Deck skirting to hide area under deck. Maintenance-Free Deck:

Building Deck Skirting
With Composite Deck Boards

In This Article:

2x4 nailing strips are fastened to the deck structure and short pieces of composite deck boards are screwed to the nailers.

Related Articles:
Skill Level: 2+ (Basic or Higher) Time Taken: About 8 Hours

By , Editor


While extending an existing deck for some friends, they asked me to use a new composite (wood and plastic) decking product called Portico® to cover up the space beneath the deck. It seems that the kids were always losing baseballs and toys under the deck.

Besides, the original deck was not very attractive with all that open space around the sides.


Deck before installing skirting. The deck before the skirting was installed.

The synthetic handrails have already made a big improvement in the appearance, but the gaping void below the deck is even more obvious.

This is the south side.


The east side of the same deck.


I'll need to build a wooden structure at ground level to provide a nailing surface for the skirt boards.

Note the position of the "beam", (red arrow) about 16 inches back from the rim joist. Since there is no structure at ground level below the cantilevered part of the deck, I'll need to do some special framing to attach the nailers.


I laid some 2x4's against the support posts to see what might work. At this point I was just exploring various possibilities.


Using a reciprocating saw I cut a small notch at the bottom corner of the 2x8 beam.

This short protruding end of the 2x8 is only supporting the rim joist above, so cutting a small amount of material (perhaps up to one-third of the joist height) from the bottom should not affect the strength of any structural member.

This is not to be confused with cutting into the middle of the span of a beam or joist. In those cases there are specific rules about where notches can be made.

My initial plan was to have these boards meet at this support post.

But... I didn't have the best lengths of 2x4. I just brought some recycled boards that were about 7 feet long.


The break between the boards needed to be somewhere else, so I fastened a "down-rigger" (red arrow) to the rim joist to support the ends of the boards.

The lower end of the down-rigger is about 6 inches deep in the soil.


At the end closest to the house I dug a hole and clamped a 2-foot long 2x4 to the rim joist. I fastened this down-rigger with 3" deck screws.


The completed bottom "nailer" boards along the south side of the deck.


A down-rigger at the break point between boards.


It wasn't necessary for the 2x4's to be at the same height. I just need the ends to be fastened securely so the nailing structure doesn't flop around when I attach the skirt boards.


I added the down-rigger on the right just before fastening the 2x4, because I realized that the horizontal board didn't have enough support and could move too much.


The East Side:

Along this cantilevered face there was no structure to attach the boards to.

I dug a small hole and connected a 2x4 down-rigger to the rim joist, and fastened an 8-foot treated 2x4 to it.


In the middle of that 8-foot horizontal board I fastened a short "kicker" board to prevent the long board from moving backwards. This should keep the skirting from flexing when someone pushes against it.


I temporarily attached two pieces of skirting at the corner to hold the nailers in place.


Down-rigger Installation Tips:

I made a mark on the rim joist to indicate the end point of the board I planned to use. Then I dug a small hole, about 6 inches deep, and fastened the down-rigger to the rim joist. When I back-filled the hole I used a  block of wood and a hammer to pack down the soil. By hammering on the soil I could push the down-rigger forward or backward to ensure that it was plumb.


Where the nailer met the stair stringer, I fastened a piece of 2x4 to the back side of the stringer. The horizontal nailer will be fastened to this block.


The completed nailer strip.


Installing The Skirt Boards:

My starting point for the skirt boards was the stair stringer.


I wanted the skirt boards to line up with the edges of the stair tread boards and deck boards. This meant ripping some boards narrower.

The Portico decking material cuts very easily on a table saw.


Ripping a board leaves a square-cut edge, and these composite deck boards have radiused edges.


So I ran the board through a router table.


Then the board looked just like original.


I used a one-quarter inch radius round-over bit.

This material routs just like wood, maybe even better, because there is no splintering. It doesn't seem to have any problems with burning if you feed too slowly or pause for a moment.


Other Methods For Edge Rounding:

I discovered that this composite material was easy to sand down using a belt sander with 50 grit sandpaper. I was able to make a decent rounded edge using a belt sander, and I removed circular saw marks as well.


I cut the skirt boards a little too long (about ¼") so they would fit tightly.

I hammered on the end of the board to pack down the soil. But... it's easy to mash up the visible top edge, so careful hammering is necessary.


Fastening Composite Boards:

I pre-drilled ALL of the screw holes, even though the screw manufacturer says pre-drilling is not needed.


Fastening skirting to deck stairs. I drove the TrapEase® screws with my Makita 12 volt impact driver. This tool can drive big huge lag screws, yet it seems to be rather taxed by these special screws.


Note how the vertical skirt boards line up with the edges of the stair treads. The taller board here was ripped to about 4-5/8" wide.


Where possible I tried to use a heavy-duty low RPM corded drill to drive the special screws. But a regular drill tends to make the bit creep out of the square-drive head. If any screw slipped just a few "clicks", I stopped and used the impact driver instead.

The impact driver seemed to make the #2 square-drive bit seat better in the screw head. The bit rarely slipped while using the impact driver.

Note the small nail between the boards. I used two thin siding nails as spacers. The decking manufacturer says to use a small space to allow for thermal expansion.

Within a few minutes I had a good start.

I began installing these boards at this end because I'd rather finish this stretch of boards at the other end, where there are no complicating factors like stairs.

Deck skirting made from scraps of synthetic decking.


Additional Pointers:

I used a small torpedo level to make sure each board was plumb.


I also used the level as a drill guide so all of the top row screws were in a straight line.


Special Corner Treatment:

At a glance the boards all look normal.


But the 4 boards near the corner are all about 4½" wide, instead of the standard 5¼". This was necessary to prevent the last board from being a little skinny stick, which would not only look weird but also be very difficult to attach to the nailers.


The east side of the deck after the skirting was completed

On the south side where the skirting met the house, the last board needed to be notched into an "L" shape. But to keep the skirt boards lined up with the deck boards would require that this last board be very narrow, which left very little material to fasten to the nailing strips.

My solution was to break with convention and use a full-width board for the last piece of skirting. To cut the notch, I used a table saw and a miter saw, although a jig saw would also work.

The narrow board was installed in the second-last position, which meant all the boards could be easily screwed to the structure.


Deck with handrail and skirting to conceal space below deck. The finished skirting on the south side.

What an improvement over the original deck... seen in this picture from the beginning of the article.


Additional pictures of the completed deck, with new skirting and handrails.


Related Articles:




Tools Used:

  • Cordless Drill/Driver
  • Cordless Impact Driver
  • Heavy-Duty Drill
  • Basic Carpentry Tools
  • Miter Saw
  • Table Saw
  • Router Table (or Router) With ¼" Round-over Bit

Materials Used:

  • Portico® Composite Deck Boards
  • TrapEase® Composite Decking Screws, 2½"
  • 2x4 Treated Lumber
  • Deck Screws, 3"

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Written May 27, 2005