I came across a new construction home with sprayed polyurethane foam applied to the roof sheathing. I suspect it is an open-cell product rather than a closed-cell. My question is regarding a bathroom-style fan installed in the attic.
Situation and info:
New construction in Colorado, Zone 5
This is a 1-year warranty inspection
There is no attic ventilation (soffit/roof/ridge etc.) due to a conditioned space (Encapsulated)
A bathroom-style fan in the attic terminates to the exterior of the rooftop
The fan switch is located in the attic
Access to the attic is a ceiling hatch which will require a ladder
The fan was shut off at the time of inspection
The fan switch does not appear to have a thermostat
The fan has a module for CFM and Time only
Questions:
Where is the fan drawing air from? There are several small gaps around the can lights, but wouldn’t that cause debris collection around it from air intake?
Why is it not automated with a thermostat?
Why is it so difficult to access? The homeowner had no idea it was even there! (single person with no need for a ladder)
Should the fan be turned on 24/7?
Why is a fan even necessary? I know airflow is good, but how does it work in this situation?
This is my proposed narrative and I am looking forward to critiques.:
“The attic was insulated with spray foam applied to the roof sheathing. This approach can create a conditioned attic space, which, when properly sealed, eliminates the need for traditional ventilation. However, an attic fan was present, which is unusual for a conditioned attic. If the attic is intended to be fully encapsulated, the fan may be unnecessary or even counterproductive by introducing unconditioned air into the space or expelling conditioned air to the outside. The fan switch is located in the attic, which is impractical for manual operation, and it does not appear to be connected to a thermostat for automatic control. I recommend consulting the builder to determine the intended function of the attic fan and whether it is needed in this setup.”
Unvented attics and unvented enclosed roof framing assemblies created by ceilings that are applied directly to the underside of the roof framing members and structural roof sheathing applied directly to the top of the roof framing members/rafters, shall be permitted where all the following conditions are met:
1.The unvented attic space is completely within the building thermal envelope.
2.No interior Class I vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly or on the ceiling side of the unvented enclosed roof framing assembly.
3.Where wood shingles or shakes are used, a minimum 1/4-inch (6.4 mm) vented airspace separates the shingles or shakes and the roofing underlayment above the structural sheathing.
4.In Climate Zones 5, 6, 7 and 8, any air-impermeable insulation shall be a Class II vapor retarder, or shall have a Class II vapor retarder coating or covering in direct contact with the underside of the insulation.
5.Insulation shall comply with Item 5.3 and Item 5.1. As an alternative, where air-permeable insulation is located on top of the attic floor or on top of the attic ceiling, insulation shall comply with Item 5.3 and Item 5.2.
5.1.Item 5.1.1, 5.1.2, 5.1.3 or 5.1.4 shall be met, depending on the air permeability of the insulation directly under the structural roof sheathing.
1. 5.1.1.Where only air-impermeable insulation is provided, it shall be applied in direct contact with the underside of the structural roof sheathing.
2. 5.1.2.Where air-permeable insulation is provided inside the building thermal envelope, it shall be installed in accordance with Section 5.1.1. In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board or sheet insulation shall be installed directly above the structural roof sheathing in accordance with the R-values in Table R806.5 for condensation control.
3. 5.1.3.Where both air-impermeable and air-permeable insulation are provided, the air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing in accordance with Item 5.1.1 and shall be in accordance with the R-values in Table R806.5 for condensation control. The air-permeable insulation shall be installed directly under the air-impermeable insulation.
4. 5.1.4.Alternatively, sufficient rigid board or sheet insulation shall be installed directly above the structural roof sheathing to maintain the monthly average temperature of the underside of the structural roof sheathing above 45°F (7°C). For calculation purposes, an interior air temperature of 68°F (20°C) is assumed and the exterior air temperature is assumed to be the monthly average outside air temperature of the three coldest months.
5.2.In Climate Zones 1, 2 and 3, air-permeable insulation installed in unvented attics on the top of the attic floor or on top of the ceiling shall meet the following requirements:
1. 5.2.1.An approved vapor diffusion port shall be installed not more than 12 inches (305 mm) from the highest point of the roof, measured vertically from the highest point of the roof to the lower edge of the port.
2. 5.2.2.The port area shall be greater than or equal to 1:600 of the ceiling area. Where there are multiple ports in the attic, the sum of the port areas shall be greater than or equal to the area requirement.
3. 5.2.3.The vapor-permeable membrane in the vapor diffusion port shall have a vapor permeance rating of greater than or equal to 20 perms when tested in accordance with Procedure A of ASTM E96.
4. 5.2.4.The vapor diffusion port shall serve as an air barrier between the attic and the exterior of the building.
5. 5.2.5.The vapor diffusion port shall protect the attic against the entrance of rain and snow.
5.3.Where preformed insulation board is used as the air-impermeable insulation layer, it shall be sealed at the perimeter of each individual sheet interior surface to form a continuous layer.
An exhaust fan is not the greatest way to ventilate an encapsulated attic, but it may have met the AHJ’s requirements. You could recommend a timer be added. I’d also want a way to verify from outside the attic that the fan is operating. But if it were mine, it wouldn’t be done this way. I would install an HVAC supply and return for the space.
I’ve run into one and familiar with another attic where the two-part foam was not mixed/combined properly and was off gassing toxins. I recommend an air quality test if there is a return air vent in a spray foam insulated conditioned attic.
