Balancing Energy Efficiency and Historic Values: Best Practices for Windows
Historic homes have their charms – tall ceilings, beautiful woodwork, brick fireplaces – but also challenges. One of the largest challenges involves making your home more comfortable and energy efficient without removing or altering historic components. This is trickiest when it comes to historic windows, which are made of wood and are often double-hung with a single layer of glass. Over time, they may have warped, become inoperable or drafty, or otherwise become a target for replacement. If these are restored to working order and a few modern touches are incorporated, however, you can both enjoy the lower energy bills and the beauty of your historic home.
Generally, the first step is analyzing your windows to determine the level of repair necessary to bring them back to working order. Windows often have the following problems:
- Upper sash painted shut: This keeps the window from operating as intended. Often the sash is not raised fully when painted, so the upper and bottom sash rails don’t align and the window can’t be locked. This allows for gaps between the sashes through which air can enter the home. Remove the paint using a heat gun or eco-friendly paint remover and, if necessary, replace/ repair the counterweights as needed.
- Sashes warped: If slightly warped, remove all built-up paint from the sashes and the frames to maximize ability to move up and down. Consider installing two sash locks instead of one for a tighter seal. If the sash is too warped, you may need to replace the rails of the unit with new wood.
- Peeling paint or rotten wood: Peeling paint demonstrates a moisture problem, but not necessarily rotten wood. Remove all peeling paint, and attempt to determine the source of the moisture. Often a sill isn’t sloped to the exterior to ensure water drains, or there are gaps in the exterior trim or frame. Fill the gaps with caulk (or putty, if larger openings). Replace the sill with a sloped piece of wood (or stone, if appropriate) that has a drip edge. For rotten wood, remove the offending portion of wood and replace with new.
- Loose glass: Ill-fitting or loose glass makes noise in addition to allowing cold air to come in. Have your glass re-installed or replaced. Glazing compound must be used on the interior and exterior faces to ensure a tight seal.
- No movement: Can be caused by paint build-up on the frames or sashes, or by past renovators cutting the cords for the weights. Remove paint and re-install counterweights.
Now that you have a fully functioning window, here are some ideas:
- Install weather-stripping at the sides, bottoms and tops of sashes, plus rails where the sashes join. The best option is silicone-bulb weather-stripping. It requires routing out a groove in the wood, which is more work, but provides a long-term dependable seal where the sashes come together with each other and the frame. Weather-stripping will reduce (hopefully eliminate) drafts, improving comfort and efficiency.
- For South-facing windows, consider these options to reduce heat gain in the summer months:
- Apply low-e film to the glass
- If shutters are appropriate to the building, install or make existing ones usable. Closing shutters during the day can significantly reduce heat gain.
- Incorporate other shading devices, like interior shades or window treatments or trees in the yard.
- Install storm windows. Both exterior and interior types are available. Exterior storm windows with Low-e coatings have the added benefit of protecting the sashes from water and UV degradation. Interior storms are easier to install in upper floors. Storm windows can reduce heat loss by 25% to 50%.
- Use the windows! In appropriate weather conditions, open the windows (screens may be temporary or part of the storm window assembly, or designed into the shutters). Windows are typically placed to maximize cross ventilation. By teaming the windows (open upper and lower sashes part-way) with ceiling fans (cool air comes in through the bottom sash, hot air leaves through the top) and shading devices, you can drastically reduce the use of your HVAC.
Studies have shown that properly restored windows with storms are negligibly less efficient that new replacement windows – and cost a lot less!
REGREEN, the residential remodeling program created by ASID and USGBC
Fine Homebuilding “How Not to Save Energy”
Fine Homebuilding “Should Your Old Wood Windows Be Saved?”
Fine Homebuilding “Taking Issue: Energy Upgrades Threaten Older Homes”
National Park Service Preservation Brief “The Repair of Historic Wooden Windows”
U.S. Department of Energy “Energy Savers Tips”