Timber_Sound

Existing home owners can effectively reduce noise levels by erecting a high timber sound fence.

A timber sound fence is a cost effective solution to the problem of increasing road noise.

A timber fence is also an attractive addition to the residential landscape and provides the home owner with additional security and privacy.

To be effective, a sound fence must block the line of sight between the noise source and the receiver and be continuous and solid with few, if any, holes, cracks or openings.

Since traffic noise is in effect a long line of sound, a sound fence needs to be long enough so that sound does not reach the listener via each end. For this reason, neighbours should be persuaded to erect a similar fence. Alternatively, you can return the fence down the side boundaries until they are parallel with the front face of the house.

The information contained in this guide is only applicable to individual residential allotments.

Sound fence details for commercial development are available from the Timber Facts Advisory Service.

To achieve long term performance out of the finish and the fence timber, use a high quality light coloured paint or stain.

Prior to assembling the fence: posts, rails and palings should receive a coat of water repellent wood preservative or oil-based primer to stop the timber from drying too quickly and distorting (irrespective of the timber used). Once this pre-treatment has dried, the palings can be coated with the first coat of the selected finish.

All end grain, cuts, notches and holes should be primed using the water repellent wood preservative or oil-based primer. Apply the finishing coats after assembly has been completed.

All fixings should be hot-dipped galvanised.

Select the fencing timber you use for quality and durability, not just for price. Suitable timbers are CYPRESS, HARDWOOD and TREATED PINE.

Using your scale drawing (see Figure 1), mark in all corner and gate posts (a). Then divide the spaces between these posts into intervals (maximum 2.4 m) and mark in your intermediate posts (b). Try to purchase rails at least twice the length of the post spacings (4.8 m) and stagger the joins on alternative posts for a stronger fence (see Figure 1 ). The board and batten paling system must have a 25mm lap to ensure there are no gaps in the fence face (see Figure 2). A plinth board on the bottom keeps the noise from going under the fence.

SETTING THE FENCE LINE top

If the neighbours are not installing sound fences, your fence will need to return down the side boundaries until parallel with the front face of the house. For the side boundaries, the centre line of the posts should be positioned over the line of the boundary. However, the fence must be within the front boundary line. Dig the post holes to 900 mm, then stand and brace the posts in the holes. Check that the posts are plumb and at the correct height before setting them permanently.

Setting and aligning the intermediate posts is the most difficult part of building the fence, so a lot of care is needed. Stretch two string lines between the corner posts, one at the top and the other at the bottom. Measure along the top string line and mark the intermediate post positions. Transfer this mark to the bottom line using a plumb bob. Set each post in the ground and cheek the verticals. When all the posts are in make a final check by eye along the fence line (see Figure 3).

Pine posts and sapwood in hardwood posts should be CCA treated to H5 level. Cypress and hardwood post bases and end grain should be coated with creosote before being put into the hole (see Figure 4). The coating should be from the base to just above ground level. Place the base of the post on a 100 mm layer of gravel and backfill half the hole with gravel, tamping firmly every 150 mm. Fill the remainder with dry, lean concrete mix of 1 part cement, 3 parts sand, 5 parts gravel, or 2 pre-mix bags per 3 posts.

POSTS AND RAILS top

See Table 1

Prior to construction, the posts are to be notched in half the rail width (rails are 38mm thick, therefore notch into posts 19mm - see Figure 5).

After the concrete is 4 days old, lay the rails on saw stools beside the posts to which they will be screwed, remembering to stagger the joints. Mark, trim and half notch the ends and middle of the rails to fit into the post notch (see Figure 5).

Apply an oil primer or water repellent wood preservative to all surfaces where rails and posts touch for protection against decay.

Clamp each rail in turn to the post in their correct position and drill a pilot hole through the rail end into the post and fix the rail with a 45mm long galvanised wood screw. The pilot drill bit should be at least 2 sizes smaller than the screw size being used.

To ensure no noise travels under the fence, the plinth board is embedded in the ground and attached to the bottom 30mm of bottom rail (see Figure 6). To do this , cut a shallow ditch with a spade, screw the plinth to the bottom rail every 500mm using wood screws and backfill, making sure all gaps are filled.

Cut a piece of timber 50 mm wide and attach a small cleat to one end. Use this as a spacer block by hanging it by the cleat from the rail and sliding the paling up against it before nailing (see Figure 7). Periodically cheek that the palings keep their vertical line by using a spirit level or by taking a parallel measurement from both the top and bottom of the paling to the next post.

Using the same spacer block, the outer row can now be nailed. By hanging the spacer in the middle of the attached paling, the outer paling can be butted hard against the spacer and nailed off (see Figure 7). Since the paling widths can vary slightly, periodically check that a lap of 25mm is maintained.

The palings should be fixed to the rails using hot-dipped galvanised nails (see Table 2).

The cap rail is fixed to the top rail using two 75 mm long, 3.75 diameter hot-dipped galvanised nails at 450 centres. The top edges of the cap are raised 10mm. The cap rail is used to cover the end grain of the palings and therefore is positioned to cover the outer palings (see Figure 8).

The framing member sizes and details (Table 3) have been set for 2.7 m wide driveways. For a driveway of 3 m width, use 100 x 38 mm frame members and alter details to suit.

The gate should be hung 100 mm above ground level to allow for free swinging and settlement of the frame. Levelling the ground will neaten the gate appearance and assist in hanging the gate frame.

The vertical frame members (stiles) are notched 38 mm to accommodate the horizontal rails. Roughly square the frame and screw the rails into position with two 8 gauge 55 mm long wood screws. Run a diagonal metal speedbrace (1) from the top gate hinge corner to the bottom free corner. Check the gate for square by making sure the diagonal measurements are equal and then fix the brace with two nails where it crosses each rail.

Where the top two hinges are positioned a 75 x 38 x 300 mm long blocking piece (2) is to be butted against the vertical member and nailed onto the frame. The blocking piece will need to be notched to accommodate the speedbrace under it. The bottom blocking piece, 50 x 38 x 300 mm (3) will be cut to allow for the inclusion of the timber brace.

Line the timber brace (4) diagonally from the bottom gate hinge corner to the top free corner. Mark and cut the brace to fit into the bottom gate and top free corner. Mark and cut the 50 x 38 x 300 mm blocking, piece for inclusion of the brace in the bottom corner. Clamp the brace onto the frame and except for the bottom corner, screw into position with two 8 gauge 55mm long wood screws.

Align the 3 heavy duty hinge plates with the top of the frame members and coach screw into position (5) making sure the coach screws are at least 55 mm long. Nail off the palings and cap rail. Along the bottom frame member attach a 175 mm or wider, thick, flexible, rubber/plastic strip (6) to stop the noise from coming under the gate (making sure the strip is longer than the frame to get an overlap in the middle). Use 8 gauge 30 mm long screws with wide washers every 150 mm to attach the strip.

Hang the gate allowing for a 10 mm gap between the gate and post and 20 mm gap where the frames meet in the middle (ie. 10 mm gap either side of the frame). Coach screw the hinges.

Meet the gate frames in the middle and screw at 300 mm centres a 75 x 38 x 1800 mm long piece of timber (7) onto one of the stiles such that it bridges the 20 mm gap. This will stop noise going through the middle gap. Once the gate is in position, nail on the outside a 25 x 25 mm bead (8) down the length of the post on either side of the gate opening to seat the 10 mm gaps. The bead should be set snug against the paling when the gate is closed.

Careful thought must be given to both the gate design and location since gates are notorious for letting noise through the fence.

The gate is recessed and should be hung 100 mm above ground level to allow for free swinging and settlement of the frame. Levelling the ground will neaten the gate appearance and assist in hanging the gate frame.

Square up the frame on a hard flat surface and hammer 'knuckle' type nail plates (1) to the butt joins on both sides. The joints where the diagonal brace meet the horizontal and vertical members will need larger plates.

Nail the palings to the frame. Align the heavy duty hinge plates (2) with the top of the frame members. Coach screw the plates to the frame and nail off the palings and cap rail.

Along the bottom frame member attach a 175 mm or wider rubber/plastic strip to close the gap under the gate frame. Use 8 gauge 30 mm long screws with wide washers every 150mm to attach the strip.

Hang the gate (allowing 10 mm on either side), scribe the hole positions and coach screw the hinges (4). Fit the latch (1.2 - 1.4 m high) to the frame and post (5).

Once the gate is in position, nail on the outside a 35 x 38 mm bead (6) down the length of the post on either side of the gate opening to seal the 10 mm gaps. The bead should be set snug against the paling when the gate is closed.

TIMBER MEMBER SIZES

MEMBER	TIMBER SIZE (mm)	MEMBER	TIMBER SIZE (mm)
Corner & Gate Posts	125 x 100 x 2700	Plinth	125 x 38
Intermediate Posts	125 x 75 x 2700	Hardwood Palings	100 x 15 x 1800
Rails	75 x 38	Cypress Palings	100 x 25 x 1800
Cap Rails	100 x 38	Treated Pine Palings	100 x 25 x 1800

FIGURE 1 back FIGURE 2 back	FIGURE 7 back
FIGURE 3 back	FIGURE 8 back
FIGURE 4 back FIGURE 5 back	FIGURE 9 back
FIGURE 6 back	FIGURE 10 back

Information sourced from TRADAC Home Improvement Guide.
(Timber Research and Development Council)