Jelle Langmans

What are the hygrothermal consequences of applying exterior air barriers in timber frame construction in Europe

Moisture-induced damage is one of the major causes of degradations and reduced thermal performance in wood frame buildings. It is therefore crucial to incorporate the hygrothermal assessment of new timber frame building envelopes systems from the early development phase onwards. The article at hand presents the simulation results studying the hygrothermal performance of various timber frame wall configurations with exterior air barrier systems. A parameter analysis explores the impact of different European climates, insulation materials, exterior air barrier materials and verifies in addition to the impact of bad workmanship in the installation of the insulation layer. This study reveals that the application of mineral wool (MW) insulated timber frame walls in combination with exterior air barriers results in increased moisture loads. Moreover, small air gap channels between the MW and the adjacent exterior air barrier significantly increase natural convection and add up to harmful moisture levels. Yet the simulations indicate that the use of blown-in cellulose insulation can avoid these issues. The study further indicates that the technique of exterior air barrier is more suitable for continental climates rather than for moderate sea climates in Europe.

Numerical and experimental investigation of the hygrothermal response of timber frame walls with an exterior air barrier

Laboratory tests and numerical simulations to study the hygrothermal consequences of using an exterior air barrier in light-weight building envelopes are discussed. Full-scale test walls are placed between a vertical hot and coldbox, operating at controlled temperatures, humidity levels and total air pressures. The test walls are exposed to different boundary conditions during five consecutive measuring stages. Each test wall is provided with 18 thermocouples, 15 relative humidity, 3 heat flux and 1 pressure gauge sensor, covering the most important positions of the wall. In this way, the obtained results can be used as detailed validation data for heat, air and moisture (HAM)-models with a strong focus on natural and forced air convection. The main emphasis of this article is the evaluation of a numerical model with the current dataset. The model used is a modified version of DELPHIN 5 including a quasi-steady state airflow model with the ability to capture natural convection.

Durability of self-adhesive tapes for exterior air barrier applications: a laboratory investigation

ABSTRACT In timber frame construction in Europe, air barrier systems are typically realised at the interior side of the building envelope. Yet, in some applications such as renovation projects, it can be easier to provide the air barrier layer at the exterior. An exterior air barrier system, typically board materials in which the joints are sealed with tape, needs to withstand severe outdoor weather conditions and maintain pre-defined air permeability values. The aim of the present article is to investigate the impact of severe climatic conditions on the airtightness of typical taped joints. The airtightness of 32 wood fibre cement board samples has been investigated. Each specimen has a 2 mm wide joint. Two different kinds of commercially available tapes were used to seal these joints. Airtightness of all specimens has been tested before and after accelerated ageing procedures that mimic real exterior climate conditions. Three different ageing protocols were selected: (1) temperature cycles, (2) temperature, rain and frost cycles and (3) UV exposure alternate with high humid conditions. The present paper discusses the durability of the two tapes by comparing the air permeability of the specimens before and after accelerated ageing exposure. The results indicate that for both tapes tested the impact of the three artificial ageing methods on the air permeability is limited (increment less than 2 × 10−5 m3/m/h/Pa).