[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"detail-sidebar-cat-0-en-105":3,"doc-seo-663039-105":59,"doc-detail-663039-en":130},{"code":4,"msg":5,"data":6},0,"success",[7,13,18,23,28,33,38,43,48,51,55],{"id":8,"doc_module":4,"doc_module_name":9,"category_name":10,"show_sort_weight":11,"slug":12},1,"Document","Story & Novel",90,"story-novel",{"id":14,"doc_module":4,"doc_module_name":9,"category_name":15,"show_sort_weight":16,"slug":17},2,"Literature",80,"literature",{"id":19,"doc_module":4,"doc_module_name":9,"category_name":20,"show_sort_weight":21,"slug":22},4,"Exam",70,"exam",{"id":24,"doc_module":4,"doc_module_name":9,"category_name":25,"show_sort_weight":26,"slug":27},5,"Comic",60,"comic",{"id":29,"doc_module":4,"doc_module_name":9,"category_name":30,"show_sort_weight":31,"slug":32},6,"Technology",50,"technology",{"id":34,"doc_module":4,"doc_module_name":9,"category_name":35,"show_sort_weight":36,"slug":37},7,"Healthcare",40,"healthcare",{"id":39,"doc_module":4,"doc_module_name":9,"category_name":40,"show_sort_weight":41,"slug":42},8,"Research & Report",30,"research-report",{"id":44,"doc_module":4,"doc_module_name":9,"category_name":45,"show_sort_weight":46,"slug":47},9,"Religion & Spirituality",20,"religion-spirituality",{"id":46,"doc_module":4,"doc_module_name":9,"category_name":49,"show_sort_weight":46,"slug":50},"World Cup","world-cup",{"id":52,"doc_module":4,"doc_module_name":9,"category_name":53,"show_sort_weight":52,"slug":54},10,"Lifestyle","lifestyle",{"id":56,"doc_module":4,"doc_module_name":9,"category_name":57,"show_sort_weight":24,"slug":58},19,"General","general",{"code":4,"msg":60,"data":61},"ok",{"site_id":62,"language":63,"slug":64,"title":65,"keywords":66,"description":67,"schema_data":68,"social_meta":123,"head_meta":125,"extra_data":127,"updated_unix":129},105,"en","roof-design-research-report-0404-roof-design","Roof Design - Research Report-0404 - Roof Design","","Roofs can be designed as vented or unvented in any hygro-thermal zone, with air barrier systems commonly used for moisture and pressure management. Air pressure control is increasingly important, especially during remedial work on existing structures. Vapor diffusion is treated as a secondary moisture transport mechanism, and specific vapor retarders are often unnecessary when air movement and condensing surface temperatures are controlled. The report explains ventilation ratios, ice dam risks, and climate-zone vapor retarder requirements for vented and unvented roofs.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":40,"@type":76,"position":81},"https://docshare.wps.com/document/research-report/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/roof-design-research-report-0404-roof-design/663039/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/roof-design-research-report-0404-roof-design/663039.png","ImageObject",300,407,{"name":92,"@type":93},"4398046744996","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-30","2026-10-28",true,{"@type":102,"interactionType":103,"userInteractionCount":81},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"How should roofs be designed to be vented or unvented in different hygro-thermal zones?","Question",{"text":112,"@type":113},"Roofs can be constructed as either vented or unvented across hygro-thermal zones. The choice depends on how moisture transport and condensing surface temperatures are controlled.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"What is the main purpose of attic ventilation in cold climates?",{"text":117,"@type":113},"Attic ventilation helps keep the roof cold to avoid ice dams and vents moisture migrating from the conditioned space to the attic.",{"name":119,"@type":110,"acceptedAnswer":120},"When are vapor retarders required in vented roof assemblies, and how does it vary by climate zone?",{"text":121,"@type":113},"A Class II vapor retarder is recommended in Climate Zones 6 and 7, and Class III is acceptable in Zone 5. Class I vapor barriers can be installed in Zones 6 and 7 but should be avoided in Zone 5 due to potential top-side condensation during air conditioning seasons.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},663039,1793224772,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":66,"doc_module":4,"category_id":39,"category_name":40,"doc_title":65,"doc_description":67,"doc_content":133,"file_id":134,"file_url":135,"file_type":136,"file_size":137,"view_count":81,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":39,"language":138,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":139,"faqs":140,"seo_title":141,"seo_description":67,"update_tm":129,"read_time":46},4398046744996,"[building science.com](building science.com)  \n© 2006 Building Science Press All rights of reproduction in any form reserved.  \nRoof Design  \nResearch Report-0404 2004  \nJoseph Lstiburek  \nAbstract:  \nRoofs can be designed and constructed to be either vented or unvented in any hygro-thermal zone. Air barrier systems are typically the most common approach, however, air pressure control approaches are be-coming more common especially in cases involving remedial work on existing structures. Vapor diffusion should be considered as a secondary moisture transport mechanism when designing and building roofs. Specific vapor retarders are often unnecessary if appropriate air movement control is provided or if control of condensing surface temperatures is provided.  \nRoof Design  \nRoofs can be designed and constructed to be either vented or unvented in any hygro-thermal zone.  \nIn cold climates, the primary purpose of attic ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow, and to vent moisture that moves  \nfrom the conditioned space to the attic. Melted snow, in this case, is caused by heat loss from the conditioned space.  \nIn hot climates, the primary purpose of attic ventilation is to expel solar heated hot air from the attic to lessen the building cooling load.  \nThe amount of roof cavity ventilation is specified by numerous ratios of free vent area to insulated ceiling area ranging from 1:150 to 1:600 depending on which building code is consulted, the 1:300 ratio being the most common.  \nControl of ice dams, moisture accumulation and heat gain can also be facilitated by unvented roof design.  \nApproach  \nIn cold climates the main strategy that should be utilized when designing roofs to be free from moisture problems and ice dams along with control of heat gain or heat loss regardless of ventilation approach is the elimination of air movement, particularly exfiltrating air. This can be accomplished by the installation of an air barrier system or by the control of the air pressure difference across the roof system.  \nAir barrier systems are typically the most common approach, however, air pressure control approaches are becoming more common especially in cases involving remedial work on existing structures.  \nVapor diffusion should be considered as a secondary moisture transport mechanism when designing and building roofs. Specific vapor retarders are often unnecessary if appropriate air movement control is provided or if control of condensing surface temperatures is provided.  \nVented Roof Design  \nVented roofs should not communicate with the conditioned space—they are coupled to the exterior. Therefore, an air barrier at the ceiling line should be present to isolate the attic space from the conditioned space. No services such as HVAC distribution ducts, air handlers, plumbing or fire sprinkler systems should be located external to the air barrier (Figure 1) .  \nThe recommended ventilation ratio to provide in vented roof assemblies when an air barrier is present, is the 1:300 ratio (as specified by most codes) .  \nIn vented cathedral ceiling assemblies a minimum 2-inch clear airspace is recommended between the underside of  \nthe roof deck and the top of the cavity insulation. This not a code requirement but ought to be (only 1-inch is typically specified) .  \nIn addition to an air barrier at the ceiling line, a Class II vapor retarder should be installed in Climate Zone 6 and Climate Zone 7. A Class III vapor retarder is acceptable in Climate Zone 5.  \nClass I vapor retarders (i.e. vapor barriers) can be installed in vented roof assemblies in Climate Zone 6 and Climate Zone 7 but should be avoided in Climate Zone 5 as top side condensation may occur in the summer months during air conditioning periods.  \nNo interior roof assembly-side vapor control is required or recommended in climate zones other than cold or very cold.  \nContinuous ridge ventilation  \nRigid insulation  \n(taped or sealed ","cbCaihQ0QR9FxGLD","https://ap.wps.com/l/cbCaihQ0QR9FxGLD","pdf",845898,"English","# Roof Design\n## Ventilation Purpose in Cold and Hot Climates\n## Moisture Control Approaches\n## Vented Roof Design\n## Unvented Roof Design","[{\"question\":\"How should roofs be designed to be vented or unvented in different hygro-thermal zones?\",\"answer\":\"Roofs can be constructed as either vented or unvented across hygro-thermal zones. The choice depends on how moisture transport and condensing surface temperatures are controlled.\"},{\"question\":\"What is the main purpose of attic ventilation in cold climates?\",\"answer\":\"Attic ventilation helps keep the roof cold to avoid ice dams and vents moisture migrating from the conditioned space to the attic.\"},{\"question\":\"When are vapor retarders required in vented roof assemblies, and how does it vary by climate zone?\",\"answer\":\"A Class II vapor retarder is recommended in Climate Zones 6 and 7, and Class III is acceptable in Zone 5. Class I vapor barriers can be installed in Zones 6 and 7 but should be avoided in Zone 5 due to potential top-side condensation during air conditioning seasons.\"}]","Roof Design - Research Report-0404 - Roof Design | PDF"]