Structural Systems – Roof Structures and Attic – Ventilation Systems

Roof Structure Ventilation 


All around ventilated rooftop structures use air development to debilitate heat from the loft or rooftop structure to the outside. Poor rooftop ventilation can abbreviate the drawn-out assistance life of sorts of roofing materials, particularly those which contain black-top, for example, dark felt underlayment and black-top shingles. Ventilation likewise impacts dampness levels in the upper room and solace levels in the home.


Roofing materials ingest daylight as warmth. This warmth is then discharged both upward away from any confining influence air and descending into the rooftop structure.


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Cools the Roof


Keeping the attic space or rafter bays cooler helps continue material and underlayment cooler and broadens their drawn-out assistance life. Loss of volatiles, which helps keep shingles adaptable and waterproof, is quickened by poor ventilation. Loss of volatiles adds to the twisting you find in the natural shingles.


Cools the Living Space


Clearing heat before it arrives at the living space helps keep the home cooler and increasingly comfortable and lessens cooling costs.


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Removes Moisture


The third advantage of rooftop ventilation is that it can evacuate inordinate dampness fume. Over the top dampness fume can cause issues, for example, mold, rot, corrosion, and rooftop sheathing extension.


The rooftop sheathing in this new home extended after the shingles were introduced, bringing about buckling of the shingles around the board edges. Oriented strand board, generally known as OSB, is commonly utilized for rooftop sheathing, and leaves the factory with a 3% or 4% moisture content, so it is dry.


Installing sheathing and material it over too early in an atmosphere with high dampness can cause this issue. Rooftop sheathing needs an ideal opportunity to change in accordance with nearby stickiness levels. Another approach to state this is rooftop sheathing needs to reach “equilibrium moisture content” (EMC) with the house site’s condition before roofing materials are introduced.


Rooftop structure ventilation frameworks can be partitioned into two essential sorts: dynamic and latent.

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Thermostatically Controlled Fan


An active ventilation system requires power to operate. Two types of powered ventilators are common: attic fans and whole-house fans. Attic fans are usually automatically controlled by a thermostat.


These are often installed in a gabled end, as you see here. That is the adjustable thermostat circled in yellow.


You may also see them installed between rafters, as you see here. The white conductor should be stapled to the framing member nearest to the fan.


This is what a roof-mounted fan looks like from the roof.


Whole-House Fan


Whole-house fans are large fans, usually 24 to 30 inches, installed in the ceiling of the top-most floor in a central part of the home. The hallway ceiling is a common location. The fan may be controlled by a thermostat, a timer, or a manual switch.


Whole-house fans pull hot air from the living space and exhaust it to the outside through the attic space. They are typically used with a downstairs window open or with a window-mounted cooling appliance, such as an evaporative cooler, to create a flow of cool air through the home.

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If they are used improperly, whole-house fans can cause dangerous backdrafting.


“Backdrafting” is a term used to describe the conditions that result when air is pulled into the home through an exhaust flue.


Instead of flowing up into the exhaust flue and to the outside, exhaust gasses are pushed into the living space by air being pulled down the flue.


This can happen when no fresh air is supplied to replace air pulled out of the living space by the whole-house fan. If no window is left open, replacement air will be pulled into the home through the path of least resistance. If the power of the whole-house fan exceeds the forces propelling the byproducts of combustion to the outside, backdrafting will occur.


Backdrafting is more likely to occur in homes with atmospheric furnaces, which are furnaces that have no exhaust fans.


It is also more likely to happen in tightly built homes that have no system for providing makeup air. An example would be a heat-recovery ventilator, also known as an HRV.


It’s a good idea to include in your library of narratives one which describes the potential dangers associated with whole-house fans, and recommends providing a source of outdoor air, such as an open window or an evaporative cooler that is installed in an open window.


An air conditioner will not provide outdoor air since all it does is cool the air that re-circulates through the living space.

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