Thermal beam: effective know-how or useless material

Recommendation points

• Why thermobeam?
• Are there any disadvantages?
• Features of the construction process

From the review you can learn more about such material as thermobeam, its properties and possibilities of application in construction. The periodic appearance of new building materials on the market is due to attempts to neutralize the negative properties of existing and tested.

Why thermobeam?

The disadvantages of solid wood and even glued beams are obvious to those developers who prefer wooden houses. Low heat engineering properties of wood and its high cost force to look for alternative solutions, which in some cases are expressed in the use of building materials with a composite structure. The manufacturers of thermo-beams also followed this path, gluing a core made of expanded polystyrene between two wooden lamellas.

One problem was solved in this way: the wood content in the finished product was approximately halved, respectively, the cost of the material decreased quite noticeably. If you compare the cost per cubic meter of first grade lumber and quality XPS (or even PUR), the difference will be very clear. The total cost of buildings made of solid and composite timber reaches 1.5 times. Also, one cannot argue with the fact that the thermal conductivity of the material is several times lower due to thermal break. By a similar principle, the correct reinforced concrete lintels are arranged over the openings, which, without a separator, remain pronounced bridges of cold.

Equally important, when using a thermobeam, the restriction on the thickness of the walls of a wooden house ceases to apply. If in the case of glued laminated timber it rarely exceeds 150 mm, then the composite material can have a cross section of 300 mm and more, while the difference in cost becomes even more significant.

An interesting fact is that houses made of thermo-timber do not require exposure to atmospheric conditions for a long time. It is not entirely clear what exactly contributes to minimizing shrinkage: a decrease in the proportion of sawn timber in the enclosing structures or the absence of a direct connection between the outer and inner sides, operating under various conditions. However, the result is obvious: even with instant settlement in the built house, there is no discrepancy between the joints between the crowns and at the intersections..

Taking into account the above, a house made of thermo-beam can be considered as an analogue of a building made of self-supporting insulated wire panels with the difference that there is no need for costly internal and external finishing, the wood content in the enclosing structures is higher, the release of volatile compounds from the adhesive composition into the atmosphere is guaranteed.

Are there any disadvantages?

In short, there are many of them, but some can be leveled by special measures, while some are characteristic only of low-quality timber. But first things first:

1. High flammability of the heat-insulating core. Manufacturers supplying to the market a thermo-beam filled with polyisocyanurate (PIR) – the only material that is capable of having a flammability class G1 and a low smoke-generating ability – are a rare exception. Note that we are talking about the material in its original form, because foamed polyurethane can also have similar properties in the presence of special additives. However, what are the characteristics of the filler in a particular thermo-beam – it is better to check independently experimentally.
2. Foamed filler is not plastic, while wooden lamellas are constantly in motion and change shape with fluctuations in humidity and temperature. As a result, cracks may appear in the core, which in itself is not so scary, as well as delamination of wood, which will become a very serious building defect. Technologically, such a drawback can be eliminated by using connections between the lamellas or a selection of T-shaped grooves on the inner side of the lamella, which do not allow the product to lose its structural integrity..
3. The strength characteristics of the composite timber are far from those of solid or glued materials. In the case of a log house, this does not play a decisive role, because the walls are subjected to compression loads strictly along the vertical axis. Problems arise in the event of eccentricity of loads, which may be the result of a design error, a change in geomorphology, or the impact on the construction of various cataclysms.
4. There are difficulties with the correct execution of the junctions. In the edges – with the attachment of the window, at the ends of the overhangs – with the closure of the bare insulation. It cannot be said that these problems are insoluble in principle, however, the adoption of additional measures requires close attention during the development of the project, as well as high qualifications and conscientiousness of the working personnel..
5. Lamellas of a composite beam are glued together from small fragments with milling of the joint with a comb. On the one hand, this minimizes twisting and warping of the wood, but negatively affects the aesthetic qualities. The direction of milling plays a role – with a longitudinal comb it will not be visible on the front side, only a straight joint in texture, which is considered the best option.
6. In the process of curing the foam core filler, shrinkage often occurs, during which a cavity is formed in the central part of the contact surfaces. This does not apply to products that are formed by gluing under a press, having shaped grooves on the back surface of the lamellas or with a proven production technology that guarantees no shrinkage during curing.

Features of the construction process

Since the form factor of a thermo-beam is standard, in general, the construction technology from it is inherited from the rules for using a profile beam and follows the principle of assembling a ready-made house kit manufactured at a factory. There is, however, some application specificity associated with structural heterogeneity and material behavior under the influence of external influences. In particular, the construction of a log house from a thermobeam without overhanging is categorically unacceptable: such a structure does not have structural strength and folds when the slightest eccentricity occurs.

It will not be possible to build a whole house from thermobeam alone: ​​individual structural elements must be made of solid or glued sawn timber. First of all, this applies to the cap, which, ideally, should be presented not just solid, but stabilized wood. Such a crown not only acts as a barrier in the path of migrating moisture, but also acts as a kind of plug, protecting the insulating core of the wall from atmospheric influences.

The crowns, on which the slabs and Mauerlat are supported, must also be solid, path and without special processing. This is necessary to avoid eccentricity of the load and distribute it evenly over both rows of lamellas. In this case, one-piece crowns turn into solid temperature bridges, which means that they should, according to the project, be placed entirely in the cross-sectional area of ​​the inner thermal protection belt. For the flange, this is realized by raising the insulated floor, for supporting crowns – using truss structures, due to which the thickness of the frame is increased below the bearing plane in order to place reinforced thermal protection in the ceiling cavity.

Elements of load-bearing structures – floor frames, rafters, rigid ties should be made of premium wood, free from defects. Otherwise, when calculating loads and limit states, coefficients should be used to compensate for the presence of defects in the wood..

Since the use of standard dowels for fastening crowns is impossible, composite plastic reinforcement is used in the construction of thermobeam. Its diameter should not exceed 12 mm, so that there is enough body in the 40 mm lamella. The fittings are installed on both external and internal lamellas in 1 meter increments, staggered. Ideally, the reinforcement should stitch the entire log house, but in practice this can only be achieved by performing precise additives on the factory equipment, therefore, stitching at least 3-4 crowns is considered the norm.

Special attention should be paid to the open ends of the timber. On the cut, the core should be cut to a depth of 20–25 mm and plugs should be inserted. If the goal is to preserve the authentic look of the log house, the corks are made from circular cuts, otherwise a carefully fitted board can be used. Fastening is recommended with pins or self-tapping screws, in the latter case, the fastener caps can be hidden by corner overlays.

When installing a window in the openings, a similar technique is used, however, instead of cutting out the insulation throughout the entire thickness, only a groove up to 60 mm wide is selected, which is subsequently fixed with through pins. This is necessary in order to prevent the formation of a continuous cold bridge and to isolate the thermal insulation of the window block from the structural elements of the building..

The thermobeam does not require time for shrinkage and shrinkage, and therefore it is better if the protective and decorative processing of the wood is performed immediately after the assembly of the frame. You cannot save on paints and varnishes: the higher the quality of protection, the lower the risk of even minimal shrinkage. From the outside, it is recommended to use a glazing antiseptic, which gives the wood additional hydrophobicity, a polyurethane varnish coating and a thin caulk using the “warm seam” technology. On the inside, it is better to use water-soluble stains, and to hide traces of gluing the lamellas – with compositions with a deep degree of toning.