Microclimate of Air Cavities in Ventilated Roof and Façade Systems in Nordic Climates

Abstract

Accurate values for the climatic conditions in an air cavity, hereby called the microclimate, are crucial when calculating and simulating the performance of a ventilated roof and façade system. The climatic stress of its components and their mould and rot potential influence the long-term durability of the roof or façade. A scoping study is conducted to gain an overview on research and the scientific literature on the microclimate of air cavities in ventilated roofing and claddings in Nordic climates. From the body of the research literature, 21 scientific works were of particular interest, and their findings are summarized. The review shows that only a limited number of studies discuss the microclimate of air cavities. Roofs are discussed to a greater and more varied degree compared to façades and air cavities behind solar panels. However, the results cannot be compared and validated against each other to generally describe the microclimate of air cavities, as the surveyed papers approach the subject differently. This knowledge gap indicates that calculations and simulations can be performed without knowing whether the results represent reality. If the structure of ventilated roof and façade systems are only designed based on experience, it can be difficult to be proactive and adapt to future climate changes. Further studies are needed to determine the relation between the exterior climate and the air cavity microclimate, so that future climate predictions can be used to simulate the long-term performance of ventilated roof and façade systems.

Moisture safety strategy for construction of CLT structures in a coastal Nordic climate

“…In two years of operation, the indoor climate monitoring has not indicated any elevated levels of volatile organic compounds [11], which could be a sign of mould growth. Elevated levels of moisture have been measured in the air cavities of the building's façades and roof [14], but these measurements concern precipitation loads on the exterior parts of the building envelope and not built-in moisture.…”

A Numerical Study of Methods to Improve Moisture Safety of Ventilated Wooden Roofs

“…The increased moisture content of the outdoor air and precipitation levels in Finland as a result of climate change (Jylhä et al, 2020) will likely further increase the moisture risk (Nik et al, 2012). However, a review study by Ingebretsen et al (2022) showed that only a limited number of studies have discussed the moisture conditions and microclimate in roof cavities in Nordic countries, most of these originating from Norway.…”

“…In the Nordic countries, wood-framed external walls and roofs typically have a ventilated cavity between the wind barrier and the cladding to protect the wind barrier from weather, reducing the risk of leaks, and ensure that the building component can dry out (TenWolde & Carll, 1992;Ingebretsen et al, 2022). As the thermal conditions in the cold season in the ventilation cavity of the roofs are close to the outdoor air (Ojanen & Hyvärinen, 2008;Viljanen, 2023), the moisture conditions in the cavity may deteriorate even with a small moisture load directed to the cavity (Viljanen, 2023;Viljanen et al, 2021;Viljanen et al, 2020).…”

Watertight insertion of heavy sliding doors in exterior walls

“…The primary source of precipitation stress on a building façade is wind-driven rain [5]. Wind-driven rain is commonly managed in Norway using dual-barrier weatherproofing [6], where the building's cladding acts as a main rain barrier, shielding a wind barrier which stops air penetration. The two are separated by an air cavity that allows the materials to dry.…”