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7 Steps to an Energy-Efficient House: 2. The Roof

Superinsulate and air-seal the roof

Image 1 of 2
Air sealing comes first. Before beefing up attic insulation, it's essential to seal cracks in the attic floor.
Image Credit: GreenHomes America
Air sealing comes first. Before beefing up attic insulation, it's essential to seal cracks in the attic floor.
Image Credit: GreenHomes America
Capping the roof with thick insulation. A re-roofing job provides an opportunity to beef up the roof insulation. This roof is being retrofit with two layers of 3-in-thick polyisocyanurate foam.
Image Credit: Alex Cheimets

Editor’s introduction: With energy prices rising again, many homeowners are planning energy-efficiency improvements to their homes. But most people are unsure of where to begin, and even seasoned builders don’t always know which priorities should rise to the top of the list. Betsy Pettit, an architect at Building Science Corporation
, recommends starting where you can get the most bang for the buck.

Step 2: To stop air leaks and reduce heat loss, seal up your home’s cap

If air leaks in at the bottom of a house, it also leaks out at the top, making the house cold and drafty in winter. A poorly insulated roof also can make a house hot in summer.

Air-sealing work should always accompany any insulation improvements. Using spray foam under a roof can eliminate the need for roof venting, which is tricky in complicated roofs. Other insulation options include cellulose on the attic floor or rigid insulation on top of the roof sheathing.

This article is adapted from Betsy Pettit’s Remodeling for Energy Efficiency
in Fine Homebuilding


In Green Basics:

Air Barriers

Insulating Attics

Insulating Flat Ceilings and Roofs

In Community Forum:

Attic Insulation and Sealing

How Should I Insulate My Roof?

How to Insulate My Roof?

In Strategies and Details:

Air Sealing An Attic Hatch

In Blogs:

Attic Insulation Upgrades

Blower Door Basics

Roofing and Siding Jobs Are Energy Retrofit Opportunities


  1. Doug McEvers | | #1

    Attic air sealing
    Many of the homes built in MN have soffits for kitchen cabinets that are open to the attic, the ceiling plane of plaster or drywall is not continuous at this point. It is important to address the open soffits with rigid foam or boardstock of some type to seal these major bypasses.

  2. Bryan | | #2

    Just wondering if it's really necessary to stretch this "series" into 7 posts? If every 'article' is only two paragraphs, I'm pretty sure you could fit it all nicely into one larger easier to manage post. Just a thought.

  3. John Brooks | | #3

    Mission Impossible
    To me......Image 2 is a striking image.
    Yes, it is possible.... but it sure looks precarious.(and not-exactly-OSHA)
    It reminds me of the Tom Cruise movie where he is suspended above the laser beams.

    My eye is also drawn to the Not-So-Even surface of the polyiso.
    I realize that it has not been screwed down yet..but still .. the reality is not what you would expect if you were to look at "perfect"construction drawings.(AutoCad or Sketchup)

    John Straube makes a very good point about real 2x4's not really being like AutoCad 2x4's
    I think the same can be said about polyiso panels.
    I can imagine a cavernous 3d-network between the faces of panels.

  4. 2jRjmoTLAg | | #4

    Roof Venting is Critical
    Roof venting is critical to a cool roof. with venting at soffit and ridge hot air can rise out and be replaced by cool air. Basic thermodynamics informs us that temperature difference is a major factor in heat transfer, so cool air in the space between roof deck and insulation and ceiling will reduce heat transfer from roof deck to the interior of the structure.

    If air flow between roof deck and insulation is a design goal there is no need for roof venting to be "tricky"

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