In order to insulate a pre-existing concrete pad you will have to employ sleepers and install floor planks. What follows are some generalized instructions on how to complete those tasks.
Before heading out to the store to purchase materials you will need to do some measuring and check to see what the recommended R-value for floor insulation is in your region.
A Word about R-Values and Margins of Error
Most floor R-value’s range from 11 to 22. In order to get the best return on your investment be sure to get the proper R-value.
Do not over or under insulate otherwise you will be defeating the purpose of insulating the concrete pad in the first place.
Measure the surface area that you are planning to cover and be sure to add a little extra to your flooring and insulation materials total to allow for cuts and margins of error.
In order to insulate a pre-existing concrete pad you will first need to assemble the following materials
• Roll of polyethylene vapor barrier
• Masonry nails
• Waterproofing compound
• Brush for applying waterproofing compound
• Tape measure
• Spread out a polyethylene vapor barrier
• Rigid foam insulation
• Construction adhesive
• Flooring planks
Before you insulate the concrete floor you will want to repair any cracks and holes in the floor’s surface. Once the floor’s surface is blemish free you will want to apply waterproofing compound to it to help prevent future moisture issues.
Remember that wet insulation is like having no insulation at all so a dry smooth floor is imperative. As waterproofing compounds can vary be sure to apply it to the floor using the waterproofing manufacturer’s instructions. Allow the floor to properly dry again before proceeding to the next step.
After the concrete pad has been properly prepared take out the roll of polyethylene and lay it out lengthwise being sure to cover the entire surface of the floor. The polyethylene will act as your insulation’s vapor barrier.
Next take the 2×4 boards and lay them on top of the polyethylene in 16 inch intervals. “Sleepers” are the 2x4s.
Permanently fasten the sleepers to the concrete pad every 16 inches using masonry nails. Once the sleeper boards are securely attached to the floor it is time to lay out the rigid insulation boards.
Measure and cut the rigid insulation boards so that they will fit properly in between the sleeper boards. Affix them to the polyethylene using construction adhesive.
Note: some parts of the country have codes that disallow the use of rigid insulation boards. If this is the case in your area, alternative insulation materials will have to be used. Consult with your local building code enforcement agency or insulation specialist for clarity.
When fitting the rigid boards be sure to so allow some room for the board to expand and contract during extreme temperature changes. Insulation that has no room to breathe coupled with extreme temperature changes could cause condensation to form.
Once the sleeper and insulation boards are in place it is time to install the floor planks. As you measure, cut and lay the floor planks be sure that you cut them in such a way so as the plank joints are centered over the sleepers.
Securely nail the floor planks to the sleepers until the entire surface has been covered.
At this point you may or may not want to add a finished floor on top of your new sub-floor. In the case of covering a concrete pad, a finished floor is entirely optional.
Do-It-Yourself folks that want more information on insulating a pre-existing concrete pad should consult with their local, licensed professional.