Many window treatments are mounted on lumber instead of decorative or functional poles and rods. Therefore, it is important to understand lumber and some of its characteristics in order to choose the best wood for each product.

The lumber used in constructing window treatments is the same softwood lumber used in general construction. It is referred to as Dimensional Lumber, or lumber that is from one inch up to, but not including, five inches thick and that is two or more inches in width. Dimension also is classified as framing, joists, planks, rafters, etc. These are primarily cut from the evergreen families of pine, spruce and fir.

There are many many different types and grades of lumber. For our purposes, this article will concentrate on the type, sizes and grades which are optimal choices for the window treatment industry in terms of price and functionality. This article also compares the quality and suitability of different flat panel options which are used for framing arched treatments and for the faces of cornice boards.

LUMBER IS CUT, MILLED & GRADED FOR QUALITY:

Cut:

Trees are cut and the rounded sides are cut off, creating a square trunk. From the square trunks, planks are rough cut in nominal sizes of 1x4. 1x6, 2x4, etc. The nominal designation of the plank is the label by which it is sold.

Milled:

The milling process trims and smooths the rough planks down to dimensional sizes (actual sizes) which are sold to the end user. The milling process takes a nominal 1x4 and mills it to a dimensional 3/4" x 3.5".

Graded:

The lumber is then graded on its quality. The grading process is complicated and based on a set of criteria by which to judge various pieces of lumber or panels in terms of strength and appearance. Regional grading agencies draw up rules for grading based on the voluntary product standards issued by the U.S. Bureau of Standards.

Strength: A measurement of strength in lumber involves the basic properties of wood: fiber stress in bending, tension parallel to grain, horizontal shear, compression perpendicular to grain, and elasticity.

Knots also affect the strength of a plank. They are formed by a branch or limb embedded in a tree and cut through in the process of manufacturing. Knots are classified according to size, occurance and tight/loose (loose knots fall out, leaving a hole in the wood). Knots can be a problem in that they are more dense than the surrounding wood, making it difficult to staple into and/or will more readily split when a screw is inserted.

Appearance: The size and number of knots also affects the clean appearance of the board. However, dust boards and legs are covered with lining and/or fabric, hiding the knots. Appearance is also judged by the number and size of other imperfections: splits, gouges, etc.

 

CHOOSING THE RIGHT LUMBER FOR THE JOB.

Pine is the best choice for all window treatments. It is relatively inexpensive, yet durable and easy to work with. To choose lumber for a job, first select the grade most appropriate for the job, then examine the wood for warping and imperfections.

Grades:

#2 grade -

• Has some knots, usually small to medium in size.
• Minor imperfections
• Dried to a range of less than 19% humidity. Stable in areas of normal ranges of humidity.
• Least cost of three grades discussed here.
• Suitable for most standard dust boards and legs.

#1 grade -

• Has fewer knots, usually small
• Few imperfections.
• Dried to a range of less than 19% humidity.
• Stronger than #2 grade
• Slightly more expensive.
• Suitable for treatments where extra long boards and/or wider boards are required. Also recommended for treatments of considerable weight. Basically, you would choose this grade because of its additional strength.

Clear grade -

• Free of knots and imperfections.
• Probably dried to 6-8% humidity range. Most stable in humid conditions
• Decidedly more expensive than #1 grade.
• This is furniture grade lumber. It is no stronger than the previous grade. The higher price is for appearance only. Since dustboards and legs are covered with fabric, the appearance would not be a factor and this grade of wood would be excessive for most window treatments.

Appearance:

Examine the board to ensure it is clean and free of dirt, gouges, splits and large or loose knots. Also check for black mold. This form of mold is known to cause deadly illness in small infants and people with weak immune systems. A board with black mold should never be used in a window treatment.

Test for warpage. Ideally, the board should lay flat on the floor on all four sides. A board which bows front to back cannot be used for a window treatment as it needs to be flat againt the wall. A board which bows in a U shape can be straightened at the time of the install using extra "L" brackets. The severity of the bow will determine whether or not it is suitable for the job.

 

STORAGE.

If you stockpile lumber for future jobs, storage is an important issue.

Lumber is best laid flat on a supported surface which does not allow the center to bow. If you must stand it up, prop it securely against the wall in a manner in which it is supported and does not bow.

Storage area must be relatively dry and clean. Do not store in a dark, damp area which will encourage the growth of mold.

Always purchase the longest boards you can store easily. In this way, you can cut long dust boards from full size boards and smaller boards from the scraps, thereby optimizing your lumber purchases.

 

FLAT PANELS FOR CORNICES & FRAMING ARCHES

Cornice boards are constructed using dimensional lumber for the dustboard and sides. A panel product is used for the face. Frames for arched windows or unusually shaped window treatments also use panel products because they come in larger sizes and are easy to cut to a specific shape.

The three most commonly considered panel products for cornices are oriented strand board (OSB), particle board and plywood. All come in standard sheets of 4' x 8' and in a variety of thicknesses.

Oriented Strand Board (OSB):

An offshoot of wafer board, OSB is a structural panel made of narrow strands of fiber oriented lengthwise and crosswise in layers, with a resin binder. OSB's strength comes mainly from the uninterrupted wood fiber, interweaving of the long strands or wafers and degree of orientation of strands in the surface layers. Waterproof and boil proof resin binders are combined with the strands to provide internal strength, rigidity and moisture resistance.

Because OSB is constructed of small pieces of wood glued together, screws and staples do not always hold securely and could tend to pull out if enough tension is applied. Also, because it is often used in exterior construction, arsenic and/or rat poison are sometimes added to the OSB mix to discourage rodents from chewing on it. While OSB is an inexpensive alternative, its use should be limited in the window treatment industry.

Particle Board:

Particle board, another form of composition board, is made by binding wood particles ranging in size from flakes to sawdust together with a suitable adhesive, such as a plastic resin, and pressing or extruding them to form sheets. Particle board is used as a cheaper substitute for plywood in some applications.

Because of its higher density, particle board is less resistant to puncture. It is considerably heavier than the other choices and very difficult to staple into. Its weight and density make it difficult to use in the window treatment industry.

Plywood:

Plywood is a flat panel made up of a number of thin sheets, or veneers, of wood in which the grain direction of each ply, or layer, is at right angles to the one adjacent to it. The veneer sheets are united, under pressure, by a bonding agent.

This panel product cuts easily and screws stay secure. Plywood is probably the best choice for cornice faces. It is easy to cut and handle and is stable under humid conditions.

For most window treatment applications, 1/2" to 5/8" thick plywood is best. Small cornices could use 3/8" thick plywood, but larger cornices will be more stable with thicker measures. It is not necessary to purchase plywood thicker than 5/8" because the construction of cornices and arch frames is such that the panel piece will be supported and stable. Thicker plywood would simply make the treatment heavier and more cumbersome.

Plywood comes in three finish choices:

Unfinished on both sides. Both surfaces of the plywood are rough and gouged. The holes would have to be filled with wood putty and sanded smooth before the plywood could be used for a window treatment. Least cost of three choices.

Finished on one side. One surface of the plywood is unfinished. The other surface is usually a layer of oak or birch which is sanded smooth and has no holes. Higher cost than unfinished.

Finished on both sides. Both surfaces of the plywood are finished with a layer of oak or birch and sanded smooth. Most expensive of the three alternatives.

It is the workroom's discretion whether to use unfinished or finished plywood. The smooth surfaces of the finished plywood will contribute to a finer finished product with less time and effort spent trying to fill in or hide the roughness of the unfinished sides.

 

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