Super Insulated Building Envelope Details
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What is It?
Super insulated building envelope details refers to a passive strategy to reduce energy use by making the building airtight and using more insulation with higher R-values than a conventional building. Attention is given to each of the details pertaining to connections and penetrations that exist in the building envelope (i.e., windows, doors, and connections at trusses).
Why is it Important?
Super insulated building details are important because they:
- Maintain the integrity of the super insulated building envelope. The commissioning process often discovers systemic problems due to poor attention to construction details.
- Significantly reduce energy use by keeping heat inside the building in the winter and keeping heat outside the building in the summer.
- Help restore the planet's eco-systems by burning less fossil fuel for heating and cooling the building.
- Keep the fresh air and comfortable temperatures inside no matter what the outside conditions are.
- Maintain proper humidity levels while allowing moisture control.
When to Use It?
Super insulated building details are needed:
- Where connections exist between different materials. Care must be taken to insure the joints will maintain the integrity of the super insulation.
- Where building planes change (i.e. floor to wall, wall to roof).
- Where penetrations occur in the building envelope. Fresh air, plumbing vents etc., all must come through the building envelope.
- It is easier to insure the connection integrity during construction than after.
Things to Remember:
- Some connections need to be flexible.
- Design must give thought to future deconstruction, so the reuse of the materials is possible.
- Maintain a high level of indoor air quality.
- Keep air-changes per hour to less than 0.10 throughout the building envelope.
- Minimize thermal bridging.
- Reduce energy use of existing building by at least 70%.
- Provide daylight to the interior without compromising energy conservation goals.
- Use envelope and insulation materials that do not harm building occupants or the environment.
- Use envelope and insulation materials that are existing, recycled, and/or local materials wherever possible.
- Control moisture and humidity within the envelope components of the building.
Strategy and Conceptual Design
The major elements of our super insulated building envelope details strategy are:
- Roof: Seal up penetrations and truss bearing pockets.
- Walls: Provide continuous envelope connection at top and bottom.
- Floor: Insure or minimize thermal bridging at the exterior perimeter.
- Windows and doors: Maximize insulation value and minimize air infiltration.
Things to remember:
- Choose insulating materials with the highest R-values, least environmental impact, and best indoor air quality properties.
- Eliminate or minimize thermal bridging and infiltration sources by design wherever possible.
- Test components at each stage of construction to verify that they meet performance goals and fine tune as needed.
- Historic side
- The strategy in the roof details design entails keeping the historic roof intact and placing the new, super insulated roof on top of it. This keeps materials from the old roof from entering the waste stream and preserves the historic appearance of the interior. The historic bow trusses that used to support the original structure have been evaluated by a local structural engineer. The trusses are capable of handling an additional 15 psf over the entire roof area. Structural Insulated Panels (SIPS) are being used to cover the old roof because they are a lightweight, high R-value material that fit the barrel vault shape of the historic roof. The critical detail is the joint between the wall system and the structural insulated panel.
- A portion of the original roof decking will need to be cut out to allow for a continuous plane of insulation to envelope the building.
- Cover historic roof with Insulspan structural insulated panels (SIPS). R-50 for 12" SIP.
- See if Insulspan contractor can make vertical leg for SIP that will make connection to wall below energy tight.
- The parapet walls above the historic building currently form a continuous thermal bridge, transferring exterior temperatures directly to the building interior through the masonry wall. We are currently looking at removing the parapet and having new SIPs cover the wall. This maintains the integrity of the building envelope.
- Annex side
- Use flat roof reinforced to carry additional weight of PV and solar heating panels.
- R-40 for 12" thickness.
- Historic side
- Install 4" of Polyisocyanurate foam using two layers. Seams on the layers will be staggered with a 1" airspace between foam and existing brick/block. This will be fastened to masonry with 1" foam spacers.
- Weep holes at base of wall to drain moisture from behind masonry layer.
- This also helps control moisture build up in the wall by providing a path for condensation or rain water to run down to weep holes.
- Build second (stud) wall inside the foam sheathing to accommodate (5") cellulose insulation, while preserving historic appearance and keeping block from entering waste stream. These studs will not touch the outer foam layers, so the cellulose will fill stud space and the space between the outside face of the stud and the back of the foam. This provides a total thermal break between the exterior masonry and the interior drywall.
- Total thermal resistance for the walls is R-42
- Total wall thickness is 18.5"
- Critical Details
- Connection at top of wall to SIP over roof.
- Foam layer on exterior of wall must be continuous with foam under floor.
Floor Design In addition to being a component of the super insulation strategy, the floor of our building will house the tubing for the radiant heating and cooling system we are installing. This system may require maintenance and tuning, so our floor system allows easy access and still provides insulation value.
- Historic side
- Existing 4" concrete slab.
- Leveling course of slag/sand 0-approx 6".
- Pex tubing for cooling system to be installed in sand of low areas.
- 2" polyiso foam.
- 2x sleeper joist material.
- Pex tubing for heating system will be installed in this space.
- Reclaimed solid core flush doors as finish floor
- Total thermal resistance for the floor is R-18
- Annex side
- Remove 2' of concrete from the perimeter of the existing 4" concrete slab.
- 2" x 2' polyiso foam will be placed horizontally around the exterior perimeter.
- Pex tubing for heating system will be placed in this perimeter and poured in the replacement concrete.
Window and Door Design
- Double-glazed, low-e
- Window to wall ratio less than 0.27
- U-value less than 0.30
- All windows operable to permit natural ventilation
- Details of the window to wall connection, and how to minimize air infiltration are critical.
- Mulled sections of the historic window replacement will be critical. This area is often overlooked during construction.
For more information, please see the Green Garage's Sustainable Window Design
- Details to be completed with door selection.
Thermal Bridging and Infiltration
- Thermal Bridging
Thermal bridging occurs when a material conducts heat or cold from the exterior of the structure to the interior. An example would be the frame of an aluminum window. The glass may have good thermal properties if it is a gas-filled double pane window. But the frame will conduct the outside temperature directly through the wall and into the space. Where this occurs, a thermal break can be designed. Foam, cork, and plain air are common materials that can be used.
- Because our interior wall is not structural, our floor to wall connection is a simple foam-to-foam connection. We avoid thermal bridging within the walls by attaching the foam board to the exterior masonry, which holds the panels away from the stud layer.
- Where the bow truss ends penetrate the walls, the cavity will be filled with foam to minimize thermal bridging.
- All windows and doors, floor joints, truss-to-wall connections, roof penetrations will be sealed to prevent infiltration.
- Sealing all air leaks also helps to achieve whole-building pressure differences as part of our ventilation and moisture control strategies.
- Each component will be tested during construction to ensure performance is meeting our goals.
Proposed Materials / Suppliers
The Super Insulated Envelope Details - Development Story page contains many images and videos documenting the process used at the Green Garage to design, build and operate our super insulated building envelope.
Related Internal Links
- SIP details
- Structural Insulated Panel Association Typical details for SIPs.
- Wall Systems
- Building Science Insight 001: The Perfect Wall
- Oak Ridge National Lab Wall Insulation Guidelines ...nice picture of basic system.
- Oak Ridge National Lab Wall Moisture Insulation Guidelines by Climate
- Vapor Barrier Guidelines Put the vapor barrier on the warm side of the exterior structure.
- Wall System R Value Calculator
- Development Story
Peggy edited this page :)