Modern windows: Energy black holes or not? Part 1

Windows are among the most complex building components in a home, and also the most expensive. Look at what we ask windows to do. We want a visual connection to the outdoors that lets in the most daylight. We expect windows to provide fresh air when open, and are completely airtight when closed. We also want them to pass the suns heat in winter and shade the suns heat in summer. We need windows to be durable, resistant to condensation; wind, and driving rain, and we want them to integrate with the rest of the building envelope; and given they are a big investment they should last for several decades.

In addition to the important architectural contribution, windows have far-reaching energy consequences. Their performance, total area, and orientation can make or break the energy efficiency of a high-performance home.

The National Fenestration Rating Council (NFRC) rates windows on three criteria: U-factor, Solar Heat Gain Coefficient (SHGC), and visual transmittance (VT). NFRC ratings are whole window ratings that takes into account the different U-factors of the window’s frame, sash, edge of glass, and center of glass and not glass-only ratings. Glass only ratings can be 10% to 40% better than the whole product value, so look for the NFRC label on rated windows, and be suspicious of those without one.

U-factor measures how much heat is transmitted through the glass due to conduction, convection, and radiation. The lower the U-factor, the more efficiently the window blocks heat transfer. A 2015 Prescott energy code window has a maximum U-factor of 0.35, the equivalent of an R-2.8 insulated wall.

SHGC indicates how much of the sun’s radiant energy striking the window is transmitted through the window as heat. It is the fraction of solar radiation, expressed as a number between 0 and 1. Low SHGC means less heat is transmitted through the glass. A 2015 Prescott energy code window must have a maximum SHGC of 0.4.

Visual transmittance (VT) is the fraction of visible light energy that makes it through the window glass. Visible light is made up of those wavelengths detectable by the human eye. Visible light contains about 47% of the energy in sunlight. The higher the fraction, the more visible light will reach into the room.

Maximizing VT while getting the right combination of U-factor and SHGC can be challenging. All three properties must be considered and balanced to evaluate overall window performance. You may also find that you need different window styles and performance levels throughout your home depending on design preferences, the direction that your windows face and your local climate.

There are many different window designs, with the most popular being:  Fixed or picture windows that cannot be opened; and used for light or visibility alone. Sliding windows that open horizontally, can feature two or more sashes and offer a clear opening for good ventilation.  Single-hung sash windows open vertically (usually the bottom sash) and the other is fixed. Double hung windows open both sashes vertically, and screens can be installed outside the window frame.

Casement windows are hinged at the sides and open outward, with screens on the inside; they may be left-handed, right-handed, or both and are usually opened using a crank. An awning window is a casement window that is hung horizontally, and hinged on top. Casement windows are the dominant type now found in modern buildings.

A bay window is a multi-panel window, with at least three panels set at different angles to create a protrusion from the wall line. Eyebrow windows are a curved top window in a wall or in an eyebrow dormer. Bifold windows have two or more panels folding onto themselves, and louver windows have a series of blades that tilt to open.

Next time we will look at the various window design considerations, materials and performance enhancements.

For more information contact Paul Scrivens

The pros and cons of concrete pavers

Beautifying your outdoor space in an affordable and attractive hardscape definitely requires some careful deliberation. Every aspect of your home is an investment, even your exterior surroundings. Walkways, driveways and backyard patios should all be tied together to accent and enhance the overall personal and architectural style of your home.

Aesthetically, poured concrete is pretty plain and does not really add value to the look of your home; however, there are techniques including stamped and textured effects that can increase character.  On the other hand, concrete pavers come in a vast array of colors, shapes and textures, and are generally more visually appealing than concrete slabs.

One of the most important parts of a concrete driveway installation begins after all of the work is done. Concrete doesn’t dry out; rather, it undergoes a slow chemical curing process that hardens and strengthens the material.  You will need to wait at least a week before driving on a new driveway, and at least a month before parking heavy vehicles on it.

It is a proven fact that concrete and stamped concrete will eventually crack, stain, and fade; therefore, many contractors do not guarantee the installation. Common causes of cracking are when the base moves due to heavy loads or ground settlement, and concrete tends to shrink over time.  As these cracks form year after year, it is often difficult to match the color and composition of the original material, and as such, the concrete surface gets uglier and uglier with each repair.

The alternative to repairing concrete is to replace the entire structure when the cracks become unbearable; unfortunately, repairs can be rather involved requiring heavy machinery and high cost. Concrete slabs can also be slippery when wet. This can cause cars to lose traction and leave tire marks on a newly installed concrete driveway, and a slippery pool deck or patio can be dangerous if someone were to slip.

Concrete slabs are generally lower in cost than pavers. A basic concrete driveway installed over a gravel base will cost $4 to $10 per square foot, and while a concrete slab is more affordable upfront, the long-term costs for repairs and/or replacements will almost always outweigh the initial savings.

On the other hand concrete pavers are considered to be one of the only hardscape products that instantly add value to your home upon installation. Pavers are less susceptible to cracking and breakage because they move with the earth.  They are also molded under extreme pressure and are much stronger and durable than poured concrete. Another benefit is that most manufacturers back up their products with a Lifetime Warranty against breaking and cracking and unlike poured concrete do not require a curing period once installed.

Pavers do require more preparation than poured concrete, and like any good surface material, they perform best when installed over a well-prepared base. In this case, compact sand over a gravel or paver base. Once installed, sweep sand over the surface and compact to fill the joints.  Be careful, because a poor quality installation can leave you with an undulating surface with unaligned stones.

Typical paver maintenance includes resealing the joints every few years, and weeds, moss and grass can grow in between joints, so it is necessary to treat the area with weed killer from time to time. On flat surfaces play sand works well when resealing joints; however, if you have a steep incline the sand will wash away quickly; in this case engineered sand that contains polymers and mortar is a better solution as it hardens with water misting, and rain water runs off, but it is essential to follow the usage instructions precisely. Because pavers are set in sand, utility repairs under driveways and pool decks can be accomplished by easily lifting the pavers and making repairs.

On a greener and safer note, because of the high level of joints in the surface, paver’s aide in the drainage of rain and snow into the soil, recharging groundwater and trapping contaminants.  They also offer greater vehicle and walking traction and reduce surface water glare. Therefore, with a properly graded installation, drainage issues should never occur.  An added advantage is that interlocking pavers are eligible for LEED® credits under the U.S. Green Building Councils Guidelines.

Costs for a paver driveway can vary significantly. A professionally installed job can run between $10 and $15 per square foot, while pavers themselves will run between $4 and $7. Because they are small and easy to handle, and don’t require heavy equipment to install, they are a great material for the DIY enthusiast. However, you might tackle a path or small patio, but for driveways and big projects a professional is recommended.

Finally, homeowners can take pleasure in having a cohesive outdoor environment, and experience an increase in home value without a rise in real estate taxes.

For more information contact Paul Scrivens