Smart and material-efficient solution aligns lintel and floor into the same level

Contractors aim for maximum labour and material-efficiency. Against the backdrop of increasing resource efficiency, the latter also plays an important role in timber construction. German house builder Holzhaus Fabrik shows how to implement the window lintel detail in order to meet these complex challenges.

The dimensions of the lintel in timber frame construction are influenced by three main factors: the structural design and the floor construction determine the height, while the wall depth is decisive for the width. This usually results in large and heavy components. The latter prove to be unwieldy in the processing procedure. In addition, a lot of material is used. At the same time, there is no space for a roller shutter box in the solid component - especially when floor-to-ceiling windows are required, this type of construction reaches its limits. The large amount of vertical timber also carries an increased risk of settlement in the floor. This settlement behaviour can lead to problems - especially in multi-storey buildings. Among other things, these are typical challenges for Holzhaus Fabrik. The young company with 42 employees specialises in multi-storey residential buildings, public buildings and schools in a modern way of construction. 

The lintel made of Kerto LVL laminated veneer lumber convinces as an L-detail with high statics and quality.

Photo: Holzhaus Fabrik

Architectural requirements 

"Floor-to-ceiling windows are in demand both in multi-storey residential buildings and in single-family homes. For example, with a room height of 2.5 meters, a window height of 2.4 meters must often be achieved - and thus a lintel height of only a 100 mm must be implemented. At the same time, the lintel must be flush with the outside façade and thermal bridges should be avoided. We also need adequate shading options," explains Heiko Dietzenbach, founder and managing director of Holzhaus Fabrik. Conventionally solved, this means that either the wall thickness would have to be increased, the room height would have to be adjusted or the window height would have to be reduced. However, a greater wall thickness leads to increased material consumption and at the same time reduces the available space. If the room height is increased, it does not only increase cost, but in extreme cases can mean the loss of a storey - thus less living space can be realised if the eaves or ridge height is fixed. Visual losses are also a consequence. With the usual large building component cross-sections, it is therefore not possible to fulfill all of the diverse requirements.  

High-performance laminated veneer lumber 

Holzhaus Fabrik replaces the solid cross-section of the lintel with a slender, high-performance material: Kerto LVL. This resource efficient product consists of three-millimeter thick softwood veneers which are bonded together to form a continuous billet. The billet is then cut to length and sawn into LVL beams or panels.  

For the window lintel detail, Holzhaus Fabrik uses beams made of Kerto LVL Q-panel. Due to the individual veneer layers, which are arranged lengthwise and crosswise, the material withstands high biaxial loads and at the same time enables slender construction elements.  It ensures excellent dimensional stability and enhances the transverse strength and stiffness of the panel. 

The laminated veneer lumber is installed vertically with a small, slender cross-section and thus has a high structural load-bearing capacity. Window widths of up to four metres can be realised without any problems.

Photo: Holzhaus Fabrik

 Vertical with slim cross-section 

"The laminated veneer lumber is installed vertically with a small, slender cross-section. At the same time, it has a high structural load-bearing capacity which allows window widths of up to four meters.  We form the lintel into an L-shape. A support strip is screwed onto the edge beams," Dietzenbach explains. Slabs with a maximum span of six metres lie on the L-detail. The load-bearing support is created with posts. Thus the load does not go over the small support area of the L-detail. The shear strength provided by the material enables the floor slab to be connected to the lower edge of the lintel component. On the façade side, the vertically installed narrow cross-section creates space for roller shutter and venetian blind solutions.  

Standardised production 

From Dietzenbach's point of view, Kerto LVL impresses also in processing in the factory: "The high dimensional accuracy is an important factor for us, as we run a fully automated production. With its material properties, Kerto LVL also enables a high degree of standardisation for different requirements. The material is very straight and has no warping. Reworking is therefore not necessary, so production speed can be maximised. The material can also be used particularly well when we have very high requirements in the flushness of wall ends - i.e. for window and door jambs." The material itself can either be screwed, nailed or glued. Processing can be done with standard tools. Since Holzhaus Fabrik relies on a standard detail for all floor types - and also chooses this for both external venetian blind and roller shutter solutions - the high degree of repetition also reduces the susceptibility to errors. "As soon as we ourselves are commissioned with the structural engineering or at least have a say in this area, we always recommend Kerto LVL for the window lintel and rely on our standardised detail," Dietzenbach explains.  

Bottom view of the lintel: Lintel and ceiling are brought into same level with the use of Kerto LVL in L-detail.
Photo: Holzhaus Fabrik

Reduction of material, costs and loads 

Because Kerto LVL is very strong and efficient, it offers reduced material consumption. Holzhaus Fabrik has calculated that a low lintel made with Kerto LVL can bring cost savings of up to 20 percent compared to traditional methods. Due to the optimised use of materials and narrower wall thicknesses, the components have a lower overall weight and reduced dimensions. This means that the quantity of walls per transporter can be increased and at the same time the capacity and footprint of the crane required on the construction site can be reduced. This also has a positive impact on costs.  

High quality standard 

Last but not least, Kerto LVL in window lintels also impresses with its quality. The material does not shrink, does not settle and is dry. Since less vertical wood is used, there is generally less settlement. The latter can also be a visual problem if it causes cracks. This is because the veneer layer structure reduces the amount of vertical timber. The creation of the airtight layer is also simplified when the lintel is shaped to an L-detail on the construction site. Traditionally, the airtight membrane is glued on, the floor system is laid on top and the membrane is looped back - a procedure that is particularly complicated for the details in the corners. "The vertical installation of the narrow cross-section with Kerto LVL enables a simple and uncomplicated configuration of the airtight building envelope across the storey joint. The time-consuming looping in is no longer necessary," explains Dietzenbach. The vapour barrier is located in the L-detail instead of far outside, so the risk of interstitial condensation is reduced. Less foil is needed - and the quality is improved at the same time. 

Kerto LVL makes the lintel detail more efficient and safer for the installer. At the same time, it is a contemporary solution that meets the design and functional demands of architects and builders alike.  

With floor-to-ceiling windows, the small difference between room height and window height offers little space for the lintel. With a window lintel of ten centimetres, forming the lintel with Kerto LVL saves material and space.