Through provision r806 4 the irc also allows you to build an unvented roof assembly.
Unvented porch roof with finished ceiling.
I installed collar ties to leave an open space above the finished room along with r 15 insullation and installed a fan on a thermostat at the end of the roof in addition to ridge vent to suck all the hot air that collected between the roof and porch ceiling.
These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck.
Unvented assemblies work particularly well on complex roofs that would be difficult or impossible to vent properly or on roofs where it would be difficult to insulate properly if the roof were vented.
Where the attic space is finished with drywall or other ceiling materials installed against the underside of the roof rafters while we prefer in floor insulation here we ll have to insulate the roof cavity between the rafters.
Basically you should be thinking about insulating the roof floor and walls to ensure the maximum benefit.
That can be made cheaper still if using reclaimed roofing foam at a fraction of the price of virgin stock foam.
Create an unvented roof.
In terms of energy savings there isn t much benefit to insulating an unheated porch.
With simple roof lines it s cheaper to do an unvented roof with exterior side roofing polyiso and all fiber in the rafter cavities.
Unvented roofs vented roof.
However in many situations the insulation may need to be primarily or entirely below the flat roof membrane and between the roof joists if so what are the best options.
Unvented porch roof with finished ceiling.
However doing so will prevent cold air from seeping into the porch and may allow you to use the porch for a few weeks longer before winter arrives.
There are traditionally four main reasons for venting a roof.
An under roof cathedral ceiling or attic ventilation system to help the building in any way needs to be properly designed and installed with adequate intake venting at the eaves outlet venting at the ridge and with careful sealing of air leaks from the occupied space into the attic or roof cavity to avoid heat losses or increases in both moisture movement into the roof cavity and.
Un vented hot roof designs indoors finished attic.
Last year i replaced a flat porch roof with a 6 12 pitch.
Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction.
Unvented flat roofs a technical discussion flat roofs have often been built with the insulation all on top of the vapor closed drainage plane as this avoids dew point condensation issues inboard of the roofing.
If you want to install fluffy insulation between the rafters of an unvented cathedral ceiling you must also install enough rigid foam insul our new home has almost all vinyl products on the outside of it.
