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squaring a deck
by: Mac1234 posted: Tueday - January 1, 2008
when building a deck how do I make sure it is square?

Squaring a Deck
by: Drywall DIY Guy posted: Tueday - January 1, 2008
You square it off the best you can.  Then you take
diagonal measurements if it is square or rectangular -
the measurements must be equal.  Once you get it
square, attach temporary diagonal deck boards at the
corners you are not working on to keep in square.

This is how I do it anyway. I am not a deckbuilder,
just a DIY type guy that knows a little geometry. 

by: posted: Tueday - January 1, 2008
Mac-It is very important that the deck base frame 
be square to whatever you are building it against 
plus to be square to itself so that when you install 
the floor joists, dceckboards, deck rail, etc. 
everything fits easily and uniformly.  If the deck 
frame is not square you will have all kinds of 
additional headaches installing the components.  The 
normal allowance for a project such as a deck to 
be "out of square" is approx. 1/8"-1/4" to itself in 
a distance of say 20 feet.  Nothing ends up exactly 
perfect and a small incrementsuch as that will not 
substantially affect the building of the deck.  But 
always strive to be as close as possible to be 
truly "square".  As far as how you check for square 
on a deck which may have a substantial length and 
width of say 14 feet out from your house and 30 feet 
long, you must use geometry and general math 
principles.  If the deck is either a square or 
rectangle you can measure from one corner to the 
opposite diagonal corner and then do the same on the 
other side.  The measurements should be within 1/8" 
of each other if the deck is square.  Also to make 
sure the deck is "square" to the house you can sight 
the deck visually and also use the "pythagorean 
theorem" of 3-4-5.  When you measure the frame of the 
deck at the corners one side should be 3 feet one 
side should be 4 feet and the hypotenuse or the base 
of that triangle should be 5 feet.  Once you have the 
deck frame square you do need to secure the deck 
frame before working further so that you dont 
accidentally knock the deck out of square and forget 
to resquare it.  By the time you get most of the 
floor joists in the deck becomes too heavy to move.  
So install some bracing on the deck frame and use 
care so that the deck stays square while you build. 


pre-cut the deck to size...
by: BayStateHandyman posted: Wednesday - January 2, 2008
Hi Mac123,

The 3-4-5 method works great...You can double it to 6-
8-10 and so on...Brace it well and just remove a brace 
when you need to...Most likely as you approach a brace 
during the decking process...

You can use a string to check for the straightness of 
the outter box joists and when you apply the braces, 
make sure you sight down the string one more time 
after you nail the braces...


Let say your deck is 10' x 12'. Make a drawing of the 
deck with the calulated measurements and number of 
pieces needed of each measurement and just start 

I can't tell you how many decks I started on time, 
because of this method... 

Rain sleet or snow, you can still pre-cut any deck 
anytime... Your garage, the customers garage, just 
about anywhere and when the weather breaks, your ready 
to go...

Even if your pre-cut deck doesn't set-up perfectly 
square, as you bring the deck boards across the deck, 
you can always measure the remaining area the deck 
boards need to be installed-over by taking three 

Left-edge, middle and right-edge...

If all 3 measurements are the same, your golden...But 
if they're different, start making slight adjustments 
to each new course... 

If you only an 1/8 of an inch off I wouldn't check it 
again for several courses... 
The difference in measurement from one one end of 12' 
piece of decking to the other could vary at least that 
much, plus some boards wil be about 5 1/2 inches wide 
and some others 5 5/8 to 5 7/8 wide...So once you 
begin to understand the issues that creates, being 
dead-on square really isn't a big issue...

I've been building houses for decades and I don't 
think I've ever started off with a dead-on square 
foundation...Not once, so pre-cutting all you frame 
ahead of time, doesn't hurt anything, despite what my 
fellow handymen might have to say about my deck making 
skills after reading my response to your question...

If your middle measurement is more or less than the 
side measurements, just open or close the ends a 
little on your next couple of course and recheck it 

All you deck boards shoul be installed as tight 
together as you can get them...

No more spacing deck boards like years ago..

They shrink to much now to be leaving a space between 
them so if and when you make an adjustment, just make 
it a minor one...That's why you start taking 
measurement when you have several feet left to deck... 

( Lets say at least 4 or 5 ft left to deck )

Only make the adj. on one end of the deck board at a 

You can also take the remaining measurement and divide 
it by 5.5 and see if you'll end up with a full deck 
board or a sliver of a board and start making 
adjustments accordingly...

The sooner you start to take the measurements the 
sooner you'll take control of your decks final 
12 feet or 144 inches divided by 5.5 equals 
26.181818...So based on the average width of your 
stock, you should be able to start-off with a full 
board and end with a full board somewhere between 25 
or 26 boards with the proper measuring and 
adjustments...Even if your deck is not square...No 
human eye or fellow contractor will ever 
notice...Trust me on this...Good Luck...E.T.

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