Windows for Your Climate

Windows are like the eyes of your house and eyes are said to be the window to your soul. It might be true that windows are the connection to your home’s soul! Not only do they let you see out into the world, but windows also allow the light to shine in. Do you love having windows in particular spaces of your home that allow you to enjoy the view or appreciate the warmth of the sun shining in? Glass is a transparent material and glazing systems are the units that include one to three layers of glass within a frame. The placement of glazing systems in a wall or roof structure requires additional framing to support the opening, especially if the opening is a large span or dimension. Unless we are talking about glass blocks, which are in the masonry unit family, all other glazing systems are non-load bearing, meaning they can’t carry any weight or stress to any extent.

The modern architecture movement in the twentieth century brought forward the use of glass as entire wall systems with a technique called curtain wall. Curtain wall is when the wall surface is essentially hanging from the structure (slab or beam) above, so the wall is structurally supported and hangs with its own gravity load. All-glass houses such as the Farnsworth House designed by Mies van der Rohe create a fully transparent living space as if one exists entirely in the natural setting where the house is sited. However, glass is not a very good insulating material, so designs with all glass walls require more heating and cooling of the interior spaces year-round. Some exceptions will be climate locations that are temperate and comfortable, such as the California coast. The mid-century modern Eames House located in the Pacific Palisades of Los Angeles incorporates large glass window walls, but the climate is so temperate that this design doesn’t negatively affect the energy use of the house.

Glass walls and large windows can provide a sense of expanse and make us feel like we are experiencing the outdoors while sitting inside our home. However, there are also very small but intentionally placed windows in Japanese architecture that connect us to the outdoors in a different way. Some contemporary Japanese architects will incorporate small windows that might be placed close to the floor, which provide views out to the plants or rocks in the landscape surrounding a home. Thin tall windows, like slits in a wall, might be placed where there is a transition between two different interior rooms, signaling this change with light and sky that is uniquely cropped. The choreography of windows between the indoor and outdoor spaces can become an intricate dance of setting up playful and invigorating relationships – bringing the outdoors in while drawing our attention outwards in a reflective way.

The placement of windows in relation to the path of the sun is extremely important for the energetic design of your house. The sun provides a natural, abundant, and replenishing resource of heat and light. The natural daylight from the sun is valuable to your daily health and circadian rhythm (see the blog post on Natural Daylighting). The radiant heat from the sun is a great source of energy for cold winter days but can only reach inside your home with properly oriented fenestration. In the northern hemisphere, the south façade of your house is the best location to have larger windows. In the winter months, the sun’s altitude angle, or its height in the sky relative to the ground plane, is fairly low and will project its rays directly onto vertical surfaces (walls or windows) that are oriented southwards. In the summer months, the sun’s altitude angle will be higher in the sky, and roof overhangs or horizontal shading devices placed over windows can prevent the radiant heat from penetrating indoors. There is a very natural and passive fluctuation of these seasonal changes of the sun’s path and the heating and cooling needs of our indoor spaces.  

For wintertime, sun spaces are great ways to provide natural heating into the home. These make use of glazing and the greenhouse effect. The greenhouse effect in building design is when the short-wave radiation from the direct sun is allowed to enter through glass to interior spaces while the long-wave radiation in the form of residual heat cannot pass through the glass so is retained indoors. As heat continues to build up inside but not exit, the greenhouse effect takes place! More details on these types of passive heating systems will be shared in next week’s blog post, so stay tuned.

For now, consider how your south-facing windows in the cold months might be able to allow some direct sun indoors during the middle of the day. You can also take advantage of east and west facing windows in the winter months – so open up your curtains or blinds at east windows in the morning and at west windows in the afternoon. The more direct radiation you can let inside from the sun during colder days, the better! With north-facing windows, you will likely notice a chilling effect if you stand or sit close to these on a winter day. It is still helpful to receive the natural daylight from north-facing windows; but acknowledge that north-facing windows will tend to remove heat from your home due to conduction and convection. Your body will more rapidly lose heat when you sit near a north-facing window on cold days, reducing your thermal comfort.

Each season brings with it a different relationship with our windows and fenestration. In warm months, opening up the windows to catch fresh breeze through the house is super pleasant and provides a cooling effect. In cold months, closing up all windows and enhancing their insulative properties with a storm window layer and ensuring air-gaps are sealed around the frames is one of the best methods to help retain heat indoors. If you’re considering remodeling or doing an addition to your home, pay attention to the orientation, placement, and sizing of windows so that they work well with the climate and connection to the outdoors. If you are considering renovating your house and window replacement is on the wish list, pay attention to the frame material and glazing layers for your climate.

Window frame materials are quire varied and include wood, aluminum, vinyl, fiberglass, and composites. Each frame type has a slightly different insulative effect or heat resistance value, some are more durable and lasting than others, some have healthier material properties, and some cost more than others. There are so many variables to consider with window frame selection and your needs and budget. But keep your climate in mind with your selection – weatherization of wood window frames and exposure to termites can be a challenge in hot dry climates while expansion and contraction with moisture can be a challenge in humid climates, but wood frames are more eco-friendly on the manufacturing chain.

Glass may also have different properties, especially with spectrally selective coatings and placement of these coatings on particular faces of the glass within a window system. This aspect of window design is a bit technical and delves into the optical and material sciences. But the fascinating thing about these sciences is that they have enabled a vast field of customization and solar control in glass systems. For buildings and your house in particular, the climate will determine the necessity and placement of spectral coatings. Spectrally selective coatings are designed to absorb specific wavelengths of electromagnetic energy (such as UV-rays) while allowing others to pass through (such as visible light rays). Each wavelength of radiant energy has a different bandwidth and micro-material structuring can be designed to capture or transmit different bandwidths.

In hot climates, the primary goal is to keep heat out while allowing daylight in. In a double-glazed window unit, the outer layer of glass is layer one and the inner layer of glass is layer two. Spectrally selective coatings (sometime referred to as Low-E, or low-emissivity) that are placed on the outer face of layer two glass in the window system will benefit the thermal function in hot climates. In cold climates, the primary goal is to capture the sun’s radiant heat through the windows and retain it indoors. Low-E coatings that are placed on the inside face of layer one glass in the window system (the outer-most layer) will work best for cold conditions. If you are in a climate that has seasonal extremes, you’ll want to determine how many days of cooling vs. heating are needed for a house in your location and decide on the glazing system based on that calculation. There are some handy free tools for heating and cooling degree day calculators available on the web.

Be careful with this variable of the coating placements on your window selections because it is not uncommon for your windows to be purchased and ordered from a manufacturer that is located in a drastically different climate zone where they are designed for the opposite condition that your house will need. I’ve been on site for a new home build in Arizona where the window specifications indicated the low-e coating to be placed on the outside face of layer two and the windows were installed with the coating on the inside face of layer one. The windows came from a manufacturer in the Midwest where the spectral coating placement was designed primarily for cold climate conditions. The contractor had to remove the windows that were installed and luckily could just have the glazing removed and replaced in the correct order in the same frames and then re-install them in the house. We always learn from experience, and it helps to share the knowledge forward!

If you would like specific guidance about designing or renovating your house with the best windows for your situation, reach out to AIDA, LLC today for a consultation.You can always find more information and healthy home resources at Aletheia Ida Design and Architecture, LLC (AIDA, LLC) at www.aletheiaida.com.