Improving Insulation Installation

Customer Performance Targets for Insulation

The quantifiable targets use the building code as the minimum.  Common sense and energy modeling can modify these values.

Current building code requirements, at a minimum, for accessible areas
Rigid sheathing on attic kneewalls
Overlap insulation around corners
Limit thermal bridging
Enclose and insulate chases and changes in ceiling height
Air seal and Insulate Attic Entrances
Consider using effective R-values rather than rated R-values
Install vapor barriers on the proper surface, if needed

Reducing Thermal Transmission

Insulation problems are resolved by reducing thermal transmission and air leaks.  First, air seal the building envelope, then install insulation on the thermal barrier.

Correct Air Leaks.  Before insulating, air sealing has to either be done first or as part of the insulation process.  All the air sealing considerations for combustion safety, moisture control, and ventilation must also be addressed.  These are discussed as part of the air sealing improvement process.

Insulate Building Shell.  There are a variety of methods for insulating that depend on the location, type of materials used, and the environmental conditions.  For each type of insulation, the manufacturer’s instructions and best practices need to be followed for best results.

Rather than review various methods, there are principles to bear in mind.  There are also some special cases worth mentioning.

Insulating Attic Kneewalls.  Kneewalls account for a huge energy transfers because of the difference in temperature between the living space and attics.  Friction fitting is not an acceptable solution for batts because they will eventually fall away to do gravity and other factors.

6-Sided Wall Cavities. The solution is treat them like any other exterior wall, where insulation is enclosed on all six sides: each stud, top & bottom, and rigid sheathing on both sides of the wall.  Typical kneewalls are missing sheathing on the attic side and tops of the walls are not closed.  Occasionally, the bottom is open too. 

Perfect Fit. The goal is to enclose insulation cut to a perfect fit ins sealed wall cavities.  This makes the air still and avoids convection currents in the wall cavities.  An optional idea is to use radiant barrier plywood on the attic side to reflect attic heat away from the kneewall.

Wall Reconstruction. Sometimes, the wall needs to be built because of the way the kneewall is built.  If so, the insulation needs to be installed in two layers: once for the existing cavities to get and even surface against the conditioned wall.  The second layer fills the added wall cavities.

Overlapping Insulation. When the job is done, ceiling insulation should extend to the outer edge of the kneewall to avoid cold spots at the corner made by the ceiling and wall.

Vapor Retarders. Water vapor is a gas and will pass through many building materials.  There is plane inside the wall where the temperature is probably the dew point for moist air.  It changes based on seasons, temperatures, and moisture content. 

The goal is to avoid condensation in the insulation and causing the structure to deteriorate.

Function. The function of a vapor retarder (e.g., the paper on faced batt insulation) is to attempt to keep moist air warm so that it doesn’t condensing and allowing the moisture to go out of the wall cavity the same way it came in.

Vapor barriers (e.g., plastic sheets) in walls should not be use because they will trap moisture such that it can’t dry out.

Installation. Vapor retarders are critical for insulation performance.  The rule of putting the vapor retarder on the warm-in-winter side (usually the interior wall) applies (Northern states).  However, for some climates vapor retarders are either unnecessary (Southwestern states) or they are in the wrong place half the year (Southeastern states).

Selecting Vapor Barriers. If vapor retarders are used be sure to think the entire moisture problem through first, for all seasons of the year.  Also consider the rest of the wall structure, including paint and wall paper, when selecting among choices.

Spray Foam Insulation. Spray foam comes in two broad categories: open-cell and closed cell.  If you need moisture to pass through it to avoid water damage (e.g., roof decks), use open-cell foam.  If you’re try to make a vapor barrier (e.g., crawlspace subfloor), use closed cell.

Fire & Smoke Safety.  One of the major factors used to decide what materials to use as insulation and how to install them is how quickly flame spreads and the amount and type of smoke created.  Foam of any type in living space has to be covered with suitable materials, such as gypsum board (e.g., Sheetrock), plywood, OSB, or metal.  Fiberglass and cellulose have very different fire characteristics.  Fiberglass is made of sand and recycled glass.  Cellulose is made of recycled paper.

Water Retention.  Insulation materials retain water differently too.  Water in fiberglass drains almost immediately.  Cellulose retains it.  Moisture in exterior walls has to dry out.  Be sure the materials and environmental conditions are suitable for where it’s being installed.

Indoor Air Quality.  Dust of any type is unhealthy to breathe.  A lot of dust is created during the installation process.  The dust can be carried in the air we breathe, especially if it’s drawn in through duct leaks.

Many of insulation materials also out-gas, which can cause respiratory and eye irritation.  Where possible, these gases should be flushed out, perhaps with an air scrubber or opening the windows.  The choice of whether to do it or not depends on humidity conditions.  This is not the right choice in the Southeastern United States in the summer time.

Attic Openings.  The single largest hole in the insulation and air barrier is attic entrances: pull-down stairs, scuttle holes, and access panels.  The trick is to figure out to provide adequate insulation, while easily sealing up the gap between the cover and attic.

Not insulating an attic entrance is not an option.  A 10 sqft hole for pull down stairs (~R-0) in an attic otherwise rated to R-30 over the other 990 sqft reduced the effective insulation value to ~R-22 for the entire 1000 sqft attic.  Add severe air leakage, to get a huge loss of energy.

There are a variety of solutions available on the Internet.

Windows. Windows are a special category, making up part of the thermal boundary around the building.  The home improvement ideas for them are shared in a separate article dedicated to windows.

Doors. Because of high purchase and installation costs, replacing doors is not usually a cost-effective energy reduction measure.  Adding storm doors can help, but the cost benefit is still small.  However, when replacing doors for any reason, it pays to consider its thermal features.

Post Insulation Inspection. Insulation success depends on installation quality.  It’s vitally important that anyone who specifies, supervises, or installs insulation to be familiar with insulation principles, characteristics, and correct installation procedures.

For home performance contractors, final testing is mandatory when combustion appliances are present.  The concern is not so much as the insulation as it is the reduction in air leakage. The concern is ensuring the areas fireplaces, water heaters, and furnaces are in are not depressurized to the point of causing smoke to backdraft into the house.

Where there are incentives or certificates offered, the sponsor (e.g., utility company) usually requires final testing too.  Their considerations are to verify the insulation is installed properly.

We are ready, willing, and able to perform third-party testing.

In Conclusion . . .

In the home performance improvement process for energy improvement, the top three things are to air seal the building, air seal the ducts, and insulating the ducts and building.

A complete thermal barrier and air barrier is needed all the way around the conditioned spaces of the building to reduce the heat loads heating & cooling equipment has to overcome.  Done right, the building will probably be quieter.  Depending on how its done, the structure may also be more rigid, such as with spray foam or sheathing on attic kneewalls.

Here’s to a more comfortable and energy efficient house!


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