Stack construction

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  • Usually, the logs are piled with the butt end facing the road, and at right angles with the road. This way, the desired roof profile with the water running off to one side is achieved. Logs should be sorted by length and stacked separately.
  • Cross sections need to be well covered by the irrigation water. A uniform front side of the stack, ideally leaning backwards a bit, and clean removal of the buttresses is required. Never should upper logs protrude further than the ones lower down. This would create a rain protected dry area, where quality will be lost (see Fig. 1).
  • Generally, alternating stacking is not advisable, as water demand is then higher and removal more complicated. Risk of Armillaria infection is higher because the logs are more densely packed.
  • Height of stacks should not exceed 4 metres.
  • Timber should be sorted by length, diameter, tree species, quality, and owner and stacked separately. Stacks should be marked visibly and durably (good are wooden signs placed outside the irrigation zone, or structural separation) (see Fig. 2).
  • Haulers have to be instructed correctly and comprehensively (Control stack construction, give warnings where necessary).


  • Wet conservation can only be successful where strict quality measures are used for classification.
  • Homogenous lengths are important. Protruding upper logs create rain protected areas where quality is lost. After calamities, (softwood) long logs should not exceed the maximum length capacity of regular timber lorries (in Germany 19 metres). This allows for more variability regarding the transport mediums used.
  • Size classes: Timber for wet storage should be divided into two lots according to diameter class, “up to 34 cm” and “35cm and over” (“up to diameter class 3a” and “3b and above” in German classification).
  • On larger sites, especially where timber from several forest owners is stored on the same site, documentation of the whole processes is useful (stack plans showing where the various lots are located, stack books containing information on forest owners, volume of wood, timber quality, time of logging, time of rolling in, start of irrigation,…).

Monitoring timber removal

Documentation of removal of timber from wet storage sites has been neglected frequently in the past. However, real-time data on state of removal is necessary for superordinate controlling to deal successfully with matters of markets and budget. An estimate on the current state of removal can be formed by looking up sales from previous years. A sufficient overview can only be gained by consistent accounting.

Timber quality at the time of rolling in

  • Sufficient sap-wood moisture (min. 100%) is essential for quality preservation. An average relative wood moisture of 120% is recommended. This can only be achieved with green timber (speedy conversion and rolling in).
  • Logs intended for wet storage must therefore not be stored temporarily alongside the forest road. Immediate transport to the wet storage site is necessary.
  • Measuring moisture of timber in life conservation intended for wet storage can help decide whether putting the timber in wet storage does still make sense, or if it needs to be brought to market immediately after primary conversion.
  • Chemically treated timber must not be put in wet storage.
  • Time between primary conversion and rolling in must be kept as short as possible. Irrigation has to start immediately after rolling in.

Documentation of timber qualityt

  • Only best quality timber is suited, low-grade timber must not be put into wet storage.
  • Quality of timber brought to wet storage should be documented. Delivery notes can be issued by responsible on-site staff to raise timber quality state-wide. The position of the storage supervisor should be strengthened. This could go as far as entitling him/her to refuse to accept low quality timber and to issue a protocol including the reasons for non-acceptance and a time-limit for sale/removal.

Risk of deterioration of quality

  • Risk of deterioration of quality by fungi or insect infestation is relatively low, even for perennial storage. Scientific studies showed that essential technological wood properties are still within the usual range for green timber after several years of wet storage.
  • Ideal storage period for softwood is 2-3 years, in exceptional cases up to 4-5 years. Hardwood (beech) should only be stored a couple of months up to one year max.
  • After three years of wet storage, commencing deterioration of quality by Armillaria infestation has to be taken into account (see leaflet 2.6.8 “Wet Storage – Armillaria infestation”).
  • Discolouration of the sap-wood is a specific problem of longer storage over bark. The stains are caused by tannins which enter the wood while dissolved in the irrigation water or during the drying process. These discolourations are usually not very deep, they can be removed from the wood once it is dried (planing, sanding,…) and do not reappear.

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