	1/2" (12.7 mm)	144" (3658 mm)
Installed casework	1/8" (3.2 mm)	96" (2438 mm)

The gap between those two rows is what your drawing must absorb. Scribes absorb it at walls and ceilings. Shims absorb it at the floor. If the drawing makes no room for either, the installer makes room with a saw.

Worked example

A run of base cabinets spans a 12' (144") wall. The architect's plan shows the opening at 144" clear. You design the run to fill it.

The standard lets the wall be out by up to 1/4" over that length, and the floor by up to 1/2". Both are acceptable conditions you must plan for.
Put a scribe filler at one or both ends. At Custom and Premium grade, scribe fillers are furnished by the manufacturer and may not exceed 1-1/2" (38.1 mm) wide. Design the boxes to the opening less the fillers, and dimension the fillers with a note that they are cut on site.
Toe base shimming up to 1/2" is acceptable. A floor further out than that is corrected before cabinets go in, and "correction of such is not the responsibility of the cabinet installer". Show the design top height and note the shim allowance, so a site measurement can be checked against it.
Mark the 144" opening VIF, verify in field. If the site measure comes back at 142 3/4", the fillers take it. If it comes back at 140", the design changes, and the revision block records why.

Scribes, fillers and closures

The AWS installation rules for casework, by grade:

Rule	Economy	Custom	Premium
Scribing at flat surfaces	—	Required	Required
Scribing at shaped surfaces	—	—	Required
Scribing where cabinets meet finished walls or ceiling	Not required	Furnished by the manufacturer
Scribe fillers and scribe moulds	—	No wider than 1-1/2" (38.1 mm)
Colour-compatible caulk	—	Permitted, not exceeding 1/8" (3.2 mm)
Gap at back bottom edge of wall-hung cabinets	1/2" (12.7 mm)	1/4" (6.4 mm)
Closure panels at top and bottom voids of tall and wall cabinets	—	Required

A few rules apply to every grade. Inside-corner fillers where two elevations meet "must be equal in width", and no wider than 3" unless needed for hardware clearance. Scribes match the exposed surfaces and come in maximum available lengths, with no joints in material shorter than 96". Voids between cabinets and walls need a closure: at hidden voids up to 1-1/2" wide, a piece of laminate may cap them; wider hidden voids get at least a 3/4" (19 mm) filler.

The inside-corner rule is one a drafter breaks without noticing. A corner drawn with a 1" filler on one elevation and a 2 1/2" filler on the other passes on each sheet and fails at the corner. Check both elevations together.

The AWS also sets the typical scribe options, which the sample casework designs use: a scribe filler, a scribe mould, and a scribe allowance built into the cabinet. Its cabinet design series draws scribes at wall-to-wall runs no wider than 1-1/2". Choose one per location and draw it. "Scribe as required" on an elevation is the same as no scribe.

Fixings, and what they go into

A cabinet is only as secure as the wall behind it, and the wall is not your trade. The AWS puts in-wall blocking with the contractor. If the contract documents do not call for it, "the architectural woodwork installer shall not proceed with the installation until such time as the in wall blocking/backing is installed by others". Your drawing is how the contractor knows where to put it.

The AWS Submittals section requires: "Blocking or strapping requirements and their locations (blocking to be furnished by others) shown on cabinet elevations with dimensions off finished floor", and section details "showing method of cabinet attachment to walls, floors, and ceilings". The casework rules add that the manufacturer provides the blocking layout on the shop drawings for tall, base and wall-hung casework, top and bottom runs.

The anchorage rules, for all wall-anchored casework except islands, peninsulas and base casework with mechanical spacing allowances, which are engineered case by case:

Item	AWS 2nd Ed., Section 10
In-wall blocking or backing	Continuous, at least 2 × 6 nominal wood or 6" × 16 ga sheet metal, by others
Fasteners per cabinet	At least four: two at the top, two at the bottom
Horizontal spacing	Within 3" of each outside end, equally spaced, 16" on centre maximum; 12" for wall cabinets over 48" high
Vertical position	Within 3" of the top or bottom, through the anchor strip
Intermediate row	At an intermediate height on cabinets over 60" tall
Screw	At least 3" × #10 with a surface-bearing head; 1-1/2" penetration into studs, blocking or masonry
Prohibited	Drywall or bugle-head screws
Cabinet to cabinet	At least two #8 × 1-1/4" screws at the front, 30" on centre maximum
Bases and toes	Need not be anchored to the floor; separate bases are screwed to the cabinet bottom

A locking hanging cleat or other concealed system may replace screws, if it has been independently tested to the standard's wall cabinet structural test.

Worked example

A 24" (610 mm) wide wall cabinet, 30" high. How many fixings, and where does the blocking go?

Fixings sit within 3" of each end, so the outer two in a row are about 18" apart. That exceeds the 16" maximum, so each row needs a third fixing in the middle: three at the top, three at the bottom, six in total.
Top row within 3" of the cabinet top; bottom row within 3" of its bottom. With the cabinet bottom at 54" above finished floor, the rows fall near 81" and 57" AFF.
On the elevation, dimension two blocking centrelines off finished floor, each a continuous 2 × 6 (or 6" × 16 ga strap), and note BLOCKING BY OTHERS.
Now make the same cabinet 54" tall. It crosses 48", so the spacing tightens to 12". It stays under 60", so it needs no intermediate row.

The 54" mounting height is an example, not a standard. Take yours from the elevation.

The Woodwork Institute's sample set puts the responsibility on the cover: "It is the responsibility of the architect/engineer to direct and provide specific detailed requirements for anchoring of cabinets to walls/floors/ceilings." It adds that "all cabinet construction shall comply to Title 24 Calif building code". Where seismic or structural rules apply, the anchorage is an engineer's decision, and your drawing asks for it. The AWS has an appendix on seismic fabrication and installation; this chapter did not work through it.

Acclimation and moisture

Wood moves with humidity, and the installer inherits whatever the building does. The AWS installer must verify that woodwork "has been acclimated to the field conditions for a minimum of 72 hours before installation is commenced", and that the HVAC system is running and holding humidity and temperature. It must also verify the site is ventilated and protected from direct sunlight, excessive heat and moisture.

The AWS Care and Storage section, adapted from the Wood Handbook, gives the target for most of the United States and Canada: a relative humidity of 25–55%, holding wood at 5–10% moisture content in a climate-controlled space. The range of relative humidity change "should not exceed 30 percentage points". The Wood Handbook itself recommends an average of 8%, 6–10% for individual pieces, for interior woodwork in most of the United States, with lower values for the dry southwest and higher for the damp coast.

What this means on paper: a set for a building with no HVAC running, or for a coastal home left shut up for months, carries a note that install waits for conditioned air. The AWS says it "does not establish grade rules for joint flushness and or gap tolerances for woodwork products installed in a non climate controlled environment". Without the note, the joints you drew tight open in the first dry season, and the argument starts from nothing.

Service penetrations

Pipes, cables, sockets and vents all pass through or behind millwork. The AWS rule at install: equipment cutouts, "including electrical and plumbing", are cut by the installer, "provided templates are furnished prior to installation", neatly, and sized to be covered by standard cover plates or rosettes. Its casework recommendations ask the spec to state any "pipe chase allowance and/or removable backs behind base cabinets".

So the drawing shows, for each service:

Where it enters the cabinet, dimensioned off the floor and a cabinet edge, or marked LOCATE ON SITE with who locates it.
Whether the back is cut, removable, or held off the wall to form a chase.
Who supplies the template, and when.
Access: a service that will need a plumber later needs a panel that comes out without wrecking the cabinet.

The residential set shows the failure mode. Its tall unit section notes 6" BUILDOUT FOR TV. BUILD TO MATCH RAISED PANEL DOORS BRACE BEHIND AS REQUIRED. "As required" passes three decisions to the site: what the bracing is, what it fixes to, and how the television's cables reach it. The same section notes interior and under-cabinet lighting with no route for a cable. Each is a phone call in week one of install.

What ships assembled

The AWS product default is that casework is "Assembled complete by the manufacturer, with doors, drawers, and hardware installed". That default meets the building at the door. A 2,400 mm tall unit that cannot tilt up under a 2,400 mm ceiling, or a reception desk that cannot turn the corner into the lift, is built twice or cut on site.

So measure the route before you fix the splits:

Door openings, corridor widths and turns, stair and lift dimensions, from site or from the architect's plans marked VIF.
Ceiling height against the diagonal of any tall unit that stands up in place.
The weight of each piece and how many people carry it.

Then draw each split: where the joint falls, how it reconnects (bolts, connectors, a hidden rail), and how the joint looks on the face. A split that is designed and detailed is a joint. A split improvised on site is a saw cut in an occupied building, and it makes dust nobody planned for.

Weight is a safety decision, too. HSE's manual handling duties run in order: "avoid hazardous manual handling, so far as reasonably practicable", assess the risk of what cannot be avoided, and reduce it "to as low as reasonably practicable". A panel sized to need two people, sent to a job with one installer, is a drawing decision. The safety page covers splits, lifting points and access in more depth.

Gaps and flushness at install

The installed joints are judged by grade. The AWS limits for wood-to-wood joints on flat surfaces:

Measure	Economy	Custom	Premium
Gap width	0.030" (0.76 mm)	0.020" (0.51 mm)	0.015" (0.38 mm)
Flushness	0.025" (0.64 mm)	0.015" (0.38 mm)	0.010" (0.25 mm)

Gaps may run no more than 30% of a joint's length. Gaps caused by walls or ceilings beyond the building tolerance "shall not be considered a defect or the responsibility of the installer". Door and drawer fronts align vertically and horizontally and sit flush with each other, and minor adjustment is the installer's job. That last rule depends on the hardware leaving adjustment in reserve; chapter 15 covers why.

Checks before the set leaves

Every dimension taken from the architect's plan, not the site, is marked VIF.
Scribes chosen and drawn at every wall and ceiling junction, within the width the grade allows.
Inside-corner fillers equal on both elevations.
Toe base height and shim allowance noted.
Blocking drawn on the elevations, dimensioned off finished floor, noted by others.
Attachment detail for walls, floors and ceilings, with fastener type and spacing.
Anchorage by an engineer requested where seismic or structural rules apply.
Each service located, with its template source and any access panel.
Delivery route checked; splits drawn and detailed.
A note that install waits for acclimation and working HVAC.
No "as required" left on a sheet without a named person to decide it.

Sources

Architectural Woodwork Standards, 2nd Edition, 1 October 2014, © AWI, AWMAC, WI, full text hosted by the Woodwork Institute. Section 1, printed p. 32: blocking on elevations, attachment details. Section 2, printed pp. 37–39: humidity, moisture content, the 30-point range. Section 10, printed pp. 290, 294, 299, 304: cabinet design series scribes, pipe chase recommendation, toe base shimming, assembled-complete default; printed pp. 327–332: contractor and installer responsibilities, building tolerances, 72-hour acclimation, installed tolerance, scribes, closures, gaps and flushness, anchorage, equipment cutouts, hardware installation. Superseded for jobs bid under later editions. Primary (superseded edition).
USDA Forest Products Laboratory, Wood Handbook, FPL-GTR-190, chapter 13, Table 13–2: recommended moisture content at installation. Primary.
Health and Safety Executive, "Manual handling at work", hse.gov.uk. The three duties, in order. Primary.
Woodwork Institute, Sample Shop Drawings, project data sheet: installation requirements naming the architect or engineer for anchorage, and the Title 24 note. Document.
A residential millwork submittal, 16 sheets, revision 0, sheet 12: the TV buildout and lighting notes. Not reproduced: live job. Document.

The fixing layout in the worked example applies the AWS spacing rules to an example cabinet. The mounting height in it is illustrative.