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What is interstitial condensation? The same principles apply here to moisture-laden air coming into contact with a cooler surface. The difference is that interstitial condensation refers to the process occurring within the layers of the building fabric, rather than on exposed surfaces. The obvious problem is that the
condensation is unseen. Over time, this can wet materials within the building’s structure. Thermal insulation materials can lose performance if they become wet; timber elements can begin to decay over a period of years. For interstitial condensation to
occur there must be some failure in the vapour-closed nature of the construction, there may be a penetration of the AVCL. This allows air and moisture to pass into the construction. That air then needs to meet a cooler surface to the external side of the insulation layer. Poor installation of insulation, which leaves gaps or voids, can also allow warm air to circulate to cold surfaces and increase the condensation risk. How do U-values and thermal performance relate to condensation risk? Among the measures that can be employed to control condensation are raising temperatures: either of the air, or of building element surfaces. A well-insulated building slows heat transfer, but heated air movement must
also be considered. If there are pathways in the fabric that allow warm air to of heating energy can be lost Airtightness is therefore also critical,
alongside an appropriate insulation to maintain air quality and remove excess moisture. Better-insulated building fabric with
lower U-values slows the rate of heat loss and keeps surface temperatures warmer. When surfaces are warmer, humid air is less likely to cool below its dew point on contact, making surface condensation less likely. What are the best insulation solutions for condensation control? Insulation that achieves lower U-values plays a key role in reducing condensation risk, beyond just meeting minimum regulations. Thermal bridges are areas in otherwise well-insulated building fabrics where the continuity of insulation (and possibly of vapour control measures
Discontinuity of insulation in the building envelope can create pathways
Thackley Primary School in Bradford was experiencing acoustic problems within the hall. The room provided a multi-use space but the amount of hard surfaces meant that excessive reverberation made for an unpleasant acoustic environment. Head of the School, Annette Patterson decided that something needed to be done and made contact with Sound Reduction Systems Ltd (SRS). Annette sent across details of the hall, including dimensions and photographs from which the technical team were able to model the space using software in order to provide an accurate quote. SRS then visited the school to take detailed measurements and discuss the various options SRS Director, Alex Docherty commented: “It was clear that the acoustic environment was not ideal and that a treatment using one of our Class A rated Sonata products was required to solve the issue.” The estimated mid-frequency reverberation time was coming out at (Tmf) of 3.57s, which is far too high for this space. SRS calculated that 75sqm of their decorative Sonata panel absorbers would help resolve the problem, bringing the reverberation time down to (Tmf) of 1.13s, and provided the school with a design detailing where the panels would be installed. The school chose a combination of Suspended Sonata Vario panels and bonded
www.soundreduction.co.uk
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for heat loss, which lower local surface temperatures and increase the risk of condensation. And where insulation is not continuous, these cooler surfaces can become prime spots for surface or interstitial condensation. Getting thermal bridging right is just
as important to condensation control as requirements. Little wonder, then, that BS 5250:2021 Moisture management in buildings - Code of practice provides detailed guidance on the importance of junction detailing and its role in moisture management. boards can help with thermal details, service voids and vapour control insulation boards can help to provide the continuous layers of insulation that limit the transfer of heat, reduce air leakage, and help maintain warmer internal surface temperatures.
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