Lars Gullbrekken

Moisture conditions in well-insulated wood-frame walls. Simulations, laboratory measurements and field measurements

Abstract Buildings for the future, that is, zero emission buildings and passive houses, will need well-insulated building envelopes, which include increased insulation thicknesses for roof, wall and floor constructions. Increased insulation thicknesses may cause an increase in humidity levels and thereby increased risk of mould growth. There is need for better knowledge about moisture levels in wood constructions of well-insulated buildings, to ensure robust and moisture-safe solutions. Various envelope constructions were simulated using HAM-tools (Heat, Air and Moisture). In addition, a laboratory experiment was performed to investigate the effect of a slower drying out of built-in moisture. Walls with varying insulation thicknesses and with a high degree of built-in moisture were instrumented with moisture sensors, and the drying speed was monitored. A field monitoring of wood moisture levels and temperatures was performed in wall and roof constructions of five passive houses in three different locations representing different climate conditions in Norway. The general conclusion is that the risk for mould growth increases somewhat in well-insulated envelopes compared to more traditional envelopes. However, in most cases this can be counteracted by making the right choices during design and construction.

Hot-Box measurements of highly insulated wall, roof and floor structures

The purpose of this study was to investigate how natural convection in air-permeable glass wool insulation affects the thermal transmittance in walls, roofs and floor structures. The results can be used to evaluate the need for a convection barrier in thick mineral wool layers. Natural convection is affected by several parameters. In this study, the angle of inclination, the heat flow direction and the temperature difference across the test section have been studied. Thermal transmittance and temperature distribution measured using thermocouples placed inside the insulation cavity clearly showed convection in the insulation when the test section was in pitched roof and wall positions. An efficient measure to reduce the natural convection is to divide the insulation layer into two thinner layers using a diffusion open convection barrier. A convection barrier is recommended by the authors both in wall and pitched roof structures if the insulation thickness exceeds 200 mm.

Local loss coefficients inside air cavity of ventilated pitched roofs

Pitched roofs with a ventilated air cavity to avoid snow melt and ensure dry conditions beneath the roofing are a widely used construction in northern parts of Europe and America. The purpose of this study has been to determine pressure losses at the inlet (eaves) and inside the air cavity consisting of friction losses and passing of tile battens. These results are necessary to increase the accuracy of ventilation calculations of pitched roofs. Laboratory measurements, numerical analysis as well as calculations by use of empirical expressions have been used in the study. A large difference in the local loss coefficients depending on the edge design and height of the tile batten was found. The local loss coefficients of the round-edged tile battens were approximately 40% lower than the local loss coefficients of the sharp-edged tile battens. Furthermore, the local loss factor increased by increasing height of the tile batten. The numerical analysis was found to reliably reproduce the results from the measurements.