Concentration of CO2 in the Atmosphere

Weatherizing Windows … when Net Zero is not an Option

By Bob Walker, Sustainable Energy Resource Group

Roy Prochorchik installs inside storm window

Replacing windows might well be on the list of to-do’s for folks doing a ‘deep energy retrofit,’ where you are trying to make very deep savings at much higher costs with much longer paybacks. If your goals are to reach Net-Zero, this is the route to take (100% savings). The planet will appreciate it if you can possibly find a way to do so.


“Weatherizing windows is almost always more cost-effective than replacing them because new ones are very expensive and there are many things that can be done to make existing windows work better. Replacing windows rarely turns up in recommendations for Home Performance with ENERGY STAR contractors where the goal is usually to save 25%-30% energy in homes with very high return on investment – 10% -15% avg.

Weatherizing Windows

Windows are one of the first things most homeowners think about replacing when deciding they want to weatherize their homes. But replacing windows is VERY expensive and existing windows can usually be improved to work better, and have better energy performance,at a fraction of the cost of new windows. Here are a few tips and resources you can use to tighten up your windows. We are going to focus here on conventional ‘hung-sash’ windows, the most common general type.

Rick Biddle weatherstrips a window

  • Close and latch all windows and storm windows tightly.
  • If any of the storm windows do not close tightly, for instance leaving gaps at top, middle, or bottom, or leaving a gap in opposing corners when closed, you will need to loosen the storm window frame from the trim outside, square it up so it closes properly and reattach with caulk and screws.
  • Caulk the edges of exterior storm windows to the trim with high quality acrylic latex caulk with silicone – make sure not to caulk over the weep holes at the bottom of the frame that drain condensation.
  • With the main window, if you can shake the sash and they rattle, you can tighten the window latches that pull the sash together by removing the inner portion of the closing mechanism, filling old screw holes with wooden match sticks or slivers of wood, replacing the latch, drilling new holes where they will make the lock work better, and reinstalling the lock.
  • Window sash can be sealed at top, bottom and edges by installing v-shaped weatherstrip. Top and bottom weatherstrip can be installed on the window casing where the top and bottom sash close, with sash in place. To install side weatherstrip, remove the window bands from one side of the sash, remove the sash, install v-shaped weatherstrip on the window jamb the weatherstrip “pointing” in, and replace the sash and the bands. Adjust everything as needed to work well. You might first try out your window-improvement skills on a less-used window as a “guinea pig.” As a rule, don’t permanently caulk windows shut. Vinyl v-seal weatherstrip is available from most building supply warehouses. Much longer lasting bronze v-strip is available from Architectural Resource Center:
  • Sometimes window bands (the trim boards on the window unit’s sides holding the moveable sash in place), or the window stool (“sill” to most people) need to be removed and adjusted, to fit more uniformly against the sash. Do a careful job so that sash still can move.
  • Making a window insert

    If you have old window types with ropes, pulleys and counterweights, remove the inside trim piece covering the counterweight cavity on each side of window. Cut the counterweight cord and remove the counterweights (make sure sashes are latched so they do not drop when removing counterweights). Remove window stops from one side and remove sash. (This is a good time to install v-seal weatherstrip at sides – see above.) Remove cording attached to sash and remove pulleys from window jambs. If you do not need to retain opening capability of upper sash, reinstall it, temporarily screwing sash in place and caulk at edges. If you want to keep both sash operable, replace the old counterweigh pulleys with new window counterbalances, and attach the counterweight spring to sash and replace. Then fill the counterweight cavity with polyisocyanurate foam insulation board, slightly undercut around the outside and air seal edges of foam board with spray foam. (We suggest “Pullman Window Counterbalance” available at: 585-334-1350,

Bob Walker is the Executive Director for Sustainable Energy Resource Group (SERG) 802-785-4126, Thetford Center, VT



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