Green Means

Windows that Perform

By Shannon Scott

Not much beats a room with a view.  Except a room with two views out different directions through responsibly manufactured, insulated, heat reflective windows.

 If you are building or remodeling, selecting windows will be one of the single most important, energy saving and esthetically pleasing decisions you make.  Heat loss is minimal with efficient windows in a well designed passive solar home.  There’s no longer any reason to limit the amount of glass.  So enjoy the views!

The best window options are low thermal emissivity (Low-E) coated, gas-filled, multi-paned made with solid framing materials.  Look for Sustainable Forest Initiative (SFI) or Forest Stewardship Council (FSC) labels.  Choose aluminum clad hardwood or pultruded fiberglass exterior frames for low maintenance.  

Window design and placement is referred to as fenestration.  National Fenestration Rating Council (NFRC) stickers on windows verify performance factors.  Some better makes and models are Sierra Pacific, Anderson Eagle series, and Marvin Integrity.   We were able to get SFI certified Sierra Pacific windows from Franklin Lumber.  Sierra Pacific windows are made here in the west, which minimizes the negative environmental impacts of long-distance distribution.  Whenever possible, buy locally or regionally made goods. 
                                                 Performance Factors

            U-factor measures how well a product prevents heat from escaping.  Ratings generally fall between 0.20 and 1.20. The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value.  U-factors are dependent upon the type and placement of the Low-E coating.  Some placements reflect heat into a room to prevent heat loss, while others reflect it out to keep interiors cooler.

            Solar heat gain coefficient (SHGC) measures how well a product blocks the sun’s heat. The SHGC is the fraction of incident solar radiation admitted through a window, both directly transmitted and absorbed and subsequently released inward.  SHCG is expressed as a number between 0 and 1. The lower a window’s solar heat gain coefficient, the less solar heat it transmits.  The SHGC is also dependent upon Low-E coating, type, and placement.  

            Leadership in Environmental and Energy Design (LEED) gives credits for U-factors and SHGCs of .35 or less.  The smaller the number, the better the LEED rating.  

            Visible transmittance (Vt) is an optical property that indicates the amount of visible light transmitted into a room. Vt is expressed as a number between 0 and 1. The higher the Vt, the more light available. 

            Condensation Resistance (CR) measures how well a window resists the formation of condensation. CR is expressed as a number between 1 and 100. A higher number indicates better resistance to condensation.  Quality windows are dry, year round.

Designs

Casement windows have cranks or knobs that turn to open the windows along a vertical plain.  This design captures and directs air flow better than other window styles.  Don’t believe the myth about this style not holding up in strong winds.

Double-hung windows slide up or down, and often tilt in at an angle to form a horizontal plain.  Some manufactures make at least one of the two pains easily removable for cleaning.

Awning windows are similar to double-hung except there is only one pane and usually only one opening option.  An awning window will usually hinge at the top and swing out. 

Fixed, picture, or plate glass windows are windows that don’t open.  Fixed windows are cheaper because there’s no operational hardware.  These can save you money in areas where you already have air flow, or emergency exit windows.  Combine fixed and opening styles to expand views more inexpensively than having all operational windows.  Bedrooms must have egress (exit) windows in case of fire, but you can certainly combine an egress with a fixed to maximize a tranquil bedroom view.

 Gliders or sliders are the cheapest models available and there’s a reason for it.  Tracks quickly and easily become dirt filled which makes their operation less smooth.  They do not open out either vertically or horizontally to capture air flow guiding it into the home.  Air flow must be fairly direct in to the windows.  These work well for interior pass through windows, or if space to open is extremely limited.

Placement

Windows on at least two sides of every room allow light to enter at different times of the day and change the way a room looks and feels.  Residents are offered views in more than one direction and better ventilation.  Plenty of glass reduces the need for artificial lighting, which further saves energy costs, and lifts spirits by making a home brighter. 

Window heights should be proportionate to room size, and offer views out when standing and sitting. Sills approximately 2 ft. above the floor are usually good.   Sill heights above 2 ft. can limit views.   Floor to ceiling windows are grand as long as they are high enough above exterior grade so that snow loads don’t pile up against glass. If privacy from neighbors is a concern, don’t reduce glass.  Instead, strategically place trees and shrubs to block unwanted gazes.

When installing windows, caulk well with a low or non-VOC caulk.  Caulking well disallows drafts, making the building envelop as tight as possible for maximum energy efficiency.  Diligently caulking and insulating window peripheries maximizes energy efficiency.

            Avoid solid metal, and vinyl clad windows.  Metal windows conduct cold and heat directly into interior spaces.  Vinyl releases toxins (off-gasses) urea-formaldehyde a carcinogen, and phthalates found in PVC (poly-vinyl chloride).  Phthalates are carcinogens, can interfere with normal fetal or child development, can harm reproductive health, and are allergens.

Windows connect us to the outdoors, while protecting us from the elements.   How enjoyable it is to watch hawks soar, bluebirds perch, an orange sunset, or swirling snows.  Choose environmentally responsibly manufactured windows and enjoy the view with peace of mind.