Instructions for thermal interior window panels
designed by Brian Nugent

What they are
Winter insulation panels are reusable transparent panels that snug fit inside window jambs to add two extra layers of glazing for the whole winter heating season that windows stay shut tight. They approximately halve each window's heat loss typically improving a R2-..R2.5 double glazed window to about R4-5 equivilant. The layers of air inside the panel and behind the panel both contribute insulation because they are too thin for convection currents to transfer heat across the space.

Not suprisingly the winterisation panel idea is not original and a very similar design was seen outlined on a forgotten FEMA web page.

General heat losses in a house
In a typical newer house with R3-5 doors + R2-3 windows, R19 exterior walls and R19 attic, the heat loss is mostly split approximately 3 ways between all windows + doors versus all exterior walls versus the attic. The attic's approx 1/3 loss and the windows approx 1/3 loss can both be economically halved with a payback each of about two years. Improving just one reduces overall heating costs to about 5/6 while improving both reduces overall heating costs to about 4/6. In an older house with single pane windows and outside storm panels, air infiltration and very poor window insulation,the heat loss can be even more dramatically reduced using window insulation panels. However the overall benefit is harder to estimate because old walls and attic insulation can be too variable in insulation and such panels become just a bandaid.

Improvement costs & payback
Material cost for adding extra R19 fibre glass batts to a 1000sq ft attic might be about $400 with some hours of labor. This is tax deductable and becomes a permanent value added improvement Material cost for making winter insulation panels for say 15 windows is about $200 but requires about 30-90 mins each depending on panel size. Panels if used carefully and stored safely during the warm seasons could last 5 years or more. Commercially available window panels cost about $10 per sq ft of window area and are guaranteed for 10 years.

Measuring the panelsŐ frames
Panels have to be custom made for each window in every heated room to achieve an overall approximate 1/6 heating cost savings.
These panels have to be custom sized so they snug fit into each window jam and set back as close as possible to the glass glazing. Sash windows usually permit this with no obstructions. Side opening windows may have removable crank handles that need to be set aside. Other obstructions like window blind brackets need to have atleast 7/8" space behind them so the 3/4" thick panels can readily insert upwards behind them. The window jams need to have a flat surface with no fasteners sticking out.
The panels are made as a rigid wood frame and finished with a 1/2" thick poly foam tape wrapped around the 4 edges. For a snug fit, the 1/2" foam tape normally would compress to 3/8" on all sides uniformly. Windows that are not quite rectangular and off by upto 1/4" due to inaccurate finish carpentry can be measured as if they are a true rectangle. The panels poly foam tape can tolerate upto 1/4" extra compression for example in one corner while the tensioned vinyl keeps the panel square. If multiple windows have very similar measurements within a 1/4" of eachother, it's easier to tweak them to all use medium mesurements so panels can be consistent and interchangeable.

So each wood frame's height & width should be 3/4" less than the window jam's general inside height & width.

Power tools to make the frames
Table saw with finish grade carbide blade to rip strips with OK rough finish
Chopsaw with finish grade carbide blade or alternatively handsaw with mitre cutting box
Finish nail gun with 2" brads or alternatively glue corner biscuits

(If you live in N.Quabbin, MA area, I can make frames to your measurements for nominal cost.)

Hand tools to assemble vinyl and polyfoam tape
10ft tape rule and large set square
3ft metal rule or if possible a longer flat straight metal edge for windows wider or taller than 3ft
8 or so small quick grips (clamps) that can clamp up to 1 1/2".
Safety razor blades
Power staple gun or alternatively T50 staple gun and hammer
Pack of 1,500 3/8" by 3/8" staples

Frame material
Before even starting on any frame, its best to prepare a stock of usable ripped pine pieces of varying lengths with enough to make all the required frames.
The frames are made from 3/4" thick pine board ripped down to 5/4" wide strips. The board is purchased as #2 1" by 6" (which is actually 3/4" by 5 1/2 wide"). Four strips can be exactly ripped from this width. Once ripped, some pieces promptly twist or bow and many pieces will have large knots.
Overal wastage can be reduced from about 35% to 20% by immediately cutting out all the knots, twists, bows before trying to assemble any frames. Long strips with a single bend at one point should be cut at the bend to give two straight short pieces where possible.
Layout all the good pieces on a surface, side by side and in order of length to make picking best length pieces as easy as possible.
The length of boards to purchase depends on the frames dimensions which will be a mixed collection.

A good rule of thumb is to roughly add up the perimeters of all windows then divide by 2 to get the total linear feet cost. This allows for about 30% waste from knots, twisted pieces, odd cuts etc and for larger panels to have stiffening cross pieces. If most windows are a similar size ie 5ft by 3ft, buying the boards as 8ft lengths is a good idea otherwise buy them as the longest you can manage to deliver ie 16ft or all 8fts generally works. Trying to pick out best boards at the lumber store is hard as even good looking board may produce warped pieces.

Vinyl sheet
Walmart sell vinyl sheet for glazing in two forms.
The 36" wide 25ft rolls are about 4 mil thick and sell for about $12 (ie about $1.50 /yd)
The 56" wide vinyl is cut to order from rolls of various thickness. The rolls with black printed tissue for about $1.80 / yd feels similar thickness to the 36" vinyl rolls and works best and is best value.
This panel design uses staples to secure the vinyl sheet, so heat shrink plastic film is too thin to be stapled without tearing.
(An alternative to stables, is a rubber spline system as used on outside screens. However that would require all wood pieces to have front & rear side channels routed out which inturn needs a jig to do that consistently plus the wood frame joints would then have to be mitred.)

Making the frame
A simple way to make sturdy frames is with butt joints fastened together with 3 brads 2" long using a finish nail gun. If the brads are driven in parallel, well spaced apart and about 1/8" away from edges, the joint can be stiff. (The vinyl give the real stiffness.)
(An alternative is to use glued mitre joints with slots for biscuit pieces giving very good strength)
Again the 4 pieces should be cut to length so the resulting frame size is 3/4" smaller than the window jams in width & height. If the frames longer side is more than 3 ft or so, then a centre stiffening cross piece is a good idea and looks appropriate for double sash windows. Very large picture window panels say 7ft wide by 4ft are best made as 2 or 3 smaller panels. only use It would be certainly easier and likely faster to make fewer smaller panels but only cost a little extra in materials.

Fastening front vinyl side
The vinyl fastening procedure is like upholstering fabric on a frame. The process is to tension the vinyl evenly outwards in a starting criss cross then tension these creases out towards diagonals. Its best to practice on a small window panel to get a feel for pulling out creases while stapling.

Place the frame on a completely flat work surface then true up to within 1/16" by measuring both diagonals or by using the large set square
Gently unroll vinyl over it while removing the tissue separator from the vinyl. Rough trim the vinyl so there is about 2" excess on all four sides.

On the middle of two sides, use quick grips to hold the vinyl firmly tensioned.
This will introduce a temporary crease between the grips. Now use quick grips on the middle of the other sides similarly introducing a second crease criss crossing the first.
Check the frame diagonals are still the same and if not, remove the grips then go back to the trueing up step.

With the frame square, repeat the staple sequence below in the order of doing both opposites, rotate 90 degrees then do both opposites:-
Remove a grip, tension the vinyl by firmly pulling the 2" excess over the frame edge then use one staple along the frame edge center line.
With four starting staples now replacing the grips, there should still be a criss cross crease and the frame should have remained true.
Now on all four sides, mark off every 3" starting from the center staple towards both corners.

Similarly repeat the staple sequence below again doing both opposites, rotate then do both opposites:-
At a starting staple, move along left 3" and while firmly pulling the vinyl, staple it on the frame edge center line then do likewise 3" right of the starting staple.

We now have 12 staples with 3 staples along each edge's center and the criss cross creases are pulling towards the diagonals.
Repeat the above staple sequence to add another 8 staples then again & again until reaching the corners.

Finally trim off excess vinyl so that the edge is about 1/16" from each side's rear edge. This is potentially dangerous but can be done with care and practice. The trick is to grip the blade between thumb and first finger while making other fingers into a stiff guide that slide along the frame edge pulling the blade behind. It may be neccessary to do a second pass wherever vinyl reachs the edge closer than 1/16".

Fastening rear side vinyl
The steps are almost identical except for the following:- The frame is flipped over and the unrolled vinyl is rough trimmed with 1" excess on every side.
Staples are inserting on the frames rear face about 1/4" from the edge rather than along the frame's edge.
After the rear vinyl is fully stapled, it is also trimmed about 1/16" away from the edge.
Now both the front side vinyl and rear side vinyl edges almost touch but are shy by about 1/8" of an inch so they can't curl or snag into each other.

Trim duct tape
Although staples are not visible from the panel front side, both vinyl sheets edges have a tendency to curl away from the wood. This could undermine the adhesion of the final polyfoam tape. So on all 4 edges of the frame, 1" wide duct tape is applied and folded along the tape's middle thus overlapping both front and rear vinyl edges. So 1/2" duct tape covers the rear staples and 1/2" covers the edge staples.
To do this accurately, first use two quick grips to hold down a metal straight edge on a rear side 1/2" away from the edge. Now unroll the duct tape the entire length but do not fold over the edge just yet.
Remove the straight edge and press the tape down firmly to flatten down rear vinyl curls. Beware if you attempt to simply fold the tape over on to the front vinyl's edge, curling of the front vinyl introduces ugly kinks. To fold the tape over requires both hands move along together for the entire length. The leading hand uses a blunt flat metal strip to press down on vinyl curls while the trailing hand folds the tape down. The metal strip has to move smoothly and always be about 1/2" ahead of the folding operation otherwise it can get momentarily stuck to the tape.

If 1" duct tape is not available, 3/4" or 7/8" electrical insulation tape can only be used if its adhesive is as strong and tacky as duct tapes. Its better to split a a regular 1 3/4" wide roll of duct tape as deep as you can penetrate a safety razor or stanley knife thru atleast 6 or more layers. Firmly rest the stanley knife blade on a 7/8" scrap block of wood on a table surface and rotate the 1 3/4" roll against it. Each rotation of the roll cuts deeper by a couple of layers. If needing to unroll a 5ft length, its necessary to score about 8 layers deep. As you need to apply 7/8" tape, peel off either the higher of the left or the right 7/8" sides so as to evenly use up the 1 3/4" roll.

Pull tab
One or more flexible plastic pull tabs must be double stapled to the frame edge to facilitate spring time panel removal (usually with aid of pliers). These must be atleast 2" long 3/4" wide so that about 1 1/4" will be visible.
Tall panels like 3ft wide by 5ft tall only need a single pull tab at bottom center.
Wide panels over 3ft wide need a pull tab in both lower corners.
Suitable plastic would be the kind used for junk mail sample credit cards or possibly spare slats from window blinds might be strong enough (if not brittle).

Polyfoam tape up
Finally 1/2" thick 3/4" wide polyfoam tape is applied around the frames edge. Its best to start in the middle of the panels top edge because this edge never rubs (ie shears) against window jambs during insertion or removal.
Poly foam tape comes in 17ft reels but is often wound tight so the last 1 ft is often compressed to 1/8" thick. It usually springs back to 1/2" after many hours. When the tape is applied around each corner, its best to not pull tight on the adhesive backing. Bulge it back a bit so the foam has a more square corner appearance.

Conclusion
The above steps evolved after making some 50 panels so experience led to some of the intricacies. Other hopefully easier ways of making panels are being considered if they can significantly reduce assembly time without having to require jigs or multiple hands.

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