Best Practices

The asphalt shingles system “Best Practice”

Here is a guide to the best practice when building an asphalt shingle roof.

We generally start with the roof frame “rafters” spaced at 600mm centres. On top of this we install 12mm A-Bond Tongue & Groove Structural Plywood conforming to Australian Standards – stamped (AS/NZS 2269). To install Plywood you will need to follow the manufacturers guidelines but generally speaking 70mm long shank framing nails spaced every 150mm will suffice. This is also acceptable in high wind zone areas.

I cannot stress the importance of using Australian stamped plywood as it has passed the test for moisture content suitable for Australian conditions. Most imported plywood will equalise to our conditions and may shrink, buckle and warp – when this happens you will need to replace the entire roof.

You then staple down #15 Asphalt Saturated Felt Paper to the entire roof. Asphalt shingle underlayment is typically dry felt that is impregnated with an asphalt saturant. We use underlayment for the following reasons.

• Resins are produced by plywood decking. Asphalt-saturated felt protects shingles from the resins that may be released.
• Asphalt-saturated felts protect decking material from wind-driven rain.
• To validate warranties, many manufacturer’s require the use of asphalt-saturated felts on a wood deck.
• The use of asphalt-saturated felt reduces “picture framing.” According to CASMA (1992), picture framing is the visible outline of deck panels caused by irregularities in roof decking thicknesses.
• To obtain a Class A fire resistance rating, asphalt-saturated felts should be used underneath shingles reinforced with glass fiber felt.
• The underlayment should conform with No. 15 / ASTM D226 Type 1 No. 15 felt.
• See CASMA Technical Bulletin No. 3 (1992) or ARMA Form No. 219-RR-89 (1993) for more information.

We generally line the valleys with “IKO Armorguard” which is a rubberized membrane. This gives additional protection at the roofs most venerable area.

Colorbond drip edge at the fascia and barge is installed. At the fascia (bottom edge of the plywood) this should extend at lease 100mm up the roof. This flashing is used to protect the bottom edge of the plywood from water damage. The barge flashing protects the plywood from water damage and also protects the roof from any wind driven rain.

The asphalt roof shingles are then installed with galvanised clout nails (10mm head and at least 25mm long shank) the nail should penetrate through the plywood by 2-3mm.

It is the ARMA’s (Asphalt Roofing Manufacturers Association) position that nails are the preferred method of fastening asphalt shingles due to their superior holding strength. The following fastening tips apply to most IKO shingles; (check specific product application instructions for further information):

• A minimum of four fasteners per shingle are used.
• Correctly place and position fasteners below the sealant strip, but above the cut-out on three tab shingles, and in the nail line on laminated shingles.
• The fasteners must be straight and flush with the surface of the shingle, not sunk into the shingle or sticking up at any point.
• Make sure there is correct penetration of the deck as specified by ARMA and the NRCA.

See article or ARMA Form No. 221-RR-93 (1994) for more information.

Probably the most important aspect is proper ventilation for the roof. The amount of ventilation needed is determined by the size and design of the roof. For roof and attic spaces above an insulated ceiling, the vent ratio is one square metre of net free ventilating area/300 square metres. For low slope roofs or roofs with cathedral ceilings the vent ratio is one square metre/150 square metres.

See CASMA Technical Bulletin No. 1 (1992) or ARMA Form No. 209-RR-86 (1994) for more information.

The best form of ventilation is a premium ridge vent. The vent we use is the Lomanco Premium Ridge Line Vent. For full details click here. Here is an article from the ARMA on Ventilation.

The correct use of ventilation plays a number of rolls.

• It regulates the air temperature inside the roof area keeping it the same as the outside air temperature or at least +/- 10 degrees.
• In attics which are not properly vented, moisture is also created by simple condensation. The air inside an improperly vented attic will be warmer than the air outside. When this warmer, moist air comes in contact with the colder roof sheathing condensation will occur. In effect, it can actually “rain” in your attic.
• Stops buckling of roofing shingles due to deck movement.
• Rotting of Plywood.
• Stops premature failure of the roofing including blistering.

I have provided a lot of information to take in however if you fail to follow these steps you might find yourself without a manufacturer’s warranty.