Plans for deck construction are usually based on two main themes: a great number of support posts capped with a simple horizontal structure, or a fewer number of posts supporting a sturdier horizontal platform. For example, a ground-hugging deck may have a random number of footings and not be un-sightly, whereas a hillside deck requires a few well-placed supports that are solidly anchored but that do not detract from a pleasing visual design. The discussion below is confined to locating and building of footings, use of post connectors, and types and sizes of support posts.
CONCRETE FOOTING REQUIRED FOR MOST DECKS A footing made of solid concrete is required by most building codes to anchor a deck securely to its site. For a ground-hugging deck, you can use simple concrete blocks put down on tamped earth, or set on a concrete pad. Pre-cast concrete piers are also available. These piers are usually 12 inches square at the base, 6 inches square at the top, and 12 inches deep. They should be seated on compact soil or a concrete pad.
For hillside decks, the concrete footing should be a foot or more across and extend 18 to 30 inches below grade. You can cast such footings using forms made of wood, metal, or even tarpaper. The recommended formula for mixing a concrete foot-ing is 1 part cement, 2 parts clean sand, and 3 parts gravel. An easier method of casting your own footings is to use transit mix. Almost as easy but more expensive is dry mix to which you just add water.
THE PLACEMENT OF FOOTINGS
Close accuracy and placement of footings is an essential part of deck building. The weight of the deck must be evenly dis-tributed over the support posts and the ground. By using the 3-4-5 rule, any difficulty or errors in the ‘squaring off’ is auto-matically avoided: First, establish a base point (if the deck is to be attached to a house wall, use the wall as the base point). Measure along the wall a distance of three feet and mark a second point (B). Then tie a string to the base point (A) and run it out to reach the outside edge of the deck. At a distance of 4 feet out along this line, mark a third point (C). Then measure between the points B and C and if the distance is exactly 5 feet, the line is at a perfect right angle to the wall. Measure in the same way for each critical footing.
To use the 3-4-5 rule for a detached deck, drive stakes in a straight line to form one edge of the deck and use one of them as your base point.
THE USE OF POST CONNECTORS
In order to provide a flat, level surface on which the support posts will rest solidly, one of the three types of post connectors could be used. The simplest and least expensive method is the wood block (B) that is set in the top of the footing while the concrete is still in a plastic state. This method is adequate for short posts, which are then toe-nailed to the block. Another method is to extend a metal pin through the wood block before it is set in the wet concrete (C). After a hole is drilled in the post to accept the pin, toe-nail the post to the wood block. A stronger method of anchoring posts is to use metal fasteners (A). Designed to withstand great stress, they are most commonly used with hillside decks. The long prongs of the metal fasteners are seated in the wet concrete and the top part is bolted to the posts.
CHOICE OF TYPES AND SIZES FOR SUPPORT POSTS The most commonly used material for support posts is wood (although concrete and steel can also be used). The 4 by 4 post is adequate for most low decks as it will bear a load of 8.000 pounds up to a height of 8 feet. Larger posts are required for a steep hillside or where the deck is to bear such heavy loads as large groups of people, numerous plant containers and pieces of furniture, or several inches of wet snow. Your local building department will tell you the size required for the type of deck you are building.
Besides the regular sized posts, you can also use a built-up post. Those offer a compromise between structural demands and graceful appearance. There is no lack of strength if the separate members are properly joined with heavy nails or screws or bolts.
MEASURING FOR POST HEIGHT
Accurate measurement of post heights is an important phase in building a deck. Without it, you cannot build a sub-structure that is stable enough to support a horizontal platform. There are two methods for measuring, each with the same first step as follows: Find and mark a line on the house wall that is even with the top of the deck surface. Measure down the thickness of the decking plus joists to find the top of your ledger. Establish the line, check for level, then snap a chalk line to mark it. Then use either of the following two methods for measuring post height:
Method 1. Set a post in place, check for plumb, and brace it temporarily. Then run a line from the top of the ledger to estab-lish a mark on the post that is even with the top of the ledger. From that mark, subtract the depth of the support beam you will be using and make a new mark. Use a piece of scrap lumber and a carpenter’s level to check for line level. Then take down the post and cut off the excess.
Method 2. Rather than setting up the post temporarily, you can measure the length by this mathematical procedure: Establish the ledger line as in method 1, measure down to the ground line of the house to establish a base line. From the base, run a line level out to a footing and measure how far above or below the house line each footing comes. Then take the distance between the base line and the ledger line, subtract the beam thickness, and add or subtract the difference between the footing and the base line. Measure each post in this manner.
CROSS BRACING MAY BE NECESSARY
Some type of cross bracing may be required to prevent vertical movement of the deck. This is particularly true where the deck is built on a steep hillside and the posts are of extra length. The simplest kind of bracing is to use a heavy duty connector between post and beam.
Deck beams and joists
Most building codes require that a deck be designed to bear 40 pounds of weight per square foot. This figure applies mainly to the beam and joist construction-the size and span of the members and the methods of anchoring in place. The size and weight of the beam required depends entirely on its span and spacing. A good rule in general is that the depth of the beam in inches may be equalled in feet of span (a 6-inch beam can span 6 feet). Joists are normally of 2-inch dimensions and are required to support the deck surface and whatever loads are placed on that surface. The joist span is determined by the joist and beam spacing and the grade of lumber.
METHODS OF SECURING BEAMS
Once the beam is set squarely on top of the post, there are several methods for anchoring it in place . The simplest approach is toe-nailing (A), but is normally used for small, ground-hugging decks. A stronger method is to use strap metal which comes in straight pieces, L shapes, or T shapes (B, C, D).
JOINING BEAM OR JOIST ENDS
If the length of one beam is not enough to span the length or width of the deck, you will be required to join two beams. This joint should be directly over a post. The same is true with joining a joist. Each end of the member should have a resting surface of at least 1 inch on the supporting member. Toe-nail the ends together on the top and nail heavy scabs (scrap pieces of lumber) on both sides. The scabs’ should equal the depth of the member and be at least 2 feet long.
Lateral bracing for joists is usually required if the ratio of the width to the depth is less than 1:2. For example, a 2 by 4 (ratio of 1 to 2) does not need bracing, but a 2 by 6 (ratio of 1 to 3) requires bracing to prevent its twisting or buckling.
There are two easy methods for bracing. The first method uses pieces of 2 by 4 nailed in crosswise fashion at regular intervals. For an 8-foot span, cross-bracing at either end is sufficient. If the span is at least 15 feet or more, use this bracing method every 2 feet.
The second method is to use spacer blocks between the joists at or near their ends. The spacers should equal the depth of the joists and be toe-nailed in place.
METHODS OF SECURING JOISTS
Since joists individually bear a lesser load than do beams, they can be placed on top of the beams or attached flush with their tops . The stronger method is the first. If the joists are seated on top of the beams, toe-nailing them in place will be adequate (A). If you want the joists to be set flush with the beams, it is best to use an angle iron or joist hanger (B and C). If the beams are deeper than the joist, tack a ledger strip of wood to the beam and rest the smaller member on it and toe-nail in place (D).
A ledger is a 2 by 4,2 by 6, or other plank nailed or bolted to a house wall to support the surface boards of a deck or the deck joists. Ledgers can be attached to the studs of wood walls with either nails or expansion screws. Once you have located the height of the ledger, snap a chalk line to mark it. If the ledger is fairly long, it is a good idea to nail several pieces of scrap lumber on the wall to support the ledger while you are nailing it in place. Start your first nail or screw at the center of the ledger; then tack each end. Check with a level to make sure it hasn’t slipped. Use two or more nails or lags at each stud.
If you are attaching the ledger to a masonry wall, use expansion bolts. Make a mark for the bolts about 16 inches apart, and use an electric drill with a masonry bit to drill a hole at least 2 inches into the wall. Insert the expansion shield in the hole and secure the ledger with the bolts, including washers.
There is a wide range of possible patterns for decking. The two simplest patterns are to lay the decking parallel to a wall, or at right angles to it. These patterns require no modification of beam and joist construction.
This pattern of decking may be laid on a diagonal to the joists, at any angle greater than 45°. It is often used to relieve the monotony of the normal square or rectangularly shaped decks, or to give a distinctive shape to the deck. Standard framing is used for this pattern, but it should be noted that the diagonal decking spans are greater and the joists may have to be set closer together than would be necessary with standard pattern decking. It should also be noted that if one side of the deck follows the diagonal, an edging or facing should be attached to the joist ends to help support the decking.
GEOMETRIC SHAPES AND FREE FORMS
These variations of standard or diagonal decking patterns include triangles, hexagons, circles, and curves. Almost any form or shape can be achieved as long as the joists are closely spaced and a braced joist lies near the edge of the deck.
PARQUET AND DIAMOND PATTERN DECKS
These sectional patterns of a deck require a grid pattern of support which is achieved by using block supports between the joists at a distance equal to the joist spacing. If the joists are of 2-inch dimension, the support blocks should also be of 2-inch dimension. The exception to the framing requirements of this pattern is when it is laid directly on concrete or sand. In this instance, a framework of 2 by 4*s will be adequate for support and nailing the deck surface in place.
FRAMING AROUND TREES
The planning of either low-level or high-level decks may necessitate provisions for encircling a tree. Both framing and decking must allow ample clearance for trunk growth and for possible swaying in a strong wind.