Storm Window for a SideLite

When my home was built in 1950, oil cost only US$2.77 per barrel.  I know, I know, you are thinking everything was less expensive back then, and that is true.  But even adjusting for inflation, oil in 1950 was only $26.46 per barrel.  In these days of $100 per barrel oil, it is fair to say that by any measure, oil in 1950 was cheap.

So it should come as no surprise that when the front door was put on my 50's Ranch in Lexington, MA, it had almost no insulating value.  The glass in the door is only single pane with an R-value of about 1 and the thin raised panels on the door are made of solid wood have have an R-value approaching 1 as well.  By contrast, a 2×4 wall with fiberglass insulation has an R-value of about 13.  So from an insulating standpoint, my front door is doing very little indeed.



    If a picture is worth a thousand words, an IR image is probably worth two thousand words.   In the above infrared image, the white portions are hot which is bad because that means the heat is getting outside the house.  A couple of things are clear from these images.  First, the storm door helps hold in some of the heat (although it is not nearly as good as the insulated walls around it shown by the blue color).  Second, the storm door doesn't cover the cover the sidelite of the door and as a result, the sidelite has very little insulating value.


 The view from inside the door tells a similar story.  From inside the house, we should focus on the blue color because that indicates cold, which is bad.  The image show the sidelite is dark blue which means it is less than 56°F and much worse than some parts of the main door which are yellow or green in color.  Also notable is that the raised panels are very thin as can be seen from the blue color around the edges of the raised panels.

Due to the high cost of home heating oil and the "Global Hotting Up" thing I keep hearing about on the news, I would like to "fix" this door.

The Standard Solution

The typical "solution" to this poorly insulated front door is to buy a new fiberglass one with foam insulation and double pane windows.  Frankly, I am not a fan of this "solution" because it would likely cost thousands of dollars (installed anyway) and be a relatively small improvement.  To clarify this a little further, perhaps it is worth giving a little bit of background.

Background
   In the world of insulation, there is something called the R-value which is a numerical value showing how well something insulates.  A low value such as 1 is poor, and a high value such as 30 is good.

    In the 1950's, when my house was built, walls had no insulation at all and had an R-value of 1.  Around the time of the 1973 OPEC oil crisis, it became common to insulate 2×4 wall cavities with fiberglass insulation which achieved a much better R-13 value.  This is also about the same value that a home like mine with blow-in cellulose insulation achieves.  In more recent times, building codes often require 2×6 walls so that more insulation can be put in the walls to achieve  R-19.  That is some significant progress.

R-1  2×4 uninsulated
R-13  2×4 insulated
R-19  2×6 insulated

   In the 1950's, windows were single pane and had an insulating value of R-1.  Later, in response to the 1973 OPEC oil embargo, storm windows were added increasing the R value modestly to about R-2.5.  In the modern times, double pane glass is the norm and offers an R-4.

R-1     single pane glass
R-2.5 single pane glass with storm
R-4    double pane glass


  So in the modern world, it is normal to expect to see homes with R-19 insulation in the walls and R-4 insulation for the windows.   People talk up these windows as if they have wonderful insulating qualities, but they just don't.  Frankly, modern double pane windows are &^$%.  Architects have access to SuperWindows with R-10 insulation  but home owners can't even get windows with half that insulation value.

     Here is what it is like putting a modern double pane window in a home. You start with an R-19 wall, cut a 3 foot wide by 4 foot tall opening and then shove back into the opening only a 1" thick piece of fiberglass.  It is pathetic and we need to do better.

  Replacement windows are one of the most oversold and questionable "investments" of modern times.  Consider a home like mine that has functioning single pane windows with functioning storm windows yielding an R-2.5.  The standard solution is to replace them with double pane windows and no storm with an R-4.   This small improvement, from R-2.5 to R-4 will cost about $1000 per window (installed) which could never be justified by the energy savings.  Of course, if the existing windows didn't have functioning storms, were very drafty, or didn't function well, the home owner may choose to replace the windows for those reasons, but not for the energy savings alone.  Don't get me wrong, on new construction, double pane windows are really are definitely better than the old single panes plus storm.  But if you have single pane windows with functioning storms, think twice before "investing" in double pane windows.

The Better Solution for the SideLite
  A brand new Home-Depot insulated door would have an measly R-4 value. My goal was to exceed R-value that and spend less money to boot.  The proposed solution is to build a storm window to cover the existing sidelite. The design has a two pronged approach.  First, a new double insulated glass unit will be used and placed in front of the existing single pane, effective providing triple glazing with about R-6.  Second, the lower part of the storm window would use 2" of rigid foam to achieve R-10 insulating value.

The above video shows how the storm window was created including a cool little animation from Pro/Engineer, the CAD software tool I used to design the pieces and virtually assemble them.

  The first step was to create a wooden frame for the face of the storm window as shown in the above image.  The lower portion has a wooden raised panel that mimics the look of the existing sidelite.  The upper portion has a pocket cut out to a depth of 0.5" so that the glass can be installed inside.

  The next step was to obtain a piece of double pane glass.  This was the part of the process that had me most worried.  I have purchased single pane glass many times, but was not sure how to go about getting double pane glass.  It turns out that you can buy double pane glass in any size you want and it is very easy.

   I called down to a local glass shop (Century Glass in Waltham, MA) and told them I wanted a 42 3/4×9 3/4×1/2" pane of low-e glass.  They placed the order with Guardian Industries (Webster, MA) by converting my request into a part number, ICNU70CL1260C.i3.1TC+6.4+3.1TC.  I would love to know what all that means.  It is pretty clear that the 3.1 is the thickness of the glass in millimeters, and 6.4 is the spacer between the glass panes in millimeters.  The resulting glass thickness is 3.1+6.4+3.1=12.6mm or 1/2".  The part actually came in at 0.560" but close enough.  The glass panel cost $65 and took about one week for delivery.

A bead of clear silicone caulk (GE5000, 0 77027 05000 4) was put into the window frame and the glass was then pressed into it.  An additional bead of silicone was added to the back of the glass.  The glass was held in place by a secondary frame and 14 #8 stainless steel wood screws that were 3" long.  Later, additional #8×1.5" stainless steel screws will be used to hold the storm window to the house.  Including shipping, the screws cost a staggering $25 from McMaster-Carr..  I could have done this for much less money using zinc plate screws from Home-Depot but I just could not bear the thought of these screws rusting in a few years.

   Joyfully, for the lower portion of the storm window, there was room for 2" of rigid foam.  This was cut to the right size on a table saw.  I could have just left the foam as it was, but I didn't like the fact that the foam could be easily damage if the storm window was ever removed from the house for any reason, e.g. maintenance.  So I cover the foam on five sides with 1/4" thick plywood for good measure.  The plywood was bonded in place using Loctite PL300 Foamboard construction adhesive (0 79340 68650 2) which advertises "Won't melt or burn foam."

 The foam and plywood assembly was bonded to the back of the raised wood panel again using the Loctite adhesive.

  The completed assembly was primed and then painted three coats Behr Premium Plus Exterior Satin Enamel (Base 9340, 267413187349) custom blended to match the door color (wineberry).  The cost of a quart of paint was about $25.  Yep, costs are starting to add up.


  In order to be effective, the storm window needs to seal against the existing window frame.  Since I wanted the frame to be removable, I decided to attach weather stripping to the storm window rather than caulk it in place.
 
The weatherstripping used was Frost King V25G and cost about $5.  The "D" shape of the foam is very compliant and allows it to fill a wide range of gap thicknesses.

  The completed storm window was screwed into the existing window frame and seals nicely.  Prior to installing it, I measured the inside temperature of the sidelite which was a chilly 55°F.  After installing the storm window and waiting an hour, the temperature increased to 66°F, showing the value of the added insulation which the storm window provides.  Some day I will again rent the IR camera from Home Depot and hope to show some impressive improvement from the old IR pictures.  But it is not worth the $45 rental just for that one picture.

Wrap Up, Thoughts
   I am very pleased with appearance of the storm window, its "better-than-commercially-available" insulating qualities, and its cost of just over $100.  However, I have some reservations about the economic value of the exercise.

  The insulating value of this storm window is perhaps about R-8 which is still lower than the surrounding walls with R-13.  More troubling is that all this time and money was spent to improve just about 6 square feet of surface area.  I have basement walls that could benefit from added insulation and with the same $100 I spent on the storm window could have purchased enough 2" thick pink foam to cover 80 square feet.  In other words, I could have gotten more "bang for my insulating buck" elsewhere in my home.

   But I like to think more optimistically about these things.  I have fixed what had been the least insulated part of the first floor of my home. That is one good step in the right direction and a slight hedge against the inevitable day when oil reaches $400 per barrel.

UPDATE: JANUARY 25, 2015
It's been two years since the original post and I've finally gotten around to renting the IR camera again, and the results of the modifications to the sidelite are impressive.

Unfortunately, it looks like I used a different color palette for the false color images and some of them are a little washed out, but I think the main points are still clear.

Looking at the image below, at the lower right panel of the door, it is clear that the rigid foam insulation has done its job.  That area looks as good or better than the wall.  Unfortunately the double paned window above it as washed out in color and not much can be observed.

On the inside, the impact of the double pane window can be clearly seen.  On the door windows (top right) there is a very dark color indicating cold.  On the sidelite (left) the window glass is a much lighter color indicating that it is warmer.

The most striking difference can be seen in the last image.  The wood panel in the sidelite (lower left) is clearly much warmer than the raised panels seen on the door on the right.

However, while I'm please with the improvements to the sidelite, the main door has a larger area and is still clearly very cold.