Limiting air infiltration is one the most important aspects of creating an energy efficient house. Leaky houses use more energy to re-heat or cool the lost air. Air infiltration is often measured as Air Changes per Hour (ACH) SIP Homes are extremely tight.
Air sealing done properly eliminates both the energy consumption and the durability problems. To meet these needs, the air sealing system must remain robust for decades, be easy to assemble on the job site (under New England’s weather conditions), and be cost-effective. Unfortunately, there doesn’t seem to be one material or solution that meets these needs for all the different types of panel joinery.
Foard Panel uses 3 materials (spray foam, mastic & tape) and 4 primary methods for air sealing: “Drill and Fill”, “Gapping (for Timber Frames)”, “Panel Mastic” & “Panel Mastic Reinforced with Tape”. Each method is meant to achieve the best seal for a particular situation. What we, and most other panel installers like about these methods is that the panels are put up “dry” with air sealing done as a separate step. This makes the process cleaner, quicker, and allows for undivided attention to be given to this important job. Below is a list of eight key situations that require air sealing and the appropriate method to use.
|1||Where wall panels meet the deck||mastic & tape|
|2||Spline and butt joints on wall and roof panels||drill and fill|
|3||Panel to panel connections @ corners||gap or mastic & tape|
|4||At intersection of wall and roof along eaves and rakes||gap or mastic & tape|
|5||At roof ridge hips and valleys||gap or mastic & tape|
|6||Behind rough opening framing||mastic|
|7||After window/door installation between jamb and r.o. blocking*||gap|
|8||At any penetrations such as vent stacks**||gap|
*When foaming around installed windows/doors, use low expanding urethane foam – not the foam supplied by Foard Panel. It is possible to “blow-out” the jambs with the triple expanding foam Foard uses.
** Standard chimney openings that require clearance should not be foamed.
Panel mastic is applied in a single, bead on the mating surface of one component, often wood, and then the opposing component is installed so that the bead is compressed in between over the whole length of the joint. Bringing both mating materials into firm contact with the bead of mastic is critical. In cases where conditions prevent this, see the Spray Foam Alternate To Panel Mastic.
Spray Foam Alternate to Panel Mastic
In cases where panel mastic is called for, but the joint will not fit tightly enough for panel mastic to be practical, spray foam can be used. Fully assemble and fasten and fasten the connection. Drill 1/2” dia. holes at an angle to access the void space and inject foam using the same basic method as the Spray Foam Drill & Fill method described above. Use enough spray foam to completely fill the void in the connection. Use the size of the foam balls created at the injection sites as a guide for foam volume and blast length.
Mastic & Tape
In panel joints that contain full-thickness lumber, we take the belt-&-suspenders approach of using panel mastic and an air sealing tape. Tape should be applied to joints that contain sawn lumber, SCL, and I-joists. The tape should be applied on the warm-side of the joint (the interior side in New England).
GappingFor some ridges, hips, valleys, and timber-frame corners, intentional gaps are left between panels to be filled with spray foam. Fill the full depth of the gap with spray foam. Once filled, leave the foam 24 hours to harden before breaking off any protruding foam.
Drill and Fill
Drill and Fill is performed from the exterior of the house. All interior splines must be fastened before foaming begins. At the panel joint, drill holes approximately 10”o.c. for walls, 6”o.c. for roof, to the depth of the spray foam channel and inject foam using two to four second blasts. Push the nozzle as far into the joint as you can, ideally until contacting the back of the interior spline. Begin foaming there and slowly pull out, pausing at the spray foam channel to allow foam to travel in the channel. Blast duration varies depending on temperature and humidity and how much pressure is left in the can. Enough foam must be injected so that ping-pong sized balls of foam protrude from the drilled holes after the foam has cured. The balls can be easily scraped off after the foam has cured. Do not disturb the foam until it has completely cured, generally 24 hours.
Start foaming from the bottom and work your way up. This will keep the uncured foam from falling on you while you work. Fasten exterior splines as you go instead of going over the same area later. First timers should experiment with scrap material to get a feel for the proper amount of foam needed. Cut a cross-section out of practice pieces to evaluate the technique.