Tag Archives: timber frame

Timber Frame Porch–Complete

new outside light

Installation of an Arts & Crafts-inspired light finishes up the porch project.


12 housed mortise and tenons,
12 bird’s mouth joints, and
66 lap joints
later, I finished up the porch build by installing an Arts & Crafts-inspired light. Follow the links for details on the design and build.

Ridge Cap
Ridge Beam & Rafters
Mortise & Tenon

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Timber Frame Porch–Ridge Cap

Cedar ridge cap

Butt-joined cedar 1″ x 10″s form the foundation for the ridge cap. Three layers of cedar shingles top it off.

I’d balked at using the polycarbonate ridge cap also made by the panel manufacturer, a decision I had cause to question as I assembled the ridge cap. I’d decided on a cedar cap, two wide boards joined with a simple butt joint, and originally intended to clad it in copper. A quick look at copper prices sent me looking for other options. It seemed like a good time to use the bundle of cedar shingles I’d purchased for the fence build but didn’t end up using.
I began by ripping a bevel on both boards, and act of geometry that almost defeated my limited mental faculties. To produce the 110-degree angle at the roof peak, I needed to rip a 70-degree bevel along the ridge cap boards. The table saw does not cut at 70-degrees. Stand a board on edge and rip it at 20-degrees, though, and you are left with a 70-degree bevel. After ripping the boards to final width, I drilled some pocket holes and brushed on the glue and screwed the whole thing together. Continue reading

Timber Frame Porch–Roof Panels

The streak of dry weather we’d been enjoying came to an end about the same time I was installing the first panel on the second side of the porch roof. I sank a screw and felt the first drops hit my face, then looked more closely at the first row of panels I’d installed. From my current vantage, the panels looked to meet at a jagged edge along the base of the roof. I’d need to re-do the whole row. My resigned sigh puffed out a cloud of vapor in air just above freezing, and the rain turned from a few tentative drops to a persistent fall. Continue reading

Timber Frame Porch–Purlins


Half-lapped purlins create another layer of visual interest while supporting the roof panels.

The roofing panels I selected required purlins 24 inches on center to prevent sag. Initially, I’d considered installing blocking between the rafters, but after reviewing timber frame images with purlins that ran over the rafters, I drew versions with blocking and overlaid purlins and decided half-lapped purlins looked better than blocking or a simple overlay.

To cut the half laps, I laid out the joints on 2 x 6 stock and used a straight bit in the router guided by a dado jig to notch the stock. After cutting the joints, I ripped the 2 x 6 stock into 2.5 inch strips and rounded over the cut edges with a 1/8″ roundover bit.

After the joinery, installation was easy. The first purlin was set in place at the end of each rafter and screwed into place at every joint. I then used spacer blocks to position the next purlin and fastened it in place. Repeat ten more times, and the porch was ready for a roof.

Timber Frame Porch–Ridge Beam and Rafters

half lap jig

The angled fence guides a top-mounted bearing in a flush cut bit and a stop positions the fence at the correct location for the half lap.

I debated whether to include a ridge beam in the  porch design since it would reiterate the three-beam look of the house’s fascia, and the fact that it would simplify installing rafters finally persuaded me. The joinery was identical to the other beams: an end bevelled on the miter saw and two housed mortises cut with a router and jig. I pinned the half posts into the ridge beam and hauled the whole unwieldy assembly up a ladder and dropped it into place. With the base complete, I was ready to move on to rafters.  Continue reading

Timber Frame Porch–Base Assembly

After pinning the post tenon, the peg is sawn flush to beam.

After pinning the post tenon, the peg is sawn flush to beam.

White oak has a pleasant, nutty scent, a fact of which I was reminded as I sawed the pegs flush to the beams during the last part of base assembly on a surprisingly sunny November day. Assembly began with a final test fit of each tenon into its respective mortise. Once they fit smoothly, I drilled the beams for the pins, and marked the tenons for the offset holes required for drawboring the joint. The offset helps to pull the joint tight and to keep it tight even if wood shrinkage tends to pull it apart.

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Tree Nail

A V-groove hold the blank in position. The rough circle shows the finished outline of the peg.

A V-groove hold the blank in position. The rough circle shows the finished outline of the peg.

The tree nail, or trunnel, is a wooden peg used to pin the tenons of a timber frame to their mortises. Commercially available pegs are turned on a lathe, but traditionally they are shaped from rived wood, often using a draw knife to round the wood while it’s secured in a shaving horse. Riving, or splitting peg blanks instead of sawing them, ensures the grain of the wood runs continuously through their entire length and minimizes the risk of the peg splitting when it is hammered home. Since timber frame joints are usually drawbored–the hole in the tenon is offset slightly from the hole in the mortise walls–the continuous grain of a rived peg is especially desirable. Continue reading

Cutting tenons for a Timber Frame

After defining the tenon shoulders with a handsaw, I cut the cheeks on the bandsaw, then tuned with rasp and chisel to fit.

After defining the tenon shoulders with a handsaw, I cut the cheeks on the bandsaw, then tuned with rasp and chisel to fit.

A survey of resource suggested the following considerations for sizing the tenons used in timber frame construction:

  • The thickness of the tenon is usually one-quarter the width of the timber but no more than one-third. 
  • The tenon usually runs the whole width of the member being tenoned.
  • The walls of the mortise should be at least the thickness of the tenon.

Since I was working with 4 x 4 and 4 x 6 stock, I made my tenons an inch thick and two inches deep. And since I think a little shoulder is a good thing, I reduced the width of the tenon by a half inch to leave a quarter-inch shoulder on the sides of the tenons. Continue reading