Visible Timbers: Three practical ways to expose the beauty of structural wood in your next project.
March 11, 2021
By Steve Maxwell
Canada probably grows more big trees than any other country in the world, but you’d never know it by looking at Canadian houses. Even though wood is always involved in construction, it’s typically sawn into boring, uniform 1-1/2” planks, spiked together with no thought for appearance, then hidden under drywall. That’s too bad because the reality is that it’s never been easier to incorporate majestic, visible timbers into renovations and new construction. This isn’t the kind of thing that makes sense for every project, but for clients interested in adding wood in a rustic way, the techniques you’ll see here are perfect. Over the last 30 years I’ve used various unconventional methods to incorporate timbers into my building projects and it’s paid off. Here are three I particularly like.
Timber Frame/Stud Frame Hybrid
Traditional timber frame structures are still built today as they’ve always been, with big wood joined together without metal fasteners, then raised upright to form walls and roofs. One way to ease the cost and complexity of this process, while still retaining most of the stunning appearance of traditional timber framing, involves combining modern stud frame outer walls with timber frame posts and beams raised one at a time wherever they’ll be visible in the completed structure. While this approach may offend purists, it does make it much more affordable and practical for unspecialized contractors to make timbers part of projects.
Traditional timber joinery techniques such as pegged mortise and tenons, dovetails, let-in knee braces and visible overhead beams are all still possible and practical with this hybrid approach, while the effort of raising the components is significantly reduced. My favourite timber framing guidebook is Building the Timber Frame House: The Revival of a Forgotten Craft by Tedd Benson. It covers everything you need to know about the old-fashioned joinery side of things. As for how your traditional timber beams and posts interface with modern stud frame walls, this involves a couple of simple tricks.
The main engineering difference between stud frame walls and timber frame construction has to do with how loads are distributed. Stud frame walls distribute loads much more evenly across their length than the large point loads typical of timber beams. To accommodate this fact you need to create composite posts within stud walls wherever they’re supporting beams above. Where an 8x10 main beam joins to an outside 2x6 wall, for instance, spike four or five 2x6 studs together vertically within the wall frame, immediately below the beam. Smaller beams, such as 6x8s spaced 24” on centre to replace conventional floor joists, can rest directly on the double top plate of a stud wall. Either way, I use 8”, 10” and 12” spikes to secure timbers to the underlying stud frame wall structures. Predrill holes through the beams to make sure the spikes drive straight.
Exposed, Built-Up Beams
Sometimes even the weight of handling and raising solid timbers one at a time is beyond the budget of a project, and at times like these built-up timbers make sense.
They’re made from ordinary, construction-grade 2x8, 2x10 and 2x12 planks bolted together, but don’t let that homely description fool you. Built-up beams provide surprisingly beautiful results when sanded, routed and bolted together with care. This approach works well indoors or in sheltered outdoor applications, too. Built-up beams are also less likely to puzzle your building inspector. Concealed versions of built-up beams are a regular part of modern home building, so any inspector has charts for allowable span, beam width and beam thickness. The fact that you’re using them in an exposed application makes no technical difference, though there are steps to follow if you want built-up beams to look good when you’re done.
If you bolt three or four 2x10s together, the result will look pretty much like three or four 2x10s bolted together. That’s not terrific, but it doesn’t have to be this way. Three simple steps make all the difference.
My favourite approach begins with a small 45º chamfer bit in a small laminate router to mill angled edges wherever planks meet each other as they’re bolted together. Besides looking great, chamfered edges hide the slight but inevitable mismatches that occur between boards. The outer edges of composite beams also look best milled with a much larger chamfer bit, with the profile stopping several inches before the edge of the beam meets adjoining surfaces. You’ll find wooden hand screws most useful for aligning multiple boards as you’re marking, drilling and bolting them together.
While you could use nails or screws to hold the layers of a builtup beam tight, 1/2” diameter carriage bolts, flat washers and nuts are better on three counts. First, they let you pull the layers of wood together and hold them with a lot of force. The domed heads of carriage bolts also look pretty good. And if your composite beam will spend its life in a heated, indoor space, bolts also allow the option of tightening things up when the layers of wood inevitably shrink.
There’s one other situation where built-up beams really shine. In cases where you need a beam to support a roof valley, the built-up approach can’t be beat. The layered design allows inward sloping angles to be sawn on the top edges of the planks before the layers come together. This creates the ideal troughlike shape necessary along the top of the beam to properly support roof sheathing. This is even more important when you’re building a roof with structural insulated panels because of the higher point loads involved.
Metal Joinery Hardware
Preparing interlocking joints is the most difficult part of timber framing work, and it’s why metal connection hardware was invented. Besides the typical bolted platetype connectors, metal hardware exists for holding posts and beams together invisibly, too. Timberlinx (www.timberlinx.com; 877.900.3111) is a Canadian firm that offers a unique range of hidden timber fasteners that require nothing more than accurately drilled 1-1/8” holes. A special jig makes it easy to bore these holes square. I’ve used this system in traditional solid wood beams as well as modern glulam or microlam timbers.
Custom-fabricated metal brackets are another option. Make a full-size model of the bracket you need using corrugated cardboard and hot melt glue, then hand it over to a welding shop to be built in mild steel.
Few countries in the world have the kind of big wood at reasonable prices that we do. More Canadian homes should reflect our heritage of craftsmanship and timber availability – a heritage that most of the world can only dream of. Mention it to the right kind of clients and you could win yourself some interesting projects.