b'VentilationFigure 3: Various roof ventilation strategies employed for similar roofs in the Ahuntsic-Cartierville borough of Montreal.the top of the insulation and the bot- roof vents. However, soffit vents areandmulti-bladeformats;multi-tom of the trusss upper chord. 9Ararelydesignedandincorporatedblade units draw more air from the typical expectation, and an NBCCinto new low-rise structures, as ar- roofcavity.requirement,isthataminimumchitects are opting for designs thatThe use of roof ventilators is the 3-in.(75-mm)distanceremainbe- do not have projections near roofpredominant ventilation strategy for tween the top of the insulation andlevel and the cladding is extended allmodern-day low-rise structures with Think Safe, the underside of the roof deck. the way to the parapet. flatroofs.Thesedeviceseffectively Work Safe, WiththeintroductionoftheLongitudinal vents are a relative- draw air from the roof cavity; how-since 1988 1/150 vent ratio, the NBCC 1977 5 ly recent feature; they are continu- ever,withinsufficientoutsideair also introduced the idea of installingous vents situated within the roofintake, humid air from the interior 2- by 2-in. (50- by 50-mm) purlins inbasin(area)andraisedfromthespaces can be aspirated into the roof Top-Line Roofing & Sheet-Metal Inc. specializes in the installation, repair, and maintenance oftheperpendiculardirectionoftheroof deck to exhaust the air withincavityandmayaggravatethefor-industrial roofs throughout Southern Ontario.roofjoiststopromotecross-venti- the cavity. Even when the height ofmationoffrost,condensationand OUR SERVICES: lation and the dissipation of humidthe roof assembly is limited, longi- subsequent mold growth. Excessive Commercial roofing Re-roofing air to the exterior. Sufficient cross- tudinalventscanmaximizestackdepressurization of the roof cavity, Roof maintenance Skylight installation ventilation within the roof cavity isaction when used in combinationrelative to the occupied space, may Roof inspection,Sheet metal flashing, evaluation & report fabrication & installation importanttominimizetheriskofwith soffit vents. However, it seemscreate a significant pressure differen-Historical restoration Retro-fit curb installation condensation, regardless of the em- that longitudinal vents are not oftential such that the humid interior air Emergency roof repairs ployed ventilation strategies. used because active ventilation pro- finds a way into the roof cavity. 9Ventilation of flat-roof structuresvides a more cost-effective solution. AsshowninFigures1-3,the (905) 602-0760 can be passive or active. In general,Activeventilationisoftensidesofmanybuildingsontheis-1325 Fewster Dr the means for passive ventilation ofachievedthroughtheinstallationlandofMontrealareattachedto Mississauga, ONL4W 1A2toplineroofing.ca flat-roof systems are limited to goose- ofroofventilators.Roofventila- other properties. In many cases, the necks, soffit vents and longitudinaltorsareavailableinsingle-bladeadjacent properties use different ven-18ONTARIO ROOFING NEWSISSUE 1 2024 THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ORN'