Supporting Structure

4. SUPPORTING STRUCTURE

This deck will be level with whatever door allows access to it (kitchen and/or living room).  You will step out of your house onto the deck.  The deck boards will butt into your house right below the threshold of the door.  This is so rainwater or melting snow won’t run into your house.  Below the deck boards are the joists.   At one end of the joists and attached to your house is the ledger board while at the other end are the three supporting posts.  The posts are located at each corner and center away from your house.  The ledger board must run the full width of the deck.  It doesn’t matter if its one continuous board or two since it won’t be seen.

The ledger board will be located at the same height as the joists.  It will also be the same size as the joists.  The deck boards are usually 1” or 1 1/2” thick.  Depending on the span of the deck (from the house out), the joists may be 7 1/4”, 9 1/4 ” or 11 1/4”.   This example deck is 10’0" so a 2 x 10 joist is appropriate.  Therefore the ledger board must also be a 2 x 10.  A span-rating chart will determine which size joist to use and how far apart they must be placed.  Any lumberyard should be able to provide you with a chart for the kind and type of material being used.  If they can’t provide this information, then go to a different lumber yard where the salespeople are more knowledgeable.   You’re spending a lot of money so make sure you have competent people helping you.  This is critical information that you must know because different types of decking necessitate different joist spacing.  Placing your joists 16” on center is correct for the pressure treated yellow pine used in this example.  Please be aware that some types of composite wood need joists 12” on center while Brazilian Ironwood (Ipe, pronounced “ee-pay”) can have joists at 60” on center (yep, 5’0” apart).  The span rating depends on the load rating above it. See Section 8.

All dimensional lumber has two sets of sizing values called nominal and actual.  The nominal size is the name of the lumber.  The actual size is what it really measures.  Dimensional lumber includes boards (any width that actually measures 3/4” thick), stair treads and decking (measuring 1”), framing lumber (measuring 1 1/2”) and timbers (measuring 2 1/2” or more in thickness).  Don’t be confused by the use of the word “decking” in the previous sentence.   There is wood that may be used for the purpose of decking that measures 1” thick though this is not always the case.  Any product used above the substructure, as surfacing material, is legitimately called decking.  The most common width for decking is 6” (actually 5 1/2”).   The nominal size, or name, of each piece of lumber is as follows: boards are called 1x (spoken as “one by”), the decking is 5/4 x (spoken as “five quarter by – never call this one and a quarter or inch and a quarter), framing is 2x and timbers are called 3x or 4x or 6x, etc.  When you buy lumber, remember we live in a three dimensional world.  The lumber you will need has three dimensions to it.  Specify lumber sizing by thickness first then width then length. Our joists, therefore, are 2x10x10’s (nominally speaking).  The first two numbers are always in inches while the last is always in feet.  Remember that what you’re buying is actually 1 1/2 x 9 1/4 x 10’0”.  By the way, lumber lengths may only be purchased by even numbers (8,10,12,14,16,18,20).  An 8’0” length will be the shortest standard length available, while 20’0” is usually the longest.   If you happen to need an odd length, buy the standard size and cut it to size yourself.  The place where you bought it will probably charge you to cut it.  The sizing chart shows you both the nominal size and the actual size.

Years ago, these were one in the same but not now.  Pressure treated southern yellow pine is probably the most widely used deck material.  Check out Section 8 for other types of wood and non-wood materials.

The decking and railing is the most visible aspect of your deck.  Choose the kind and type of material you want now.  As mentioned before, the placement of the joists, beams and ledger board depend on this choice.   The deck in this example is being made of treated yellow pine.

The joists on this deck will be 16” on center.  There is still a decision to be made.  Should the decking be ⁵/4x6 or 2x6?  Both can be used in this situation.  There is also a choice to be made as to the grade of the lumber.  Different species of wood have different grading rules.  These rules govern the physical appearance of the wood.  The higher the grade, the prettier it looks and the more expensive it becomes.  Because of supply and demand and politics, you may find that pricing and availability vary radically.  Again, competent sales help can explain all this stuff and even show you the difference.   Your choice comes down to price and aesthetics.  This deck will use the 2x6 because it’s easier to type.  All of the substructure will be a #2 grade of Yellow Pine.   The decking and railing will be #1.  It should be noted that the grading of woods has more to do with appearance than structural integrity. 

The first thing to do is attach the ledger board to your house.  It should be mentioned that another alternative construction method is the freestanding deck that simply adjoins your house.  This, of course, requires posts at both ends of the deck and no ledger board at all.  In a high wind situation, where there is the potential of your deck being carried off by Mother Nature (she obviously likes your work), a freestanding deck won’t rip out some of the foundation of your house.   If your posts and ledger are properly anchored, then this shouldn’t be a concern.  The ledger board can be attached in two different ways.  It can be anchored directly into the foundation wall or bolted completely through the wall of your house.

In the latter case, there is a rim joist inside your house which holds your floor joists in place.   This rim joist is the interior version of your ledger board.  So you’re drilling through your wall and this rim joist every 2’0”.  Begin drilling approximately 1’0” from each end of where the ledger board will be located. Deckster recommends two holes vertically aligned about 6” apart.  The holes must be about 1 1/4” to 1 1/2” from the top and bottom edge of the board.  This is to prevent splitting the wood.   At a minimum, make a  3/8" diameter hole. A 1/2” hole is also acceptable.   The length of these bolts must be determined on site.   The wall of your house is constructed of many vertical members called studs which are usually located 16” apart.  You do not want to drill through a stud.  This is a structural part of your house and you don’t want to damage it in any way.  So how does one find a stud? (sorry ladies, the business of construction has many names and labels that may be construed as sexual in orientation)  Studs are nailed to, and in between, two other pieces of wood called plates.  A gadget called a studfinder will locate the metal hidden behind the wall (the nails used to fasten the studs to the bottom plates).  Another type of metal hidden in the wall is used to hold the joists to the rim board and is called a joist hanger.  The joists and rim boards are located below the bottom plates.  Mark the location of every metal “hit” on the wall at the height where the ledger will be located.   One more word of warning has to do with plastic or metal utilities in your wall.  You don’t want to drill through your plumbing or air conditioning ducts either.  Measure their location in relation to the finished floor, and then transfer this information to the outside.  Now you have a picture of where not to drill.

If you’re going to anchor the ledger right into the foundation wall, drill into the masonry (please don’t pronounce this as “masonary”, there’s no such word) joint between the cinder block or brick.  There are several types of hardware that may be used to secure the ledger board.  These are lag screws, wedge anchors or sleeve anchors.  Lag screws work best with a lead shield.  Go to a hardware store, pick somebody else’s brain and decide.  One works just as well as another.  Whichever you choose needs to be about 4” to 4 1/2” long.  Don’t forget that the ledger board is 1 1/2” thick.

Drill the upper hole (implies a lower hole) at each end of your ledger first a couple inches from each end as well as the top and bottom.  Loosely hang the ledger and make sure its level. Now you can drill all the rest of the holes and secure it in place.  You should only drill into the mortar joints between the brick or block.   Keep in mind that you’ll be nailing joist hangers every 16” onto this ledger.  Now take some clear silicone caulk and a caulking gun and run a bead around the whole ledger board.  This seam of caulk must be in contact with both your house and the wood to be effective.  This will help prevent water and bugs from getting behind the board and damaging it.  The first, middle and last joists to be installed will be doubled up and rest on top of each post.  The three double joists should be installed first. The middle double joist will be of equal length. Both doubled end joists must have the outer joist 1 ½” longer than the inner joist. You’ll see why later. The posts will start out 8’0” long. 3’0” will be buried in the ground and 4’0” above then cut to the proper height.  Remember to subtract the depth of the joist.  Embedding the post will use one that’s 6’2 1/2”.  Using a post anchor base, the post need be only
3’2 1/2”.  If you buy one (1) 4x4x10, you can get all three of your posts from it.  Make sure the joists are level and perpendicular to the ledger.   You can use a carpenter’s square for this.  It’s a small flat right-angled measuring device.  You’ll also use it for the stairs.   All of the top and bottom edges of the joists, ledger and header must be flush.  Nail the boards together alternating top then bottom and space the nails about 15” apart.   You should also nail from both sides alternately.  Blunt the point of the nails before you drive them into the wood.  This can be done by rubbing the points across a file a few times.  This allows them to cut through the wood fibers rather than splitting them apart.  Use a 3” galvanized nail (a 10d nail).  The “d” following the nail size is leftover from our European heritage.  It was used as an abbreviation for “pennyweight”.  This referred to how many nails one could buy with the old English penny.  The two boards are 1 1/2” thick each.  Attach a double 2x10 joist hanger to the ledger board. Use either Kant Sag® (www.uspconnectors.com/catalogs.htm) or Simpson® (www.strongtie.com) hardware (using the links provided, go to either of the sites to view pictures of the hardware mentioned).  This double joist is 10’0” long so it will protrude past the post 2’0”.  The proper hardware to hold the joists to the post is a post cap.  All nails to be used in this project will be double hot-dipped galvanized.  All nails used in conjunction with hardware will be 1 1/4” in length (3d).  These three sets of doubled joists add strength and support to your deck.  All the rest of your joists will be single boards and all must be parallel.

The next step is to attach the header board to the end of your double joists opposite the ledger board.  This also is doubled for strength and support and to connect all the ends of the joist system.  For this, use two 2x10x20’s. You’re going to install them one at a time.  The first board must be cut to measure 19’6”.  The first Cardinal Rule of carpentry is to “measure twice and cut once”.  Don’t be a “wood butcher”.  That is anybody that rushes through a job, makes mistakes and uses much more wood than necessary.  After cutting, find the center point of the board and mark the top edge with a black crayon or chalk (called keel).   This mark needs to be centered between the double joists at the center post.  Use six 10d nails per double joist.   Think of the six-of-clubs playing card.  Drive one nail through the header into the butt-end of the joist at each end.  Make sure this header is level and that the top edge of the header is flush (even) with the tops of the joists.  Remember to leave a 1” to 1 1/2” from both the top and bottom when you nail.  Finish the rest of the nailing. Now you’re going to nail a second 2x10x20 on top of the first header.  This board should measure 19’9”.  Center this board as you did the first one and use the same nailing pattern except about an inch wider.  Now finish the same type of nailing pattern you used for the three double joists.

Now you’ll install the joists at both ends.  The inner 2x10x10 needs to be cut to 9’10 1/2”.  Leave the outer 2x10x10 alone.  There is a 1 1/2” difference here.  You’ll see why when you install this end joist.  When you measure the offset from the first and second header, you’ll notice a 1 1/2” difference at each end.  This offset will neatly accept the double end joists.  Make sure the distance from the double joist on the post to this double end joist is the same at both ends.  Install a 2x10 double joist hanger on the ledger board so as to accept this double end joist.   Just rest the end joist in the joist hanger while you’re nailing the opposite end joist to the header.  Use three 10d nails at the top, middle and bottom. Nailing from the side of the deck, nail thru the end joist into the header.   This means nailing about 3/4” from the end.   This should create a neat herringbone corner.  Now go back and nail the joist into the joist hanger at the ledger board.  Lastly, from inside your deck, at the junction of the side and front, in both corners, nail an all-purpose framing anchor.  In this instance, use 10d nails.   It may not have been mentioned earlier, but all of the framing hardware specified has holes predrilled in them.   Nail through the holes provided.  You need not nail through every single hole provided.  Now you have five sets of double joists installed along with the double header tying all of them together.

The last thing to install is the remaining 12 single joists.  There will be six single joists on either side of the center double joist.  These will not be exactly 16” on center.  Space them equal distance apart anyway.  Nail up all of the remaining single 2x10 joist hangers.  Lay in all of your joists.  Make sure everything is level, parallel and flush across the top.  Nail the joists into their respective hangers.   Take the rest of the day off.  You’ve earned it.  You’ve completed the hardest part of building a deck.  Go have a drink of your favorite beverage and stare in amazement at your marvelous creation.

Section 5 - Decking