H3.2 vs H4 Timber

Put every member on the correct side of the soil line

These are orientation examples. Confirm the exact product against project documents and the producer's intended-use statement.

Why an H4 post does not make the whole assembly durable

A fence can combine H4 posts with H3.2 rails and palings. Durability then depends on water shedding, end-grain treatment, compatible fasteners, concrete or soil detailing, ventilation and maintenance. One higher-treated member does not protect neighbouring timber or hardware.

Likewise, installing an H4 member above ground does not automatically improve a deck. The timber may have a different preservative, moisture condition, surface quality or approval scope. Strength must still be established by grade and design.

The cut end is part of the specification

• Plan lengths to minimise field cuts in critical exposure zones.
• Use the producer-specified supplementary treatment for permitted cuts and drillings.
• Never assume a surface brush treatment recreates full industrial penetration.
• Keep treated sawdust out of gardens and waterways and follow current disposal advice.
• Use fixings compatible with treatment chemistry and site corrosion exposure.

A deck-and-fence order example

For a boundary deck with a new paling fence, separate the schedule into H3.2 decking subframe, the selected decking surface, H4 fence posts, H3.2 rails and H3.2 palings. Add structural grades, sizes, lengths and fixing systems to their own columns. This prevents a quote from silently replacing H4 posts with an H3.2 exterior product or supplying ungraded rails where the design expects a grade.

1. Mark soil contact, splash zones and water traps on the drawing.
2. Assign an exposure requirement from current documents.
3. Select a producer-documented product for that use.
4. Add grade and dimensions independently.
5. Check every proposed substitution against the same matrix.

Detail the transition zone

Many failures develop where an above-ground member meets a ground-contact post: a rail end tight against a post, a deck bearer pocket that traps water, or concrete shaped to hold water against end grain. Assigning H3.2 and H4 correctly does not excuse a wet detail. Provide drainage, air movement and separations required by the design.

Concrete around a fence post should follow the project detail; generic rules about crowning or gravel are not substitutes for a wind and ground design. The important purchasing point is to order enough post length for the documented embedment while keeping the correct top height, rather than shortening embedment to avoid buying the next length.

• Mark finished ground and paving levels before cutting posts.
• Keep soil and mulch away from members specified as above-ground.
• Avoid end-grain ledges that collect runoff.
• Check metal compatibility at the H3.2/H4 junction.

Three substitutions to reject pending review