How the Timber-Frame Pavilion weathers: a natural-finish record

The Timber-Frame Pavilion was left unpainted and unstained. That makes it a clear way to see how thermally modified wood changes outdoors, and what stays the same.

This is a living record. The photos below show the pavilion as photographed for its case study. We will add follow-up photos from the same positions as the wood ages.

Starting point

Thermal modification darkens the wood all the way through to an even, deep brown. On day one, the ceiling, posts, beams and gable soffits all share that tone.

What will change: color

Unfinished wood exposed to sunlight turns grey. UV light breaks down lignin at the surface, and rain washes it away. Thermally modified wood does the same. Over months in full sun, the brown surface moves toward a soft silver-grey.

The change is only at the surface. Below it, the wood keeps its thermally darkened color.

Two exposures on one structure

The pavilion will not weather evenly, and that is expected:

• Gable soffits and fascia take direct sun and wind-driven rain. They will grey first.
• Vaulted ceiling boards sit under the roof, out of direct sun. They should hold their brown tone much longer.
• Posts will weather most on the faces that get the most sun.

What should not change

Greying changes how the wood looks, not how it performs. Thermal modification reduces the wood's capacity to take on moisture. The result is less swelling, shrinking and cupping through the seasons, and better resistance to decay than the same species untreated. On an open structure like this, that means joints, board gaps and light cut-outs stay tight while the color shifts.

Keeping the original tone

Owners who prefer the brown to the grey have two options:

1. Apply a UV-protective, penetrating oil before the first season, then reapply as the maker recommends. Exposed faces usually need it more often than sheltered ones.
2. Restore later. A light cleaning or sanding removes the grey surface and shows the thermally darkened wood underneath, ready for oil.

Film-forming paints and solid stains are not needed for durability, and they bring the peeling and upkeep this project was built to avoid.

What comes next

We will photograph the soffits, ceiling and posts from the same positions at regular intervals and add each set here. Questions about finishing an exterior project? Talk to an Emberline specialist.