Where the roof meets the wall, the water control layer of the roof is not connected to the water control layer of the wall. The water control function is "transitioned" to the wall by providing overhangs to protect the top of the wall. Essentially, the roof overhang is like a large flashing over the top of the wall.

Because the water control layer of the roof is not connected to the water control layer of the wall, the transition detail for the roof-to-wall intersection is not affected by the position of the water control layer in the wall assembly. The illustrations in this section depicting a transition to a retrofit wall are equally applicable to DER projects employing the wall retrofit assembly Wall 1A as to those employing Wall 1B.

The transition of air control is both critical and difficult at the roof-wall intersection. Continuous air control at the top of the building is critical to performance because the difference between interior and exterior pressure during the heating season tends to be greatest at the top of the building. These pressure differences are the driving force behind air leakage. Implementing uninterrupted air control can be complicated by the geometry of the roof overhang, by the location of the air control layer in the wall being on a different side of the enclosure than it is for the attic or roof, and by intervening framing.

The most effective way to address or remove these complications is to pursue what is often called a "chainsaw" roof-wall connection. In this approach, the overhang of the existing roof is cut back flush with the face of the exterior wall sheathing. Then an air control membrane can be wrapped from the surface of the existing roof sheathing to the surface of the existing wall sheathing without interruption. Insulation can also be placed in a continuous, uninterrupted manner over this intersection with the roof cladding and overhang installed to the outside of the insulation. This approach is only practical where the roof is insulated and re-clad above the existing roof sheathing (Roof 1 assembly) and where the roof rafters are not supported beyond the face of the exterior wall (as when the rafters bear on cantilevered ceiling joists).

This section illustrates both "chainsaw" and non-chainsaw approaches to the roof-wall transition. Because of the enormous variety of framing conditions at the roof-wall intersection, the illustrations in this section are necessarily schematic in nature.

Particularly in the non-chainsaw roof-wall transitions, effective continuity of the air control will rely on careful implementation and an understanding of the many connections that must be made airtight in order to connect the air control of the wall to that of the attic or roof.

Attic 1 to Wall 1-Eave

• This transition applies for both Wall 1A and to Wall 1B.
• Modify or relocate blocking between the rafters as needed in order to maintain the 2" ventilation space across each rafter bay.
• Total R-value at top of wall, including R-value of rafter baffle and spray foam, should
  be at least R-40.

Attic 1 to Wall 1-Rake

• This transition applies for both Wall 1A and Wall 1B.

Attic 1 to Untreated Wall-Eave

• It may be necessary to modify or relocate blocking between the rafters in order to maintain the 2" ventilation space across each rafter bay.
• Temporarily remove siding at top of wall as needed for access to the existing house- wrap or building paper.
• Total R-value at top of wall, including R-value of rafter baffle and spray foam, should
  be at least R-40.

Attic 1 to Untreated Wall-Rake

Roof 1 to Wall 1 (Chainsaw)-Eave

• This transition applies for both Wall 1A and Wall 1B
• This transition only applies if the rafter tails can be cut off without compromising the roof framing structure.
• Chainsaw air control and thermal control functions are more robust than those for the non-chainsaw retrofit.

Roof 1 to Wall 1 (Non-Chainsaw)-Eave

• This transition applies for both Wall 1A and Wall 1B
• This transition is to be used if roof framing structure cantilevers beyond the walls.
• Some existing insulation at the top of the exterior wall may need to be removed so that the closed-cell spray foam establishes a seal with the back side of the wall sheathing.

Roof 1 to Wall 1-Rake

• This transition applies for both Wall 1A and Wall 1B.
• Even if the attic is unfinished space, cavity insulation of the gable wall is required; if closed-cell spray foam is used, it should be limited to a thickness of 1" so that the wall can dry to the interior.

Roof 1 to Untreated Wall (Chainsaw)-Eave

• This transition only applies if the rafter tails can be cut off without compromising the roof framing structure.
• Chainsaw air control and thermal control functions are more robust than those for the non-chainsaw retrofit.
• The insulating sheathing installed at the top of the wall should be as thick as the insulating sheathing that will be used for the upgraded wall.

Roof 1 to Untreated Wall (Non-Chainsaw)-Eave

• This transition is to be used if roof framing structure cantilevers beyond the walls.
• Some existing insulation at the top of the exterior wall may need to be removed so that the closed-cell spray foam establishes a seal with the back side of the wall sheathing.

Roof 1 to Untreated Wall-Rake

• Even if the attic is unfinished space, cavity insulation of the gable wall is required; if closed-cell spray foam is used, it should be limited to a thickness of 1" so that exist- ing condition for drying to the inside is not changed
• Temporarily remove siding at top of wall as needed for access to the existing house- wrap or building paper.

Roof 2 to Wall 1-Eave

• This transition applies for both Wall 1A and Wall 1B.

Roof 2 to Wall 1-Rake

• This transition applies for both Wall 1A and Wall 1B.
• If the gable has existing insulation, some of this must be removed at the top so the closed-cell spray foam establishes a seal with the back side of the existing wall sheathing.
• Even if the attic is unfinished space, cavity insulation of the gable wall is required; if closed-cell spray foam is used in the gable wall cavity, it should be limited to a thick- ness of 1" so that the wall can dry to the interior.

Roof 2 to Untreated Wall-Eave

Roof 2 to Untreated Wall-Rake

• If the gable has existing insulation, some of this must be removed at the top so the closed-cell spray foam establishes a seal with the back side of the existing wall sheathing.
• Even if the attic is unfinished space, cavity insulation of the gable wall is required; if closed-cell spray foam is used in the gable wall cavity, it should be limited to a thickness of 1" so that existing conditions for drying to the inside are not changed.

Untreated Roof/Attic to Wall 1-Eave

• This transition applies for both Wall 1A and Wall 1B.
• If the untreated attic/roof is vented, the top of the insulating sheathing must be cut back to maintain the existing ventilation gap.

Untreated Roof/Attic to Wall 1-Rake

• This transition applies for both Wall 1A and Wall 1B.
• Even if the attic is unfinished space, cavity insulation of the gable wall is required; if closed-cell spray foam is used in the gable wall cavity, it should be limited to a thickness of 1" so that the wall can dry to the interior.