5. Envelopes Archives - Hammer & Hand

5. ENVELOPES

sproutbox — Mon, 16 Sep 2024 14:58:16 +0000

The building envelope is arguably the single most important determinant of building durability, energy efficiency, and occupant comfort and health. We deliver these qualities to our buildings by carefully managing heat, air, and moisture through envelope assemblies. Put simply, we want to limit the movement of air and heat through our assemblies, limit the intrusion of moisture, and promote drying of any moisture that does intrude. The interplay between heat, air, and moisture is extremely dynamic, however, and a full understanding of that interplay in any given assembly can require extensive analysis. Nonetheless, a couple core principles can guide much of our work:

1. Start by making it airtight. If you control for air, you also make major strides in controlling for heat and moisture. This is because much of the movement of heat and moisture into and through building assemblies is carried by air. When we stop air movement through our assemblies we also stop this air-borne problem.

2. Avoid condensation where it hurts. Condensation forms where relative humidity – a function of moisture concentration and air temperature – hits 100%, aka the “dew point.” Relative humidity can reach the dew point when (1) moisture concentration increases in a given volume of air to the point where it surpasses the air’s capacity to hold that moisture in suspension, or (2) when air temperature decreases, reducing the air’s capacity to hold moisture in suspension. Major problems, including building failure, arise when the dew point occurs inside building envelope assemblies where moisture can accumulate. The most likely place for this to occur is on the surface of a building component in an assembly. Warm concentrations of moisture, carried by air or moved via vapor drive (the diffusion of moisture from areas of higher concentration to areas of lower concentration), hit a cold surface and the moisture drops out of suspension and condenses on the surface. Therefore, our assemblies must be designed and built to prevent concentrations of moisture from hitting surfaces that are cold enough to cause this condensation inside our assemblies. Furthermore, when working with materials that are subject to mold growth we need to include an additional safety factor in assembly design, as mold grows at relative humidity levels even lower than 100%.

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5.1 WALL PENETRATIONS

sproutbox — Wed, 18 Sep 2024 00:20:52 +0000

Built right, a building’s exterior wall is a comprehensive system for protecting the building from the elements and for managing heat, air, and moisture. So when we punch a hole through this system we must proceed with caution, ensuring that we maintain the integrity of the building envelope. A moisture management system is only as strong as its weakest link.

A. It is Critical That No Wall Penetrations are Overlooked

Proper planning and sequencing will ensure that every penetration is correctly detailed. The following is a list of various wall enclosure penetrations that are frequently encountered on a project:

Electrical service and meter.
Exterior electrical outlets and lighting.
Telecommunications and miscellaneous low voltage (cable, phone, satellite dish mounts, etc).
HVAC (electrical, refrigerant lines, combustion piping/flues, exhaust and intake ports, condensate drain lines, dryer exhaust vents).
Natural gas line and meter.
Hose bibs.

B. Consolidate Wires

Wires should be consolidated into as few penetrations as possible and routed through a plastic pipe that can easily be sealed (shown below). Allow space for future wiring changes to prevent the creation of future wall penetrations.

Note:

One of the best methods for sealing around wires inside pipes and conduits is to utilize a non-hardening duct seal electrical putty. This is especially critical at the electrical panel where the main conduit enters the building.

Duct Flashing with a Rain Screen

Cut hole for duct as tight as possible.
Space between duct and wall sheathing to be 1/4” or less.

Apply Joint & Seam Filler.

Apply FastFlash to a distance of 9” from outer edge of pipe and 2” up the sides.
Only extend downward slightly so FastFlash does not adhere to the back side of the transition strip.

Stick top edge of transition strip membrane to FastFlash.
Bead and tool FastFlash to the top edge of transition strip.

Slip WRB under transition strip for correct lapping.

Attach furring for rain screen.
Include strips for vent hood blocking.

Secure vent hood trim block.

Install metal flashing at top of block.
Apply fluid flashing at top of flashing back leg.

Attach flashing to vent hood blocking strips.

Attach vent hood.

Complete rain screen by adding siding and caulking the sides of the duct blocking, not the top or bottom.

Duct Flashing, No Rain Screen

Complete up to Step 5 from Duct Flashing with a Rain Screen.

Secure vent hood trim block.

Attach vent hood.

Carefully cut back WRB to attach flashing for trim block.

Apply Joint & Seam Filler at the top of the flashing and tool into place.

Fold down WRB flap and tape slits closed.

Complete rain screen by adding siding and caulking the sides of the duct blocking, not the top or bottom.

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5.2 AIR SEALING

sproutbox — Wed, 18 Sep 2024 20:44:18 +0000

Airtight construction controls the flow of air and therefore the flow of airborne heat and moisture into and through the building envelope. It needs to be approached in a comprehensive manner on all sides of the envelope.

The most difficult aspect of air sealing is where dissimilar materials intersect, especially in complex geometry. The details that follow illustrate strategies for tackling some of the most commonly encountered intersections.

Foundation to Sheathing

A. JOINT AND SEAM SEALANT OR APPROVED TAPE
B. SILL SEAL

1. To function as air barrier, foundation must be structural reinforced concrete.
2. Prevent sheathing-to-concrete contact.

At Sheathing

Materials:

A. RIGID PANEL WITH INTEGRAL WRB (ZIP SHEATHING OR SIMILAR)
Apply approved sealant at all joints, seams, and penetrations.
Apply fluid applied membrane at interior of punched openings.
B. RIGID PANELS WITH FLUID APPLIED WRB
Apply fluid applied system at punched openings, seams, and penetrations.
Cover entire exterior plane of envelope with fluid applied WRB.

C. RAW RIGID PANEL READY FOR FABRIC WRB
Apply fluid applied system at punched openings, joints, and penetrations.
Tile-in fabric WRB product into wet set transition sheets.
D. SEE SECTION 5.1 DUCT FLASHING WITH A RAIN SCREEN

Air Barrier: Exterior Wall Sheathing to Interior Ceiling Transition

1. Install perimeter rip of rigid panel before ceiling framing/trusses are set, extend past interior edge of top plate a minimum of 1” for flat ceiling over top plate.
2. Seal perimeter rip panel edges prior to setting trusses.
3. For vaulted ceilings extend rigid panel 1/2” past inside of top plate.

Wall to Ceiling/Roof

A. AIR BARRIER AT CEILING
B. JOINT AND SEAM SEALANT OR APPROVED TAPE

A. 1.5″ SERVICE CAVITY
B. DRYWALL
C. RIGID PANEL WITH SEALANT OR TAPE

If Vaulted Ceiling with Exterior Air Barrier, Seal Wall to Roof Sheathing

A. IF VAULTED CEILING, INSTALL OVERHANGS AS ADDITIONAL FRAMING SYSTEM ABOVE STRUCTURAL SHEATHING
B. THIS SHEATHING LAYER IS ALSO THE AIR BARRIER AND WILL BE SEALED AT ALL PANEL EDGES

C. RIGID INSULATION OR MINERAL WOOL BETWEEN FRAMING. INSULATION TO BE 1″ SHALLOWER THAN FRAMING TO ALLOW FOR VENTILATION CHANNEL

D. INSULATION ABOVE OVERHANG FRAMING TO BE PROVIDED WITH VENTED NAIL BASE OR SIMILAR

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5.3 INSULATION

sproutbox — Fri, 20 Sep 2024 02:46:01 +0000

By limiting the flow of heat through the building envelope, insulation plays a fundamental role in delivering occupant comfort and energy efficiency. To maximize the effectiveness of the insulative layer, we need to build the structure to accept the insulation and then need to install the insulation properly. The details that follow describe a handful of critical standard insulation applications.

Note: By reducing the flow of energy through the envelope, affecting the movement of moisture, and altering airflows, adding insulation can cause unintended consequences on building durability. The design of insulated assemblies must therefore be guided by an understanding of building physics and hygrothermal performance, and installation must be completed as designed.

Cavity Fill

Allow for proper access in all areas to facilitate complete and thorough filling of cavity.

Framing Example at an Inside Corner:

Poor Spacing at Corner with Insufficient Clearance

Proper Spacing at Corner

Dense Pack Blown-In Cellulose

At completion of project, insulation is to be enclosed on all 6 sides with rigid material to prevent wind washing/convection losses and settling. The specific quantity of material to be installed should always be calculated and confirmed by site superintendent. *See bag count
Ensure good access to all areas for proper fill.

Netting

Inset stapling at corner of stud to prevent intrusion of insulation to front of stud.
Use dense pack specific netting material.

Netting is to be taut prior to fill. Check density after 10% of work is complete to confirm proper installation. At initial completion, review integrity of installation and remedy any under-filled areas.

Material density determined by manufacturer, should feel like solid felt. Keep dry with NO exposure to bulk water during construction.

Fiberglass

At completion of project, insulation is to be enclosed on all 6 sides with rigid material to prevent wind washing/convection losses and settling. The specific quantity of material to be installed should always be calculated and confirmed by site superintendent. *See bag count below.
Ensure good access to all areas for proper fill.

Netting

Inset stapling of netting at corner of stud to prevent intrusion of insulation to front of stud.
Utilize netting per fiber glass manufacturer’s specifications.

Netting is to be taut prior to fill. Check density after 10% of work is complete to confirm proper installation. At initial completion, review integrity of installation and communicate any under-filled areas to insulation contractor.

Check building specifications for desired density. Keep dry during construction.

1. ‘Dense-Pack’ feels like a firm mattress. See manufacturer’s documentation for lbs/ft3 specifications.
2. ‘Standard Fill’ feels like a firm pillow. See manufacturer’s documentation for lbs/ft3 specifications.

* Bag Count Example:
435 SF of 2 x 6 wall
Framing factor of 18% (area taken up by wall framing)
(435 ft2 x 5.5/12 ft) x (100% – 18%)
(435 ft2 x .458 ft) x .82
199.375 ft3 x .82 = 163.5 ft3

Example: Fiberglass might be 1.8 lbs/ft3.
The 435 ft2 area needs 294.3 lbs of material.
Bags are 28 lbs/each, this wall needs 10.5 bags of material.

Attic Insulation

Loose Fill in Attics

Protect from wind-washing at perimeter, especially where close to roof venting.
Roof baffles for soffit venting to terminate no less than 12 inches above cellulose to prevent wind from displacing material.
Baffles between rafters to be continuous from rafter to rafter (do not use baffles which are fastened to roof sheathing). Must fill full width of cavity.
Maximum slope of ceiling below loose fill: 5/12.
Do not use blown-fiberglass due to light density/wind washing.
Insulation depth markers to be installed per manufacturer’s specification.

Note: These areas are outside the thermal envelope and air barrier and are not suitable for mechanical systems or ductwork.

Attic Walls

Where vertical walls are encountered in attic spaces (this condition occurs where ceiling heights change) install rigid material on attic side of framing and insulate from interior so area can be readily inspected post-installation of insulation material.

Attic Hatch

Ensure proper clearance is present from ceiling to bottom of rafters to allow for access, post-installation of insulation; if current location does not allow for needed clearance, relocate hatch.
Construct “dam” of plywood or other durable rigid panel (cardboard is not sufficient) to a height of final insulation depth plus 2.” Minimum height above dam to be 30” to allow for access to attic. Minimum rough framed opening of hatch per code to be 22” x 30.”
Insulate hatch area with rigid insulation to the minimum R-value of general at

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5.4 EXTERIOR CONTINUOUS INSULATION (CI) AT WALLS

sproutbox — Fri, 20 Sep 2024 18:44:56 +0000

Continuous exterior insulation is like a winter sweater wrapping a building. It is also a key component in establishing a thermal bridge-free building envelope. Thermal bridges are penetrations in a building’s insulation layer, like the wood studs of a stud wall for example, that allow heat to escape and cold to intrude through the building envelope. In otherwise high performance assemblies, thermal bridges can be a source of tremendous energy loss and condensation risk.

By insulating around would-be thermal bridges, continuous exterior insulation establishes a thermal break between these building components and the exterior environment. As with insulation in general, as we introduce exterior insulation we need to understand and detail for the effects this insulation will have on moisture movement through the overall assembly.

Types of Exterior Rigid Foam and Installation Instructions

Foil-Faced Polyisocyanurate (Polyiso)

Exterior surface may be used as a WRB, with manufacturer approval.
Install tape at seams per manufacturer specification.

1. Must use J-Roller on tape with good detailing to eliminate ‘Fish-Mouthing.’

Expanded Polystyrene (EPS)

Multiple layers with staggered seams recommended to accomodate product shrinkage.
While exterior surface may be used as a WRB, we do not recommend it.

1. Install tape at seams per manufacturer specification.
2. Must use J-Roller on tape with good detailing to eliminate ‘Fish-Mouthing.’

Extruded Polystyrene (XPS)

Limit use of this product as the material has a high Global Warming Potential.
Exterior surface may be used as a WRB.

1. Install tape at seams per manufacturer specification.
2. Must use J-Roller on tape with good detailing to eliminate ‘Fish-Mouthing.’

Rigid Foam Insulation

For cutting, use knives and (for EPS and XPS) “hot wire” devices; minimize use of saws to limit dust for site cleanliness, carpenter health, and to prevent tool damage.
If thicker than 2,” install in multiple layers with staggered seams to prevent thermal bypass.
Fastening: consult manufacturer specifications or structural architectural drawings.

When Rain Screen Furring is to be Installed Over Rigid Insulation

Steps:

1. Install first layer of rigid insulation with limited number of nails or screws with washers.
2. Install second layer of rigid insulation with limited number of nails or screws with washers.
3. Fasten furring with screws; spacing and fastener size to be decided by weight of siding material and spacing of furring.

Mineral Wool AKA ‘Rockwool’ and Installation Instructions

WRB to be placed and fully integrated at wall structure.
Exterior flashings should be installed to minimize thermal bridging (locate back dam on outer face of first layer of insulation).
Minimize cutting of product; when needed use specific mineral wool knives.

Steps for installing furring over mineral wool:

1. Install first layer of mineral wool with limited number of nails or screws with washers.
2. Install second layer of mineral wool with limited number of nails or screws with washers.
3. Align vertical edges of exterior layer to ensure coverage by furring and prevent puckering.
4. Fasten furring with screws: spacing and fastener size to be decided by weight of siding material and spacing of furring. Consult manufacturer, architectural, or structural specifications.

Examples:
(Black) Fastenmaster Hedlock
(Silver) GRK

For reference only (with all CI):

Fastenmaster Technical Evaluation Report TER No. 1009-01
Building Science Corp Report January 2014 Cladding Attachment Over Thick Exterior Insulating Sheathing

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5.5 WALL ASSEMBLY EXAMPLE

sproutbox — Sun, 22 Sep 2024 00:06:28 +0000

A. DENSE PACK INSULATION
B. SHEATHING WITH INTEGRAL WRB
C. JOINT & SEAM FILLER
D. MINERAL WOOL INSULATION
E. FLUID APPLIED SYSTEM AT PUNCHED OPENING
F. CEDAR SIDING (VERTICAL)
G. SILL PAN FLASHING
H. 2-WAY RAIN SCREEN FURRING
I. WINDOW BUCK
J. FRAMED STUD WALL
K. HEAD FLASHINGNote: Metal flashings not to return back to sheathing.

This example combines an exterior layer of mineral wool insulation, ZIP Sheathing as air barrier and water-resistive barrier, fluid-applied flashing at rough openings, and dense pack insulation (cellulose or fiberglass) in an interior stud wall for a super insulated, vapor open, and resilient high performance wall assembly. The diagrams below show how the assembly manages air, heat, water, and vapor.

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