Framing lumber, also known as structural wood, is the grade of wood used for house framing (studs, headers, roof trusses and floor joists, etc.). Its technical characteristics make it perfectly suitable when large spans are necessary. The list below outlines the different families of framing lumber.
Standard SPF (spruce-pine-fir) lumber – Softwood lumber
- Light structural lumber is mainly used in residential construction. It is milled from softwood trees (spruce, fir and pine) that are sawn and machine-planed to standard dimensions (2×4″, 2×6″, 2×8″, etc.). Wood as a framing material is advantageous in that it doesn’t undergo much transformation during processing, it has a low embodied energy, it’s a renewable resource and it stores carbon.
- Heavy timber refers to any dimensional lumber over 4.5″ and is often used for post-and-beam construction. Large dimensions of wood can support heavy loads and facilitate long spans, in addition to being extremely fire resistant.
- Finger-jointed lumber (also known as end-jointed and end-glued) is manufactured using short, dry pieces of wood that have been machined on each end and joined using a water repellent structural adhesive. This technique is ecologically beneficial, as it makes use of short pieces of wood to create a finished product that is larger, more stable and easier to align.
Worthy of note: the dimensions of light structural lumber do not match their given names. A commercially available 2×4″ is actually 1.5″ x 3.5″, a 2×6 is actually 1.5″ x 5.5″. The general rule of thumb: any width listed as 2″ will actually be 1.5″ and as for the depth, actual dimensions are .5″ less. The reason for this is planing; some true dimensions can be found at lumber yards, referred to as ‘rough’ as they are unplaned.
|Engineered wood requires more processing than standard wood. As may be expected, engineered wood is more expensive than the types described above, and has a higher embodied energy given that it undergoes multiple transformations. Even so, it has many technical and ecological advantages: it can be very strong and facilitate large spans without requiring large trees.|
It also makes use of short pieces of wood that might otherwise be heading for a landfill, so as soon as you need something larger than 2×8″, opt for engineered wood whenever possible.
|In many cases, the added cost you may incur from choosing engineered wood will be recouped through significant labour savings. Engineered framing materials are straight and consistent – compare this to a 2×8″ or 2×10″ which in any given pile may have discrepancies of 3/8″ or more from the largest to the smallest. In order to build a straight floor for example, some pieces will need to be shimmed and others will need to be shaved, and that takes a lot of time.|
If you didn’t get your money back from a quicker installation of open-web floor joists, you certainly will when your electrician and plumber easily pass wires and pipes through existing openings rather than drilling a thousand holes through solid floor joists (see images to the right).
Here are the different types of engineered wood products and their main characteristics.
- Glulam is a multi-layered type of wood that is manufactured using several thicknesses of thin pieces of solid wood held together with mildew-resistant phenol glues which emit a very small amount of toxic chemicals. This process makes it possible to produce posts and beams that are strong and well suited for wide spans.Because glulam is strong and very easy to work with, it is most often used in roof framing.
- Cross-laminated timber (CLT) is manufactured using many sheets of wood stacked on top of each other and then glued together. Each layer is oriented crosswise to the next, which makes for extremely stable and strong panels. Having established itself on the European market over the past twenty years, CLT has only recently become available in North America. This type of wood has excellent thermal and acoustic properties, is highly resistant to fire, and provides exceptional structural strength. CLT can be used to build load-bearing walls, floors and roofs. To date, it has mainly been used in residential construction, but tall wood buildings (between 5 and 10 stories) are now starting to pop up all over the world.
- OSB (Oriented Strand Board), also known as Aspenite, is a panel fabricated using small strips of wood. OSB is not as strong as plywood, or as resistant to weather. It is most often used as exterior sheathing, as well as being the centre web of engineered wooden I-Joists. OSB makes use of small pieces of waste wood and is bonded using a phenol formaldehyde, a far less toxic substitute for the urea formaldehyde of days past. All that to say, it certainly won’t improve the air quality of your home, but it is generally not thought to be too great a health hazard.
- Plywood is used for different structural elements such as studs in load-bearing walls, partitions, floor beams and roof supports. Plywood is most commonly found as a 4 x 8′ panel that is made from thin sheets of wood veneer that are bonded together using phenol formaldehyde glues. It is assembled with the grain of each layer running in the opposite direction of the previous one, making a very stable and strong final product that is highly resistant to cracking, twisting and shrinkage. Plywood is commonly used on residential construction sites as a flooring substrate, exterior wall and roof sheathing, as well as certain interior finishing applications and furniture.
- Engineered wood is at greater risk of moisture damage, learn more here.
Interior finishing wood
Mouldings for interior finishing can be made of all sorts of materials. Solid wood is one option (pine, oak, maple or yellow birch). It is still rather expensive but it has the advantage of being a durable material that doesn’t require harmful adhesives. MDF mouldings (Medium Density Fibreboard) are more reasonably priced and made largely of waste wood products, but they are fairly heavily ladden with toxic adhesives. Solid wood products with Zero VOC finishes will go a long way to helping you keep clean indoor air quality.
Regardless of the type of wood that is used, your furniture should ideally be free of volatile organic compounds (VOCs), including formaldehyde, to protect your indoor air quality. For finishings and maintenance – again to protect your air quality – look for either low or zero VOC paints and finishes.
Source : http://www.ecohome.net/guide/material-choices-wood-frame-construction