Thermal Bypass Checklist Round-Table

WHAT IS THERMAL BYPASS? 30o F 50o F 70o F 70o F

WHAT THERMAL BYPASS LOOKS LIKE

GENERAL Builder not required to sign checklist if he/she has not verified any items. Maximum of four items allowed for builder refers to numbered items, not bullets.

Insulated sloped ceilings: THERMAL BYPASS CHECKLIST: 1. INSULATION ALIGNMENT Insulated sloped ceilings: Air barrier required except if closed cell spray foam Left – Icynene at rafters – attic with duct run now inside the house because the rafters are sealed and insulated Right – rafters on right open into vertical wall of second floor room – note foam at duct not solving the big problem

THERMAL BYPASS CHECKLIST: 1. INSULATION ALIGNMENT Doors to unconditioned spaces shall meet IECC insulation requirements for exterior doors and include full weatherstripping.

THERMAL BYPASS CHECKLIST: 1. INSULATION ALIGNMENT Slab Edge Insulation: (Climate Zones 4 and higher) Plan for Flooring!!! Exterior Interior

THERMAL BYPASS CHECKLIST: 1. INSULATION ALIGNMENT Band Joists: Highly encourage, but don’t require complete air barrier detail except: Garage/House Interface (Item #1) Cantilevered Floor (Item #6) Porch Roof (Item #12) There are factory-built insulated wall assemblies available today that, by virtue of how they are manufactured and assembled in the field, ensure full alignment of insulation with the integrated air barriers including no gaps, voids or compression. One of these materials, called Structural Insulated Panels or SIPs, are whole wall panels composed of insulated foam board glued to both an internal and external layer of wood sheathing, typically OSB or plywood. This assembly will often be manufactured with precut window openings, chases to run wiring, and splines for adjoining panels together. A house built with SIPs and carefully sealed at all joints will be very comfortable and offers another good insulation option that can help avoid moisture problems.

THERMAL BYPASS CHECKLIST: 2. SHOWER/TUB EXTERIOR WALL Courtesy of Marc Milin

It must touch the surface it is intended to insulate. THERMAL BYPASS CHECKLIST: 3. INSULATED FLOOR OVER GARAGE Improper insulation! It must touch the surface it is intended to insulate. Critical to check for air gap! Improper insulation - must touch the surface it is intended to insulate

THERMAL BYPASS CHECKLIST: 4. WALLS ADJOINING UNCOND. SPACES Key Areas: Attic Knee Walls Double Walls Skylight Shafts Porches (TBC # 14) The above-garage “bonus room” shown here amplifies the “hot wall” problem shown in the prior image because of exposure to extreme temperatures in attics and the garage. For example, in the summer the garage could get to 100oF while the side attic spaces on each side reach over 110oF and the attic above 125oF or higher. Under these conditions, the bonus room is like a low temperature oven! Now consider the Comfort Equation: Air Temp (AT) + Surface Temp (ST) = 140oF; or AT = 140oF – ST. If the bonus room average surface temperature reaches 80oF, the room air temperature would have to be 60oF (140oF – 80oF) to feel comfortable. This is very costly for air conditioning and would cause comfort problems in other rooms that didn’t have this “hot wall” problem. However, if the average surface temperature in bonus room is 70oF, than the air temperature would only need to be 70oF (140oF – 70oF) to be comfortable. This would be much less costly for air conditioning and allow even comfort in other rooms serviced by the same air conditioning system. The first problem is that cold and hot air from the garage can pass right over the gap at the top of floor insulation less thick than the floor framing. This is called “thermal bypass” since air can flow around the intended thermal barrier. Remember, misalignment is like wearing a warm jacket loosely around your body on a cold day; you feel almost as cold as with no jacket. In this case, the floor with be very hot in the summer and very cold in the winter. The other problem is that hot attic air can flow through the knee-wall insulation to the interior finish since there is no air barrier. The solution for a bonus room that works is to completely fill the floor framing space with insulation so it is snug against the sub-floor and than provide an air barrier at the edges of the floor insulation to stop air flow through the insulation. Again, this air barrier can be thin sheathing or rigid insulation. The next step is to provide an air barrier at the knee walls with the same thin sheathing or rigid insulation. What good is an extra bonus room if it gets no use because of comfort problems? This is another example of how energy efficient construction practices can directly affect home value.

THERMAL BYPASS CHECKLIST: 4. WALLS ADJOINING UNCOND. SPACES Double Walls Air Barrier The above-garage “bonus room” shown here amplifies the “hot wall” problem shown in the prior image because of exposure to extreme temperatures in attics and the garage. For example, in the summer the garage could get to 100oF while the side attic spaces on each side reach over 110oF and the attic above 125oF or higher. Under these conditions, the bonus room is like a low temperature oven! Now consider the Comfort Equation: Air Temp (AT) + Surface Temp (ST) = 140oF; or AT = 140oF – ST. If the bonus room average surface temperature reaches 80oF, the room air temperature would have to be 60oF (140oF – 80oF) to feel comfortable. This is very costly for air conditioning and would cause comfort problems in other rooms that didn’t have this “hot wall” problem. However, if the average surface temperature in bonus room is 70oF, than the air temperature would only need to be 70oF (140oF – 70oF) to be comfortable. This would be much less costly for air conditioning and allow even comfort in other rooms serviced by the same air conditioning system. The first problem is that cold and hot air from the garage can pass right over the gap at the top of floor insulation less thick than the floor framing. This is called “thermal bypass” since air can flow around the intended thermal barrier. Remember, misalignment is like wearing a warm jacket loosely around your body on a cold day; you feel almost as cold as with no jacket. In this case, the floor with be very hot in the summer and very cold in the winter. The other problem is that hot attic air can flow through the knee-wall insulation to the interior finish since there is no air barrier. The solution for a bonus room that works is to completely fill the floor framing space with insulation so it is snug against the sub-floor and than provide an air barrier at the edges of the floor insulation to stop air flow through the insulation. Again, this air barrier can be thin sheathing or rigid insulation. The next step is to provide an air barrier at the knee walls with the same thin sheathing or rigid insulation. What good is an extra bonus room if it gets no use because of comfort problems? This is another example of how energy efficient construction practices can directly affect home value. Heat

THERMAL BYPASS CHECKLIST: 4. WALLS ADJOINING UNCOND. SPACES Courtesy of Consol

THERMAL BYPASS CHECKLIST: 4. WALLS ADJOINING UNCOND. SPACES Courtesy of Consol

THERMAL BYPASS CHECKLIST: 4. WALLS ADJOINING UNCOND. SPACES Courtesy of Consol

THERMAL BYPASS CHECKLIST: 4. WALLS ADJOINING UNCOND. SPACES Skylight Shaft Skylight Attic Air Barrier Air Barrier Insulation

THERMAL BYPASS CHECKLIST: 4. WALLS ADJOINING UNCOND. SPACES Tubular Skylight 14” Exposed area = ~30 sq.ft. Need insulation and air barrier 1.2’ diamater x 3.1412 x 8’ = 30 sq. ft. exposed surface area’

THERMAL BYPASS CHECKLIST: 6. CANTILEVERED FLOOR Tips: Consider spray foam insulation installed to desired thickness because it can serve as both insulation and an air barrier. Critical to check air gap at floor. Add Blocking Fill with Insulation Thermal Bypass Seal Edges Cantilevered floor assemblies are another common problem. Often they are insulated similar to a “bonus room” above a garage with the insulation attached to the bottom edge of the floor framing. This leaves an air gap above or misalignment between the insulation and the sub-floor above. Heat transfer can easily occur at the band joist due to very low R-value of wood and result in a cold floor in the winter and warm floor in the summer. Remember, misalignment is an insulation value killer. Moreover, the risks of moisture problems are much greater because warm air from the home can now flow above and through the insulation to the cold outside wood band joist in winter where it can condense and result in mold and dry rot. The fix to this common problem is very similar that recommended for bonus rooms. First, completely fill the framing space with insulation so it is in full contact with the floor above. Then add an air barrier with thin sheathing or rigid insulation to the edge of the insulation so it blocks air flow from inside the home. Not only will these proper insulation details improve the energy efficiency, they will improve comfort, air quality and durability.

THERMAL BYPASS CHECKLIST: 8. FLUE SHAFT TIP: Specially colored fire-rated foam now available for sealing difficult air gaps at flue openings Image courtesy of EnergyLogic Image courtesy of EnergyLogic

THERMAL BYPASS CHECKLIST: 11. FIREPLACE SHAFT WALL

WRAP-UP Any other concerns?

“It wasn’t raining when Noah built the Ark.” ANSWER... One more thought… “It wasn’t raining when Noah built the Ark.” Howard Duff

HOW TO GET MORE INFORMATION On the Web at: http://www.energystar.gov/homes