Decks: Building and Maintaining for Dependability

Decks are perfect for outdoor entertaining and also add value to homes by creating an extra living area. Approximately 6% of Australian homes have a deck¹ and those who don't have one - want one. So how do you ensure the quality and longevity of such a critical structure? Here is some information that can help save lives while also creating a structure that will last a lifetime.

A balcony collapse that caused injury to several people. (Photo courtesy of Archicentre)

With almost 2000 unsafe decks and balconies across Australia¹ (meaning that it is either in a bad state of repair or badly built), Australians should be ensuring that their deck isn't an accident waiting to happen.

"Apart from the possible injury or death to family members, home owners would be foolish to ignore the legal liability and damages claims which could arise from a collapsing deck which is proven to be in poor repair", commented Robert Caulfield, Managing Director of Archicentre.

While these potentially fatal situations could well be the result of poor DIY skills, builders need to be wary. Both builders and home owners need to consider the correct building and maintenance practices.

Selecting the right materials

The satisfactory performance and life expectancy of timber used in outdoor applications is dependent upon a number of factors including:

• The type and level of hazard to which the timber is exposed
• The durability of the timber
• The type and level of preservative treatment (if any)
• Protective coatings and supplementary preservatives - and their ongoing maintenance
• Corrosive resistance of metal fasteners

Inappropriate timbers are still being used for decks and balconies. Some timbers like Oregon and Victorian Ash should not be used in weather exposed applications (unless treated).

The use of treated softwood is becoming more popular as Hardwood availability diminishes, and as plantation softwoods are able to offer the large end sections required for structural components.

Carter Holt Harvey Woodproducts Australia Group is one of Australia's largest softwood timber suppliers and offers a range of outdoor plantation pine under the brand name Ironwood^®. Ironwood is preservative treated timber that is available in different hazard levels for different applications and purposes. Table 1 indicates the hazard ratings for Ironwood; these guidelines should also be adhered to when building outdoor structures with any treated timbers.

 View larger version of Hazard Table

Ironwood decking products include decking boards and structural components including joists, bearers and posts. These products are available in the appropriate hazard class for the application and in a range of sizes and lengths.

Reed up or down?

There is much debate amongst builders and in the timber industry whether the reeded side of the decking board should be face up or face down.

Carter Holt Harvey Woodproducts Australia Group recommends the reeded surface be face down to create a way for moisture to escape between the board and joist. However, if the boards are already installed reeded face up, be sure not to allow water or dirt to sit in-between the grooves as this may promote mould and reduce the lifespan of the boards.

Protecting timber

People want to see their deck last a lifetime. However, little is generally done during the building stage to ensure that the timber is adequately protected and sealed. All timber, no matter the species, will crack and turn grey if it is not protected with a finish or sealant. While Ironwood will not rot, it will weather like all timbers.

The application of a quality Decking oil / Stain will help to maintain the surface and appearance of timber in outdoor areas. Ideally coat all timber with one application before assembly to ensure complete coverage. Decking boards should be coated on all four sides before installation, as painting of the underside of the deck is particularly difficult after construction.

Additional coats can be applied to the finished job as required. Be sure to coat your deck in line with the manufacturer's recommendations. When it comes to painting Ironwood there is a variety of options available, your local paint retailer can offer advice on available products.

Supplementary treatments

When timber is preservative treated, the treatment may not penetrate right into the middle of the stick. Sawn timber has two key characteristics, Sapwood which is quite absorbent and easily treated, and Heartwood which is denser and not easily treated. This means that when a stick is cut, planed or notched there is likely to be a break in the envelope of treatment. This creates a pathway for moisture to get into the timber and make it vulnerable to rot.

For ultimate protection of treated timber it is recommended that all cuts in the timber must be resealed with a preservative before assembly.

There are a range of treatments available from timber and paint outlets. These range from brush on types to spray cans.

Water

Application of a quality water repellant (available in a prime, clear and stains), stain or paint will help minimize the cycles of moisture take up and loss. This helps:

• Protect from the effects of weathering
• Reduce cracking, splitting and checking

When building details such as built-in timber planter boxes, be sure to consider adequate drainage and moisture control to avoid creating a moisture trap.

Correct fittings and connectors

Uncoated steel nails should never be used with treated timber, these react with the copper and corrode, creating weak spots in the structure and unsightly rust marks. Ironwood decks should always have hot-dipped galvanized or stainless steel fittings. When building within 500m of the sea, stainless steel fittings should always be used to ensure the long term life of the structure.

Here is some commonly agreed fitting advice:

• All nails should have a spiral or twist shank
• Bolts or screws should be used in most instances rather than nails
• Fittings used for untreated timbers are unsuitable
• Zinc coatings only have a moderate corrosion-resistance and are not recommended

If you have time, do some investigation to understand what fittings are best for the job, this is a very important part in maintaining the strength and life of the structure.

Avoiding termites

Termites tend to attack houses and structures from underground. Fortunately Ironwood is resistant to termite attack and guarantees decking products for 40 years against both termites and fungus.

Ask for a warranty

If a deck is well built and installed correctly, even at 5 years it should be as structurally sound as the day it was installed. Ironwood is perfect for outdoor conditions and it comes with a warranty against termites and fungal decay on all decking products, be sure to ask your timber merchant for a copy of the warranty.

Tips for building a top deck

1. Be sure you don't block off any termite barrier systems or ventilation points for the home when installing a deck.
2. Use correctly branded/certified treated pine - such as Ironwood.
3. Use hot dip galvanized fittings for treated pine, or if close to the sea use stainless steel fittings.
4. Use two spiral nails every joist/board connection
5. Finish or seal every board before installation to ensure maximum protection.
6. Cut ends should have a preservative sealant applied
7. Advise the owner to:
   a. Reapply finishes at regular intervals depending on finish type and degree of exposure.
   b. Annually inspect handrails and balustrades for connections and overall strength.
8. Connection of the deck to the supporting structure is critical and may require an engineer's certificate.

For more information on working with Ironwood check out the Ironwood working with and warranty information.

¹Archicentre