Every email, in the open

Day 0 · Email 1/5

Your frame is measured shoulder to shoulder

First thing to know, and it undoes a reflex.

On a timber-frame drawing, the governing dimension is not the overall length of the piece. It is the SHOULDER-TO-SHOULDER length. The tenon runs past it; it does not count in the building's geometry.

Why: a short tenon moves no wall. Bad arithmetic on the shoulders does — and you find out at the raising.

In practice: a 12 ft sill measures 12 ft − 15 in = 10 ft 9 in shoulder to shoulder, because at each end a post takes its perfect timber (7½ in for an 8×8).

The generator dimensions this way, and gives you both: shoulders to build, cut length to order.

— Biobâtir

Day 2 · Email 2/5

The beam does not fail where you think

A beam fails in horizontal shear, along the neutral axis. Not in bending. Once the split starts, complete failure is likely.

H = 3V / (2·b·d) for a solid beam. Cut a tenon on the underside and the neutral axis rises: the factor becomes (d/h)². Tenon at half the depth → a QUARTER left.

A white pine 6×6 with a 3 in tenon: 510 lb safe load. With a 4½ in tenon: 1,147.5 lb.

The fix, which costs nothing: cut the shoulder on a BEVEL instead of square. The strength returns to the net depth of the tenon and the factor disappears.

The detail, with the formulas: https://timberframe.app/en/moitie-quart.html

— Biobâtir

Day 4 · Email 3/5

A peg hole drilled straight will never draw up

The drawbore. It is the difference between a joint that tightens as it dries and one that opens.

You bore the host hole. You insert the tenon and mark through it. Then you move the mark TOWARD THE SHOULDER by a strong ⅛ in (¾ in peg, softwood) and bore there. Going in, the peg bends and draws the joint up.

When green timber shrinks, the peg acts as a spring and keeps it tight. A joint pulled up with a come-along and bored straight will NEVER retighten.

The check before driving: looking through the hole, you must see at least half the tenon hole. Less than half, or offset the wrong way → take it apart, glue a plug, rebore.

The generator gives the offset and its direction, piece by piece.

— Biobâtir

Day 6 · Email 4/5

Your town's snow, not the book's

The example frame in every American book is calculated for 50 psf of snow — the western Massachusetts figure.

Here: S = C_b·Ss + Sr, with your town's Ss and Sr (appendix C, 2020 NBC), and C_b = 0.55 — or 0.45 if your roof is 4.3 m wide or less. The 2.0 kPa default underestimates by 30 to 48 % outside Montreal.

Rafters and plates move first. No section taken from an American book carries over unchanged.

And the caveat that goes with it, because it is true: timber framing falls outside the acceptable solutions of part 9 of the Code. An engineer's seal is MANDATORY on the structure. The generator clears the ground — constants pre-filled and cited, three criteria checked — the engineer certifies.

— Biobâtir

Day 8 · Email 5/5

Your frame, exploded, piece by piece

You enter your span, your length, your number of bents, your plate height and your pitch. You get YOUR frame.

What the machine checks before showing it to you, for every joint:
— the tenon enters the mortise, with ⅛ in of clearance at the bottom so it never bottoms out;
— the shoulder bears flat (1 mm of float and it is refused);
— 2 in of relish is left at the end of the mortised piece, or the mortise breaks out and water gets in;
— the mortise does not go past 5/8 of the depth of a bending member;
— two mortises do not overlap in the same piece;
— the peg is drawbored TOWARD the shoulder, by the right amount, and at least half the hole shows;
— and finally, no piece occupies the same wood as another: the volume of every piece is probed after machining, and one single collision refuses the frame.

If a single one of these fails, the frame is not delivered: it is refused, and the reason is written out.

The generator: https://timberframe.app/en/generateur.html

— Biobâtir