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Abstract
Flat roofs of cold-deck design require effective ventilation of the void below the deck to ensure satisfactory performance. This must be sufficient to remove any moisture vapor diffusing from the building below, to minimize the risk of condensation within the roof and persistent hazardous levels of moisture content of timber components. The performance of the two roofs of cold-deck design was monitored through the winter months: the first an experimental building of simple plan with through ventilation; and the other a school with roofs of more complex design. The performance criteria included the measured moisture content of timber joists and of chipboard and plywood decks; evidence of mold growth on surfaces within the roofs; and measurements of air change rates within the roof voids. The area of the ventilation openings on the experimental building was varied from 0 percent to 0.8 percent of the roof plan area, using fascia-to-fascia vents. The results indicate that present recommendations in the UK for a minimum of 0.4 percent total ventilation area are not always sufficient to ensure moisture contents below the threshold of risk of decay for timber-based materials: There was evidence of mold growth on both plywood and chipboard decks. It appears to be necessary to provide at least 0.6 percent total ventilation area, equally divided between the two sides of the roof, to reduce these moisture hazard risks to an acceptable level.
Flat roofs of cold-deck design require effective ventilation of the void below the deck to ensure satisfactory performance. This must be sufficient to remove any moisture vapor diffusing from the building below, to minimize the risk of condensation within the roof and persistent hazardous levels of moisture content of timber components. The performance of the two roofs of cold-deck design was monitored through the winter months: the first an experimental building of simple plan with through ventilation; and the other a school with roofs of more complex design. The performance criteria included the measured moisture content of timber joists and of chipboard and plywood decks; evidence of mold growth on surfaces within the roofs; and measurements of air change rates within the roof voids. The area of the ventilation openings on the experimental building was varied from 0 percent to 0.8 percent of the roof plan area, using fascia-to-fascia vents. The results indicate that present recommendations in the UK for a minimum of 0.4 percent total ventilation area are not always sufficient to ensure moisture contents below the threshold of risk of decay for timber-based materials: There was evidence of mold growth on both plywood and chipboard decks. It appears to be necessary to provide at least 0.6 percent total ventilation area, equally divided between the two sides of the roof, to reduce these moisture hazard risks to an acceptable level.
Date
0/1988
0/1988
Author(s)
J C Beech; S Uberoi
J C Beech; S Uberoi
Page(s)
163-176
163-176
Source
Society of Chemical Industry
Society of Chemical Industry
Keyword(s)
ventilation requirement; cold-deck design; flat roof; moisture content; timber joist; mold; air change rate
ventilation requirement; cold-deck design; flat roof; moisture content; timber joist; mold; air change rate