Exterior wood exchanges moisture with its surroundings and can change dimensions. Treat the intended gap as an installation decision tied to the actual product and conditions. Do not assume that a fixed calendar acclimation period or a gap copied from another project fits every fence.
Understand the planning consequence
Oregon State University Extension explains that wood shrinks and swells as moisture changes. For a fence owner, the practical consequence is that the visible spacing can change after installation. A layout mockup records an appearance at one moment. Discuss the expected behavior with the supplier and installer before choosing a very tight pattern. Keep the discussion specific to the supplied boards rather than treating all hardwoods as dimensionally identical.
Record the supplied condition
Ask how the material should be stored and prepared at the site, and who is responsible for checking it before fitting. Follow the relevant product instructions for moisture assessment and preparation. Note delivery and installation dates, exposure and any unusual site conditions in the project record. Protect the identity of different material batches during staging so pieces with different histories are not casually mixed into a tightly coordinated visual pattern.
Detail for inspection
Provide a practical way to inspect both faces and keep vegetation or debris from hiding recurring wet areas. The American Wood Council's exterior exposure guidance reinforces that moisture conditions matter, although its structural design factors are outside this infill guide. If boards begin contacting one another, distorting or repeatedly staining, have the assembly reviewed rather than forcing the original appearance with improvised fixes. Keep photographs taken from the same position over time; they make gradual changes easier to distinguish from ordinary variation.
Evidence & scope
General reminder that exterior exposure matters; deck structural factors are not fence specifications. Search excerpt verified; direct fetch returned 403.
General wood moisture behavior only; no species-specific movement allowance.
Original planning guidance. References support their stated technical scope; examples and workflows do not establish product approval.