Eight hundred years ago, cathedral builders worked out that a pointed arch could carry more, span further and stand taller than a round one. We build the same shape out of local hemlock and polycarbonate — and use it to wrap warm, sunlit space around the houses that are already here.
A Roman arch is a half circle: the span fixes the height, and the whole structure shoves outward at the bottom. The gothic builders broke that link. By meeting two steep curves at a point, they could choose the height independently of the span, aim the load more steeply into the ground, and open the walls up to glass.
What they couldn't do was carry tension. Stone only pushes — so every one of those cathedrals needed flying buttresses standing outside to catch the sideways thrust. Laminated wood pushes and pulls. That single difference is what lets the Sophab Arch trade a stone buttress for one tie beam, and a footing for a screw pile.
Our rib is an arc of an ellipse, drawn so that it leaves the ground dead vertical and arrives at the house raked over at about 24°. Used singly it's a lean-to on your wall. Mirror it — or stand two back to back — and the pointed arch appears, with a 133° point at the crown.
Drawn from the as-built profile of the first full-sized arch — 17'-4¾" of run, 16'-7" of rise, 25'-3" of arc per rib.
Because the rib is vertical where it meets the ground, the force arriving at the foundation points almost straight down. Screw piles are very strong pushed along their length and weak pushed sideways — so the geometry is drawn to give them the load they're good at.
What sideways push is left shows up at the top, where the arch rakes into the house. A two-ply 2×10 tie beam bolted to the existing wall closes that loop. The wall you already own does the job a flying buttress used to.
A semicircle is flat on top, so snow sits on it — and lopsided snow load is the case that governs curved roofs. The 133° point means there is no flat spot at the crown for it to build up on.
The rib turns tightest low down — about a 10 ft radius through the shoulder — then opens out to nearly straight near the top. Stiffness is concentrated where the loads pile up, and the upper reach stays open for headroom and glazing.
A beam resists load by bending across it; an arch pushes it along itself in compression. That's the whole trick — it's why a 6" × 10" stick of hemlock can carry 25 feet of arc, which no straight beam of that size would manage.
Each rib is two 3" laminated chords held 4" apart by blocks every 2 feet — 10" deep overall, with 4" of it air. Stiffness comes from depth, not mass: it keeps 94% of a solid 6" × 10"'s bending stiffness while using 60% of the wood.
Here in Fredericton the midday sun sits about 21° above the horizon at the winter solstice and 67° at the summer one. A flat roof is built for the wrong one of those, and a vertical window for the other. The arch is both.
Low down, where the shell is steep, winter sun lands almost square on the glazing — the full strength of the beam gets in. Up at the crown, where the shell lies over, that same winter sun only grazes it, but high summer sun hits it straight on and stops there instead of down at floor level. The shape does the seasonal switching, with nothing to adjust and nothing to power.
Ungraded hemlock from a sawmill about half an hour from the build. Sawn, not manufactured; the embodied carbon is a rounding error next to steel or concrete.
Each chord is four ¾" boards bent around a form, glued and crown-stapled. No steam box, no CNC, no factory press — the tightest curve in the whole arch is still 140 times the thickness of a single board.
Screw piles go in with a machine in a morning and take load immediately. The ribs go up by hand, one at a time, by a small crew. Nothing needs to cure and nothing needs to be lifted in one piece.
Multiwall polycarbonate cold-bends to a radius far tighter than the arch ever asks for, so the skin simply springs onto the ribs. No curved glass, no bespoke units, no heat forming.
The arch is parametric: the same ellipse is refitted to your run and rise, and the drawing set is adapted to match — so your engineer reviews a worked design instead of deriving one from scratch.
Bolted timber, screw piles and polycarbonate sheet, designed to last in the Maritime climate. And if it ever does come down, almost all of it can be unbolted and used again or recycled rather than landfilled.
The numbers on this page aren't illustrative — they're measured off the as-built drawings for the first full-sized arch, the one in the photographs.
| Item | As built |
|---|---|
| Arch run × rise (inner face) | 17'-4¾" × 16'-7" |
| Arc length per rib | 25'-3" |
| Tangent at the spring / at the top | 89° (vertical) / 24° |
| Rib section | 6" breadth × 10" radial depth, spaced built-up "ladder" arch |
| Chords | 2 × 3", each four ¾" hemlock laminations, 4" clear gap |
| Spacer blocking | 4" × 6" × 6" at 24" o.c. along the arch |
| Adhesive / fastening | PL Premium + galvanized crown staples at 6" o.c. |
| Ribs | 13 at 49" o.c., 49'-0" overall |
| Purlins | 2×4 rough-cut at 24" o.c. along the arc |
| Base beam / tie beam | 3-ply 2×10 on piles / 2-ply 2×10 to the existing wall |
| Foundation | 10 screw piles, 11" helix, 10'-0" minimum embedment |
| Gravel pad to underside of soffit | 19'-6" |
| Timber | Ungraded hemlock, locally milled |
Rev5 as-built geometry, measured off the structural drawings for the first full-sized arch. Every Sophab is adapted from this set to your own building's dimensions, and reviewed and sealed by your engineer of record.