MODERN WOOD 01 - FRAMING LUMBER

Framing lumber is graded and specified by the amount of weight it can carry over a given span.  It is designed to counter the overturning forces of bending moment, failure through shear and deflection.  As previously discussed, the quality of currently available framing lumber is not what it used to be.   The best commonly available grade of framing lumber is ‘No. 2’, with ‘Select Structural’ and ‘No. 1' grades virtually non-existent.  Regular framing lumber is also subject to warping and twisting, and there isn’t a job site in America that doesn’t have mold on some of the new framing members.

To combat this – the lumber industry giant, Weyerhauser, has for the past several years been producing computer-inspected, mechanically graded dimensional lumber.  Their M-12 grade lumber, known commonly as the Framer Series, is available locally and has recently found its way into our specifications.  Guaranteed by Weyerhauser not to warp, the common concerns associated with dimensional lumber of creaky floors or cracked drywall are assuaged.  In addition to this guarantee, Weyerhauser applies a mold inhibitor to the lumber.

The Framer Series lumber is an excellent alternative, in our opinion, to engineered wood I-joists.  One of the primary values of wood I-joists (eg TJIs) is their lack of susceptibility to movement and warp, and because of this, they’ve taken over the market.  Unfortunately, while they can be designed into fire-rated assemblies and the thin vertical plywood web will last long enough to get occupants out, I don’t think it makes for a safe floor for firefighters to enter on to.  Framer Series lumber is true dimensional material, and is suitable for all such fire-rated assemblies.   Dimensional lumber isn’t going to last forever in a fire, but I would suspect it would last longer than the web of an I-joist.  Also, while I-joists can be designed to meet bending, shear and deflection criteria they can still result in a somewhat springy floor.  This is not the case with dimensional lumber.  And while Framer Series comes at a cost premium over regular dimensional lumber (ranging from 20-50% more than similarly sized No. 2 Doug Fir), it prices out at less than half the cost of TJIs sized to result in optimal floor performance (from a springiness perspective).

It ain't what it used to be...

I wrote a blog post earlier this summer about the importance of field priming the back sides of exterior lumber (back-priming).  This is a relatively new practice – you certainly won’t find the original trim on a century old house back-primed, yet it may be in pretty good condition.  Part of the reason for this is the quality of the lumber itself.  The photo above is of 2 studs – one pulled from a house constructed around the turn of the last century and one installed this past year.  Present day lumber indicated as ‘stud-grade’ is only suitable for vertical load applications.  It has a very low allowable bending stress and modulus of elasticity (the criteria for determining the allowable loads and spans of horizontal elements like floor joists and roof rafters). 

Immediately evident is the difference in the growth ring pattern of these two samples.  All trees grow radially and add a ring of growth each year.  Lighter colored ‘earlywood’ is added in the spring and summer while the darker areas of ‘latewood’ develop toward the end of the growing season.  This latewood is inherently denser and therefore stronger and more resistant to decay.   The 100 yr old piece of wood exhibits over 60 very tightly spaced growth rings, while the modern counterpart has only 6.  More growth rings means a greater amount of latewood resulting in a denser, stronger, more decay resistant piece of lumber.  The large expanses of earlywood in the modern piece are inviting to decay penetration. 

Additionally, one can see that the curvature of the modern rings is very pronounced – this is from a very small diameter, relatively young tree.  Wood moves, in response to changes in moisture content and humidity, and it moves in different amounts relative to the orientation to the growth rings.  This modern piece of wood is highly susceptible to movement, especially to cupping or warping given the radial nature of the rings.

We can lament the loss of this vintage material and even if there were old-growth forests around I would not be advocating harvesting the lumber for commercial purposes.  Instead, I think the fact that modern dimensional lumber cannot compete with its vintage relative is a reason to use engineered alternatives. 

Over subsequent blog posts, I will explore alternatives to conventional framing and trim lumber that we have specified and will be specifying in the coming year.  Stay tuned.

The Value of Construction Administration

We all remember the telephone game as children.  Each transfer of information invites the opportunity for error.  As a children’s game the result is often a hilarious distortion of the original message.  It’s not quite so funny when it happens on a construction project.

Every project begins as the conception of the owner. It develops through a series of conversations with the architect, who then transposes it into a set of construction documents.  These documents are then handed off to a contractor and, if the architect removes himself at this point, the opportunity for misinterpretation enters into the equation.  When an idea is translated into two-dimensional drawings to be used to construction three-dimensional space, honest misunderstandings will arise – just like that innocent game of telephone.  With the architect on board during construction, the contractor isn’t left to make assumptions about what the client wants or how something is to be constructed. 

It is routine for contractors to submit questions to the architect during the construction phase, known in industry parlance as Requests for Information, or RFIs.  RFIs often arise from information gained in the field that was unavailable at the time the drawings were generated.  Timely responses by the architect protect against flawed execution and their subsequent costly corrections.  Architectural specifications also call for particular materials and systems but may include the note “Or Approved Equal” in recognition that factors such as material cost and availability may render a selection impractical.  The architect reviews the requests by the contractor to substitute alternate materials.  Is the substitution a prudent opportunity to save money or is it an effort to cut corners?  Are there compatibility issues with the substitution that didn’t exist with the originally specified material?  Will the proposed substitution meet all the appropriate code requirements?  The architect must weigh all the pros and cons and when the issue requires the involvement of the client he must present the information so the client can make a well-informed decision, usually with an impact on the budget, timeline or both.

Lastly, especially on renovation projects, existing conditions arise that differ from that which was anticipated.  Without fail, a proposed toilet location will land on an existing floor joist leaving nowhere for the 3” waste pipe to go.  The solution requires modification to the structure, the plumbing, the interior layout or a combination of all three.  Without the architect’s involvement, the vision for the space can be lost and the structural integrity of the property compromised. 

An architect’s involvement during construction ensures that issues can be resolved quickly before work advances too far and a proper solution becomes too costly.

At the outset of a project, the costs associated with Construction Administration may seem unnecessary.  But for what ends up being somewhere between 1-2% of the cost of construction it is well worth it to ensure the project is executed as intended.