Author’s note: Edited 8/10/15 to update window and patio door glazing as WITHIN 2014 Energy Star performance standards.
From the outset, developing a strong thermal envelope was foremost in my mind. In addition to increasing energy efficiency with regard to climate control, a strong thermal envelope will increase my chances of having the container home Energy Star certified. Such certification then leads to the potential for thousands in tax credits, and I believe it would bolster my credibility as a green builder from a marketing standpoint.
Besides insulation, windows and doors are the primary saviors of thermal efficiency within a home. They’re so crucial to the performance of the thermal envelope that Energy Star has a special criteria just for them. When you buy an old home (a fixer-upper), you’re buying all the old windows and doors, too (unless they’ve been replaced, of course, but in my limited experience I find this rare). So a 40- or even 60-year-old house may have doors built with 40- and 60-year-old technologies and considerations. Add to that the shifting sands of time wearing on the foundation, and eventually the cracks literally begin to show around windows and doors in the form of lost heating, cooling, and the money that purchases each. In fact, “A typical home contains a half-mile of cracks and gaps behind walls and around windows and doors, along with dozens of holes for pipes, vents, ducts, lighting, and wiring.”
These windows are cookin’ with gas
With the plans mostly finalized, it was time to actually select the windows and doors that would transform the container (at least visually) from a big metal box into a tiny metal house. My architect contacted Womble Company in OKC, and Greg took our order from there. Womble deals in Pella windows, and the models we chose for the kitchen, bath and bedroom windows all contain “Advanced Low-E Insulating Glass.”
“Low-E” refers to “low emissivity,” which means a coating has been added to the glass during manufacture that makes it better at distributing and absorbing heat and cold than an untreated window. The effectiveness of the coating is measured by what’s called a U-factor or U-value; values closer to 1.0 are inefficient, while values closer to zero are more efficient. For example, untreated glass has a U-factor of 0.84, but my kitchen, bath and bedroom windows have U-factors at
or below 0.25 0.29, which is JUST within the 2014 Energy Star minimum of 0.30 for this geographic region. (Because the windows were purchased in 2014, they are beholden to the 2014 standard). You can learn more about emissivity here.
Most low-e glazing furthers efficiency with the use of argon or krypton gas filling the internal gap (or gaps, if triple glazed) between the panes. Mine have argon filling their gaps. Krypton is more expensive, but, according to Green Building Advisor, “Don’t be tempted to buy glazing without argon or krypton gas … In almost any location in the U.S., argon gas and low-e coatings will quickly yield energy savings exceeding their cost.”
A final set of three windows will be added to the natural opening of the container, but I’m waiting until being closer to completion to do that, the idea being that I may need to move large objects in or out of the cargo doors. The cargo doors, by the way, will remain functional once the windows are installed in that opening, as I wanted to retain the option to shut the doors and lock them in case of severe weather, extended absence or zombie apocalypse.
The sliding-glass patio doors are 0.32 u-factor, which is also within the 2014 Energy Star range. I also have a barn door-type panel that I can close to reduce sunlight exposure on the patio doors.
Otherwise, the doors of the container home are metal security doors from Tell. We decided to go with their Spartan series of doors for the main entry and bedroom openings. The handles for the doors are from the Cortland series in satin chrome, and the deadbolts are single cylinders in satin nickel. Both are currently primer gray, but I will likely paint them once construction has finished.