Historic windows are some of the most significant defining features on a building; windows hold the potential to completely alter the appearance and impression of a structure. Sometimes, as we know, the windows are replaced completely. Other times, the wood storm windows are removed and if replaced, it is often with aluminum triple track windows. When talking energy efficiency, storm windows can be one way to retain the historic windows and meet energy standards. Yet, new storm windows (assuming they are not wood like the originals) can change the building’s historic integrity. Original storm windows (such as those in yesterday’s Preservation Photos #144) are a rare sight.
A creative solution is to use interior storm windows, which retains the appearance and integrity of the building’s exterior.
Interior storm windows on Debevoise Hall located on the campus of Vermont Law School in South Royalton, VT.
Interior storm windows.
However, the windows are then altered on the interior: losing the depth of the window casing and losing the window sill, and some of the feel of the historic windows. What is your impression?
Interior storm seen from inside the building.
So, if you had to choose, what would you do? Interior storms? Exterior storms? Good replacement windows? Perhaps interior storms that are not white would be a better fit, and could fade into the background. This is an issue that is often considered with tax credit projects and energy efficiency ratings.
Preservation in Pink 
Interior storms can cause condensation on the inside sill which was not designed to shed water.
The ratings and standards are somewhat bogus as they rate glass which will never be energy efficient.
It is all the places where the glass and the frame join that really matter – and why old windows, poorly taken care of, are drafty. It is not the glass.
The air space between the window and the storm and the tight seal around each sash is the insulation.
So one solution is to add layers over the windows, shades, blinds, shutters, curtains that fold and trap the cold/heat, liners. A very traditional answer..
I know of some interior storms, but none I have monitored over the years. maybe someone else can comment.
Interior storm windows should only be a last resort and there are much more attractive ones built by companies like http://www.innerglass.com. Exterior storm windows are not the most attractive things (at least if they are aluminum triple tracks) but they do protect the windows, provide awesome energy efficiency when installed correctly, and are reversible – meaning they can come off without harming the building. There are many companies that build wooden storm windows which are very attractive but require more maintenance. Bottom line, storm windows mounted on the exterior are the best way to go.
I think it all depends on various factors contributing to the decision to implement a storm window in the first place.
In a recent project with an overall goal of decreasing energy consumption by 50% using a variety of techniques, I was able to implement three types of storm windows and compare their impact on the historic fabric, their performance towards the energy efficiency goals of the project and their general usability and aesthetic. Replacing the sash was never an option considered, but all sash were fully conserved as a component of the project.
In this case exterior storm windows were not historically correct (no evidence was found for their use at any time on this building) for the house. As an NHL, the addition of exterior storm windows was not really an easy option. The one exception being a wing that had had exterior storm windows installed approximately 20-30 years ago and thus were “grandfathered in”. Because of this exception, this particular project offered the opportunity to also install exterior storm windows – both wooden and aluminum. Both exterior solutions were low profile solutions with the storm window set in the window opening. As they are color matched to the trim, they are not really invisible, but you’d have to know to look to confirm they are there (at least from the outside).
The early measurements indicate that the interior storm windows are performing better than the exterior storm windows with respect to air infiltration (approximately 10% better). The use of low-E glass with the interior storm windows provides additional energy savings given the large number of window openings. The interior storm windows were also less invasive on the historic fabric and have yet (albeit after only one year) to develop a condensation problem – a definite concern if the storm window is not well sealed in the opening. Thus far, the biggest drawback of the interior storm windows is that they prevent the operation of the primary sash. In this case, the building is not a residence and is air conditioned and heated so this is a reasonable compromise based on how the property is used. A residence might have to weigh these factors a little differently.
The interior storm windows were about half the price of the exterior storm windows. Admittedly, the custom low profile exterior storm windows utilized in this project were more expense than a stock “triple track”, but if aesthetic is an important consideration, price might be one deciding factor.
Interestingly, there was no less conservation required on those sash that were “protected” by the exterior storm windows.
Please note that this picture is of Vermont Law School’s Debevoise Hall (not Oakes Hall) in South Royalton village. The 2005 rehab (which underwent Vermont Act 250 review) of the Queen Anne-style South Royalton Graded School (1893; a contributing resource within the South Royalton Village National Register Historic District) achieved LEED-NC 2.1 Silver certification. In my opinion, this is one of the better examples of a historic rehab achieving both good preservation and good sustainable results.
Hi Greg,
Thanks for the correction and sorry about the oversight (all corrected). And glad to hear your thoughts on the issue of interior storms. It is a beautiful building; did you do HP work on it? I agree that the interior storms are better than exterior storms in this case, but the lack of the window depth inside is something to get used to.