Oct 8

Written by: Home Improvement Bids
10/8/2008 10:48 PM

Energy Efficiency in Remodeling: Roofs & Ceilings

Opportunities
Whether retrofitting existing attics/ceilings or building new ones as part of an addition, there are several opportunities available to improve energy efficiency, comfort, safety/health, and building durability. Energy-related improvements in ceilings and roofs fall into three major categories -- insulation, air leakage, and ventilation.

Compared to homes built today, older homes, especially those built before 1980, tend to be poorly insulated and relatively leaky. A remodeling project presents an excellent opportunity to upgrade insulation levels and reduce air leakage, more conveniently and less expensively than retrofitting these items separately, depending on the type of work slated as part of the project. Remember, the worse the home is to start with, the more savings and other benefits possible.

With any new construction, there is the opportunity to design the structure to be more easily insulated, increase insulation levels, check the quality of insulating work, and assure air tightness.

Benefits
Comfort can be improved by creating warmer surfaces due to higher insulation values and eliminating air leakage which leads to drafts. Building durability can be improved by reducing condensation, also affected by insulation and air sealing, and by improved ventilation which serves to reduce moisture levels in winter and reduce attic temperatures in summer. And, an air-tight ceiling is especially important in reducing the stack effect that can lead to backdrafting of combustion appliances.

One little recognized benefit of improved insulation values and reduced air leakage is the potential ability to install smaller capacity heating and/or cooling equipment. Such equipment is cheaper to buy and, in the case of air conditioners and heat pumps, operates more efficiently and provides better dehumidification.

Factors to Consider
Air sealing should be performed as part of any attic or ceiling construction or retrofit, before any new or additional insulating is done. In many homes, more heat is lost by air leakage than by heat transfer through insulation. Air leakage can also reduce the ability of the insulation to perform its function, so that insulating without also air sealing results in effectively lower R-values. When air sealing, you should consider the cost and method(s), and be aware of impacts on ventilation and the behavior of naturally drafted "appliances" such as furnaces, water heaters, and fireplaces.

When insulating attics and ceilings, some of the factors to consider include cost, savings, and installation methods. Depending on the present insulation levels in various parts of your home, you may be able to achieve worthwhile energy and dollar savings, as well as improved comfort, by improving R-values.

Installation Issues
Blown insulation must be carefully installed to prevent "overblowing" which reduces the R-value for a given, installed thickness. Careful installation of blown insulation in attics assures even coverage, avoiding high and low areas with varying R-values, and avoids blocking ventilation paths. Ask how the insulation contractor controls for the proper amount of insulation material and depth.

The use of a blower door can help identify leakage locations, making air sealing more effective.

Related Issues
Moisture damage to roof sheathing, framing members, and finished ceilings can result from some combination of air leakage, insulation, and ventilation problems. Air leakage through ceilings (including the top of walls) is a major source of attic moisture (and heat loss) in many homes. Generally speaking, flat and cathedral ceilings should be air sealed to prevent entry of warm, moist air from the house and should also be well ventilated and well insulated. Ice dams form most commonly where there is excessive air leakage and inadequate insulation (which warms the attic/roof, causing snow to melt). Inadequate ventilation may also play a role in the creation of ice dams. However, if heat loss to the attic is reduced by addressing air leakage and insulation, saving money as well as preventing ice dams, you may find that additional ventilation is not needed.

Material/Equipment Options
A wide variety of materials, in various combinations, can be used to construct durable, energy efficient attics/roofs. Listed below are commonly used, and newer, less widely used, material options for insulation, air sealing, and ventilating.

Batt Insulation

• Typically made from fiberglass fibers, also available: mineral or rock wool, cotton, wool, and some new types of fiberglass
• R-3.1 to 4.3 per inch
• Attic spaces: available in R-11, 13, 15, 19, 21, 30, 38
• Available with or without a kraft paper or foil vapor barrier
• Blown Insulation -- Loose-fill Fiberglass and Cellulose
• Made from fiberglass fibers or treated cellulose (recycled newspaper)
• R-2.2 to 3.7 per inch
• Can be installed to any depth/R-value
• Poor resistance to moisture transmission
• Cellulose provides good resistance to air leakage
• Blown Insulation -- Spray Foams
• Various types of foam, commonly a type of urethane
• R-3.6-6.2 per inch
• Good inherent resistance to air leakage and moisture transmission

Foam Sheathing

• Common types:
  • Expanded polystyrene or EPS (white, beaded appearance), R-4.0 to 4.5 per inch
  • Extruded polystyrene or XPS (various colors, smooth surface), R-5.0 per inch
  • Urethanes and isocyanurates (yellowish, often foil faced), R-6 to 7 per inch

• May be applied on top of roof rafters (for cathedral ceilings), between layers of sheathing
• Available in thicknesses of _ inch and up
• More consistent insulation as fewer interruptions are made for framing members
• Material itself provides good to very good resistance to moisture transmission
• Must be detailed properly at seams to provide good overall resistance to moisture transmission and air leakage

Stress-skin, or Structural Insulating Panels (SIPS)

• Layers of foam (thicker versions of panels used for sheathing) sandwiched between layers of OSB or plywood
• Can be used to provide greater insulation for a cathedral ceiling
• R-4.0 to 6.5 per inch
• Commonly available in thicknesses of 4.5 and 6.5 inches of foam
• More consistent insulation as fewer interruptions are made for framing members
• Good resistance to air leakage - sealing required at connections to floor, each other
• Generally good resistance to moisture transmission

Airtight Drywall

• Combination of drywall applied over gaskets or drywall adhesive
• Gaskets or sealants applied to framing members to seal edges
• Additional sealing done at penetrations such as for electrical boxes
• Resists air movement
• Allows passage of water vapor

Polyethylene Sheeting
• Plastic sheets applied to the framing members
• Sometimes applied directly behind drywall (appropriate in northern climates only)
• Provides very good resistance to air leakage, if installed properly
• Provides very good resistance to moisture movement, if installed properly

Spray Foam/Caulk
• Used for various small cracks/holes such as around chimneys, pipes, ducts, and wires
• Provides very good resistance to air leakage
• Provides very good resistance to moisture movement

Ventilation Options/Materials
• Baffles - used to provide air space between roof sheathing and insulation. Made from cardboard and polystyrene foam. Use in combination with other ventilation products, below.
• Continuous ridge and soffit vents - most effective system. Various types of ridge vent, especially, are available.
• Plugs - small, round metal vents best suited for retrofit of soffit ventilation.
• Electric gable or roof fans - can provide lots of air movement and cooler attics, but may actually increase air leakage from house and presents potential safety problem due to backdrafting. Energy used to run may offset potential energy savings.
• Gable vents - can be effective based on total area and exact attic configuration.
• Mushroom vents - can be used to meet code requirements where other methods can't be used.

Remodeling Scenarios

Existing Construction
• Air seal ceiling plane
• Install additional insulation

Can use:
• Batts, if batts are already in place
• Blown fiberglass or cellulose if blown insulation is already in place
• Improve ventilation, preferably with continuous ridge and soffit vents
• Insulate attic access hatches and stairways
• Air seal attic access hatches and stairways
• Air seal chases (shafts) and dropped soffits (bulkheads)

New Construction
• Air seal ceiling plane
• Ventilate well, preferably with continuous ridge and soffit vents
• Cathedral ceiling insulation can be increased by using foam panels on interior or exterior
• Insulate to full insulation depth over exterior walls by using one of the below methods:
o Raised-heel trusses
o Deeper rafters
o Attaching rafters above ceiling joists (not to wall)
• Insulate attic access hatches and stairways
• Air seal attic access hatches and stairways
• Air seal chases (shafts) and dropped soffits (bulkheads)

Savings
The tables below indicate the estimated annual heating and cooling savings per 100 square feet of ceiling that can be expected by upgrading to the new insulating value.

EXISTING INSULATION R-VALUE

New Insulation R-Value	8	15	19
19	$5.90	$1.40
30	$7.80	$3.30	$1.90
38	$8.50	$4.00	$2.60
45	$8.95	$4.40	$3.00

Based on house with 80% AFUE furnace and 6.5 SEER air conditioner.
Baltimore, MD climate, fuel prices $.08 per kWh and $.55 per therm.

EXISTING INSULATION R-VALUE

New Insulation R-Value	8	15	19
19	$6.13	$1.47
30	$8.46	$3.80	$2.33
38	$9.44	$4.78	$3.31
45	$10.05	$5.39	$3.92

Based on house with 6.5 HSPF heat pump and 9 SEER air conditioner
Baltimore, MD climate, fuel prices $.08 per kWh and $.55 per therm.

Article courtesy of ToolBase Services

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