Timber Storage – Dry Storage
Storage under drying conditions was not intended for
storing windblown timber. It was rather developed for pre-drying of roundwood.
Due to the risks and costs of this storage method, it can not be recommended as
a standard conservation procedure following calamities, especially for those without
sufficient experience and knowledge of local conditions.
The aim is to dehumidify the timber to below fibre
saturation point (approx. 30% timber moisture) as quickly as possible. The
relatively dry logs then do not provide suitable living conditions for insects
and wood-decaying fungi (which can cause e.g. red stripes and blue stains).
Dropping the moisture under fibre saturation point can
lead to crack formation in roundwood. These cracks can limit further use and
are entry points for fungi. Such entry points can also be caused through
damaging wood while debarking.
- Technically simple
- Simple forwarders
with a crane can be used to build the stacks
- No investment costs
- No license/permit
- Ideal when customers
demand pre-dried timber
- Success of storage
depends on climatic conditions and can not be actively influenced.
- If the timber dries
too slowly, damage by fungi can occur. If it dries too quickly, crack formation
and discolourations can result.
Evaluation and recommendation
The success of this storage method is highly dependent
on site conditions and is influenced by changes in weather. The drying process
can not be directly controlled (or only with difficulty, as experienced after "Vivian" and "Wiebke" 1990 showed). In Baden-Wuerttemberg, this method was not
favoured after "Lothar" and was only used on a small scale.
The method can not be recommended as standard practice
after calamities. Pre-dried logs should only be allocated where the customer
explicitly demands them. Compliance with the preconditions is compulsory, but
even where all preconditions are met, development of timber quality can not be
controlled. Experience from Baden-Wuerttemberg shows that there is no guaranty
whatsoever for the success of this storage method.
- Timber quality
- Only healthy,
sparingly limbed, debarked, usually winter cut and larger dimensioned,
homogenous conifer logs (where possible diameter class 3 or above) may be used.
- Time scope
- The time span
between processing and debarking may not exceed three weeks; the logs should be
in storage by March/April, depending on altitude (following winter storms).
- The logs have to be
debarked as gently as possible, as damage to the stem may lead to fungus
infection. The method can not be recommended for storing summer wood due to the
higher risk of fungal infection.
- Careful stacking, strong cross
logs, large ground clearance, sufficient intermediate layers (25 – 30 cm),
usually 2 to 5 layers, long side facing windward side.
- Storage location
- Exposed to wind,
constantly ventilated, dry, warm, not shady. The logs may only be exposed to
extreme solar radiation if storage duration is kept short.
ventilation underneath the roof is needed. The roofing should extend over on
the sides. Roofing is very expensive; the need has to be examined carefully.
Drying and ventilation of the pile can be hindered near the roof if the roofing
is mounted improperly.
Cross pile without roofing....
...and with roofing (maximum storage period with roofing one year), drawings: B. Textor, Forest Research Institute Baden-Wuerttemberg, Department for Forest Utilisation.
The costs of the method amount to approx. 7,- to 13,- €/cubic
metre (incl. debarking and transport). Extension of the storage period does not
have direct effects on costs.
Roofed storage/medium-term: 1 year
Storage without roofing/short-term: three to maximum
12 (- 24) months
Needs to be dried and put into storage within three months, but red stripes and blueness possible
12 (- 24 months)
Risk of blueness
Drying of logs in roofed cross stacks, period of storage >5 months
- Only prime cut logs;
- Preferably allow one
to two weeks after debarking (pre-drying) ;
- Choose a site with
firm, supporting ground, preferably free of vegetation;
- The site may be
exposed to direct sunlight, the roofing regulates the microclimate within the
- Use strengthened
tarps with eyelets all around. It’s recommended to use two tarps (e.g. 8mx10m
or 8mx12m each), as these sizes are often available ready-made (e.g. from
cooperative agricultural suppliers, sailing supplies or outdoor shops; prices
start at approx. 0,8 €/m²); silage film can not hold the tension continually
and is therefore not recommended;
- Prepare big timber
wedges with a band-saw (approx. 25 per stack) and pre-drill them for long
Fig. 1: Securing logs with timber wedges.
- Sufficient ground
clearance by using large logs as under layer;
- Further stacking
(2-4 layers) is best done in teams of two people; the cross logs (where
appropriate top logs) can then be placed without shifting the crane truck;
- Only place wedges
during stacking if logs seem to sit unstably, there is usually enough time for
securing the stack with wedges after it is finished; wedges must be placed in
any case to support the topmost, widest layer, on which the gable will be piled
up; (Fig. 1);
- Logs damaged by
debarking should be placed so that the damages face the inside of the stack;
- A protruding top
layer is essential, otherwise the outside logs are at risk of permanent
dampness (Fig. 2 & 3);
- Approved are stack
sizes up to 150 cubic metres;
- Construction takes
approx. 2.5 hours (not counting transport).
- Roofing does not
have to happen at once, but the timber should be protected from precipitation
as quickly as possible;
- Start with one tarp,
pull a bit over the top and fix along one side (nails through eyelets);
- Pull tarp over the
stack, tighten, fold excess tarp back and put underneath the first tarp layer;
- Use pieces of lath
wood to nail the tightened tarp to the other side; proceed in the same way with
the second tarp;
- To secure the
overlapping tarp, thread a safety rope (PE, approx. 6mm Ø,
approx. -,30 € per running metre) through the eyelets of the top tarp
and tie down to the stack;
- Roofing takes
approx. 1.5 hours per stack;
- The roofing is
principally maintenance-free (if applied properly).
Fig. 2: Wrong! Top layer not protruding.
Fig. 3: Right.
- Schumacher, P.; Makas, M.; Wegener, G.; Eisenbarth, E.; Edelmann, P.; Bücking, M. (1998): Vorgetrocknetes Fichtenstammholz hoher Qualität. Holzzentralblatt Nr. 140, S. 2110 - 2111.