Thread: unvented attic

I know the IRC recently made changes to allow this if certain conditions are met. Anyone familiar with Flordia, I have a house I am looking at currently that has no venting per the architects design. That is great , only there is no foam on the sheathing and they have installed batt insulation. The builder believes this is ok. I understand that air impermeable insulation is needed on the underside of the decking between the rafters and no vapor retarders are to be installed on the ceiling side of the unvented attic space. The spray foam is obviously missing. Do batts not have a vapor retardering layer as well? I am I missing something? Or is this just a misinterpretation b y me or the builder?

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Does the home have comp shingles? If so, the lack of proper ventilation will not only deteriorate the roofing prematurely it will, in most cases void the warranty on the shingles.

wood shake; testing has proven that the extra heat created by unvented attics varies no more than a southern vs northen exposure or shingle color. still alot of unknowns.

Do you have the plans and the energy calculation sheets for the home? If they are available for your review, they may specify type of insulation to be installed for the non vented attic area.

The few wood shake or shingle roofs I run across up here typically have no additonal ventilation provisions installed. The problems I see is when somebody upgrades from a wood shingle roof to an asphalt shingle roof and doesn't install ventilation. The asphalt shingles don't breathe and the roof decking installed beneath the shingles blocks air flow. Mold growth is typically in the near future.

Jerome,

From the 2004 Florida Building Code (which the Florida Residential Code refers to for the Administration section). (underlining is mine)
- 104.11 Alternative materials, design and methods of construction and equipment.
- - The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety. When alternate life safety systems are designed, the SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings, or other methods approved by the building official may be used. The building official shall require that sufficient evidence or proof be submitted to substantiate any claim made regarding the alternative.

Yes, that is allowed.

No, sprayed on foam is not a requirement for unvented, sealed, attic.

It all must be designed by a professional designer, in this case that would be the architect - they are 'the design professional of record' and have full responsibility for their designs which use the 'alternative materials and methods' route.

How new is the house?

in your area [philly?]: "sufficient insulation must be installed to maintain the monthly average temperature of the condensing surface above 45 F. The condensing surface is defined as either the structural roof deck or the surface side of the air impermeable insulation"

Jerry,
built 2007; wood shake; 4.2 Mil; Buyer is wearing me out! Or just earning my fee!