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 | | NEW INTUMESCENT SOLUTION SOLVES THE CAVITY WALL CONUNDRUM | | | Tenmat Ltd | | 04/08/2008 | | | External wall cavities are a well tried and tested method of maintaining a thermal, acoustic and moisture barrier between the internal and external structure of a dwelling. To maintain an effective barrier the critical feature of a wall cavity is that it is not “bridged” which would allow the outside elements to enter the internal structure, in addition to which the cavity requires adequate ventilation to allow moisture vapour to be removed.
CONFLICTING REQUIREMENTS
FIRE
The simple solution for optimum external wall cavity performance would be to maintain an open cavity and adequately ventilate that cavity at its base and top. However, the simple fact that a wall cavity extends both upwards and around a building structure makes it a perfect path for the spread of fire.
Indeed a wall cavity becomes a chimney for hot gases, smoke and flames, this is a particularly issue in buildings utilising combustible structures such as timber.
The latest edition of Building Regulations Approved Document B has identified wall cavities as a major fire spread risk and has dealt with this by requiring cavity barriers to be fitted wherever a fire compartment wall or floor meets the external wall. In addition to this, cavity barriers are also required at regular intervals in large wall expanses even where fire compartment walls or floors do not meet the external wall.
ACOUSTICS
To optimise the acoustic performance of the “still air barrier” in a wall cavity, the inner and outer components of the wall should remain unconnected thus preventing the transmission of sound via those connections, therefore the fewer cavity trays, solid cavity barriers and even wall ties then the better the performance from an acoustic point of view.
VENTILATION
To allow a wall cavity to remove the moisture which penetrates the outer wall or that is created via condensation then it must be effectively ventilated. This is particularly important with timber framed constructions as the structure itself can be degraded by the presence of moisture.
If a cavity is fitted with solid cavity barriers then each of the barriers will normally require protection from moisture bridging via a cavity tray and in addition that sealed cavity will now require separate ventilation and water drainage, all of which both detract from the cavities performance and add significant cost to the construction.
MOISTURE AND THERMAL BRIDGING
As soon as a wall cavity is “bridged” with a cavity tray or solid cavity barrier then a solid connection exists between the inner and outer wall and this makes moisture and thermal bridging a real possibility, the more connections which exist then the greater the risk.
LATEST SOLUTION TO THESE ISSUES
The world of intumescent fire protection is always moving forwards at a pace to keep ahead of emerging fire legislation and to provide solutions to problems such as the cavity wall issues.
Imagine how much money and labour time could be saved if the wall cavities could be left completely open? The benefits are obvious, the wall would perform much better from a ventilation and acoustic point of view and expensive cavity tray and drainage weep holes and their installation costs would be a thing of the past.
The latest range of fire activated, intumescent “Ventilated Cavity Fire Barriers” allow the cavity to remain open, this is because they only seal the cavity when a fire is present, when not activated the barriers are typically only 4-6 mm thick. Once fitted with these “Ventilated Cavity Fire Barriers” the wall can simply be ventilated at the top and bottom with no risk of moisture or thermal bridging.
It must be sometime since such a simple but clever solution has had the potential to offer such improvements in construction methods whilst also reducing cost. | |
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