Tips for a stable and sustainable deck

Tips for a stable and sustainable deck

23 February, 2017

In our northern climate, building, extending or renovating a deck are tasks that follow very strict guidelines. Between freezing and thawing temperatures, wood can rise or subside and sometimes cause structural damage.

We’ve gathered top tips from real experts, certified “Réno-Maîtres” (Renovation Masters lit.), to getting it right first time round.

To begin with, if there’s no existing structure, the priority is to determine where the deck is to go:
“You have to map out the best location and check with the customer if he plans eventually to extend it, what kind of equipment he’s expecting it to support (e.g. spa, swimming pool, outdoor furniture), so you can plan for the required space” recommends Nicolas Girouard, owner of a construction and green-building firm ‘Les Projets de Nicolas’. “Also, check whether the deck is less than four feet from your neighbor’s property; city regulations could stipulate that you use non-flammable materials.”

Renovating a deck

Adding heavy machinery, extensions (e.g. solarium) or poor design could require stabilizing or reinforcing the structure. Billy Laberge, owner of ‘C.R. Authentique’, construction and deck renovation specialists, always tries to preserve the structure whenever possible (e.g. if the wood hasn’t decayed).

“Nevertheless, it’s crucial that the floor joists be at very least 2×8” he warns, “also, the maximum distance between joists has to be of 16 inches. If the distance is 24”, you can keep the joists that are sound but you’ll need to insert another joist between them.”

Foundations with screw-in piling

If the job consists of building a new deck or extending an existing once, all the experts we spoke to recommended the use of screw piles. For them, it’s simply the best option to rest the deck on a solid footing. In most cases, Billy Laberge uses screw piles. He offers no guarantee of stability to customers who insist on concrete pillars. He even goes as far as to require a liability waiver from those customers who choose that option.

Before proceeding, though, it’s in every contractor’s best interest to get in touch with the Info-Excavation service (or the appropriate local authority), who will advise if there are any underground networks of services, such as water, sewer pipes, gas, power or telecom lines that might be buried on the property.

To return to the subject of screw piles, this type of foundation offers many advantages. It’s fast and easy to install, doesn’t require unsightly excavation of your back yard and offers excellent, long lasting stability. It’s also quite affordable at around 170$ per screw, installation included. For a deck measuring 12 sq. feet, three of these screws would be amply sufficient. They can be installed by the contractor if he has the machinery or by undertakings such as Techno Pieux or Vistec that specialize in screw-pile installations. Construction firms such as Nicolas Girouard’s, thought they own the proper equipment, often rely on the services of firms like these because they save time and money, allowing him to free up his carpenters’ time to focus on their work.

Depending on the load that the deck’s foundation will need to support, there are four sizes of screw (P1 through P4), whose diameters range from 1.7/8 to 5in. The P1 alone can bear a load of 6800 pounds, P2, a load of 9600 pounds (enough to support the weight of a solarium), P3, 23000 pounds and the P4 29000 pounds; these last two are designed for heavy residential use, e.g. two floors.

Nicolas has some tips on how to obtain the best results from screw piles. The best time to do it is when the ground isn’t frozen. This is because the screw needs to reach a depth that’s below the soil that’s going to freeze in winter. This depth can vary according to the latitude, but in Montreal, the ground needs to be excavated to a depth of at least 4 ½ feet.

Avoid working on fresh backfill, and if this cannot be avoided, you have to keep digging until you reach solid ground. As a “green constructor” Nicolas also likes the screw piles’ minimal environmental impact compared to pillars made with sonotubes. The latter require significant excavation, pouring concrete (an environmentally unfriendly material at best), and the use of heavier machinery, which pollutes more.

Cardboard/polywoven tube foundations (sonotubes)

Jonathan Racine, owner of Habitations Jaro, believes that sonotubes still have the edge over other types of foundations when dealing with very unstable or damp soil. Like screw piles, they require excavation to 4 ½ feet, or until you reach a solid base. The hole needs to be at least 2 ft in diameter to accommodate a plastic mold called a footing mold. This conical mold has a height and width of 2 ft. Its shape is narrower at the top to allow the sonotube casing to stand upright once inserted. Once the footing mold and the sonotubes are properly installed, liquid concrete is poured down the tube, the wider shape at the bottom guaranteeing the pillar a stable foundation.

Here are a few more tips on the use of sonotubes :

  • Ensure that the concrete pillars are at least 8 inches above ground level.
  • Add reinforcing rods to the concrete to maximize its strength.
  • Use concrete that offers a good compression resistance (25 to 32 MPa) to increase its resistance to freeze/thaw cycles.
  • The excavation needed for installing concrete pillars requires the use of specialized machinery as well as pouring concrete. Jonathan Racine estimates that “the cost of such a project could reach 1 500 $ for three Sonotube piles”.


Dek-Block Foundations

Alternatively, there’s the Dek-Block; a square cement block in which you can insert pillars that support the deck. Each block serves as a foundation.
Although this is an extremely cheap solution (5$ per unit), Jonathan Racine doesn’t recommend it. The Dek-Blok doesn’t do enough to ensure the deck’s stability. At the first freeze/thaw cycle or ground subsidence, there is a risk it could shift and make the whole structure unstable.

Securely fixing a deck

Once the pillars have been properly installed, it’s important to secure the deck to the building. To do this, a galvanized steel bracket must be set in the concrete foundation with anchors for concrete. A 4½ by 8 beam is inserted into the bracket, secured with screws. During the next step, the joists are fixed to the beam with joist hangers. You must never fix the joists directly to the building’s foundation or brickwork.

Afterwards, the patio’s decking can be made from a number of materials (glass fibre, treated wood, cedar, hemlock spruce, composite materials). Nicolas Girouard favors cedar for exterior siding and hemlock spruce for the structure. This last type of timber is less expensive than red cedar and is capable of withstanding decay. “It’s more or less the same price as treated wood, but it’s better for the environment. Treated wood is only surface-resistant. If it’s not treated again with every bump and scratch, it will rot very quickly.”

Another strong contender, Nicolas Girouard likes composite materials (made from recycled plastic and wood fibres), a long-lasting option that doesn’t require any maintenance, it is however, more expensive: 8 $ per sq. ft as opposed to 1.75 $ for treated wood and 3 $ for cedar.

Billy Laberge only works with factory-made engineering fibreglass. It mimics real wood and comes in six base colors. In reality through, there’s a wide selection of over 5 000 colours to choose from.
To secure the flooring, it’s more aesthetic to do so from below, if there’s enough space. This has the added benefit of avoiding corrosion of the fastenings. If it isn’t feasible, the CAMO hidden deck fastening system allows the user to secure the deck’s flooring to the joists. The screws are practically invisible since they are inserted at an angle into the beams with a drill. The Tiger Claw system offers the same advantage.

Constructing a ground/paved terrace

When constructing this type of terrace, first lay a geotextile membrane to prevent weeds growing through. Then spread a four-inch layer of ¾ inch gravel. The final step consists of laying patio blocks.
If the terrace includes a wooden floor, it will be raised slightly above ground level to allow air circulation between the soil and the deck. This will help prevent the beams degrading through moisture. You must also plan for lateral ventilation covered by a wire mesh to prevent small animals getting inside.

This wraps up our review of the different decking options available out there, whether starting from scratch or renovating, whether above ground or at ground level. The most important thing to keep in mind is to follow each installation procedure to the letter to guarantee yourself peace of mind, stability and durability.

Reference: APCHQ, Magazine Québec Habitation, June 2016

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