Montana Kaimin, March 5, 1993

Student newspaper of the University of Montana, Missoula.https://scholarworks.umt.edu/studentnewspaper/9619/thumbnail.jp

Risikoverktøy for fuktsikker oppgradering av småhus

Om risikoverktøyet. Risikoverktøyet kan brukes til å vurdere risiko for fuktproblemer ved implementering av ulike løsninger for oppgradering av boliger. Verktøyet er overordnet, men gir opplysninger om hvor man kan finne mer detaljert informasjon om tiltaket man ønsker å implementere. Det gir ikke en fasit på hvilke løsninger som bør velges i et gitt prosjekt, men indikerer hvilke løsninger som er forbundet med høyere risiko. Dersom man kun velger tiltak med lav risiko, er det liten sannsynlighet for at det oppstår fuktproblemer. Ved bruk av flere løsninger med høy risiko, øker sannsynligheten for fuktproblemer. Ved å velge mange "høyrisiko"-løsninger vil det være nødvendig med mer omfattende prosjektering. Slike løsninger vil også være mer utsatt ved avvik i utførelsen. I tillegg er det viktig å huske på at ulike løsninger for oppgradering påvirker hverandre. Dersom man for eksempel monterer ny vindsperre og etterisolerer, vil boligens tetthet sannsynligvis øke. Da blir det større behov for å kontrollere ventilasjonen i boligen, og man bør vurdere å installere balansert ventilasjon for å unngå fuktproblemer.publishedVersio

Influence of Local Weather Conditions on Ventilation of a Pitched Wooden Roof

This paper investigates the influence of temperature and wind conditions on ventilation of the air cavity beneath the roofing in a full-scale pitched wooden roof construction. The potential for condensation in the air cavity is studied. The relevant roof construction is equipped with 81 thermocouples and four air velocity measurement devices. A weather station at the site records outdoor temperature and wind conditions. Five periods between 2016 and 2018 are investigated. The findings show distinct periods of below-ambient temperature and positive condensation potential in the ventilated air cavity of the roof. A relation between low wind speed and positive condensation potential is shown. Difference in size of periods with below-ambient temperature and periods with positive condensation potential implies that the materials in the roof regulate the humidity in the air cavity. Large negative peaks in the condensation potential indicate dry-out of the construction.publishedVersio

Effect of forced convection on the hygrothermal performance of a wood frame wall with wood fibre insulation

Wood-based thermal insulation materials have interesting hygroscopic characteristics because of their high moisture capacity. The present paper investigates the moisture conditions in wood-frame walls with wood fibre thermal insulation. The effect of forced convection of moist air into the construction is studied in particular. Laboratory measurements were carried out on a full-scale wall model divided in five sections with various configurations. The wall sections had different combinations of exterior air barrier, thermal insulation and interior vapour retarder. Each section was prepared with an air leakage to simulate supply of moist air to the wall construction through forced convection. The measurement results provided insight in the moisture conditions in the wall and internal distribution of moisture in the wall sections. The results show that walls with wood fibre insulation may have the same risk of high moisture levels as walls with mineral wool insulation. However, the results indicate that wood fibre insulation absorbs condensation and melting water, while the mineral wool does not. Hence, the results imply that the wood fibre insulation has the benefit of distributing the moisture over a larger volume than the mineral wool insulation. Furthermore, the investigations indicate that using an exterior air barrier with high thermal resistance results in a generally lower moisture level in the wall construction, which can be considered favourable regarding risk of mould growth.publishedVersio

Pitched unventilated wood frame roof with smart vapour barrier – field measurements

Unventilated wood-frame roofs may provide smaller roof thickness and less material use compared to conventional unventilated roofs with all the thermal insulation above the load bearing structure. Unventilated roofs are, however, normally built without wooden materials between the vapour barrier and roof membrane due to moisture safety. Field measurements on the pitched unventilated wood-frame roof of an office building in Norway is performed to demonstrate and document the performance of this type of roof construction. Through monitoring of moisture and temperature, the study aims to contribute to verification of simulations and laboratory measurements showing that unventilated wood-frame roofs may be built with wooden materials if a smart vapour barrier is used. The results show moisture levels below 15 weight-% on the warm side of the rafters throughout the first 15 months of measurements. On the cold side of the rafters, the moisture content increased during winter due to built-in moisture in the construction and reached levels close to 25 weight-%. The moisture content decreased to around 15 weight-% when summer arrived, which shows an expected redistribution of moisture and indicates possible drying of the construction. The measurements underline the importance of limiting built-in moisture to reduce the risk of mould growth, but the study also implies that for some given premises an unventilated pitched wood-frame roof may have acceptable moisture risk.publishedVersio

Air leakage paths in buildings: Typical locations and implications for the air change rate

The harsh Norwegian climate requires buildings designed to high standards. An airtight building envelope is crucial to achieve an energy efficient building and to avoid moisture problems. Results from the SINTEF Building defects archive show that a considerable part of the building defects is related to air leakages. In addition, air leakages increase the energy demand of buildings. A literature study has been conducted in order to map typical air leakage paths of Norwegian wooden houses. In order to increase the performance, different sealing methods including the use of tape has been reviewed. The results show that the most common air leakages reported from field measurements in the literature are in the connections between external wall and ceiling or floor, external wall and window or door, and external wall and penetrations in the barrier layers. Results from laboratory investigations showed that the traditional solutions can be further improved by introduction of modern foil materials in combination with sealing tapes. However, questions can be raised regarding the necessity of tape sealing all available joints.publishedVersio