How to Install Raised Underlayment Panels How to Install Raised Underlayment Panels

What You'll Need
Plywood
Circular saw
Wallboard knife
1/4 inch wall spacers
Tape measure
Wallboard tape
Small piece of scrap lumber
Hammer or rubber mallet

An under deck system of panels is an easy solution to a concrete floor that may be too cold to walk across during colder months of the year. Raised underlayment panels are simply installed on top of the concrete and create a smooth surface for other types of flooring materials to be added later. The most commonly used panels for this type of project are plywood squares with tongue and groove fittings. This type of fitting provides added insulation while still allowing enough air to circulate through the concrete underneath.

Step 1 - Measure for the Number of Panels

Begin at one corner of the room and measure both the length and width of the entire room. Use these dimensions to determine the number of square panels you will need to cover the entire floor area. If the room's beginning corner is not perfectly square, you will need to trim the first row of panels to fit into this corner.

Step 2 - Mark off Expansion Gap

Place each of you 1/4 inch wide wall spacers at all corners of the wall, as well as at all doors and any other room obstacles. If you don't want to spend the extra on ready-made wall spacers, you can easily make your own. Buy an extra sheet of plywood and cut out enough 1/4 inch wide pieces to cover the room perimeter. Hold your wall spacers in place against the wall close to the floor seam with small pieces of wallboard tape.

Step 3 - Cut Panels and Check Fit

Cut your square panels of plywood based on your measurements from Step 1. Lay out one row of them without hammering them in place yet; building professionals refer to this as dry-laying. If the panel fitted to the starting room corner is more than 6 inches wide, you will need to trim it to fit snugly into the corner.

Step 4 - Lay and Secure the Rest of the Panels

With each row of plywood panels, lay the first panel so the grooved side rests up against a wall spacer. Slide the next panel in place and press the tongue end of this one into the side groove of the first panel. Repeat this process with the rest of the panels in each row and check that the ends are all fitted securely against the wall spacers.

With some plywood panels that are more difficult to fit securely together, hold your piece of scrap lumber against the edge of the outer panel and tap it gently in place with your mallet or hammer. Be careful not to hammer too hard and damage any of the tongue and groove fittings. When you reach the final row of underlayment, cut the last panel to fit the last corner if necessary. Double check that each row of plywood panels is square and even before finishing up.

Step 5 - Remove Spacers

Once you have made sure all underlayment plywood panels are correctly in place and the finished floor is complete, remove each of the wall spacers from the perimeter.  

 

 

   

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