Pallet lumber that has been both kiln-dried for moisture control and heat-treated for ISPM-15 phytosanitary compliance.
Detailed Definition
KD-HT describes lumber or pallets that have been kiln dried to a target moisture content and also heat treated to the ISPM 15 schedule. The two are separate requirements: kiln drying lowers moisture to reduce shrinkage, mold and stain, while heat treatment brings the wood core to at least 56 C for 30 continuous minutes to kill pests. One kiln run can achieve both if the schedule is designed for it. For softwood dimension lumber, KD commonly means 19 percent moisture content or less.
Reading KD and HT on lumber and pallets
The letters KD and HT often appear on lumber grade stamps from agencies accredited by the American Lumber Standard Committee. A grade stamp on boards is not the same as the ISPM 15 mark on finished packaging. If an assembled pallet is going for export, it needs the full IPPC mark applied under the national program, even if every board was stamped KD-HT. Ask the supplier which mark appears on the finished unit and whether moisture was measured after drying.
When to specify both treatments
Kiln drying is worth specifying when pallets will carry food, cold-chain or moisture-sensitive goods, or will sit in closed containers where condensation and mold are a risk. Heat treatment is required for most export shipments of wood packaging. Exporters of food or moisture-sensitive goods may therefore specify both on the same order.
- State the maximum moisture content and how it is measured, for example with a calibrated meter.
- State that exported pallets must carry the ISPM 15 mark with the HT code.
- Ask how long pallets sit in the yard after drying, since wood regains moisture in wet storage.
- Confirm whether drying applies to all components, including blocks or stringers.
Related Glossary Terms
Frequently Asked Questions
Is a heat-treated pallet also kiln dried?
Not automatically. Heat treatment for ISPM 15 only has to hold the core at 56 C for 30 continuous minutes, which kills pests but may remove relatively little moisture from green lumber. Kiln drying runs longer and is controlled to reach a target moisture content. If you need both, ask for KD-HT and state the moisture limit, rather than assuming the HT mark means the wood is dry.
Can kiln-dried lumber regain moisture?
Yes. Wood absorbs and releases moisture until it balances with the surrounding air, so kiln-dried lumber or pallets stored outdoors in rain or high humidity will pick moisture back up. Covered, ventilated storage helps keep moisture content near the dried level. If moisture is critical, check it at receiving with a calibrated meter rather than relying only on the supplier's drying records.