In
This Article:
The perimeter (rim joists) of
the new structure is set up level and square, then holes are
dug for supporting posts, and load-carrying beams are
fabricated. Deck joists are installed and secured to prevent
twisting. |
Related Articles:
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Skill Level:
3 (Intermediate) |
Time Taken:
About 16 Hours |
By
Bruce W. Maki,
Editor
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Tight Squeeze:
This 3-year old house had a decent deck when it was
built, but after the homeowners installed a hot tub,
there wasn't much deck space left.
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Another view. There is lots of room to
expand the original deck. |
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Notice how the deck joists are
cantilevered over a double 2x8 "beam". This beam
is just a treated 2x8 lag-bolted to each side
of the row of support posts. This beam/post assembly had
5 posts, spaced 6 feet apart, for a total length of
almost 24 feet. |
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The first task was to tear apart the old
stairs. Since these steps were built with deck screws it
was easy to disassemble them. My Makita impact driver
made the task easier, since many of the deck screws were
quite tight.
One trick is to use a very small flat screwdriver to
clear the dirt from the screw heads, so the
driver bit doesn't slip.
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The next step was to establish the
perimeter
of the deck extension. I clamped a 6 foot long piece of
2x8 in place, using a block of 4x4 to hold up one end. |
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...and the other end was held in place
with a metal angle bracket. |
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In a few minutes I was able to establish
the perimeter of the deck extension... but these rim
joists are not yet level and square. |
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Ensuring Level Framing:
I used this inexpensive torpedo laser
level to make the rim joists level.
I used some shims to carefully adjust the device
until it was perfectly level.
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Just in front of the laser level I placed
the end of the tape measure on the top surface of
the original joist. This dimension (about 1½") is the
target number.
You can just barely see the laser dot in front of the
red arrow.
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At the diagonally opposite corner I placed
the tape measure in front of the laser beam. Of course
the dot is much wider, but I simply measure at the
center of the dot.
Luckily this corner was close to my target dimension,
so I didn't adjust the height of the rim joist. |
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In fact, I want the deck to have a slight slope away from the
house, so this dimension, about 1/8" lower than the old deck, is
just fine.
At the other corner the dot landed on 2 inches, so I
loosened the clamp and raised the rim joist by 3/8 inch.
Ensuring A Square Layout:
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I measured across the diagonals. This
diagonal was 24'-5-3/4", while the other was 24'-4-3/8",
which is 1-3/8" less. That's too far out-of-square for
me. |
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I needed to adjust the frame so this longer dimension would
shrink by more than one-half inch. I just picked up the frame and
shoved it over a bit, then re-measured the diagonals. They were
within 1/8" of being the same, which is good enough for something
like a deck.
I used a can of lawn marking paint
to lay out the post positions. |
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I made this grid layout on the grass.
There will be a 4x4 post wherever the white lines
intersect, plus posts where the long lines meet the
short rim joists. |
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Except that this was WRONG! I decided to deviate from the
original plan and put the support posts 6 feet apart, like the old
deck, instead of 8 feet apart, as originally planned. But this would
cause problems later, so I reverted back to the original plan.
I dug holes for the posts using a
flat-blade shovel to cut the grass and a post-hole
digger to reach deep. |
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Post hole depth:
Normally the bottom of deck posts need to be below
the maximum frost depth. But here in Northern Michigan
we are lucky to have soil that is mostly sand. This soil
is so well-drained that the local codes do not always
require that footings reach below the frost depth. If
there was clay in the soil then the footings would need
to be 48" deep to ensure that frozen soil does not heave
the posts upward.
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I used an 8x8 inch tamper to pack down the
soil in the bottom of the hole. This is critical.
If the soil is not properly compacted then the footing
will settle over time and the deck will sag. |
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The bottom of the hole needs to be level
so the footing block will be level. I just placed a
torpedo level against the handle of the tamper, and this
worked pretty good to ensure that the bottom was flat
and level. |
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This entire process was kinda tedious. If the tamper handle was
not close to plumb, I had to use a flat-blade shovel to scrape off
some dirt on the high side and shift it to the low side, then tamp
it again and re-check with a level. In two directions. It took
upwards of 10 or 15 minutes per hole to make these adjustments.
If the footing block is not level then the treated 4x4 post will
only have a small amount of wood that is actually bearing upon the
pad, and that might cause those wood fibers to crush and settle over
time. It's a pretty trivial concern, I'll admit.
My Preferred Method:
I would prefer to pour concrete into the hole to fill
the space below the post, using post anchors like this.
This type of anchor connects the post to the gob of
concrete. If there are any uplifting forces (such as
heaving, frozen soil that bonds to the post), the
concrete footing should prevent the post from being
lifted out of the hole. |
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I carefully dropped this 12-inch octagonal
post footing block into the hole. I pounded on the block
with a 4x4 to settle it into the soil. |
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I set a 4x4 treated post into the hole and
clamped it to the rim joist. The outer edge of this post
was 16 inches from the outside of the long rim joist
(14½" from the inside). I don't have a reason why I used
this dimension for the cantilever distance; I usually
see decks cantilever over the beam by about 24 inches. |
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I drove 4 deck screws through the rim
joist into the post. But before doing this I gave the
top of the post a couple of whacks with a hammer to make
sure it was seated well. |
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The deck so far.
There are 2 short rim joists with 2 posts each. The
long rim joist is not yet fully secured.
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I installed an intermediate joist, one
that will sit adjacent to a pair of supporting posts.
I didn't need to make a joist line up with
these posts, but this makes it easier to establish a
location for the posts, and also to hold them in place
while I build up the beam that will support all the
joists. |
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At this point the long rim joist was temporarily held up by two
short blocks of 4x4 (red arrows, above) that rested on the lawn. The
24 foot long rim joist was made of an 8 foot board plus a 16 footer.
I made these boards meet at this intermediate joist.
At the deck end I used a joist
anchor to position the joist. |
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At the cantilevered end I screwed
the rim joists to the new joist. I purposely made this
new joist land on the joint between the 16 foot and the
8 foot 2x8's that comprise the outer rim joist. |
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For the second intermediate joist, I
screwed a joist hanger to the old deck rim joist. |
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... and another joist hanger to the new
rim joist. This hanger will just be temporary.
I couldn't easily do this on the first intermediate
joist because the hanger would have to cross the gap
between two boards. |
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I placed the joist in the joist hanger. |
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I drove some deck screws through the rim
joist into the end of the new joist. |
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At this point the 4 posts in the middle of the deck are just
sitting on cement pads, I haven't yet backfilled the holes. These
posts will need to be aligned with the corresponding posts on the
outside joists, so the beam will be straight.
If a deck project required a permit and inspection of the footing
depth, this would be the time to call the building department to
have the inspector come out. This can be a real nuisance for people
who work regular jobs during the week and work on home projects on
weekends, because you can't cover up the footings until they are
inspected. Not all areas require an inspection of the footing depth,
so call your local building department for more info.
I ran two stringlines from one end of the
deck to the other. I find that the easiest way to fasten
the string is to simply wrap it under the corners of the
temporary spacer block and pull tight. |
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Why the spacer block? This is necessary to keep the
string above the joists that I am trying to align. By using a block
of wood at each end of the string, I can tell if one joist is higher
than the end joists. If I didn't use spacer blocks I would not be
able to tell if one joist was too high because it would be
hitting
the string.
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I can use these stringlines to make sure
all four joists are in the same 2-dimensional plane, and
to set the posts so each row lies in a straight line. |
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One of the intermediate joists was too low
by over 3/8". The spacer blocks were 11/16" thick, so
the distance from the joist to the string should be
same.
To fix this problem I just unclamped the temporary
support blocks and raised up the frame. |
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Note that it's important to use spacer blocks of exactly
the same thickness. The best way is to cut a piece of wood into
small pieces so they all came from the same stock.
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With a clamp loosely holding the
post, I adjusted the position of each post until it was
directly in line with the string. I used a level to make
sure the post was plumb, then I beat on the top
of the post with a hammer to make sure it was seated
against the concrete pad in the hole. |
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I also had to shift the concrete footing pad around the bottom of
the hole to ensure that the post was reasonably close to being in
the center of the pad. I used a shovel and a 4-foot-long pry bar to
push against the side of the pad. Reaching into the hole was way too
difficult.
At this point I backfilled the post holes, filling in only about
6 inches of dirt at a time and tamping the loose soil by walking on
it or pounding it with a piece of 4x4 post. Where possible I used my
8x8 tamper to compact the soil.
The structure so far. All the temporary
supports have been removed. |
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The Beam:
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I clamped a 16 foot long 2x8 to the deck
posts and used a prybar to push them up against the
underside of the intermediate joists. It's critical to
make this beam tight against the initial joists. |
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Before putting this board in position, I sighted down the edge of
the board to see which way the board curved. Long lumber almost
always has a curve to it, and you should always examine the board to
determine which edge has the "crown", or outward-curving shape.
The "crown" edge should always be placed up, so that if
the framing sags over time the board will tend to straighten out.
I drove in a pair of lag screws at each
post.
These are GRK 5/16" x 4" long lag screws that have a
Torx #30 drive. (That 6-pointed star pattern.) These
screws do not require any pre-drilling.
Here I'm using a Makita 12 volt impact driver,
which is quite capable of driving these lags. It's also
much faster than using conventional lag bolts,
pre-drilling the holes and using a mechanic's ratchet
wrench to tighten them. |
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This is the deck frame after the beams had
been bolted to the posts. There are two of these beams,
and each is made from a pair of 2x8's. |
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The connections at the post.
I used 16 foot long boards and 8 foot long boards to
to create the beam that is just under 24 feet long.
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A Small Problem:
By sighting down the top of the long rim joist I realized
that the wood was kinda bowed, as Southern Yellow Pine often is. I
had installed the 16 foot long board with the crown upwards (like
you're supposed to), so I snapped a chalk line between the upper
corners of the long rim joist, to give me a more accurate picture of
how warped the structure was.
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I used a portable power planer to remove
some wood in the highest part of the rim joist. In some
places the wood was almost 1/2 inch higher than the
chalk line. |
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I laid out the joist locations along the
old rim joist and the new rim joist. These are 16 inches
on center, except the first joist spacing, which is 3/4"
less. |
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I made a mark like this to help position
the joists.
There are all sorts of ways to mark joist layout. The
most common is to draw one line to indicate one edge of
the joist, and an X to indicate which side of the line
the joist goes on. |
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Another Problem:
When I set the 6 foot long joists in
place, I was not able to get the ends of the joists
aligned with the top of the old deck (you can that see
in the background) and the top of the new rim joist. |
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This is caused by the curvature of the 2x8's used to make the
beam. I installed those boards with the crown (curvature) upwards,
but they were so badly curved that they created problems in other
areas..
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I slipped a 3x5 file card under each of
the 4 points where the joist crossed over the beam, to
see which areas were in contact. This is easier than
crawling around in the dirt to look for the gaps.
The red mark indicates an area that was in contact.
I'll need to plane down these spots.
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The first group of five joists sitting in
place after I spent 20 minutes planing the tops of the
beams. |
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I tacked the joist hangers in place by
hammering in the built-in prongs. |
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I used 8d hot-dipped-galvanized joist
hanger nails to fasten the hanger to the old rim
joist... |
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...and 16d spiral deck nails in the angled
holes of the hanger. |
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The Easy Way:
This is the Senco palm nailer. I call this tool the
Poor Man's Air Nailer. It works with any nail that
will fit inside the tip.
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At the cantilevered end, I drove three
3" deck screws through the rim joist into the end of
each joist.
I never use nails here because nails pull out
easily when driven into the end-grain of wood.
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Extra Stuff:
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To keep the joists from twisting, I
fastened these scraps of 4x4 between the double 2x8 beam
and the joists. This is a supplement to
toe-nailing, which is not a very strong method of
joining wood.
This was simple: A couple of deck screws to hold the
block in place, and then two 16d nails to fasten each of
the three boards to the 4x4 block. |
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I only did this at the outer beam, figuring that the joist
hangers will keep the joists from twisting near the inner beam.
I toe-nailed each joist (red arrows) on
both sides. |
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The deck framing completed. Now the
handrail posts need to be attached and then the decking
installed. |
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After the new deck boards were completed
the deck looked like this. Now there is room for the hot
tub and some people on the deck. |
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Tools
Used:
- Cordless Drill/Driver
- Basic Carpentry Tools
- Level, 4'
- Miter Saw
- Table Saw (or Circular
Saw)
- Jig Saw
- Shovels
- Post Hole Digger
- Tamper, 8"x8"
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Materials Used:
- Treated Lumber, 2x8x16'
- Treated Lumber, 2x8x12'
- Treated Posts, 4x4x8'
- Concrete Post Pads, 12"
Wide
- Galvanized Nails, 16d
- Deck Screws, 3"
- GRK Lag Screws, 5/16 x 4"
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