We spoke to CEO Filip D’Haeseleer and asked specifically about their approach to wall construction. We’d already asked him about terrace wood and it was clear from that conversation how strongly Denderwood is interested in the origin of the wood. That’s no less the case with wood sorts which they use for wall construction.

Mr D’Haeseleer explains: ‘Our suppliers in Africa, Latin America, and Asia must act as partners since we want them to share our ideas in terms of service, quality, sustainability, and reliability. We only sell wood which is PEFC and FSC approved and we work solely with 100% legally chopped wood. Various things mean that we also check regularly in situ to make sure that everything is being done as prescribed. For instance, next week (editor’s note: this interview was recorded in late April) I’m visiting some of our producers to see with my own eyes how they approach due diligence.’

Volume switches to the wall.
When you hear about tropical wood, you think almost instinctively that this is hard to reconcile with a sustainable approach. The manager of Denderwood does not agree with that. You have to consider all the elements in the chain, and then tropical hardwood scores exceptionally well.

‘Wood is still popular and I’m not surprised. It’s a very easy product, which is currently highly popular for use with walls. Erecting a wooden wall in front of a home is an attractive way to provide insulation with the aesthetic benefit on top.’
‘What’s noticeable is that a large part of the volume of tropical hardwood is now used particularly for walls rather than for terraces. Hardwood is certainly an ecologically responsible choice if you take various factors into account. For instance, you have to know whether or not the wood is chopped in a sustainable manner, and you also need to be aware that unused forests are worthless. There’s been huge progress over the last 30 years. Producers have clearly realised that they have to think of their future. You don’t exhaust a forest, but you perpetuate it!’

When our conversation turns to local coniferous wood, Mr Haeseleer reacts promptly. Not everything that glitters is gold: ‘Coniferous wood has to be treated to withstand the extreme weather conditions in our part of the world and that, too, has consequences. Moreover, tropical wood has other benefits, such as for fire safety regulations. This wood doesn’t need any costly treatment to make it fireproof.’

‘If you look at it aesthetically, private clients soon decide. The charming ageing is certainly a strong argument, especially when clients also hear that there’s no longer any difference in price with coniferous wood, if you want the same quality as with tropical hardwood, with the same durability.’

Thermal ayous and fraké
We would like to know if there have been any interesting developments in terms of the wood and the fitting. Here, Filip D’Haeseleer refers firstly to the emergence of thermal ayous and thermal fraké: ‘These wood sorts have been promoted mainly as a replacement of the now unaffordable WRC, but there’s more than that. The upgrading of wood through thermal treatment plays a big part. Ayous and fraké used to have problems with stains and discolouration, and ayous certainly had lots of problems in that respect, but thermal treatment gives it a uniform shade of brown to make it much more durable. I should also say that coniferous wood is now more durable due to thermal treatment and that this is even being done with less durable hardwood. The treatment of ash is also popular. Another development has been with wall cladding boards. In the past, you only had tongue and groove, with the problematic issue of fitting, but now there are much more possibilities, with or without invisible fastening and with various widths and lengths.’

Our next question is whether wall cladding is most popular with new constructions or renovation?
‘It’s highly popular for renovating old homes because under new rules you can use it for insulation at a reasonable price. Wooden wall cladding is still popular with new homes, but that’s more for the visual aspect, where you break up wall surfaces and create a trendy construction,’ our interviewee explains. ‘At this point I’d like to give an example of the approach to the whole renovation of my own old home. We covered the entire wall in padauk, with 35cm of flake insulation at the rear. That gives you a home which has a double A quality label and consumes no more than 400 euros of electricity on an annual basis. What’s attractive is that you gain space because you insulate on the outside.’

Provide ventilation.
Then we want to talk about the number one problem, namely damp. If any problems arise with a wooden wall, damp is usually a factor. How do you prevent problems?
‘Never forget that a wall with wooden cladding is subject to standards. The most important element is that you facilitate ventilation behind the wall and therefore that you provide ventilation channels at the top and bottom. Work on a double plank system, but take care. For instance, never fit hardwood onto coniferous planks, but use wood of the same quality. It’s not a good idea to save on the base construction if you use hardwood. Always remember that wood is a live material which therefore swells and shrinks. If you use slender nails for nailing, something which is very popular in Belgium, you’ll notice that those same nails get driven out due to the capillary effect. Screws, for instance, are much better for containing the strength of certain wood sorts.’

Finally, we have to consider composite material. Denderwood also sells this material, namely the range which UPM brings onto the market in the Belux.

Filip D’Haeseleer concludes: ‘We’ve sold this range for over a decade, but it’s not really an item for us. Certainly not in Belgium, where it’s less popular than in other European countries.’