Shop AC Installation, Part 2: The Insulation Installation

In part 1 of this series, I outlined what weather stripping product I used to seal my garage door.  Now it is time to insulate the oven, I mean, garage door for less than $150.  The afternoon sun beats down on the door as it faces west.  The heat that radiates from the inside of the door is a constant reminder, or question, about my reasoning for living in a desert.

Let me get to the work.  First, I needed to choose a type of insulation for the garage door.  There are kits available for garage doors but they are expensive, coming in at about $75 per box, which contains enough insulation for a single bay door.  That would cost over $150 for my double bay door.  Then there is the fiberglass insulation that is wrapped in paper, or a paper-like material.  These are usually pre-fit to the door panels or are cut to size and fixed to the door with “pins.”  Not wanting my garage door to look like a fluffy 1970’s headboard with buttons, I chose to pass on those kits.  4′ x 8′ rigid insulation sheets seemed to be the best option.  These come in a variety of thicknesses from 3/4″ – 2″ and some have a radiant “foil” side and a plain white “styrofoam” side.  My door panels are 1-3/4″ deep so I chose to buy 1-1/2″ thick sheets.  The R-rating, or value, is next to consider.  This doesn’t mean the inanimate sheets will start swearing at you randomly (though they should if you do stupid things in your shop).  The R-value is a measure of thermal resistance.  The higher the R-value, the better the insulation.  These ratings are also used with camping mats to insulate your body from the ground.  The inexpensive rigid foam insulation comes in at just over $15 for a 4′ x 8′ sheet and has an R-value of 5.78, which is better than nothing.  However, the polyisocyanurate sheets have an R-value of 9.4 and cost roughly $10 more than the former rigid insulation.  This was clearly the winner, thanks to Dyami Plotke for the suggestion.  Looking back at the cost of the kits ($150) and the cost of 4 sheets of the polyisocyanurate insulation at $26/sheet that is a savings of $46, which was spent on other materials.

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The down side of these sheets is that both faces are covered with the “foil” lining.  I didn’t want a reflective surface in the shop, for filming purposes, so I decided to paint the inside face white.  This was done with a rattle can of Rust-oleum Universal Spray Paint (affiliate link).  This stuff sprays on easy, thanks to its trigger but it didn’t last long.  I needed a case (6 cans) which cost me $35 and that covered all the panels with $11 to spare.

I cut the sheets in half to be more manageable at the table saw and then painted the surfaces.  Once dry, the sheets were ripped to width and cross cut to final length.  Half of the door had different length panels so keep that in mind.

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Now there are several different ways to install these sheets.  One is to cut them slightly oversized and rabbet the ends and sides to fit the door panel frames.  Another is to cut the slightly oversized and bevel the edges to allow you to slip them into place.  I used both and found both to be equally as difficult as they were annoying to install.  One thing I did to utilize the off cuts of insulation was to put the strips in the deep sides of the frames.

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After some serious finagling I got the sheets to fit into the frames and the door completely insulated.  I won’t lie.  It was a lot of work and it took a full day.  And at 115 degrees outside and 108 inside the shop it wasn’t pleasant but the end goal is in sight…A/C.


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