There have been many attempts to make the double hung window tighter over the couple of centuries it has been in use. In the 1920′s, a tongue and groove type, became common, known as “Integral Weatherstripping.” This installation causes the sashes to operate very stiffly, locks to malfunction, and destroys the bump-out. After 50 years or more of over-painting and warping, the integral system usually gets so tight the windows barely operate, and then only with great effort.
We recommend replacing it with “Spring Bronze”Weatherstripping. If it is desired to keep the integral system, we can make the windows easily operable by disassembling (yes, we know how to do this without destroying the metal weatherstripping, in most cases), sanding the sashes, and running a disc grinder through the grooves where the tongues insert.
We remove the piece of metal from the back of the bottom sash, which was intended to interlock with the bottom of the top sash, but only serves to drag it down and make the lock mis-align. By re-setting a sweep lock to do its job, (see Locks), the meeting rails are locked together and the interlock is unnecessary.
The Spring Bronze Weatherstripping we prefer to use is a strip of metal as wide as the edge of a sash, which is fastened to the channel in which the sashes ride. It is stapled down one side, so the other side springs out. When closed, the sash is compressing the sprung surface, closing the gap between it and the casing, making a much more draft free assembly out of an old window.
Some people advocate adding weatherstripping to the top, middle and bottom of the sashes. We find this mostly unnecessary – because those surfaces are designed to close solidly with a properly operating lock. Adding spring bronze to the top or bottom can make the lock difficult to operate, and any form of vinyl gasketing is a temporary solution because it will eventually wear out.
The real gaps in the old double hung system are in the sides of the sashes which were desdigned to hang freely in their tracks. Any friction; such as jambing the stops against the sashes or adding that felt backed stripping, is only going to make them impossible to operate in the summer- when humidity swells the wood and reduces clearances.
That is why we use a compression weathertstripping that does not reduce clearance – it just takes up the movement and stops rattling along with drafts, creating a “silky” feeling to the window’s operation. People who have us weatherstrip all their windows are always impressed with the improvement in draft and noise reduction.
Rather than trying to make an old window perfectly air tight- which is impossible to do on a long-term basis – have us add the side weatherstripping and then add an air tight storm- such as the Harvey Tru-Channel – and remember – this will give you the same energy performance as a replacement window!
These drawings show the window and frame from above, top and bottom sashes in their channels, so you can see how the sash compresses the spring bronze weatherstripping to stop drafts.
The parting bead, sash chain, window weights and pulleys are left out for simplicity, the arrows symbolize the drafts.
Here, a draft infiltrates through the sides of the window sash, on the right the draft is stopped by weatherstripping.
The rattling you hear when the wind blows hard is caused by loose windows and sounds just like money going down the drain.