Simple about the complex: wooden monolith CLT in questions and answers

We consider new technology in terms of reliability and availability

New construction technologies that are triumphantly marching across Europe and North America, but for some reason do not take root well in Russia, always arouse great interest among developers. Are they as good as they say, what are their essence, advantages and disadvantages? In this collection, we take a detailed look at multilayer adhesive panels, aka CLT.

1. What is the essence of CLT technology?

CLT stands for Cross Laminated Timber (multi-layer adhesive panels). For this building material, the abbreviation PSP (cross-glued plates) or x-lam is also used. The panels consist of several layers (three, five or more) of lamellas, all layers in them are perpendicular to the neighboring ones. After gluing in a press under strong pressure, the panels become the strongest monolith, the bearing capacity of which is not lower than that of reinforced concrete (a 250 mm thick panel can withstand a load of 500 tons). CLT panels do not twist and do not lose their dimensional stability all the years while the house is standing.

2. Where did this technology come from in our country?

Back in 1960, engineers from Germany and Australia independently developed a new building material - panels made of glued boards. For the first time in the history of world housing construction, CLT was used in Switzerland in the 90s of the twentieth century. In 1996 Australian engineers developed modern x-lam panels. The technology is being actively implemented in many countries, the most impressive results have been achieved in Canada: there it was included in the engineering design standards. In Vancouver, the world's most famous CLT home is built: the 18-story Brock Commone on campus. In Russia, the construction of houses from CLT panels has not yet become widespread.

3. What is the difference between the technology of manufacturing CLT panels and the technology by which a plywood board is made?

According to the manufacturing technology, CLT panels are rather in the same row as glued laminated timber and structural beams. They are made not from plywood veneer, like plywood board, but from sawn boards, dried edged wood. Mostly coniferous wood is used in production: pine, larch, fir or spruce, but the use of hard wood is allowed: poplar, etc. Sometimes the panels are made from different types of wood.

4. How are CLT panels made?

First, the primary material is selected and grouped together. For the inner layers of the panels, wood with the best structural properties is taken, for the two outer layers - wood with the best aesthetic properties. From the top and bottom sides of each workpiece, cut off 2.5 mm (for better glue effect), and then 3.8 mm from the side (to obtain a flat surface). Then the wood is cut to the desired length. Through the machine, each workpiece is processed with glue at a constant speed - hermetically sealed, without voids, holes and air gaps. The blanks are connected in panels and fixed in one of two types of pressing. With vacuum pressing, pressure is distributed throughout the structure and can be applied to curved panel shapes. With hydraulic pressing, the pressure can be higher. The next stage is grinding, trimming, or, conversely, the panels are spliced ​​with side grooves into long structures.

6. Why are CLT panels one of the most effective?

In terms of its qualities, CLT is superior to most wood building materials due to the absence of shrinkage, highest strength under horizontal loads, geometry accuracy, resistance to harsh environments and fire. The light weight of CLT structures (six times lighter than those of concrete) makes it possible to do with a light foundation. As a building material, panels compete with both laminated veneer lumber and reinforced concrete.

7. What is the difference between different technologies for the production of CLT panels?

CLT production technologies differ from one manufacturer to another, for example, some foreign manufacturers do not glue the panels, but connect them into a monolith with wooden dowels. Wood blanks (bars and boards) are assembled into one panel, dry beech pins are hammered into the entire thickness of the panel. The dowel is saturated with moisture from the wood, swells and tightly unites all layers into a monolith.

8. Is it possible to build a house entirely from CLT panels?

In all known completed projects of multi-storey buildings from CLT panels, combined frames from CLT panels (2/3) and LVL beams (1/3). And houses up to five floors can be built entirely of CLT, with all floors, joints and enclosing structures.

9. How many days can a CLT house be assembled?

It usually takes two days to assemble a two-story "box" at home from ready-made modules made from CLT. Immediately after that, you can start finishing. It takes 2-3 months to build a turnkey house. The service life of such a house is about 120 years.

10. Is it possible to spoil the house during assembly?

This is an almost impossible task. Even at the factory, modules-parts of the house are made from finished panels, in which they cut openings for doors and windows and make channels and holes for laying communications. All elements are precisely matched to each other, numbered, they are brought to the customer's site according to the installation plan. The assemblers (a small but skilled team is needed) simply put the parts in place, referring to the drawing. Of all the variety of construction equipment, only a small crane and light electrical appliances are used.

11. What are the disadvantages of CLT?

The biggest disadvantage of this technology and this material is the high cost. CLT is much more expensive than laminated veneer lumber and analogues. Experts consider such a comparison to be incorrect, since CLT successfully replaces reinforced concrete, metal structures, and even brick, and the comparison with CLT brick wins in this respect. So, in researchdedicated to the prospects of CLT-panels on the Russian market, Lesprom magazine for 2018 provides the following figures: the retail price of a finished square meter of CLT housing starts at 35 thousand rubles. rubles, and in brick housing construction the average price of 1 m² is 43 thousand. rubles.

The study also shows the average retail prices for CLT panels in comparison with prices for different types of timber in July 2018, (RUB / m³): seven-layer CLT - 44,000, five-layer - 41,000, three-layer - 36,000, glued profiled timber - 24,000, glued flat - 16,000, planed timber - 10,000, sawn timber, edged, simple - 7000.

As you can see, the high cost remains a high cost, and in a number of our regions it is necessary to add additional costs for insulation of plates. The second significant drawback is the use of an adhesive base in the production of panels. Although the formaldehyde content in it does not exceed the natural background, questions about the environmental safety of the material remain. Also, some unscrupulous manufacturers can place low quality boards inside the slab. And there is information that the lamellas can be deformed during sudden temperature changes.

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On the topic of wooden housing construction read about the features of the breeds. Look, how a modern chalet was made from an old log house. In the video - about solid wall panels.