Surface R-Values

The various exterior envelope surfaces of the building are tested here at a range of different R-Values and the resulting heat-flows for key assembly types are plotted. For all surfaces, as the R-Value of the surface is increased, the heat flow through that surface is reduced. This improves overall energy performance of the building. However, this reduction in surface heat loss is lessened with each additional increase in R-Value. At a certain point the decrease in heat flow is no longer substantial enough to justify the extra cost, space, and time of additional insulation. This exact point is often very difficult to identify, but a good first-order analysis would be to identify the point on the graph for each surface where the slope of the line begins to 'flatten'. This represents the point (roughly) where the improvements from additional insulation will start to be too small to notice.

Winter Heat Loss due to Envelope Transmission

The surface heat loss of the different variants at various R-Values are plotted on the graph above. As shown above, most assemblies can benefit from additional insulation beyond the code minimums. In particular, the floor slab, wall assemblies, and roof should be well insulated to above the code minimum levels.

Recommended Assemblies

The following assembly U-Values have been assessed using Flixo Energy v8.1. All assemblies are proposed based on the Energy model results shown in previous sections. Note: All 2-dimension heat flow analysis simulations have been executed following the protocols outlined in ISO 6946 and ISO 10211 where applicable.

Cellar Floor

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Assembly Notes:

Recommended Assembly Notes:

  1. Note: All concrete sizing as per Structural Engineer or Architect. Concrete is shown for illustration purposes only.
  2. To achieve PHI Low Energy building performance, target. 6" sub-slab ( Neopor Graphite EPS or sim.). Insulation to be installed in three layers of 2" thickness with all seams staggered.
  3. Sub-slab air and vapor barrier to be installed directly below concrete (above insulation). Use 15 Mil Stego-wrap or similar
  4. Tape / seal all penetrations and seams of sub-slab air and vapor barrier using manufacturer approved tape / sealant.

Main House Wall

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Assembly Notes:

Recommended Assembly Notes:

  1. Remove exterior siding, install new vapor-permeably air and water-tight WRB membrane, Pro-Clima Adhero or sim.
  2. Install 4.7" (120mm) Gutex Multitherm or sim. exterior continuous insulation over existing sheathing.
  3. Install 1x4 wood battens over Gutex to create 'rain-screen' gap. Install new siding over battens. Use only stainless steel fasteners through insulation layer to reduce thermal bridging.
  4. Fill existing stud cavity with batt insulation, formaldehyde-free mineral wool or sim.

Cellar Wall

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Assembly Notes:

Recommended Assembly Notes:

  1. Install min. 4" continuous XPS foam board over exterior of existing concrete wall. Finish insulation with durable coating above grade.
  2. Apply damp-proof or waterproof coating to exterior of existing concrete wall.
  3. Install air-gapped drainage plane along exterior side of new exterior insulation layer, Delta- MS or sim.
  4. Install min 2" continuous EPS foam board on interior of existing concrete wall, InSoFast PF-2.0RW (UX 2.0) or sim. If required by manufacturer, tape all seams and joints of foam board with manufacturer approved tape/sealant.

Roof

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Assembly Notes:

Recommended Assembly Notes:

  1. Note: when constructing unvented insulated rafter assemblies follow all code requirements as per Res. Code 2018 of NJ, section 806.5
  2. When constructing the roof without sheathing venting, as per Res. Code 2018 of NJ, Table 806.5 , min R-15 insulation should be used above/outside the primary sheathing layer. R-15 can be achieved by:
  3. If Gutex Multitherm is used, cover with vapor-permeable WRB roof underlayment.Pro-Clima Adhero or sim.
  4. Insulate all existing rafters with batt insulation, formaldehyde-free mineral wool or sim.
  5. Air barrier / vapor control membrane to be installed along underside of insulated joists. Use vapor-variable air barrier and vapor retarder. Intello Plus or sim.
  6. Use the 'service cavity' on the underside of rafters to avoid penetrations to the vapor control membrane. No recessed lights or other equipment to be installed within or projecting into the primary inslated rafter layer. Insulate 'service cavity' with batt insulation, formaldehyde-free mineral wool or sim.

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 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.

Airtightness levels ensure building durbility and have a simple linear relationship to the building’s heat loss: the more airtight 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.

Winter Heat Loss due to Envelope Air Leakage



Code-minimum construction in most states require an airtightness rate of somewhere between 3 to 7 air-changes per hour (ACH) and the NJAC Energy Subcodes require residential buildings in ASHRAE Climate Zone 5 to demonstrate a tested airtightness level of less than 3.0 ACH@50Pa. In order to meet the PHI Low Energy Building performance level, this project would have to achieve the extremely stringent air-tightness level of 1.0 ACH@50Pa. The graph above shows the heat loss at various levels of airtightness for the building. Improving airtightness to this level (1.0 ACH@50) is one of the best ways to improve performance and increase comfort and durability and is the recommended target for this building.

Airtightness Red Line Test

Illustrated below are examples 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 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 first and foremost. 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.

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  1. Use sub-slab vapor-barrier as airtight layer. Tape / seal all joints, penetrations and seams. Sub-slab vapor barrier to be min 15Mil. sheeting or better. Ensure sub-slab membrane connects to the sub-grade masonry walls.
  2. See proposed detail below. Connect airtight vapor-barrier sheeting to existing foundation wall.
  3. See proposed detail below. Airtightness transition from below grade concrere to above grade wall exterior WRB.
  4. Use exterior WRB for primary airtightness layer on all exteror walls. Remove existing siding and install over existing sheathing before insulation.
  5. See proposed detail below. Remove / cut-back existing rafters and fascia as required. Install airbarrier / WRB continuous over eave assembly and connect to roof underlayment.
  6. Install water-proof roof underlayment as primary airtight layer for all roof assemblies.
  7. Window and door detail connections are critical airtightness details. These connections will be designed based on the final window and door frame profiles in subsequent project phases.

Airtightness Details

DETAIL: Roof Eave
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  1. Cut back existing rafter tails and trim as reququired to maintain current fascia depth / height.
  2. Primary airtightness layer to be air and water tight WRB (Water Resistive Barrier) installed over existing sheathing. Ensure all joints and penetrations are sealed as per manufacturer's instructions.
  3. Install WRB continuous around eave and up to roof underlayment.
  4. Install vapor-permeable roof underlayment over Gutex insulation. Tape / seal to wall WRB at eave.
  5. Provide Cor-A-Vent SV-5 or sim. to cap rainscreen gap at top. Cover with trim-board as required.
  6. Provide Cor-A-Vent SV-5 or sim. to at soffit to provide venting for roof sheathing.
  7. Insulate rim joist with closed-cell spray foam or mineral wool batt insulation.
  8. Air-barrier / vapor-control membrane to be installed along underside of insulated joists. Use vapor-variable air-barrier and vapor-retarder. Intello Plus or sim. Tape / seal vapor-control membrane to existing subfloor.
DETAIL: Rim-Joist at First Floor
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  1. Primary airtightness layer to be air and water tight WRB (Water Resistive Barrier) installed over existing sheathing. Ensure all joinst and penetrations are sealed as per manufacturer's instructions.
  2. Seal / Tape WRB to existing conc. foundation wall using approved sealant.
  3. Use Cor-A-Vent SV-5 or sim. to cap rainscreen gap at top and bottom.
  4. Insulate rim joist with closed-cell spray foam or mineral wool batt insulation.
  5. If air permeable insualtion (mineral wool) is used, cap insulation with 1/2" plywood layer to prevent air and moisture leakage. Coat plywood and surrounding joists with liquid applied air-barrier, Pro-Clima Visconn or sim.
DETAIL: Typ. Footing
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  1. Primary floor airtightness layer to be be sub-slab vapor barrier sheeting. Ensure all seams and penetrations are taped / sealed as per manufacturer's instructions.
  2. Sub-slab vapor barrier sheeting to be installed above insulation in direct contact with concrete.
  3. Turn vapor barrier sheeting up cellar wall min 16" at all sides. Tape / seal vapor-barrier to XPS foam layer using approved tape / sealant.
  4. Ensure min. 2" thermal break at all slab edges.
  5. Extend XPS foam insulation down to cover top and sides of any spread footings on the exterior side.