Requirements concerning Duobalken® and Triobalken®
The specification of quality criteria which exceed those required by building regulations were first defined in 2003 in an agreement on Duobalken® and Triobalken®. To minimize cracking and deformation from shrinkage caused by drying, specifications for moisture content and the type of cutting were set down. Other criteria are concerned mainly with the dimensional stability and the appearance of the timber.
The table below comes from the revised 
Agreement on Duobalken® and Triobalken® from 2015. It can also be applied to the laminated beams according to EN 15497, until revision of the agreement.
Requirements to be met by Duobalken® and Triobalken® in accordance with the National technical approval of the German building authorities as assessed by the Deutsche Institut für Bautechnik Z-9.1-440 and the agreement on Duobalken® and Triobalken®
Criterion | Requirements | Notes | |
|---|---|---|---|
Exposed areas (Si) | Non-exposed areas(NSi) | ||
Technical Approval | Z 9.1-440 |
| |
Grading class | S10 TS or | The characteristic strength, stiffness and density values of laminations with the lowest strength class in the cross-section, apart from C24, where E0,mean is E0,mean=11.600 N/mm² | |
Moisture content | max. 15% | Prerequisite for bonding | |
Dimensional stability | DIN EN 336, Dimensional stability class 2 | The dimensional stability for the longitudinal dimensions must be agreed between the customer and supplier. | |
Twisting | ≤ 4 mm/2 m | For comparison: | |
Longitudinal warping | ≤ 4 mm/2 m | In comparison: | |
Surface condition | Planed and chamfered | Leveled and chamfered | The "right" sides (near-core sides) must face outwards |
Finishing of the ends | Trimmed perpendicular |
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