· by Michael Blair, Nashville's Deck
A pergola is often disappointing in a Middle Tennessee summer, because it was designed for appearance rather than for the sun angle it actually has to block. Two decisions change that.
Orientation matters most
Rafters running north to south block more midday sun; running east to west they block more of the low morning and afternoon sun. In Nashville the hard problem is late afternoon western sun.
For a west-facing patio, orienting slats to intercept that low angle does more than adding more of them.
Slat spacing and depth
Deeper slats set on edge cast far more shade than the same material laid flat, because the sun has to pass through more of the gap. Spacing them at roughly their own depth gives meaningful shade without looking solid.
A conventional pergola with widely spaced flat boards is essentially decorative in July.
- Slats on edge, not flat
- Spacing roughly equal to slat depth
- Orient to the sun angle you actually need blocked
- Consider adjustable louvres for full control
- A solid roof section over the seating area is often the honest answer
Attached or freestanding
An attached pergola needs a ledger with the same flashing discipline as a deck, and it puts a structure on the house that must be permitted and detailed properly.
Freestanding avoids the wall penetration entirely and can be sited where the shade is actually needed, which is often not directly against the house.
Materials in our climate
Cedar looks best and needs finishing. Treated pine is cheaper and can twist as it dries, which shows badly on long rafters. Aluminum and vinyl are maintenance free and read differently.
Whatever the material, posts need proper footings and standoff bases so the end grain is not sitting in water.