Issue 9, Vol 5 Out Now
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Featured Article
| Local custom |
With money leaving local economies across Ireland to service debt and significant drops in local authority revenues, towns such as Dundalk, Ennis and Kilkenny are investigating the possibility of bringing in electronic currencies to keep money circulating locally, as Richard Douthwaite reveals.
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Official magazine of Easca  |
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External examination |
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Friday, 20 August 2010 |
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Page 4 of 13
The risk of mould
Along with thermal performance, external insulation offers another big benefit over internal: lower risk of interstitial condensation. When a wall is insulated internally, the temperature of the original wall behind the new insulation falls. The temperature drop here makes it an ideal place for water vapour to condense into liquid and cause dampness, which can lead to mould and illnesses such as asthma and allergies. External insulation keeps the whole of the original wall warm and dry, minimising the risk of condensation.
External insulation manufacturer Sto performs condensation risk analysis on all its projects, the company's Barny Parks told Construct Ireland. Sto’s simulations factor in both temperature and relative humidity inside and outside the building, and the company uses weather data from Eskdlaremuir in Scotland - which holds the UK record for the most rainfall ever in a 30 minute period - in its calculations regardless of location. "It gives us a factory of safety," Parks explains.
He says Sto rarely witness a risk of interstitial condensation in externally insulated walls - if they do, they’ll typically recommend installing a vapour barrier at an appropriate point in the build-up. While Sto perform their analysis voluntarily, Parks can see such simulations becoming mandatory in future due to the speed u at which the market for external insulation is growing.
green builders MountCarrick Environmental installed external insulation between the soft and original wall of this house in Dunleer to reduce thermal bridging
In 1998, Dr Hartwig Künzel of the Fraunhofer Institute in Germany published a paper on the moisture content in different walls types – he studied a brick wall that had been internally insulated in various ways, and a similar wall with two types of external insulation. Künzel concluded that external insulation leads to the drying of the wall, with the speed of drying depending on the vapour permeability of the insulation system used. He found that internal insulation, on the other hand, causes water content in the wall to rise due to the temperature drop in the wall. “The interior insulation of exposed walls should be combined with rain protection measures at the facade,” he concluded.
No matter how well designed an internal dry-lining wall build-up is, vapour will condense inside it every winter when the temperature of the block is at its coldest. “This is because the insulation isolates the masonry wall so that its room-face cannot warm as before and consequently becomes more uniformly cool and also wetter,” Joseph Little writes. “This is typically where the most extreme temperature change takes place and vapour condenses.”
In the last of his Breaking the Mould series of articles Little published an analysis of different theoretical single-leaf masonry walls internally insulated with different build-ups. He concludes that “a troubling amount” of the simulated build-ups experience relative humidity levels above 80% – a figure commonly used to indicate likelihood of mould within a wall build-up. Some were “dramatically above” 80%.
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