Moisture Safety in Cold Attics with Thick Thermal Insulation

Hygrothermal assessment of north facing, cold attic spaces under the eaves with varying single sided passive ventilation strategies and infiltration scenarios, in a cool, temperate climate

“…In the summer periods the attic spaces were almost identical. These findings correlate with Harderup & Arfvidsson (2013), who during the cold periods observed the highest temperatures in the externally insulating attics, compared to the uninsulated; also, a small increase in the moisture levels was observed. Finally, our measurements thus seem to indicate that the exterior insulation has both positive and negative effects on the moisture balance in this attic space with the temperature increase in the roofing underlay being good while the increase in the humidity of air by volume in the attic space is not.…”

“…Polds simulations also suggested that SSV increase moisture levels in attic spaces just to a smaller extent. Findings concerning lowered moisture levels due to reduced attic ventilation for attics with diffusion-open roofing underlay in cool temperature climate, correlate with the experimental studies by Harderup & Arfvidsson (2013) and Ojanen (2001), as well as the simulation results by Essah et al (2009). Furthermore, as it was the case for these attic spaces, Harderup & Arfvidsson also observed relative humidity favorable for mould growth during the cold periods.…”

“…Recommendations regarding design of cold attics in cold, temperate climates are to ventilate moisture away using outdoor air, and to ensure air-and vapour tightness towards the conditioned spaces. Previous studies by the Technical University of Denmark (DTU) (Bjarløv et al, 2016) and other studies (Fugler, 1999;Harderup & Arfvidsson, 2013;Roppel & Lawton, 2014) do however indicate that moisture induced damages can be found in attics even when constructed in compliance with local best practice recommendations. Some studies (Essah et al, 2009;Harderup & Arfvidsson, 2013;Ojanen, 2001;Uvsløkk, 2005) have investigated the use of diffusion-open roofing underlay as an alternative to passive ventilation, indicating a lowering of the diffusion resistance may reduce moisture levels in the attic space.…”

“…Previous studies by the Technical University of Denmark (DTU) (Bjarløv et al, 2016) and other studies (Fugler, 1999;Harderup & Arfvidsson, 2013;Roppel & Lawton, 2014) do however indicate that moisture induced damages can be found in attics even when constructed in compliance with local best practice recommendations. Some studies (Essah et al, 2009;Harderup & Arfvidsson, 2013;Ojanen, 2001;Uvsløkk, 2005) have investigated the use of diffusion-open roofing underlay as an alternative to passive ventilation, indicating a lowering of the diffusion resistance may reduce moisture levels in the attic space. Single-sided passive ventilation with one or two ventilation valves have previously been investigated by DTU (Bjarløv et al, 2016;Pold, 2015) for attics with diffusion-open roofing underlay in a cool, temperate climate.…”

“…Simulations by Nik et al (2012) support these indications for adaptive ventilation, as well as suggest superior performance compared to attics with eaveand gable ventilation, and insulated roofing underlay. Furthermore, experimental studies including (Harderup & Arfvidsson, 2013) have investigated the influence of long-wave radiation, and observed lower temperatures in the attic construction than in the outdoor air, increasing the risk of condensation on the roofing underlay.…”