Dan Morrison | March 29, 2018


Video // Siding & Exterior Trim, WRB & Flashing, Insulation & Air Sealing

Exterior Foam Insulation Retrofit: How To Install Polyiso Panels

The first layer of foam and how to cut it

 

In this video, we see Synergy Construction's details for the first layer of foam, the bottom bug barrier, how they treat exposed edges, and a few ways to cut the foam.

 

The transcript for this video is below, scroll down for more.

 

The highlights:

The windows, are inegrated with the housewrap and foam

Flashing membrane spans thew window, house wrap, and window flashing for an airtight assembly.

 

The first layer is not the primary air barrier, so (tight) scraps are OK

It is great to use large pieces when possible, for a better air barrier, but because there is a layer of house wrap and two layers of foam, it is also safe to use up some random scraps—and there will be a lot of scraps—as long as the joints are tight and the insulation is continuous, piecing in scraps should be fine.

 

Cutting foam sheets is pretty simple.

You can use utility knives with extendable blades to get the whole depth on small cuts and when cutting sheets in place. For long cuts, you can use a knife and a chalk line or a T- square or you can use a table saw.  

 

The second layer of foam is the air barrier and drainage plane.

 

OFFICIAL TRANSCRIPT FOR PART 2:

With the first layer of a two layer exterior foam retrofit installed, Calvin and Damien turn to the money layer. They begin with a starter piece, again, attaching it with two screws until the furring strips go on.  
 
You may notice that the seams are already taped. That is because they wanted to pre fit the pieces before we shot a video, and then they got carried away and taped the seams. So we had to cut the tape and shoot the installation. 

Anyway,
The foam is tucked tightly into the bug shield and they install as close to full sheets as they can. Certainly, they cover seams in the first layer with solid panels in the second.

Again, the pieces should be snug.

They work from the corner in. This is the opposite corner on the same front of the house because the center of there wall is broken up with a large entry stair.

Once the corner is plumb and level, they fasten it off. 

Succeeding pieces are fit tightly. Cantilever sections, like outside corners, have their ends staggered so that there is no straight line for air or energy leaks.

The bottom of the foam and any exposed edges, such as at a basement knee wall, are wrapped in a site-bent metal channel that keeps bugs out. The metal is sealed to the foundation with silicone caulk.

Next the seams are edges are taped with contractor tape.  The metal bug shield jus taped to the foam also, with contractor tape …

… as are the inside corners and cantilevers. 

Outside corners are sealed with a wide strip of peel and stick membrane to cover the staggered corner sheets. 

Next, foam is sliced at a downward angle to extend the sill pan sloping to the outside …
… and the peel and stick is peeled and stuck to the foam, similarly to how it is done in the rough framing.

Notice that he cuts the corner shy and bends the membrane to keep the bottom point water tight. 

With the seams, edges, and corners taped, they turn to installing strapping for a rainscreen siding assembly. 1x3 utility grade strapping is fine, as long as the strips are fastened into studs, they will do their job of giving the siding something to fasten into.  

The second layer screws are longer than the first layer screws need to be— about six inches compared to four inches. 

Screws are countersunk by cutting partial holes in the furring strips with a spade bit. 

As the furring strips are secured to the framing, the foam is compressed inward. This can make for a wavy wall, so when it is time to install siding, the crew will pull a string line across the wall and either drive in or back out the screws. 

That stringline process is not worth doing now because the wood framing may still expand or contract before it is time for siding. 
 

—David Joyce, owner of Synergy Construction in Lanchaster, MA donated his jobsite for us to shoot video. Thanks Dave. 

 

 

OFFICIAL TRANSCRIPT FOR PART 1:

Welcome to Concord, Massachusetts. This house is undergoing a deep energy retrofit and gut rehab. To boost the R-value of the walls, 4 inches of polyisocyanurate foam is being added to the walls and roof. 

The siding, a sheet product designed to mimic vertical boards, is structurally sound so it is being left in place and then covered with house wrap and foam.

The windows were installed and flashed to the openings before the house wrap, and the house wrap is sealed to the windows with a flashing tape.

 

The windows, are integrated with the housewrap and foam

Dave explains how the flashing tape connects all of the layers:

David Joyce: Our flashing membrane from the window itself, crossing the flange, right over our subflashing, and onto the house wrap.

The subflashing protects the building from any leaks that happen in the window.

How house wrap goes over that, and is adhered to that ... 

Dan: Which makes a good air seal and water seal.  The pan flashing is extended out so that it can drain water to the outside of the foam sheathing. Extra strips of flashing tape can extend the pan flashing more.

This is where split-release sheets on the back of the tape really come in handy.

 

The first layer is not the primary air barrier, so (tight) scraps are OK

The two layers of foam should have offset seams, so Calvin and Damien begin with a small rip that will fit continuously under the windows. The first course is kept level to keep the measurements consistent, and a metal cap at the bottom protects the foam from insects. 

It is great to use large pieces when possible, for a better air barrier, but because there is a layer of house wrap and two layers of foam, it is also safe to use up some random scraps—and there will be a lot of scraps—as long as the joints are tight and the insulation is continuous, piecing in scraps should be fine.

Editor's note:

Pieces of foam are kept in place with extra long screws and washers. On the first layer, you only need two screws per piece—to keep each piece from rotating. As a second layer is added and furring strips applied, there will be plenty of fasteners in the first layer to hold it forever.

As Dave said earlier, the foam will overlap the window frame to get a tight seal to this opening. In this case the guys are leaving 2-1/4 inches of frame revealed. Also at the window, they pull the pan flashing out past the foam, so that anything that leaks in is drained all the way out. 

Don’t bother to tape the seams on the first layer because as you compress the foam later the tape will be pulled away from the seams. The second layer will be taped.

As one guy installs, he can also measure for the next piece.

Working together, two installers ought to be able to keep ahead of one cut man.

 

Cutting foam sheets is pretty simple.

You can use utility knives with extendable blades to get the whole depth on small cuts and when cutting sheets in place. 
Angled cuts are needed where wall foam butts under roof foam. For long cuts, you can use a knife and a chalk line or a T- square or you can use a table saw.  

Comments

I noticed you taped the house wrap beneath the foam, then taped the outer layer of foam.  Does this lead to trapped mositure issues having two air barriers?

Daniel Morrison's picture

The wall should be able to dry inward from the housewrap and outward from the foam. 

Moisture-laden air should not make it past either layer of the air barrier system.

Some builders go the extra step of using a wrinkle-type house wrap to allow any teeny bits of moisture to drain out. 

 

I would like to see how this house gets sided.

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