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Parallam
Nail Laminated Timber (NLT)
OSB
LSL
Stud Frame
Plywood
Parallam
Nail Laminated Timber (NLT)
OSB
LSL
Stud Frame
Plywood
Dowel Laminted TIMBER (DLT)
History
Dowel-laminated timber (DLT) derives from nail laminated timber (NLT), and was originally known as ‘’Brettstapel’’, or more precisely ‘’Dübelholz’’ in German. While NLT, which can be seen in Figure 1 (a), was commonly used in the 1970s as an economical and sustainable alternative to traditional materials by using low grade lumber, it did not allow for efficient cutting due to the presence of nails. In the 1990s, Professor Julius Natterer, an engineer known for his contribution to timber engineering, found a solution to the problem by replacing the nails with wooden dowels. Variations of Natterer’s ‘’Dübelholz’’ followed in the early 2000s, such as using diagonally inserted dowels (Figure 1(c)) to minimize the separation of individual posts due to moisture content variation. This phenomenon of separation may also be resolved by using a lumber configuration similar to cross laminated timber, which involves having dowels inserted through perpendicular layers of lumber as seen in Figure 1 (d). However, the most common configuration nowadays remains Natterer’s original concept as seen in Figure 1 (b).
Manufacture
DLT is typically manufactured using selected softwood lumber that has been air or kiln dried to a moisture content varying between 12 and 15%. The pieces of lumber are aligned with their grain running parallel to each other in the direction of the primary span. Consideration is given to the location of natural defects. Hardwood dowels with a moisture content of around 8% are inserted perpendicular or at an angle to the pre-milled lumber’s grain, which interlocks the pieces together as the dowel expands due to its moisture absorption. The insertion of dowels at an angle to the grain helps decreasing the possible separation between the pieces of lumber due to extreme moisture variations. The milling and dowel-insertion processes are usually automated for a more efficient manufacturing. Beech is often used for the dowels while Spruce-Pine-Fir, Douglas Fir, Hemlock, Sitka Spruce, and Western Red or Yellow Cedar may be used for the softwood lumber. Depending on the manufacturer, the resulting panels vary from 76 to 370 mm in thickness, and can span up to about 18 meters with a 3.75-meter width. When fabricating DLT panels, the pieces of lumber may be assembled to form a flush surface, a staggered profile, or a profile with niches as seen in Figure 2. Once the DLT panels completed, they can efficiently be pre-cut to high tolerances with CNC machines due to their lack of metal fasteners.
Uses
As seen in Figure 3, panels of DLT are mainly used horizontally as roof or floor panels, as well as load-bearing walls. DLT offers many advantages due to its adaptability in shape and size. Indeed, the possible formation of voids or niches on the panel’s surface allows for great architectural flexibility since those openings may accommodate electrical services or acoustic fibre, or they may simply serve as aesthetic features if left exposed. As well, its lack of glue or nail allows for an all-timber product, consequently exposed. As well, its lack of glue or nail allows for an all-timber product, consequently optimizing the product’s sustainability by decreasing its required embodied energy and increasing its recovery efficiency. The all-wood composition of DLT also allows for its natural association with projects using prefabrication.
- D.H.
Dowel-laminated timber (DLT) derives from nail laminated timber (NLT), and was originally known as ‘’Brettstapel’’, or more precisely ‘’Dübelholz’’ in German. While NLT, which can be seen in Figure 1 (a), was commonly used in the 1970s as an economical and sustainable alternative to traditional materials by using low grade lumber, it did not allow for efficient cutting due to the presence of nails. In the 1990s, Professor Julius Natterer, an engineer known for his contribution to timber engineering, found a solution to the problem by replacing the nails with wooden dowels. Variations of Natterer’s ‘’Dübelholz’’ followed in the early 2000s, such as using diagonally inserted dowels (Figure 1(c)) to minimize the separation of individual posts due to moisture content variation. This phenomenon of separation may also be resolved by using a lumber configuration similar to cross laminated timber, which involves having dowels inserted through perpendicular layers of lumber as seen in Figure 1 (d). However, the most common configuration nowadays remains Natterer’s original concept as seen in Figure 1 (b).
Manufacture
DLT is typically manufactured using selected softwood lumber that has been air or kiln dried to a moisture content varying between 12 and 15%. The pieces of lumber are aligned with their grain running parallel to each other in the direction of the primary span. Consideration is given to the location of natural defects. Hardwood dowels with a moisture content of around 8% are inserted perpendicular or at an angle to the pre-milled lumber’s grain, which interlocks the pieces together as the dowel expands due to its moisture absorption. The insertion of dowels at an angle to the grain helps decreasing the possible separation between the pieces of lumber due to extreme moisture variations. The milling and dowel-insertion processes are usually automated for a more efficient manufacturing. Beech is often used for the dowels while Spruce-Pine-Fir, Douglas Fir, Hemlock, Sitka Spruce, and Western Red or Yellow Cedar may be used for the softwood lumber. Depending on the manufacturer, the resulting panels vary from 76 to 370 mm in thickness, and can span up to about 18 meters with a 3.75-meter width. When fabricating DLT panels, the pieces of lumber may be assembled to form a flush surface, a staggered profile, or a profile with niches as seen in Figure 2. Once the DLT panels completed, they can efficiently be pre-cut to high tolerances with CNC machines due to their lack of metal fasteners.
Uses
As seen in Figure 3, panels of DLT are mainly used horizontally as roof or floor panels, as well as load-bearing walls. DLT offers many advantages due to its adaptability in shape and size. Indeed, the possible formation of voids or niches on the panel’s surface allows for great architectural flexibility since those openings may accommodate electrical services or acoustic fibre, or they may simply serve as aesthetic features if left exposed. As well, its lack of glue or nail allows for an all-timber product, consequently exposed. As well, its lack of glue or nail allows for an all-timber product, consequently optimizing the product’s sustainability by decreasing its required embodied energy and increasing its recovery efficiency. The all-wood composition of DLT also allows for its natural association with projects using prefabrication.
- D.H.