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The preponderant number of multi-story buildings constructed in Denmark (Northern Europe) in the period between 1850-1930 were built with masonry walls incorporating wooden floor beams. Given the nature of this construction, it is supposed that significant energy savings could be achieved by simply insulating the facades of such buildings. To maintain the exterior appearance of the facade the only possible means of installing the required insulation is placing it on the interior of the wall. However, the installation of insulation on the interior of the wall assembly reduces the overall drying potential of the wall, and this in turn may lead to moisture problems at the beam ends embedded in the masonry, when the masonry facade is subjected to driving rain. This paper presents a method to investigate retrofit measures of interior insulated masonry walls having wooden floor beams based on Failure Mode and Effect Analysis combined with hygrothermal simulations. The method was first used to determine the potential for failure in retrofitted walls, their effects and causes, and thereafter, the expected hygrothermal performance of the retrofit measures were further investigated using both thermal and hygrothermal simulation software. The results show that the risk to incurring moisture problems at wooden beam ends can be resolve by not insulating that portion of the wall directly above and below the floor division.Additionally, this proposed retrofit measure would reduce the heat loss of the original wall structure by half.

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This article presents a method for the design of retrofit actions with focus on energy savings that permits a systematic and thorough assessment of potential failures, anticipated maintenance and the expected durability of the retrofit actions. The proposed method combines the use of failure mode and effect analysis (FMEA) to permit identifying likely failure modes from which maintenance actions could be planned and the limit states (LS) method to assess the durability of the given retrofit action. One case study was completed to illustrate the application of: (1) the FMEA and LS method and (2) the proposed method for a retrofit action of an internal insulated solid wall of masonry bonded with lightweight aggregate concrete and floor division of concrete. It was evident that FMEA is useful regarding failure-mode identification and maintenance planning, and the LS method has its strength in durability assessment. Combining the use of both the FMEA and LS methods allowed improved design of new energy-saving retrofit actions, given that a thorough risk assessment was possible that included a decisionmaking process on maintenance planning, durability assessment and decision on potential redesign of retrofit actions.

Wood-frame walls in cold climates are traditional constructed with a vapour barrier that also constitutes the air-tightness layer. Polyethylene foil as a vapour barrier is likely used; however, other building materials can be used to obtain correspondingly sufficient properties. 1D hygrothermal simulations were conducted for a wood-frame structure to investigate the wind–vapour barrier ratio, and if the vapour barrier of polyethylene foil could be omitted and replaced by other materials. The results were postprocessed using the VTT mould model. The results showed how wood-frame walls can be designed with respect to internal humidity class and diffusion resistance divided into three categories: no risk for mould growth, needs further investigation, and is not performing well as the risk for mould growth is present. For internal humidity classes 1–3, the ratio between wind and vapour barrier must be about 1:5, and 1:10 for classes 4 and 5 to be on the safe side. Simulations were performed for the climate of Lund, Sweden, which were used to simulate climate in Denmark too. Nevertheless, the results are related to climate data and, thus, the location.

A recently Danish study reported that no vapour barrier is needed in ceilings, if the attic is well ventilated and the ceiling towards the dwelling is airtight. Based on that study, new investigations were initiated with focus on the hygrothermal behaviour in ventilated attics with different air change rates. A test house with three sets of four different ceiling constructions – all airtight – was used in this study. The ventilation rate was reduced in two of the sets with approx. 35 % and 50 %, respectively. Air change rates were measured with tracer gas. Furthermore, temperature and relative humidity was measured every hour. Measurements in similar ceilings with mineral wool or cellulose-based insulation material show that hygroscopic properties of the insulation have very limited effect on relative humidity. Furthermore, only at low ventilation rate the effect of a vapour barrier could be measured with minor impact. Based on the short-measured period the calculations of the risk of mould growth showed no risk. The results indicate that even when the ventilation is reduced by 50 %, the ventilated attic still performs well if the ceiling is highly airtight. However, the importance of vapour barriers becomes more important at lower air change rates.