How do I Insulate a Porch Floor to Make a Sunroom?

Written by jennifer harshman
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How do I Insulate a Porch Floor to Make a Sunroom?
Fibreglass insulation (new construction image by Greg Pickens from

Insulating a porch floor before building a sunroom will decrease the draftiness of the porch and can increase the energy efficiency of the room. With a few basic tools, nearly anyone can insulate a porch floor in a few hours. There are several options in insulation, from the traditional fibreglass batt to solid foam. Use the familiar pink fibreglass to insulate your porch floor so you can turn it into living space.

Skill level:

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Things you need

  • Hard hat
  • Protective eyewear
  • Filter mask
  • Gloves
  • Serrated knife or dull handsaw
  • Utility knife
  • Dust sheet
  • 6mm-thick polythene (contractor's plastic)
  • Staple gun
  • Box of staples
  • 13 rolls of R19 insulation batting
  • 2 50-foot rolls of weed fabric, canvas or muslin (optional)

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  1. 1

    Measure the size of your porch. Insulation comes in rolls of batting designed to fit between studs and joists. How much you will need depends on the size of your porch.

  2. 2

    Put on protective eyewear and a filter mask. Open and unroll just one package of insulation. Allow it to rest and expand for a few minutes while you do the next step.

  3. 3

    Cut a length of polythene to fit the length of the porch, plus 4 inches. Put on the hard hat if desired (for protection from any nails that might be sticking out). Spread a dropcloth under the porch.

    How do I Insulate a Porch Floor to Make a Sunroom?
    Roll of contractor's plastic (tapete image by Rolf Klebsattel from
  4. 4

    Crawl under the porch, lie on your back, and begin stapling the polythene to the underside of the porch between the joists. Leave a couple of inches of polythene hanging down at the edge next to the house, and staple it to the footer (the piece of wood that supports the porch and runs along the side of the house). Move from one side to the other, stapling about every 6 inches as you go. Make sure there are no gaps, and that the polythene lies smoothly against the surface of the porch.

    How do I Insulate a Porch Floor to Make a Sunroom?
    Staple gun for attaching insulation to joists (stapler and staples image by Federico Romano from
  5. 5

    Install the first strip of insulation. The vapour barrier (the paper backing) must always be toward the living area, so you'll be installing it with the "itchy" pink side away from the living area, toward the ground (toward you). Staple through the edges of the vapour barrier into the wood of the porch. Place staples 6 inches apart, and be careful not to staple into your previously placed staples. Start by stapling the end of the strip to the footer. Staple all down the length of the insulation strip, working on each side as you go.

  6. 6

    Cut off any excess batting, and staple the end of the insulation to the wood at the edge of the porch, just like you did at the beginning of the strip.

  7. 7

    Repeat Steps 2 through 6 until each section is filled. This means open another roll of insulation if needed, cut another piece of polythene to 4 inches longer than the porch and staple the polythene into place. Then cut another strip of insulation batting and staple it into place.

  8. 8

    Staple weed fabric, canvas or muslin to the joists to contain the insulation, if desired. This will cover the insulation without trapping moisture. It will prevent pieces from being torn off of it without trapping moisture and will protect anyone who crawls under the porch.

Tips and warnings

  • It helps to have an assistant, but this job can be done by one person.
  • If the insulation sags dramatically, you may wish to place a few staples down the centre of the batting strips.
  • If your porch floor does not have joists, just staple the insulation to the floor of the porch itself, and overlap the edges of the vapour barrier so the pink batting butts up against the previous piece.
  • Only open one package of insulation at a time. It expands in size after opening. It can swell to four times the size it was in the wrapper. Also, any unopened insulation may be stored or returned for a refund.

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