Air Barrier and Insulation for a High-End Custom Passive House

Air Leakage in Plywood

Air bubbles out through plywood during a preliminary blower door test performed on a rainy day. Leakage exceeded Passive House allowable levels because of the air permeability of the building's plywood sheathing.

Plywood Leaks Air in Blower Door Test

An early blower door test of the Wayland house revealed that the structure's plywood sheathing leaked air. With rain soaking the plywood and positive air pressure applied inside the hose, major air leakage created obvious bubbles on the plywood skin.

Air Barrier Membrane for the Roof

A view of the Siga Majcoat waterproof breathable membrane roof covering, sealed with Siga Wigluv tape.

Air-Tight Membrane for the Turret

The crew applied Siga Majcoat air-tight membrane to the entire roof, including the octagon turret roof, and sealed all the joints with Siga Wigluv tape.

Air-Sealing the Walls with Membrane

The crew wrapped the entire house wall with Siga Majcoat waterproof, vapor-open fabric. Majcoat rolls were long enough to allow covering the entire perimeter with only two vertical tape joints.

Cutting Window Openings

Carpenter Tim Houldcroft cuts out a window opening in the membrane-covered wall.

Passive House Window Detail

Carpenters Tim and Casey work on a window opening prototype in the Passive House wall.

Setting the Window

Carpenters Casey and Tim install a Unilux Passive House window in the punched opening.

Air-Sealing with Tape

A closer look at the Siga Wigluv tape air-sealing detail around the window buck.

Fastening Roxul Insulation to the Roof

The Auburndale team is attaching Roxul rock wool insulation to the walls and roof of the house using a system supplied by Ramset. Here, a carpenter prepares to insert the long driver pin into the hollow fastener tube.

Pinning Insulation to the Roof

The carpenter uses a Ramset gas-fueled fastening gun to drive spiral-shank nails through the pointed end of a plastic tube fastener.

Insulating the Roof Deck

Using a Ramset T3 InsulFast gas-fueled gun, the crew applied six inches of Roxul rock wool insulation over the air-tight, vapor-permeable Siga Majcoat membrane.

Staggered Insulation Courses

Here's another look at the roof insulation job in progress, showing staggered courses of 2-foot by four-foot, three-inch-thick Roxul rock wool insulation batts.

Roof Insulation in Progress

The roof, face, and cheek walls of the dormers were also insulated with six inches of Roxul rock wool.

Insulating the Dormers

Another look at the Roxul rock wool insulation on the dormers during installation.

Strapping Over the Insulation

Framers apply vertical 2x6 strapping over the Roxul rock wool insulation, to create an air channel under what will be the sheathing for a slate roof. The uninsulated portion of roof at left will be the location for a skylight.

Screwing Down the Strapping

A framer uses long GRK structural screws to attach 2x6 strapping for the structural deck for a slate roof.

Steel Reinforcement for Roof Strapping

A framer nails steel straps onto the 2x6 roof strapping, to connect the strapping across the roof peak to strapping on the opposite side of the roof.

Reinforcement at the Hip

A framer installs metal strapping across the 2x strapping at the roof hip, to strengthen the roof against wind uplift loads.

Waterproofing for the Brick Shelf

Carpenter James Stewart applies Pittsburgh Corning PC 99 sealant to the joints between pieces of Foamglas insulation around the house perimeter. High load bearing "HLB" Foamglas will support the brick veneer cladding at this location, but the Foamglas has to be thoroughly waterproofed because of its vulnerability to freeze-thaw damage.

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