1. Thermal Bypass Checklist Round-Table

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

3. WHAT THERMAL BYPASS LOOKS LIKE

4. 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.

5. 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

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

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

8. 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.

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

10. 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

11. 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.

12. 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

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

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

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

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

17. 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 x 8’ = 30 sq. ft. exposed surface area’

18. 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.

19. 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

20. THERMAL BYPASS CHECKLIST: 11. FIREPLACE SHAFT WALL

21. WRAP-UP
Any other concerns?

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

23. HOW TO GET MORE INFORMATION
On the Web at: