CABLING, BRACING AND GUYING

STANDARD FOR SHADE TREES

These standard procedures provided by the National Arborist Association for cabling, bracing and guying of shade and ornamental trees should be undertaken by trained personnel only. Understanding the growth habits and characteristics of various species of trees, along with the knowledge of materials and their proper use, is necessary. Tool sterilization, lightening installation, and pruning shall be considered when bracing, guying and cabling trees. It is recognized that regional practices may dictate variations in this standard. Occasionally, even with the best of care, due to nature’s intervention, the tree may not be spared from damage.

INTRODUCTION:

Trees can benefit from the support and strength provided by guy wires, cables and bracing. Sometimes trees develop in such a manner that they are structurally weak, making them susceptible to damage from winds, storms, or even the weight of their own foliage. In newly transplanted trees, guys prevent wind throw until the roots become established. In established trees, cables and braces are used to prevent or reduce storm damage. The arborist’s primary responsibility is to safeguard people, property and plants. Some trees may be deteriorated or damaged beyond help from support techniques. The arborist and client must determine if the expenditure of time and money needed to make the tree reasonably safe will be worth the effort.

The most common structural weaknesses are the result of narrow-angled. V-shaped crotches. Unduly long or fruit-laden branches may also require support by cables.

After installation, cabling, bracing, or guying systems should be inspected periodically for deterioration of materials and changes in the trees which may make adjustments necessary.

Trees which are cabled or braced should be fertilized at an appropriate time to encourage the formation of callus growth around the hardware that has been installed.

DEFINITIONS:

Wood Screw Rod – A steel rod with wood screw thread, installed in a drilled hole usually 1/16” less than wood screw rod diameter. A wood screw relies on the bite of its thread to secure itself.
Bolt – A steel rod with wood screw or machine thread, installed in a drilled hole equal to or RARELY MORE THAN 1/16” larger than the bolt diameter and secured by washers and nuts, (appropriate for soft wood trees).
Drop Forged Eyebolt – A machine thread bolt with a forged, closed loop on one end. An eyebolt is inserted in a drilled hole, equal to or NO MORE THAN 1/16” larger than the bolt diameter and secured by a washer and nut.
Lag Screw Hook – An open hook with right or left hand wood screw thread. A lag screw hook is installed in a hole drilled 1/16” smaller than the diameter of the lag screw and slightly deeper that the length of the threaded shank. A lag screw hook relies on the bite of its thread to secure itself to the tree. New wood formed around the lag will increase its holding capacity.
Turnbuckle – An opposite-threaded tensioning device spliced to wire or cable.
Amon (eye) Nut – A nut with a forged eye which screws onto a threaded rod. The end of the threaded rod is peened over so that the nut cannot work off. The thimble and cable are attached to the eye.
Cable – A stranded or braided wire. There are two types of wife available for tree work.

Common grade 7-strand cable is wrapped at both ends around a thimble and affixed to an anchor or turnbuckle.
EHS cable (extra high strength) is also 7-strand non-flexible cable used only with PREFORMED cable tree grips. EHS cable has a left-hand lay and cannot be eye spliced. PREFORMED cable tree grips were designed for use with this cable. Cable tree grips are used to secure the cable around a thimble for attachment to an anchor or turnbuckle.

Eye Splice – A method of securing cable ends around a thimble and wrapping each individual strand a minimum of two turns over itself until all components form one unit. Use only 7-strand, soft lay, common grade cable for this purpose, (not extra high strength cable).
PREFORMED Cable Tree Grip – A device fitted to the end of EHS cable which includes a preformed loop. They must be used with thimbles and only EHS cable. Because of the constant loading and unloading on the cabling system in very large trees in high winds, there can be wearing of the tree grip behind the thimble. Use precaution on larger trees or heavy limbs subject to dynamic activity due to higher than normal wind loading.
Thimble – An oblong steel support with flared margins and open-ended base. Cable is placed around the thimble to prevent kinking and wear on support hardware.

STANDARDS FOR INSTALLATION

Cable bracing is the installation of flexible steel support cables in or between trees to help reduce stress damage from high winds, weight of ice or snow, split or V-shaped crotches, or heavy foliage. Such installations are particularly important where there is a possibility of property damage or personal injury. Pruning and fertilizing on a regular basis is recommended for trees requiring cable bracing. Occasionally even with the best of care, some trees may not withstand nature’s intervention.

Cables should be installed taut, but not so tight or rigidly so as to cause hardware to pull out when the tree moves in the wind. This is especially true if cables are installed during the dormant season when the tree is not supporting the weight of foliage. Conversely, the cable system installed when the tree is in foliage should be tight enough not to slacken after leaf drop. Cables should be installed at or beyond a point approximately 2/3 of the length of the limb or trunk, beyond the crotch, towards the tips of the branches.

When using 7-strand, soft lay, common grade cables, an eye splice should be made using a thimble of the same size as the cable diameter. No less than two and no more than four wraps of each strand around the cable shall be used.

Extra high strength (EHS), non-flexible cable may be used if PREFORMED tree grip dead ends are used with it. However, cables shorter than 3 feet may be difficult to install using these materials.

Cables shall be affixed to trees using either forged eye-bolts, threaded rod and amon nuts, or lag screw hooks. A forged eyebolt is the most secure anchor.

Where support hardware must be installed in columns of decay, only hardware extending through the tree limb and secured by nuts and washers shall be used. (It should be understood that in most cases, the ultimate holding power of the fixture will be in the tissue of the tree that grows over the hardware after the installation.) When in doubt about internal decay, do not use lag screws.

If an eyebolt is used, a hole the same size or 1/16” larger than the diameter of the bolt shall be drilled through the limb, the eyebolt inserted and secured by a washer and nut. Flush off excess bolt to the nut, so cambium will close over the nut. If a lag screw hook is used, a hole shall be drilled 1/16” less than the diameter of the lag and slightly deeper than the length of the lag to prevent splitting.

In either case, the holes must be drilled so that the lags or bolts are as close to perpendicular to the limb of attachment as possible. The hardware should be installed in a straight line to avoid a lateral or vertical pull, which will reduce the holding strength of the fixtures. Parallel limbs provide optimum conditions for cable installation allowing alignment of both hardware and wood grain. However, as the angle of the limbs to be supported increases, the more the installation must be adjusted. Hardware may have to be installed at a slight angle from perpendicular and the cable may have to pull at a slight angle as well. Cables must not rub against limbs or one another.

When cable is attached to the lag, the hook should be turned parallel to the limb and just touch, but not injure, the bark. The open end of the hook may be left either up or down. For most cable installations when the cable will support a weak crotch and be installed parallel to the ground, it is recommended that the open side of the lag hook be oriented downward. Other situations may dictate that the open end be up.

Only one cable should be attached to any one anchor. Since the safe workload is reduced when the angle of pull is more than 0 degrees, there are very few exceptions to the rule of attaching only one cable to the anchor. Hardware should be spaced at least one foot apart and never directly above or below each other so that cracks and dieback are minimized.

If a lag cannot be installed so connecting cable is at 0 degrees, (straight pull), then a drop forged eyebolt is preferred.

If a tree has a lightening protection system, attach bracing cables and rods to the system.

When working around energized wires, all work aloft shall be in accordance with Z133A Standards published by American National Standards Institute, Inc.

HOOKS AND BOLTS

Proper use of cables and braces can greatly extend the life of a tree. Even though wounds are made, it is better to have a few wounds than a broken limb or tree. Proper use of hardware does reduce the injury to the trees.

CABLE BRACING SYSTEMS

The four bracing systems illustrated are the most commonly used. There are many variations and combinations of these types.

Type I: Direct- Single cable installed between two limbs or trunks.

Type II: Triangular – The cabling together of limbs in combination of threes. (The preferred method of cabling for maximum support.)

Type III: Box or Rotary – A series of cables connecting four or more limbs. This allows maximum crown movement, but offers minimal lateral support

Type IV: Hub and Spoke – Uses a center ring of cable with radiating cable to four or more leaders.

“ROD BRACING OR RIGID BRACING”

The use of prepared lengths of steel rod of various diameters, threaded with wood screw thread or machine thread to provide a rigid support, is “rod bracing” or “rigid bracing”. This type of bracing is not a substitute for cabling but is to be used where a defect has developed in a crotch, cavity, limb or trunk, and additional support is required. Rod bracing may also be used to hold rubbing limbs together or to keep them apart.

When installing a wood screw rod in hardwood trees, a hose shall be drilled 1/16” less than the diameter of the rod. The hole should be drilled through the first wood member and at least fifty percent into the second, allowing sufficient depth to prevent the screw from bottoming. If the rod is installed as above, or if the hole is drilled completely through both members being joined, the ends of the wood screw rod shall be installed below the cambium to allow for closure. If a split has occurred, draw split together before drilling holes.

Prevent damage to the thread of wood screw rods by the installation wrench. Use the wrench at least 2” beyond all break marks. A break mark is a notch which is put on the screw rod to allow it to be broken at the desired length at/or below cambium level.

In decayed or softwood trees, install a bolt rather than a wood screw rod. Drill a hole not more than 1/16” larger than the diameter of the rod, completely through the sections to be joined, and secure the rod ends with round or oval washers and nuts. Washers can be seated directly on the bark.

Portions of the steel rod exposed between leaders should be coated with a rust preventive paint.

Where more than one hole must be drilled to affect a repair, holes shall be staggered to prevent the formation of large columns of decay and possible cracks. See illustration attached hereto.

See Chart attached hereto for size of rod to be used.

When bracing frost cracks, perform work in warm weather after the crack closes. Drill a hole 1/16” smaller than the rod and install washers and nuts on both ends. Space rods every twelve inches along the crack and six inches in from the lip of a crack. (See illustration attached hereto.)

HARDWARE ALIGNMENT

Never align bolts, holes, or any type of wound in vertical rows.

FROST CRACK REPAIR

Nuts and washers are placed approximately 12 inches apart to pull the wood together. In some cases, especially when the wood is rigid in its new position, wood screw rods are used to lace up frost cracks and other vertical openings.

ROD BRACING SYSTEMS

Type I: Double Wood screw Rod – Two rods installed between two limbs or trunks, or through a single section of tree.

Type II: Multiple Wood Screw Rod – A set of three of more rods installed through one or two tree limbs or trunks. It is sometimes difficult to aim the drill through trunks, especially when the drill operator is suspended in the air. Great care should be taken to avoid misplacing drill holes.

Type III: Single Rod or Bolt – A single rod installed through a split trunk or leader with the addition of nuts and round washers installed on both ends of wood screw rod. The single bolt may be threaded with either machine or wood screw thread. Several rods my be used for a log split, but should be staggered.

Type IV: Safety Rod or Bolt – Similar to a single bolt with the following additional provisions; the inner face of both limbs shall be secured by washers and nuts to ensure rigidity of the crotch. Safety bolts shall be installed an appropriate distance above a limb joint and a minimum of 3’ above the hardware. The exposed section may be covered by a tight fitting plastic pipe.

WASHERS

Washers should be countersunk so that they lay flush against the wood beneath the bark. A sharp instrument should be used to cut the bark and a socket wrench of the proper size should be used to tighten the nut so as not to damage the bark.

GUYING ESTABLISHED TREES

Type I: Tree to Ground – Single or multiple cables with or without turnbuckles are attached to the weak tree by lag screw hooks or eyebolts, and to a ground fixture. Cables shall not be attached to the tree at a point less than ½ the tree height. PVC should be placed over the guy cable for pedestrian visibility and safety.

When support fixtures must be installed where there may be columns of decay, only hardware secured through the tree trunk or limb with nuts and washers shall be used.

Type II: Tree to Tree- Method I – Single or multiple cables, with or without turnbuckles are attached to the weakened tree with lag screw hooks or eyebolts and attached to the anchor tree at a pint at least ten feet above the ground. Cables shall be attached to the weakened tree at a height above the half-way point of the tree. When guying tree to tree, care must be taken to select an anchor tree of proper size and never use shallow-rooted trees as anchors. The anchor tree must be on the client’s property and not near energized wires.

Type II: Tree to Tree – Method II – Single or multiple cables, with or with turnbuckles, are attached to the weakened tree and to two or more surrounding trees. Cables are attached by lag screw hooks or eyebolts.

Where possible, angle support cables downward from the weakest to the strongest tree, with the lowest cable providing at least 10’ head clearance. Refer to method I.

GUYING NEWLY TRANSPLANTED TREES

Method I: The preferred method of guying trees over 6” D.B.H. is the use of three or more cables with turnbuckles or compression springs, attached to the tree by lag screw hooks or eyebolts, and secured to sunken deadmen. Attachment to the tree shall be made at or above a point one-half the height of the tree. Lag screw hooks should be spaced 8-10” apart vertically. In some cases, if the location and the tree lend themselves, cable covered by ¾” rubber hose and secured around the lowest crotch may be substituted for lag hooks.

Deadmen may be made from black locust, catalpa, cedar, or other decay-resistant wood. Deadmen shall be a minimum of four feet in length, 6 inches in diameter, and be buried a minimum of 4 feet. Commercially available earth anchors may be substituted for deadmen if manufacturer’s instructions are followed.

Deadmen or other ground anchors shall be located no closer to the trunk base than two-thirds the distance from the trunk base to the height of the cable attachment to the tree.

Wire or cable should be marked by colored plastic ribbon “flags” or other suitable material and never placed across paths, etc.

Method II: When guying trees less that 6”D.B.H. wire may be substituted for cables. When wire is used, each attachment shall consist of 4 to 6 pieces of number 10 gauge wire, hose covered, wrapped upon itself and returned to the ground anchoring device as in Method I above.

Since the hose and wire will eventually girdle the tree trunk, the wire should be checked after each year’s growth and adjusted or removed after the second year.

Wire or cable should be marked by colored plastic ribbon “flags” or other suitable material to prevent accidents.