The dormers and the attic space over the outside porch were sealed off from the rest of the attic by making a wall of plywood, then insulating the wall with closed-cell SPF. Following this, closed-cell SPF was also installed to the underside of the roof deck. Building codes and attic assemblies Since , International Code Council ICC supplements to the International Residential Code IRC mean unvented attic assemblies have been accepted by the building codes in residential, but not commercial, applications.
IBC requires ventilation in attics and crawl spaces and does not address the unvented attic concept. However, many building code officials have accepted unvented attics on a case-by-case basis when presented with compelling evidence —such as hygrothermal modeling of proposed assemblies—that the assembly will function properly. The requirements have changed slightly over the years, but many of the elements have remained the same. Medium-density SPF at 51 to 76 mm 2 to 3 in.
The vapor retarder classes are important to correctly specify unvented attic assemblies. Depending on the air impermeability of the insulation directly under the structural roof sheathing, the IRC section also requires one of these conditions:.
This section would apply to flash and batt systems where a layer of closed-cell SPF is installed to the underside of the roof deck and another insulation such as fiberglass is installed directly to the SPF. Issues with unvented attics Acceptance of the unvented attics and crawl spaces concept has generated some worry from those unfamiliar with the physical properties and moisture-control capabilities of SPF. However, closed-cell foam repels liquid water. It seals cracks and crevices in the wood deck so any water getting past the roofing system stays atop the wood deck.
If the exterior surface of wood is wet when the foam is installed, then drying would occur from the roof-side to the exterior, not through the wood to the foam. This would be the same if the foam was not in place. If the wood is saturated, industry best practice calls for not installing the foam. If foam is installed to wet wood, it is apparent to the applicator and there would be open cells and lower density, allowing absorption of water into the foam.
In this case, leaks would show up on the interior. Regardless, a roofing system should be regularly inspected to detect evidence of roof leaks and potential roof-deck damage. Foam insulation does not make damages more difficult to detect. In colder climates, SPF can reduce the potential for ice damming. It prevents warm air from reaching the underside of the roof where it could melt snow, causing water to flow down and refreeze into the eaves.
It is important to extend the insulation beyond the interior stud wall along the soffit space. If the air gaps are not sealed at the top of the wall, warm air can heat the underside of the roof deck and potentially cause ice dams in cold climates. Traditional vented attic assembly with both batt and blown-in insulation. Photo courtesy CertainTeed Attics with small and unusual configurations might also benefit using unvented assemblies. Engineering studies conducted by Carl Cash former chair of ASTM D08 Committee on Roofing explored the premise of attic ventilation and its effect on shingle temperature compared to other factors that could influence shingle temperatures.
According to Cash:. Venting the roof deck reduces the average temperature of the roof —1. Another oft-cited concern is since closed-cell spray foam is a vapor retarder, it cannot be used in warm, humid climates as it prevents water vapor from going in and out of the assembly.
Closed-cell spray foam has a perm rating of approximately 1. This combination allows a controlled moisture vapor flow, while separating the inside and outside environments. The result is better control of condensation within the building envelope so long as there is sufficient SPF insulation to prevent condensation. In most applications, It should be noted hygrothermal modeling calculations are recommended when atypical conditions occur, such as extreme environments and unusual construction or design.
When using a hybrid insulation system, such as closed-cell sprayfoam covered with fiberglass or cellulose insulation, a greater thickness of closed-cell foam is needed to reduce the potential for condensation.
Another question on the use of sprayfoam is what happens when an applicator unintentionally sprays foam to wet lumber, particularly wet-framing members. Research has been conducted on installing SPF to wet lumber. This research demonstrates closed-cell foam under typical building conditions i. How Attic Ventilation Works Effective ventilation in an unfinished attic usually includes intake vents down low along the soffits, and exhaust vents up high at the peak or roof ridge.
Why Adequate Roof Ventilation is Important Proper ventilation in your attic helps address excess heat and moisture that can otherwise wreak havoc on your home. Exposure to this excessive heat can warp the roof sheathing and distort and prematurely age the shingles. In locales where the temperature drops below freezing during the winter, warm air escaping into the attic from the heated living space below rises to the underside of the roof deck. As the roof deck warms, the bottom layer of accumulated snow on the rooftop begins to melt, causing water to trickle down the roof.
Once the runoff reaches the cold outer edge, it refreezes into ice. When this happens repeatedly, an ice dam forms along the eaves, blocking the escape of further runoff. Once the water has nowhere to go, it can back up under the shingles. A properly installed self-adhered underlayment is a final defense against ice damming. This tear-resistant, waterproofing product seals tight around nails.
It helps prevent water overflow from entering exterior walls or the attic where it can saturate the floor insulation, ruin the drywall underneath or get into the interior walls. Humidity, generated from your living area or from outside, that enters a cool attic condenses into a liquid when it meets colder surfaces.
Over time, that moisture can cause deterioration of the roof system and interior structural elements or ruin the attic insulation. Spotting the Signs of Improper Ventilation An inadequate attic ventilation system can cause a variety of problems that manifest themselves in different ways. Share this Post:. Which Shingle Is Right For You Getting the color and shape of shingle you always wanted is a great way to express your individual personality and add real value.
Learn More. Looking For A Contractor? Contact Us Careers Investors. The insulation will resist heat transfer into the house. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. Attic fans are intended to cool hot attics by drawing in cooler outside air from attic vents soffit and gable and pushing hot air to the outside. However, if your attic has blocked soffit vents and is not well-sealed from the rest of the house, attic fans will suck cool conditioned air up out of the house and into the attic.
This will use more energy and make your air conditioner work harder, which will increase your summer utility bill. You don't want your unfinished attic cooled by your air conditioner. To prevent this, follow the air sealing and insulation strategies in this guide and make sure the attic is well-ventilated using passive vents and natural air flow. Laying fiberglass rolls is easiest for a DIY job. If you have any type of insulation between the rafters, install the second layer over and perpendicular to the first again, the second layer of roll insulation should be unfaced — with no vapor retarder.
This will help cover the tops of the joists and reduce heat loss or gain through the frame. Also, when laying down additional insulation, work from the perimeter toward the attic opening. Never lay insulation over recessed light fixtures or soffit vents.
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