Recommended Assemblies

Below we have included recommendations for the building envelope assemblies based on the Energy model results shown in previous sections. These are recommendations only and should be reviewed by the design team to ensure they are appropriate for the project.

The following assembly U-Values have been assessed using Flixo Energy v8.2. All assemblies are proposed based on the Energy model results shown in previous sections. Note: All 2-dimensional heat flow analysis simulations have been executed following the protocols outlined in ISO 6946 and ISO 10211 where applicable.

Assembly Types:

Floor 01: Below Grade Slab [Target R-10]

Note: Concrete floor shown for illustration only. Concrete floor thickness to be determined by structural engineer or architect.

• Target 4" sub-slab XPS foam board (or Graphite-EPS) below concrete.
• Sub-slab air and vapor barrier to be installed directly above insulation. Use 15 Mil Stego-wrap or sim.
• Tape / seal all penetrations and seams of sub-slab air and vapor barrier.

Wall 01: NEW Below Grade Walls [Target R-10.9]

• Achieve code-minimum (R-10.9) for all NEW below-grade walls.
• Install 2 inches of XPS (R-5/inch) insulation on the EXTERIOR of all new foundation walls.
• Finish insulation above grade with cement-board cover.

Wall 02: EXISTING Masonry Partywalls [Target R-4.7]

• Apply liquid air-sealing membrane on inside face of all partywalls.
• Add acoustic insulation if desired.

Wall 03: EXISTING Masonry Front Facade Walls [Target R-4.7]

• Apply liquid air-sealing membrane on inside face of all front facade walls.
• Leave all front facade walls un-insulated.

Wall 04: EXISTING Masonry West Facade Walls [Target R-4.7]

• Apply liquid air-sealing membrane on inside face of all front facade walls.
• Leave all front facade walls un-insulated.

Wall 05: NEW Rear Extension Walls [Target R-16.4]

• Fill all stud bays with batt insulation.
• Install min R-8.5 continuous exterior insulation.
• Primary air-barrier to be continuous air/water resistive membrane installed on the exterior side wall sheathing, underneath continuous insulation. ProClima Adhero or sim.
• Provide smart-vapor-retarding membrane ProClima Intello Plus or sim. on interior side of wall framing.
• Install ‘service cavity’ drop-ceiling in order to run all electrical and plumbing elements as needed.

Wall 06: NEW Bulkhead Walls [Target R-16.4]

• Fill all stud bays with batt insulation.
• Install min R-8.5 continuous exterior insulation.
• Primary air-barrier to be continuous air/water resistive membrane installed on the exterior side wall sheathing, underneath continuous insulation. ProClima Adhero or sim.
• Provide smart-vapor-retarding membrane ProClima Intello Plus or sim. on interior side of wall framing.
• Install ‘service cavity’ drop-ceiling in order to run all electrical and plumbing elements as needed.

Roof 01: Rear Terrace Deck [Target R-50]

Note: 3x8 framing shown based on Structural drawings (June 18, 2024). Final roof framing to be determined by structural engineer or architect.

• Flat roof assembly designed for code compliance according to 2021 IRC R806.5.5.1.4:
  • "…sufficient rigid board or sheet insulation shall be installed directly above the structural roof sheathing to maintain the monthly average temperature of the underside of the structural roof sheathing above 45°F (7°C). For calculation purposes, an interior air temperature of 68°F (20°C) is assumed and the exterior air temperature is assumed to be the monthly average outside air temperature of the three coldest months."
• Install Min. 4" XPS insulation above roof sheathing to ensure sheathing is not at condensation risk.
• Provide sufficient exterior insulation to achieve code-min R-50 (U-0.02)
• Fill all joist-bays with batt insulation.
• Provide air-barrier/smart-vapor-retarding membrane ProClima Intello Plus or similar at interior side of roof framing.
• Install ‘service cavity’ drop-ceiling in order to run all electrical and plumbing elements as needed.

Roof 02: Main Roof [Target R-50]

Note: 2x10 framing shown based on Structural drawings (June 18, 2024). Final roof framing to be determined by structural engineer or architect.

• Flat roof assembly designed for code compliance according to 2021 IRC R806.5.5.1.4:
  • "…sufficient rigid board or sheet insulation shall be installed directly above the structural roof sheathing to maintain the monthly average temperature of the underside of the structural roof sheathing above 45°F (7°C). For calculation purposes, an interior air temperature of 68°F (20°C) is assumed and the exterior air temperature is assumed to be the monthly average outside air temperature of the three coldest months."
• Install Min. 4" XPS insulation above roof sheathing to ensure sheathing is not at condensation risk.
• Provide sufficient exterior insulation to achieve code-min R-50 (U-0.02)
• Fill all joist-bays with batt insulation.
• Provide air-barrier/smart-vapor-retarding membrane ProClima Intello Plus or similar at interior side of roof framing.
• Install ‘service cavity’ drop-ceiling in order to run all electrical and plumbing elements as needed.

Roof 03: Bulkhead Roof [Target R-50]

Note: 1000S162-43 Steel C-Joist framing shown based on Structural drawings (June 18, 2024). Final roof framing to be determined by structural engineer or architect.

• Flat roof assembly designed for code compliance according to 2021 IRC R806.5.5.1.4:
  • "…sufficient rigid board or sheet insulation shall be installed directly above the structural roof sheathing to maintain the monthly average temperature of the underside of the structural roof sheathing above 45°F (7°C). For calculation purposes, an interior air temperature of 68°F (20°C) is assumed and the exterior air temperature is assumed to be the monthly average outside air temperature of the three coldest months."
• Install Min. 4" XPS insulation above roof sheathing to ensure sheathing is not at condensation risk.
• Provide sufficient exterior insulation to achieve code-min R-50 (U-0.02)
• Fill all joist-bays with batt insulation.
• Provide air-barrier/smart-vapor-retarding membrane ProClima Intello Plus or similar at interior side of roof framing.
• Install ‘service cavity’ drop-ceiling in order to run all electrical and plumbing elements as needed.

Building Airtightness

The primary role of airtightness in buildings is to avoid interstitial condensation and mold/moisture damage to the structure during the winter and shoulder season months. Additionally, in hot climates the airtightness plays an additional important role in restricting warm outdoor air and moisture vapor ingress from the exterior. This helps to reduce energy consumption needed for cooling and dehumidification while improving occupant comfort and building resiliency.

As well as its role in ensuring building durability, airtightness levels have a simple linear relationship to the building’s heat loss: the more air- tight the construction the less heat is lost in winter and the better the energy performance. In addition, the airtightness of the building has a large effect on the indoor relative humidity during the summer months with a corresponding reduction of cooling energy consumption and dehumidification need.

Code-minimum construction in most states require an airtightness rate of somewhere between 3 to 7 air-changes per hour (ACH), and the NYS Energy Code 2020 / Zone 4(A) requires residential buildings in Climate Zones 3 to 8 to demonstrate an airtightness level of less than 3.0 ACH@50Pa. In order to meet the recommended building performance level, this project would have to achieve the extremely stringent airtightness level of less than 1.0 ACH@50Pa. The graph above shows the heat loss at various levels of airtightness for the building. Improving airtightness to this low level (1.0 ACH@50Pa) is one of the best ways to improve performance and increase comfort and durability and is the recommended target for this building.

Masonry Rowhouse Air-sealing Primer

BLDGTYP has prepared a comprehensive Masonry Rowhouse Air-Sealing Primer memo which covers all aspects of air-sealing for typical masonry residential buildings in NYC. This guides discusses the value of air-sealing, common air-sealing methods for various assembly types, recommended products, and various testing strategies. Download the guide below:

Building Redline Test

Illustrated below is an example of the ‘red line’ evaluation test. This test, commonly used in Passive House design, requires that a single continuous air barrier (commonly denoted with a red line) is able to be traced around the entire conditioned envelope of the home. Any area where the air barrier line is broken or ambiguous is marked for further development and clarification by the design team.

The goal of this exercise is to identify and clearly document all critical junctions, transitions and penetrations of the air barrier. In the diagrams below, the areas marked with callouts are judged to be critical details and we recommend that the detailing phase address these items and clearly identify the air-tightness layers, products and transition details. Establishing an unambiguous air barrier for this project with all needed project details will be critical to its success and achieving the high-performance targets.

Assemblies:

1. Floor Slab: [Sub-Slab Vapor-Barrier Sheeting] Tape / seal all joints, penetrations and seams. Sub-slab vapor barrier to be min 15Mil. sheeting or better. Install sub-slab vapor-barrier above insulation, in direct contact with concrete. Turn sub-slab vapor-barrier up wall and seal with elastic sealant and tape. Use termination bar to ensure permanent bond.

2. Existing Below Grade Wall: [Sub-Slab Vapor-Barrier Sheeting] Extend sub-slab vapor-barrier sheeting up the entire below-grade wall. Tape all seams and penetrations with manufacturer approved tapes and sealants.

3. Existing Above Grade Masonry Wall: [Liquid Applied Air-Barrier] Provide vapor-permeable liquid-applied air barrier on the interior face of all existing masonry walls.

4. Existing Roof: [Roof Membrane] Airtightness layer to be air barrier/WRB installed over plywood sheathing. Seal all joints, seams and penetrations as per manufacturer’s instructions. If the joist bays of the roof are insulated, install a continuous smart-vapor-retarder along the underside of all joists as well. Include a drop-ceiling for all electrical and plumbing elements to be installed within.

5. Bulkhead Walls: [Exterior WRB] For all new bulkhead walls, install continuous air and water barrier on the exterior side of the sheathing BEFORE continuous insulation. If the stud-bays are insulated, ensure that a smart-vapor-retarder membrane is installed on the inboard side of the studs as well. Include a ‘service cavity’ for all electrical and plumbing elements to be installed within.

6. Bulkhead Roof: [Roof Membrane] Airtightness layer to be air barrier/WRB installed over plywood sheathing. Seal all joints, seams and penetrations as per manufacturer’s instructions. If the joist bays of the roof are insulated, install a continuous smart-vapor-retarder along the underside of all joists and include a drop-ceiling for all electrical and plumbing elements to be installed within.

7. New Rear Walls: Provide vapor-permeable liquid-applied air barrier on the interior face of all existing masonry walls.

8. Slab on Grade: [Sub-Slab Vapor-Barrier Sheeting] Tape / seal all joints, penetrations and seams. Sub-slab vapor barrier to be min 15Mil. sheeting or better. Install sub-slab vapor-barrier above insulation, in direct contact with concrete. Turn sub-slab vapor-barrier up wall and seal with elastic sealant and tape. Use termination bar to ensure permanent bond.

Details:

1. [D1] Existing-wall-to-interior-floor: Ensure continuity of interior side liquid-applied air-barrier at all interior floors. Recommended to remove the first floor joist against the masonry wall, apply air-barrier, and reinstall floor joist to ensure best continuity at this junction.
2. [D2] Existing-wall-to-roof: Transition from interior side liquid-applied to roof-membrane. Extend liquid-applied air-barrier up to at least the underside of the roof-deck and seal with flexible sealant or tape connection. Ideally, extend liquid-applied air-barrier up onto parapet wall past roof deck to ensure good connection with roof-membrane.
3. [D3] Bulkhead-wall-to-roof: Transition from bulkhead wall air-barrier (exterior WRB) to roof membrane. Ensure continuity of membrane up and over any parapet details.
4. [D4] New-wall-to-roof: Transition from exterior air-barrier / WRB to roof membrane. Ensure continuity of membrane up and over any parapet details.
5. [D5] New-wall-to-floor-slab: Transition from exterior air-barrier / WRB to sub-slab air-barrier sheeting.

Aerobarrier

Achieving Passive House levels of airtightness in existing buildings can be challenging. The dedicated air barrier layers described above will provide excellent, durable airtightness. The goal should be to achieve Passive House airtightness levels with the dedicated air barrier systems described above. However, some areas may be inaccessible due to existing conditions or otherwise impractical to expose in order to accomplish perfect air sealing. In cases where air sealing results are uncertain, we recommend having a backup plan in place.

Aerobarrier provides whole-building air sealing using an aerosolized polymer that “finds” leaks and seals them. We recommend consulting early in the build with an Aerobarrier installer so that they can be included in the project schedule should their services be required.