unvented attic

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Pondering an Attic Conversion in New York

A homeowner wonders whether the advice he’s getting on insulating his attic will lead to trouble

Posted on Dec 25 2017 by Scott Gibson

An energy auditEnergy audit that also includes inspections and tests to assess moisture flow, combustion safety, thermal comfort, indoor air quality, and durability. on BuildingNewb's upstate New York home has prompted a recommendation that he insulate the rafter bays with dense-packed cellulose, transforming what is now a ventilated attic into conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. .


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Image Credits:

  1. Images #1 and #2: BuildingNewb

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Does a Bigger Volume Mean More Heating and Cooling Load?

Many people answer this question incorrectly

Posted on Mar 15 2017 by Allison A. Bailes III, PhD
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What happens to the heating and cooling loads when you encapsulate an attic? With the insulation and air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. at the ceiling below the attic, you're excluding the attic space. That volume of air up there isn't involved in the conditioning of the home. But when you move the enclosure to the roofline (usually by installing spray foam insulation beneath the roof deck), now the attic's volume is included in the conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. .

Occasionally I hear people say the loads will be higher because of the extra volume. Does having more air inside really increase the loads?


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Image Credits:

  1. Energy Vanguard

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Three Reasons to Remove Attic Floor Insulation in a Sealed Attic

Attics insulated with spray foam have different characteristics from vented attics

Posted on Aug 10 2016 by Allison A. Bailes III, PhD
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I get asked a lot of questions about spray foam. Do I need an ignition barrier? Should I use open-cell or closed-cell spray foam? Will open-cell spray foam really rot my roof?

But the question I get more than any other on this topic is about whether or not the insulation on the attic floor should be removed when insulating the roof deck in an existing home. As you can tell from the title of this article, my answer is to remove it. Here are my three reasons, in increasing order of importance.


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Image Credits:

  1. Energy Vanguard

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Can Unvented Roof Assemblies Be Insulated With Fiberglass?

Owens Corning is promoting an insulation method that has long been considered risky

Posted on Aug 21 2015 by Martin Holladay
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Experts usually advise builders that you can’t install fiberglass insulation directly against the underside of roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. . If you want to install fiberglass between your rafters, you have two basic choices: either include a ventilation channel between the top of the fiberglass insulation and the underside of the roof sheathing, or install enough rigid foam above the roof sheathing to keep the roof sheathing above the dew point during the winter. These rules were developed to prevent damp roof sheathing.


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Image Credits:

  1. Images #1 thorugh #5: Owens Corning
  2. Image #6: U.S. Department of Energy

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All About Attic Venting

We vent attics for four reasons, and all four goals can be better achieved by adopting measures other than attic venting

Posted on Dec 6 2013 by Martin Holladay

Most homeowners and builders believe that attics should be vented. If you walk down to your local lumberyard and lean on the counter, the employees and nearby customers will offer a variety of opinions about why attics need to be vented. Unfortunately, it’s highly unlikely that the statements you hear will be true.


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Image Credits:

  1. Fine Homebuilding
  2. Morrison Hershfield

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Spray Foam Insulation Does Not Work with All HVAC Systems

Before you use spray foam insulation in an attic, make sure the HVAC system is compatible

Posted on Sep 18 2013 by Allison A. Bailes III, PhD

Earlier this year I got a question about a home that had spray foam insulation in the attic. There's nothing unusual about that. A lot of builders and homeowners are going with spray foam insulation because of the airtightness benefits.

But then the questioner mentioned that the spray foam contractor had intentionally left big holes to the outside by not sealing the gable vents.


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Image Credits:

  1. Energy Vanguard

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Pondering an Attic Conversion

Adding spray foam to the underside of the roof sheathing will turn a vented attic into a conditioned space — but will it also create problems?

Posted on May 20 2013 by Scott Gibson

Rob Graff is getting a new roof, and with it an opportunity to turn his vented attic into an insulated, conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. .

But he’s also got some concerns.


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Image Credits:

  1. Fine Homebuilding

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Attic Insulation Upgrades

Historic homes require compromises

Posted on Nov 2 2009 by Michael Maines

Two projects my company is currently working on involve a common problem: not enough insulation in the attic. Both homes are old; one dates from 1860, the other from 1705. In both cases we initially recommended insulating the rafter bays. In both cases, however, we were not able to get over homeowner biases against heating “storage spaces,” and instead opted for insulating the attic floor.


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Image Credits:

  1. Harborside Design

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