I Can See Clearly Now: Installing the windows

I only drink fortified wines during bad weather. Snowstorm, hurricane, tornado--I'm not particular, as long as it's bad. After all, any storm for a Port.
Paul S. Winalski

Even with a very strong window, there are two remaining concerns: 1) The strongest window in the world will not save a house in a storm if it doesn’t stay in its opening, so the way the windows are installed and sealed makes a big difference in the security of the structure. 2) Water penetration around the window from horizontal, wind-blown rain can wreak havoc in the forms of rot and mold in both the interior of the house and within the walls. Windows are designed for both positive and negative design pressures (DP). Positive pressures are those acting to push the windows in from the outside, and negative pressures are suction forces trying to pull the windows out of the house. Both types of forces need to be addressed to withstand a hurricane. Shwinco windows use a type of tie bracket that is screwed around the edge of the window and spaced to withstand a given load. These clips are screwed into the framing and prevent the windows from popping out. There is also a nailing flange that is made from a very stiff vinyl. A strong polyurethane adhesive is applied around the flange, and then the flange is nailed as the window is set. The flange faces the outside of the window opening and keeps the window from being pushed into the house. It is important that the rough openings for the windows be kept tight for this purpose. The window literally uses the house to push against as its support, so the integrity of the framing helps to maintain the integrity of the window system. The need to maintain structural strength reinforces the need for fasteners that don’t corrode, like type 316 stainless steel, so that any pieces that do get wet or damp do not weaken with time.

Different environments cause varying potential loads, which drive the decision for applicable design pressures and allowable window sizes. Since the windows are edge supported, the building envelope must be able to support given loads, determining the maximum sized windows that will still meet the positive and negative design pressures in a situation. A fixed window can be larger than an opening window and still uphold the needed DP, because the glass in a fixed window is incorporated into the window frame, which stiffens the frame and makes it stronger.

Preventing leaks in a high velocity hurricane zone is an entirely different beast to conquer. Prior to installation, the window opening is prepared and sealed. For this application, Dupont Flex Wrap was applied snugly around the rough window opening and OVER the house wrap to maintain a waterfall concept for possible water flow. (FlexWrap is a flexible, self-adhesive flashing tape constructed from a layer of tough Tyvek laminated on a layer of high adhesive butyl rubber.) Because it bends, this product goes around corners without having to be cut and fitted, lessening the chance for a leak in an awkward spot. To get a snug application, the FlexWrap should be “rubbed” into place for good adhesion to the surface. This flexible tape is tested for water intrusion both as a newly installed item and also after thermal aging.

Once the window is in place, a drip edge is installed across the top of the window. A drip edge takes the water off the plane, so that accumulated water falls beyond and not down across the window. The bottom of the window is not sealed and not nailed. Shwinco windows have a weep mechanism that allows water to drain out if it gets past the first seal, and the windows actually have three seals to keep water out of the house where the window meets the frame. If the window is designed properly and the path is not blocked, gravity will take any water out. The rough opening under each window has an added piece of sloping cedar under the FlexWrap as an added assurance that the water will run in the right direction and not pool in the window sill.

Here is a slideshow of some of the first floor windows being prepared and installed:

A note about casement windows versus single hung windows: Single hung windows are intrinsically more prone to higher leakage rates simply because the opening part of the window has to slide in a channel and needs clearance (space between the window and the frame) to do so. A casement window, in contrast, is closed up against the window opening and is locked down, eliminating virtually all clearance when latched.

When designing a house to a certain type of constraint, like withstanding a hurricane with 150 mph winds, it is important to realize that being willing and able to compromise in terms of design can mean the difference between saving and losing a house. In the end, the questions to ask oneself are those that begin with “what if,” or “when” a storm comes. We happen to really like casement windows, but even if we didn’t, it would be easier to accept the casement windows than it would be to face the loss or damage to the house.

With the window specifications that Vince ordered and Shwinco manufactured, and with the careful installation by PJ Stuart and Currituck Construction Company, we have given the house a good fighting chance in a big storm, though it will be perfectly OK not to ever test the house and the windows to their full capacity.

For what I have received, may the Lord make me truly thankful.
And more truly for what I have not received.
Storm Jameson