Note this page is deliberately narrow to make it printable in portrait format.

BUILDING INTERIOR WINDOW INSULATION PANELS I will be offering public demonstrations and training on how to assemble these window panels: Public training to make window insulation panels for local residents November 8+9 Saturday: training 9:00-11:00  assembling 3:00-5:00 and Sunday 1:00-3:00 (assembling) UCC Church, Bath, Maine Register by calling 443-2187 or email faithcommunity@faithinbath.org Materials Sources Construction overview Assembling the frames Applying film and weather strip As home heating costs began their rapid climb this year (2008) I decided to address one of the principal sources of heat loss in homes.  Windows.   Small bathroom window, before and after installing panel, and detail.  White primed wood used for example purpose, but actual frames can be made from natural wood to match natural windows.   Topher Belknap is a fellow member of the Midcoast Green Collaborative here in Maine and he came up with a very simple design for double pane thermal window panels that simply push into the widow frame with foam insulation around the edges.  Topher says that these panels will increase the R-value of your windows by around 2.3, however on a southern exposure they will reduce the solar heat gain by about 15%.  For most windows, this is a good tradeoff. The panes are made of clear polyolefin shrink film.  The simple wood frame can be constructed inexpensively from either natural or pre-primed lumber.  The net cost of material per window is under $1.00 per square foot and it takes 2 people about 40-45 minutes per window to make them up.   These window panels serve 2 functions, as a double barrier they will more than double the R value of a single pane window and they also completely block all air movement through the window.  So they block both drafts and transmitted heat, cutting heat loss in half or better.  The projected savings for single pane windows in Maine is between $4 and $10 per square foot of window per heating season, depending on your windows.  This assumes you are paying over $3.50/gallon for oil.  Drafty single pane windows will reap the most benefit from the new panels.  In more moderate climates it may take longer to recoup the investment.  You can use this tool to calculate your estimated energy savings. Be advised that the panels are inexpensive in materials, but costly in time to make.  Count on investing at least 45 minutes to actually build each window, plus a few hours for measuring and ordering or buying the materials.  An average home can have around 20 windows, so that's a commitment of over 10 hours in time to make them. Last year we invested in commercial versions of these windows for our home -- at over $9.00 per square foot these nice aluminum framed units are white finished and very well made.  They are effective but also expensive.  I wanted to see how inexpensively I could make them and then share this information with the world so we can all save on heating costs and live more sustainably. We swap these panels out when we install and remove screen windows in the spring and fall.  Removing the screens in the fall will allow 3-4% more solar gain so remember to remove them and clean the windows to get as much light as possible.  Some panels can be left in place all year if desired if they are hard to get to or the window is never opened.

Materials Sources:
what	retail	cost	volume	cost
1X4 clear pine lumber or pre-primed	Big box hardware store	$.95-1.50/ft.	Ask your lumber yard for a discount many will give you a break for more than 100 feet.	$.95-1.50/ft.
Polyolefin heat shrink film	A variety of kits that include shrink film and double stick tape are available in hardware and big box stores.  Shrink film also comes in wide rolls.	$9.99	Uline 20" x 3,500ft. 75ga Polyolefin Shrink Film Roll (will do hundreds of windows)	$200.00
1/2" wide double stick tape	double stick tape by the roll be sure to get 1/2" wide tape!	$3.00	Scotch Adhesive Transfer Tape, 1/2 Wide X 36 Yards (requires dispenser gun)	$7-10.00
2.6 mil 2" clear packing tape and dispenser	Staples® Clear View Packaging Tape, Clear, 1.89" x 54.7 yds, 6 Rolls will do hundreds of windows	$15.99	Staples® Clear View Packaging Tape, Clear, 1.89" x 54.7 yds, 6 Rolls will do hundreds of windows	$15.99
.5 X .5" open cell foam weather strip	Get OPEN CELL poly foam that is grey - not white!	$4.21	Ether Foam Tape from Foamtapes.net (case of 12 70ft. rolls)	$50.52

Materials notes: If you buy the lumber from a big box store, you can get it as 1X2 (rather than 1X4 and ripping it in half yourself) and have them cut it all to the lengths you need for a nominal fee. Most hardware stores sell the shrink film in small rolls 40" and 80" wide and also packs that include double stick adhesive tape with a backing. Be sure to buy 1/2" wide double stick tape, 3/4" is hard to center on the wood frame.  Remember that window kits provide the tape. Make sure to buy the highest quality packing tape that is over 2mil thick, this will protect the frame better and will not yellow or age as badly as cheap tape. The weather strip that I have specified is OPEN CELL poly foam that is grey in color.  Most hardware stores sell it. It is 1/2" wide and 3/8" thick and usually comes in 17ft. rolls.  Don't get the white kind - it degrades badly. I highly recommend that you buy the Ether Foam tape since it has very good adhesive, and also is a full half inch thick.  Most retail foam is only 3/8" thick and this is not enough to allow for error on most windows.  Ether Foam is also a higher quality foam that should last longer than store bought foam weather strip.  If you do buy retail foam look for open cell foam that is gray colored, the light or white colored foam tape will not last because it degrades in UV exposure.

Construction overview: The basic steps are as follows: Measure the inner dimensions of the window frames.  I created a sheet that aids in the process download it click here or on the image at right.  In older homes it is important to measure the diagonal dimension to see how out of square the window is.  Be sure there are no obstructions like blinds, curtain rods or screws in the frame. Calculate how much wood is needed for all the windows.  The panel frame dimensions need to be 1/2 inch smaller in each dimension to allow room for the foam weather strip, this also allows for out of square windows.  Then just add the height to the width for each window.  You will use 1 X 4 lumber and rip it in half to make each side of the frame.  Allow an additional 10% for waste - or order an extra 8 foot length per 10 windows. I created a spreadsheet to aid in pricing.  Click the image at right to download it.  Begin by calculating your cost per unit of materials such as pennies per square foot of shrink film, and enter that in the red section.  Your costs may vary depending on your bulk purchase options.  Then enter the specific window details and dimensions in the blue section.  The sheet will calculate the total amount of linear feet of wood needed.  The outer dimensions for the frame subtracting a half inch for the foam (brown section at the right), cost per square ft., and total cost for materials. Order the wood.  Surprisingly pre-primed wood (white primer painted) is cheaper than clear pine by over 45 cents per foot at my local lumber yard (Hancock Lumber in Damariscotta) .  Order 1 X 4 lumber of either type to match the trim of the windows. Assemble the wood frames.  I prefer a butt joint for it's simplicity and ease of assembly.  Butt joints can be screwed or nailed together which makes for a strong joint - no glue required. Attach the film and weather stripping: Apply double stick tape around the outer edge of the frame Cut a piece of window film about 8-10" over size stretch the window film onto the frame so that it sticks to the edge, and trim off the excess repeat the 3 steps above for the other side of the frame Take 2" clear packing tape and wrap the entire edge of the frame to secure and protect the edges Use a hair dryer to heat shrink the film on both sides Apply 1/2" open cell foam weather stripping around all edges.

Assembling the frames This part takes about 15 minutes per window

You can purchase 1X4 lumber with a white primer already applied from most lumber yards and big box hardware stores, you will need to rip this in half on a table saw to make best use of it.  Or you can buy clear pine (unpainted) in 1X2.  Lumber yards do not seem to sell 1X2 wood with a primed finish. If you rip down primed 1X4 boards note that the cut edge should go on the outer edge of the frame where it will not be seen.  With store bought clear 1X2 lumber this is not an issue unless you want to paint it, in which case you need not paint the outer edge.  This makes it easier to handle while painting it. If you lack carpentry skills or a chop saw, most big box hardware stores will cut 1X2 clear pine to length for you.  Then simply assemble with nails or screws as below.   Note that so-called one-by-two lumber is actually .75" X 1.5" when you purchase it.

If you bought 1X4 boards, begin by cutting them to length first and stacking them in matched pairs for each window.  It is helpful to keep each pair matched throughout the process if you have many different sized windows.  Then use a table saw to rip them exactly in half.

I have learned that a butt joint is quicker to make than others styles, but be aware that in a butt joint one pair of  boards will need to be shorter when you cut them.  This should be the shortest side of the frame, so the length of these boards will be the width of the window minus 1/2" AND minus 2X the width of your boards. Also note that this joint is the most forgiving of wood that has different widths.  When 1X4 is ripped in half each side may not be exactly the same.

The butt joint has the advantage of simplicity and strength and that you don't need glue so there is no delay while it dries.  I use 2.5" brad nails or drywall screws and pre-drill a clearance hole through the side first.  I suggest that the nails or screws go through the longest sides of the frame as it makes it simpler to assemble when nailing.

You can use a framing clamp (available at most hardware stores for under $10) to hold the corner together while you drill and screw it together.  Cordless drills make fast work of this assembly.

If you ripped down primed 1X4 boards note that the cut edge should go on the outer edge of the frame where it will not be seen.  Be careful when handling the primed or painted wood as it will mar easily, you can select the "bad" sides for the outside face when you assemble the frame.  Be sure to let the paint dry for a few days before applying the film.

Now is a good time to label the frame.  I suggest using a pencil or thin marker to label the top edge on the outside surface - this is the side that faces the window so you won't see the label.  Try and be descriptive enough that next year you can easily figure our which panels go where.  For instance "Second floor bedroom, south wall".  The label will be protected by film and clear packing tape. If you are really fussy you can paint the primed wood frames, but I don't see the value in this effort unless they will be highly visible.  In most cases they will be hidden by drapes or visually unobtrusive.

Applying film and weather strip This part takes 2 people about 30 minutes per window

Tools required for applying the film include (left to right): Packing tape dispenser, utility knife, scissors, tape measure, Adhesive transfer (aka "snot tape") dispenser (optional) and a hair dryer.  Click here for a printable assembly sequence list you can refer to at a glance while you work.   A large work table is essential.  I used a full 4X8 sheet of MDF on top of my table saw, or on saw horses.  It is good to have a clean flat surface.  If you use plywood I recommend covering it with paper and taping the edges so your clothing will not snag on it.

I bought a 3700ft. roll of film so I could do a lot of panels for friends and neighbors.  This huge 40lb roll is 20" wide, but the film unfolds to 40".  If you use store bought sheets or rolls of film, be sure to keep the inner surface off the work table so it does not pick up dust.

I use a commercial adhesive transfer tape dispenser to put double sticky on the outside edge of the whole frame.  These guns hold 100 foot rolls and are very convenient.  If you use double stick tape then just apply it firmly and peel back the backing just before applying the film.

The film on the roll is folded in half and separating the 2 layers is hard, the trick is to use 2 small pieces of blue masking tape right at the corner to pull the 2 layers of film apart.  You may have the same issue with store bought rolls of film too.

Cut a length of the film so that you have at least 4 to 6" extra all around the frame. Unfold the film and smooth it out to it's full size, then lay the frame on top centering it carefully.  If you used double stick tape then now is the time to remove the backing. Begin at one end and carefully lift the film up and over the frame so that it sticks to the edge, rub the edge to ensure that it is well adhered.  Then do the other end being sure to pull it tight to take out any wrinkles.  On the longer sides it is best to have 2 people doing this together so that you can tension the film to prevent wrinkles.  I find it easier to start at one end, then pull the film tight to the other end before doing the longer sides.  It is important to watch for wrinkles and try to pull them out before the film sticks.  Pay attention when pulling the final side, you need to pull firmly to ensure the film is stretched tight.  The film will only shrink about 1%.

After each edge of the film is stuck, you will need to cut off the excess.  By pulling the film upwards, you can slide a utility knife along the frame to cut the film off flush with the wood.  It takes practice to get the knife to cut well, a 45 degree angle works best as shown with the blade just resting flat on the wood.  This takes practice to do well and requires a very sharp blade.  The knife should just glide along easily without encountering resistance.

Now repeat the steps above to apply more double stick tape all around the edge over the film you just applied and then apply the film to the opposite side. Keep in mind that this film is both strong and resilient and also very fragile when exposed to sharp objects.  Small tears can be repaired with clear packing tape, larger ones may require removing all the tape and film and re-applying it, so handle them carefully.

Next use the packing tape gun to wrap the entire edge of the frame.  I use high quality clear tape for it's strength and clarity.  This tape protects the film at the edge of the frame during handling and insertion and removal from the windows.  I have found that it is simplest to do each side separately.  Start by pulling out a bit of tape and wrapping an inch or so over the edge being careful to center it on the frame.

Now pull the tape out to a few inches past the other end and lay it down so that the entire length centers on the frame.  Cut off the tape and wrap it over the end.  Now smooth the tape firmly down along the whole edge.  Then begin at one end and fold the tape over and down the sides.  You need to make a tight fold here or you will get bubbles in the tape.  If bubbles get trapped you can puncture them with a knife then rub them out.  Rub the tape down firmly so it disappears.

NOTE!  Now is the time to install pull tabs made from clear packing tape.  Use a short length of tape and stick it to the outer edge then fold it over and stick about 1"  to the inside surface.  Locate them where they will be easy to reach - typically a foot or so from the bottom.  These panels will be VERY difficult to remove without a tab.  (Note the picture shows the foam already applied, but do this step before applying the foam strip).  You can add a label onto the tape using a white address label that says "pull to remove" if you want to make it easier to find.

Use a hair dryer set on high to shrink the film.  I have found that starting in the middle and working out to the edges works best to remove wrinkles.  Keep the hair dryer moving at all times and be sure to heat every part of the film so you don't have loose spots or wrinkles.  Don't use a heat gun - it will melt right through the film!

The open cell foam weather strip that I use is 1/2" by 1/2".  I first measure it to length and cut it an inch or so long.   Note that I made a jig to hold the frame vertically on the floor.  I glued 3 pieces of 1X lumber together.  2 wide ones and a narrow one with a layer of thick paper in the glue joint to space it out a bit.  This forms a long U channel that holds the frame snugly allowing for the thickness of the film and tape.  The channel is then glued to a larger board for stability.

Peeling the backing off the foam tape is tricky.  This is annoying as it is hard to get it to start, but if you get your fingernail right up against a corner and pull the foam off the backing tape it will come off fairly easily.  Now peel back a few inches and stick that down to the end of the frame with a slight overhang at the end.

Slowly pull the backing tape off as you guide the foam so that it sticks in the center of the edge of the frame.  One person can lead by pulling out the backing tape as the other centers the foam and presses it down.

Apply foam to 2 opposite sides first.  Then when you cut the foam off of the ends be sure not to undercut.  You want the foam to hang over the end slightly so that the foam can overlap and stick to the foam and form a square edge.

I tried just wrapping the foam around the corners but it leaves a rounded gap that looks unsightly and leaks air.  The point here is to eliminate all drafts.  Here's how it looks before you cut off the edge.

That's it!  Repeat as needed for all the windows in your home.  Then in the spring review your heating energy bill and SMILE!

Materials Sources
Construction overview
Assembling the frames
Applying film and weather strip

This page was substantially revised on October 6, 2008 based on my experiences
training many groups to make these window panels.  I have endeavored to
simplify the process for the average home handyman.  Please contact me if
you have questions or suggestions for improvement.