“You mean you can frame houses with that stuff?” “That wood doesn’t look real good. What's wrong with it?” “Don’t you need some more supports under there?” “What's the difference between a glulam and an LVL?” “Shouldn’t this stuff be going to the landfill instead of inside of my walls?” “So explain it to me again why you're using this wood?” In all of my years of building, these are just a few of the questions I've been asked about engineered wood. So allow me to answer the last question first.
There's a number of reasons why I use engineered wood. First, as a sustainable builder, I walk my talk by using reclaimed or recycled materials -- such as engineered wood -- where possible. If more builders were to use these materials, we would be putting less waste in the landfills and the price would come down as supply increased to meet demand.
But the most important reason I use engineered wood is that it's truly a better product. Ok I hear you saying “Yeah, right. Prove it.”
Ok, here's an example. Have any of you had the experience where the studs in the walls twisted, turned, or bulged and pushed the drywall out of line? Did the nails pop up? Why does that happen?
That's because these days, stud-grade lumber is cut very young, usually at 7 to 8 years, then it's flashed dried in kilns and shipped to the lumber yards very quickly. It’s too young and still contains a lot of moisture. Years ago lumber for studs was harvested when it was 10 – 12 years old and allowed to air dry for up to a year. But now, with these accelerated harvesting and drying methods, as the lumber dries inside your walls, it moves and creates problems with your drywall.
An alternative is to use finger-jointed studs, an engineered wood product. I've used finger-jointed studs for 10+ years, and I've never had a call-back to repair drywall. (Not to mention, it's better to use screws in drywall, not nails.) Now the best part is that the price of finger-jointed studs is about the same as that of young-growth lumber. You just have to do a little more digging because you can't find the product everywhere; for example, most big-box retailers don’t carry this stuff.
So what is engineered wood? Normally I would go into a long explanation in my own words, but I found that Wikipedia has done a better job for me. So I am going to use their definitions of terms. Call it plagiarism, stealing or whatever. Since this is not a term paper, I’m not worried; I’m just passing on important information. Hats off to Wikipedia.
Plywood. The original engineered wood product. Manufactured from sheets of cross-laminated veneer and bonded under heat and pressure with durable, moisture-resistant adhesives. By alternating the grain direction of the veneers from layer to layer, or “cross-orienting”, panel strength and stiffness in both directions are maximized. Other structural wood panels include oriented strand board and structural composite panels.
Oriented strand board (OSB). Made from rectangular-shaped strands of wood that are oriented lengthwise and then arranged in layers, laid up into mats, and bonded together with moisture-resistant, heat-cured adhesives. The individual layers are cross-oriented to provide strength and stiffness to the panel. Produced in huge, continuous mats, OSB is a solid panel product of consistent quality with no laps, gaps or voids.
Glued laminated timber (glulam) is composed of several layers of dimensional timber glued together with moisture-resistant adhesives, creating a large, strong, structural member that can be used as vertical columns or horizontal beams. Glulam can also be produced in curved shapes, offering extensive design flexibility.
Laminated veneer lumber (LVL). Produced by bonding thin wood veneers together in a large billet. The grain of all veneers in the LVL billet is parallel to the long direction. The resulting product features enhanced mechanical properties and dimensional stability that offer a broader range in product width, depth and length than conventional lumber. LVL is a member of the structural composite lumber (SCL) family of engineered wood products that are commonly used in the same structural applications as conventional sawn lumber and timber, including rafters, headers, beams, joists, rim boards, studs and columns.
Cross-Laminated Timber (CLT) is a versatile multi-layered panel made of lumber. Each layer of boards is placed cross-wise to adjacent layers for increased rigidity and strength. CLT can be used for long spans and all assemblies, e.g. floors, walls or roofs.
Parallel strand lumber (PSL) consists of long veneer strands laid in parallel formation and bonded together with an adhesive to form the finished structural section. A strong, consistent material, it has a high load carrying ability and is resistant to seasoning stresses so it is well suited for use as beams and columns for post and beam construction, and for beams, headers, and lintels for light framing construction. PSL is a member of the structural composite lumber (SCL) family of engineered wood products.
Laminated strand lumber (LSL) and oriented strand lumber (OSL) are manufactured from flaked wood strands that have a high length-to-thickness ratio. Combined with an adhesive, the strands are oriented and formed into a large mat or billet and pressed. LSL and OSL offer good fastener-holding strength and mechanical connector performance and are commonly used in a variety of applications, such as beams, headers, studs, rim boards, and millwork components. These products are members of the structural composite lumber (SCL) family of engineered wood products.
Finger-jointed lumber is made up of short pieces of wood combined to form longer lengths and is used in door jambs, mouldings and studs. It is also produced in long lengths and wide dimensions for floors.
I-joists. Designed for use in floor and roof construction. An I-joist consists of top and bottom flanges of various widths united with webs of various depths. The flanges resist common bending stresses, and the web provides shear performance. I-joists are designed to carry heavy loads over long distances while using less lumber than a dimensional solid wood joist of a size necessary to do the same task. As of 2005, approximately half of all wood light framed floors were framed using I-joists.
Roof trusses. Structural frames relying on a triangular arrangement of webs and chords to transfer loads to reaction points.
Engineered wood products are used in a variety of ways, often in applications similar to solid wood products. Engineered wood products may be preferred over solid wood in some applications due to certain comparative advantages:
- Because engineered wood is man-made, it can be designed to meet application-specific performance requirements.
- Engineered wood products are versatile and available in a wide variety of thicknesses, sizes, grades, and exposure durability classifications, making the products ideal for use in unlimited construction, industrial and home project application.
- Engineered wood products are designed and manufactured to maximize the natural strength and stiffness characteristics of wood. The products are very stable and some offer greater structural strength than typical wood building materials. Eight-storey Stadthaus, an apartment complex in London, England, was made with cross-laminated timber panels and is the tallest habitable timber building in the world.
- Glued laminated timber (glulam) has greater strength and stiffness than comparable dimensional lumber and, pound for pound, is stronger than steel. Glulam products are also a better environmental choice than steel because they have less embodied energy.
- Some engineered wood products offer more design options without sacrificing structural requirements.
- Engineered wood panels are easy to work with using ordinary tools and basic skills. They can be cut, drilled, routed, jointed, glued, and fastened. Plywood can be bent to form curved surfaces without loss of strength. And large panel size speeds construction by reducing the number of pieces to be handled and installed.
- Engineered wood products provide the natural warmth and beauty of wood. Many products are available in a variety of surface textures and treatments for nearly every aesthetic taste, from rustic to elegant. The products can be easily and beautifully finished with paints, stains, and varnishes.
- Engineered wood products make more efficient use of wood. They can be made from small pieces of wood, wood that has defects or underutilized species.
- Wooden trusses are competitive in many roof and floor applications, and their high strength-to-weight ratios permit long spans offering flexibility in floor layouts.
Engineered wood products also have some disadvantages:
- Some products may burn more quickly than solid lumber.
- They require more primary energy for their manufacture than solid lumber.
- The adhesives used in some products may be toxic. A concern with some resins is the release of formaldehyde in the finished product, often seen with urea-formaldehyde bonded products.
- Cutting and otherwise working with some products can expose workers to toxic compounds.
- Some engineered wood products, such as those specified for interior use, may be weaker and more prone to humidity-induced warping than equivalent solid woods. Most particle and fiber-based boards are not appropriate for outdoor use because they readily soak up water.
So there you have it folks, everything you ever wanted to know about engineered wood. Well almost. I just hope that the next questions will be something like, “Hey can’t you use more of that engineered wood?” or “You do use finger-jointed studs, don’t you?” or “Can we change the roof design to accommodate using trusses?” or “Does your scrap get recycled into engineered wood?” Well, actually most of the scrap on my construction jobs goes into the walls for blocking as part of our aging-in-place design, but that is a whole other blog topic. (BTW, are you wary of formaldehyde and other volatile organic compounds (VOCs)? Me, too. Get info about formaldehyde regulations and structural wood products here.)