Number Needed

[Guest]

A deck is to be built with 2x4's 8 feet long.

Dimensions of deck:

8 feet wide.

30 feet long.

3/8" spacing between boards.

Boards are to be placed flat.

The board at the end can be cut lengthwise to fit, if needed, where no one is likely to observe it.

Calculate number of boards needed.

Thank you for your help.

[Guest]

82 boards fit exactly....no space at ends......leave spaces a loose 3/8" about 1/64" more......25/64" instead of 24/64"
and start with centre of a space in the middle......

OR

83 boards and cut ( 1 3/8" ) of width of each end board......and 3/8" spacing......and start with the centre of a board in the middle....

Simple.....

[Guest]

Please show your solution.

Also, I have read that a 2x4 is not actually a "2x4". That is the nominal size rough sawn from the log. After drying and planed, the actual size is 1.5 x 3.5. The problem, however, stated 2x4's.

Thanks again.

[Guest]

Definition: Dimensional Lumber is lumber that is cut to certain pre-defined sizes. This type of lumber is sawn, planed, and smoothed (though not always smoothed) and ready for building applications.
The most common type of dimensional lumber is the 2x4 (two-by-four). Due to the thickness of the saw, the 2x4 is not 2 inches wide, 4 inches deep but is 1 1⁄2 in × 3 1⁄2 in (38 mm × 89 mm).

Dimensions are only given to the width and depth. Thus, a 2x4 board can be 8 feet long, 10 feet long, 12 feet, and so on, but the length is never figured into the dimensions.

Also Known As: cut lumber, finished lumber

The above is a cut and paste from about.com..............

There are dimensional tolerances associated with everything we do.........
How accurate is the speedometer in your car..........

How did you measure the 30 foot length of your decking...........Your measurement may be out by as much as 1 inch..
Did you simply step it out...or measure with a tape measure .....or even one of the modern light beam meters..????

An accuracy of 1inch in 360 inches is equal to 0.28 percent.....pretty accurate but will mean you will have to cut 1 inch off your last board if you don't balance out the differences.......

The best would be to go to the builders yard and measure a few boards.......

I will show you how to work it out on the next post......so simple

[Guest]

Let N = number of boards
Let W = width of boards
Let S = size of space between boards
There will be N boards and (N-1) spaces
so feet of decking is 360 inches

So for equations......
N(W + S) -S = 360

If we take......
W = 3.5
S = 0.375.......3/8 inches
Then.......
3.875N = 360.375
therefore N = 93......exactly......no cutting and start with the centre of a board in the middle of the decking....
because the number of boards is odd......

...........Simple........

[Guest]

Let N = number of boards
Let W = width of boards
Let S = size of space between boards
There will be N boards and (N-1) spaces
30 feet of decking is 360 inches
(correction line above....should read 30 on previous post)

So for equations......
N(W + S) -S = 360

If we take......
W = 3.5
S = 0.375.......3/8 inches
Then.......
3.875N = 360.375
therefore N = 93

The number of boards needed is 93 ......exactly......no cutting and start with the centre of a board in the middle of the decking....because the number of boards is odd......

...........Simple........