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Energy-efficient windows

High-Performance Homes: Energy-Efficient Windows, Exterior Doors and Skylights

Energy-efficient windows and doors can boost your home’s comfort, reduce your energy bills and increase its property value while reducing your carbon footprint. Your home’s windows and doors can account for up to 25 percent of your home’s heating loss.

Achieving energy efficiency is a simple enough concept: consume less energy while enjoying the same or greater level of comfort and performance. Your HVAC system is responsible for nearly half of your home’s energy requirements, so finding ways to improve your home’s energy efficiency and thermal performance is typically the most effective approach to reducing energy costs.

Energy performance can be measured in four categories:

  • U-factor, which measures how well the window or door prevents heat from escaping the inside of your home,
  • Solar heat gain coefficient, a measure of how successfully the window or door keeps out unwanted heat from the outside,
  • Air leakage, a measure of the airtightness of the building, and the potential for drafts, and
  • Visible transmittance, the measure of how much natural light makes its way through the unit.

Windows, doors and skylights represent potentially serious penetrations in your airtight building envelope and its continuous, super insulation around the entire shell, with an insulated slab, walls, and roof.

Windows

Energy-efficient windows help your home maintain a consistent temperature by providing a thermal break from the outside air, while either harnessing the energy of the sun or keeping it at bay. On existing homes, windows can sometimes be repaired by servicing the latches, cranks and locks, by retrofitting them with caulking and weatherstripping or by adding additional glazing or storm windows.

In most cases, your best choice for retrofits will be the replacement of the window and frame units with brand-new high-performance Energy Star® certified windows. If your frames are still in excellent condition, you may be able to install inserts, which include a new sash and glazing unit. Professionally installed energy-efficient windows will increase the comfort in your home, by preventing cold spots and drafts near the windows.

Whether remodelling or building new, high-performance energy-efficient windows will have most or all of these features:

  • triple- or quadruple-glazing
  • an inert gas, such as argon or krypton in the sealed unit
  • low-emissivity (low-E) glass
  • insulated frames and sashes
  • excellent air tightness

It’s important to note that triple-glazing will only deliver maximum benefits when paired with a frame that matches the energy efficiency the glass provides. High-performance building projects such as the PassivHaus Standard require triple-glazed windows with a U-value of no more than 0.8.

Solar heat gain coefficient (SHGC) refers to a window’s ability to resist solar radiation transmitted by the sun. Windows with a low solar heat gain coefficient will not allow much of the sun’s energy to pass through the glass to heat the room, which makes them a good choice for hotter climates. Windows with a high solar heat gain coefficient allow the sun’s rays to heat the room, which could make them a good choice for colder climates.

Vinyl, fibreglass and fibreglass composite window frames have become very popular. Vinyl window frames are made from extruded polyvinyl chloride (PVC) and may include metal to increase the structural stiffness. Vinyl windows currently account for more than half of residential window sales.

Vinyl windows are very affordable and are energy efficient due to the hollow cavities that can be filled with insulation to trap air, improving their R-value. Vinyl frames are virtually maintenance-free because they don’t need to be painted. Vinyl and fibreglass windows are both manufactured from inert substances that are not going to rot or suffer damage from termites or carpenter ants. Vinyl, however, loses its resiliency over its lifespan, a drawback fibreglass does not have.

Fibreglass is stronger, which allows the frames to deliver the same level of energy efficiency from a lower profile frame; generally considered the more aesthetically pleasing option. Fibreglass frames can also be textured to appear like wood when they are painted. Recent fibreglass composites are a mixture of fibreglass and polyester resins. Fibreglass is sourced from glass, the same material used in the window panes; therefore the frames and glass expand and contract at the same rate, which can help prevent seal failure in the IGU (insulated glass unit).

Energy Star® certified windows are approximately 20% more energy efficient than conventional windows. Energy Star is a government program that helps consumers save money on energy costs and protect the environment through superior energy efficiency.

Doors

Energy-efficient doors are typically made of fibreglass, aluminum, steel or wood, with an insulating core that helps insulate the door. The door’s U-factor measures how much heat or cold flows through the door. The lower the value, the more energy-efficient the door is. The R-value measures insulation, so the higher the door’s R-value, the more energy efficient it is. By factoring in both values, your designer can determine if doors meet the Energy Star Certification requirements in British Columbia.

Energy-efficient doors can save you money on monthly energy bills, by preventing air-conditioning or heat from escaping; and they can also help your Passive House or Net Zero home achieve its overall energy targets. When properly installed, energy-efficient doors will help seal the building envelope, while the insulated core helps to block hot or cold from seeping into the room.

High-performance doors typically look similar to a vault door. For example, Passive House-certified doors are at least 10.2cm (4″) thick, and they have three seals between the door and the frame, and three or more locking points to ensure maximum insulation and a tight seal. They also have two seals along the bottom and a highly insulated body with at least R-10 insulation. If there is glass in the door it will be triple-glazed with argon or krypton gas filling the space between panes.

Passive House certified doors typically have a U-factor of 0.14 Btu/hr-ft2-°F or less and are designed to improve energy efficiency and thermal performance, by reducing air leakage and heat transfer. Through a combination of low U-values and high insulation R-values, zero thermal bridging (thermally broken design), triple glazing with a warm edge (thermal spacer), and airtightness, you should enjoy noticeably lower energy bills. Energy Star® certified doors are about 15% more efficient than conventional doors.

Skylights

Skylights can be some of the hardest-working windows in your home. They flood your spaces with natural light, open up dim corridors and can add a luxurious pleasing warmth to the freestanding soaker tub area in your master bathroom, without sacrificing privacy.

Skylights can also reduce your reliance on artificial lighting during the day, resulting in small savings on your energy bill. They can provide additional free ventilation too, for removing hot, moist air produced by bathroom showers or cooktops.

Orientation is an important consideration. In colder climates, south-facing skylight windows can increase the passive solar heat entering your home, helping to offset heating costs. Whereas, in a warmer climate, where air conditioning is a major energy cost, you’ll want a north-facing slope. East- and west-facing skylights might be the perfect neutral choice in moderate areas like BC’s West Coast.

Skylight shades, screens, and blinds can significantly reduce heat gain by blocking excess solar energy on hotter days. They are a great adjustable option for homes that experience a wide range of temperatures. Smart technology can make these shading solutions fully automated or manageable by remote control.

Your design-builder can use energy modelling software to determine whether double-pane glass will do the job, or whether you’ll need triple-glazed skylights to achieve your energy target. It’s worth noting that the more panes of glass you add to your skylight window unit, the less natural light will enter your home.

Energy Star® certified skylights are typically 35% more efficient than conventional skylights.

Interior and exterior caulking and weatherstripping

High-performance homes usually incorporate a sealed building envelope. On the interior, air leakage around windows, doors and skylights can be greatly reduced by applying a continuous bead of caulk around the trim, where it meets the wall, in any mitred joints, and between the trim and the frame. Indoors, you will want to use paintable caulk that is intended for indoor applications.

On the exterior, your windows should have a properly applied flashing and drainage plane. Caulking then forms the last, albeit the weakest, defence against any rain entering the wall from the outside. The exterior caulking is applied only after the interior sealing is completed, so moist air is not trapped within the wall. Windows are weatherstripped around the sash to reduce air leakage.

The takeaway

Whether you’re building a custom Passive House or BC Step Code 5-compliant Net Zero ready home, or retrofitting your existing house, upgrading the windows and exterior doors will help you prevent drafts, eliminate cold spots and save energy. Energy-efficient windows, doors and skylights are designed to insulate better, with a range of features that will help prevent heat loss in the winter, and heat gain during the summer.

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