11.04.2025. The construction of 10 new kilns at IFO’s production site—Interholco’s subsidiary in the North of Congo—has been completed.

Which is the advantage of kiln-dried wood? Christophe Janssen, Chief Operating Officer at Interholco, shares his insights in the interview below.

IHC : Wood drying adds value. Why is drying so important?

Christophe Janssen : Drying is a crucial stage in wood processing. Its primary purpose is to stabilize the shape and size of the wood to a moisture level close to its end-use environment. The drying process enables us to offer lumber that can be processed directly by users in the manufacture of their finished products. Our clients' cash requirements are therefore lower than for undried lumber. Dimensions are guaranteed and our lumber is systematically sorted after drying. Deformed pieces are removed from the batch by our quality control experts, so Interholco supports drying 100%.  With our new kilns, we’re even better equipped to meet the growing demand for dried hardwood.

Our production of Tali decking boards. © Interholco

IHC : Kiln-dried wood has high value. How do you mitigate the risk of losses?

Christophe Janssen : It’s true—if wood is not dried carefully, the resulting degradation can be costly. That’s why we’ve developed a broad range of customized drying programmes tailored to the unique characteristics of African species. Also, for quality reasons and to avoid ‘forcing’ the process, all the material intended for the kilns is first stored in our pre-drying area for several months. This will allow for gentle artificial drying, improving the final quality. Over-drying can create internal and external deformations that can render the goods unfit for end use. Our pre-drying process and post-production quality sorting has enabled IHC to deliver consistent and verified quality for many years.  

Our pre-KD stock. © Interholco

IHC : What does it take to develop an optimal drying programme?

Christophe Janssen : Wood is a living material—unlike plastic or metal. Each piece of wood placed in the kiln has its own unique properties, even within the same species. The kiln manufacturer provides us with standard drying programmes per species, but these need to be adjusted to our specific requirements. To do so, we have invested in research to ensure optimal drying conditions—fine-tuning variables such as air circulation speed, airflow direction, relative humidity, temperature, and wood moisture variation. Based on these parameters, each drying programme is customized for the species, thickness, and final use of the timber.

Here, Tali decking—a premium choice for any terrace exposed to the elements. © Interholco

IHC : What measures have you implemented to guarantee quality output?

Christophe Janssen : Depending on the requirements of the different markets, we adapt our drying processes: between 12 and 14% for the EU, between 8 and 10% for the USA, 15% for decks for better uniformity and stability, etc. Our clients usually expect exact dimensions, so we have to account for the dimensional loss (shrinkage) resulting from the drying process. To compensate, we apply a dimensional allowance during the sawing process. After drying, all wood is sorted again—rigorous quality control ensures that only top-grade KD wood proceeds to the final transformation stage or is declared ready for export. Quality control is non-negotiable.Our new kilns are specifically designed to dry gently, in order to avoid all risk of cracking or deformation. Broadly speaking, pre-drying and drying may take up to 4 to 12 months, depending on the size and type of wood. This is a major financial investment, but it gives our clients peace of mind and the lasting guarantee of our quality.

About Interholco

The valorisation of a natural forest of 1.16 million hectares in the Republic of Congo Brazzaville is our DNA here at INTERHOLCO. As an FSC^® (Forest Stewardship Council^®, FSC^® C022952) and PEFC and PAFC certified producer, INTERHOLCO is a well-established player in the trade of its edged boules, sawn timber, glue laminated scantlings, decking boards and more.

We are a leading provider of high-quality wood products ‘Made in Africa’ holding a verified environmental and health performance statement (FDES requirement in France). Our teams carefully manage the supply chain from forest to customer. Our story is fully illustrated by enabling the people living in Ngombe to access better life conditions. We make it possible to design and build a healthy living environment with bio-based, eco-friendly materials, one of the real solutions for the planet and climate. Follow us on LinkedIn

Communication contact Interholco

Tullia Baldassarri Höger von Högersthal
INTERHOLCO AG, Neuhofstr. 25, 6340 Baar, Switzerland
Tel.: +41 (0)41 767 03 82 
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