How to build decks with greater durability - material choices and construction techniques for longer lifespans
Deck building topics:
- Meeting setbacks and getting permits in Canada
- Creating a solid base structure: cement pillars (Sonotubes), screw piles, floating deck blocks
- Wood selection - pressure treated or hemlock base, cedar or composite decking
- Durability strategies for a longer lifespan
Permits and setbacks:
The first step of building a deck in Canada should be staying on the right side of the law. Find out where exactly your property line is so you know you meet the necessary setbacks. Depending on how meticulous your municipality is, you may need a permit and you may need to show drawings to get one. This is why you should first learn what the local setbacks and permit requirements are so you don't waste your time coming up with plans and applying for a permit that would be instantly refused. So the first step is to call your municipality to see what the limitations are and what they will require from you.
A solid base:
It is important to understand what will cause your deck to shift so you can build accordingly to avoid that; frost heave being the biggest concern. That is why you are normally advised to go 4 or 5 feet below ground level for your base. This will ensure the ground below your post does not freeze and heave.
All of this can be done by an ambitious DIYer; you can either dig a wide hole with a shovel, or rent a gas powered or hand posthole digger. Find out the recommended local depth to get below the frost line and start digging. Drop a Sonotube (cardboard form) in the hole, level it, back fill it, and start mixing concrete.
The one type of soil that may cause you grief and have you revisit your plans would be if you are building on clay. Clay will expand and shrink depending on its moisture content, so it isn't just about a potential heave over the winter; a deck built on clay can be susceptible to movement depending on rainfall, if it goes from very wet to very dry, or vice versa, anytime during the summer.
If you find bedrock when you dig, that is a good thing because that means your deck won't be going anywhere. Don't be tricked into thinking a big rock is bedrock, though if you hit one that seems extremely large and solid, the bottom of it could well be below the frost line in which case it should work fine.
If the term is unfamiliar, these are posts that are screwed into the ground to a suitable depth and left there as the structure. It works very well - you just need to be very accurate with placement and ensure that they are level. The top is not as big as a Sonotube so you don't have much wiggle room if they are installed out of square. Screw piles for decks can be purchased from building supply stores and they will have a hole for putting in a 2x4 for turning leverage. Those work pretty well unless there are a lot of rocks, in which case you are best to call a screw-pile contractor who drive them in with machines.
Floating deck blocks:
This is a fairly safe way to go about things, though keeping them perfectly level may require a bit of maintenance over time if there is any movement. Rather than going below the frost line, deck blocks sit directly on the ground so they are a bit more susceptible to movement, though if the ground is pretty consistent where you plan to build, it really shouldn't move much. The advantage of this is quite a savings in cost at the beginning, and a bit of movement won't do any harm since it isn't attached to the house.
Something to remember - the reason we dig down 4 or 5 feet is so the ground acts as insulation against frost heave. 'Insulation' insulates as well, so laying a rigid board down (foam or stone wool) below and around the deck block (underneath a layer of crushed stone) may reduce the chances of movement from frost heave.
Pressure treated wood is far less toxic than it was in years past, but it's still not as benign as natural wood. It could in theory last longer, along with mineral-based powder wood treatment, but applying durability measures with any type of wood is the only sure-fire way to extend the life span of deck structures.
Red cedar has natural anti-rot characteristics but comes with a pretty steep price tag, so in Eastern Canada, local white cedar from small mills is a much more affordable option. Hemlock (Eastern fir) or Douglas fir are very strong woods, and if you take steps to keep them dry they should last quite a long time.
Cedar is by far the most common natural untreated decking material, usually 1.25" thick. It can be left raw and will last a long time, but staining it will give it longer life and keep it from going grey while exposed to weather and UV rays.
Another option here is recycled plastic composite decking boards; they are not wood but rather plastic made to look like wood (we say that loosely because you would definitely be able to tell them apart in a police lineup).
Composite deck products are only offered as decking material, there is nothing we've found that can be used for building sub-structures. When price comparing you will find its quite a bit more expensive even than cedar, but its lifespan is likely longer than yours.
So there's even more reason to take some durability measures (which we will get to shortly) so you don't end up having the structure underneath rot while the decking itself is still quite functional. A galvanized sub-structure is an option worth looking into. We would also recommend using stainless steel screws, even coated deck screws can start to rust after a decade or so.
For maintenance you shouldn't need to do more than power wash it every few years to remove streaks and mildew. This is a great alternative to wood for building structures that will be continually saturated with water and moisture, such as docks or garden boxes.
Finally, there are tropical woods that are very durable, such as Ipe and Teak, but the market for these woods is causing a pretty big dent in tropical rainforests, which are unfortunately pretty important to all life forms on the planet. So we prefer to see people working with Canadian wood, there is no shortage of trees here. If you are going for exotic wood you could look into finding some that is FSC certified, which is wood that comes from sustainably managed forests.
Ten Tips for building better decks:
This is where we are hoping to tap into the collective brain power of all deck builders out there. Through trial and error and sharing ideas we can all up the quality of our builds, so if you have tips of your own to add please drop them on the comments section below.
1) Cover your joists: As long as wood can dry, it's okay for it to get a bit wet on occasion. The important thing to avoid is standing water. We are big fans of putting a drip edge on top of the joists before laying the decking. You can lay a thin sheet of metal on top first, or an elastomeric membrane, so water that falls through the decking gaps is not left standing on the top of the joists. When choosing that material and colour, be aware that it will probably be slightly visible between the gaps in boards.
2) Gaps are necessary between boards for drainage, but also so they don't build up debris. Too small a gap will let water flow until it clogs up with dirt, then it will hold moisture. Make sure the gaps are big enough that you can sweep it and the debris falls through. The thickness of the head of a deck screw should about do it.
Some builders install boards tight together for the aesthetic of tighter joints, running with the assumption that they will shrink, but that isn't always the case. If the wood you are working with is quite wet it may stay the same size or shrink a bit, but if the wood is dry it may actually expand when exposed to regular rainfalls.
3) Don't sink the screws too far into the decking or you will create tiny reservoirs where water will sit and soak in. Don't count on the screw to pull your board tight, put some weight on it if need be and leave screws flush with the top surface so the wood can better shed water.
4) Under-mounted deck fasteners: this one requires a bit more effort - a lot of people who choose this method seem to do so for the clean look of boards with no screws, in doing so it alleviates the problem of water damage at screw holes. To do this, a metal bracket is screwed to the side of the joist so you actually screw up into the bottom of the board and pull it down.
It's a great look, but it can be more time consuming. And the downside is that you don't have a lot of meat for the screws to hold unless you are using 2x4 or 2x6 decking. Take care not to drive screws too hard and strip the wood.
5) Double joists at the joints: there will always be a slight gap where two deck boards meet, allowing water to run down between them and sit on the top of the joist. A way to avoid this is to build your base with doubled joists with a gap between them. This takes more planning in design because you need to decide ahead of time where your joints will be and it takes a few more joists, but it can extend the life of your decking.
Double deck joists to create a gap for drainage © Ecohome
The cut ends of wood are at a lot more risk of absorbing water, and if you look at an older deck you can see that it is the joints in the decking that are pretty much always the first parts to go.
If you plan this well and order the right lengths of decking, you can reduce waste from cutting, and using longer lengths of decking can reduce the amount of double joists you'd need.
6) Diamond lath to keep out visitors: less than being about durability and more about quality of life, having raccoons or skunks set up a homestead under your deck is no fun; screwing diamond lath to the back of the deck joists and burying it should dissuade most animals.
7) When staining decks: if you are doing this in the autumn or the spring, first check the weather and the drying time of the stain. Written on the can should be the functional temperature range for application as well as how long it will take to dry. Make sure the weather isn't predicted to go below the recommended temperature within the listed drying time.
8) Wood grain: if you work with the growth rings of the wood facing up in a convex (rather than concave) direction, the grain will in theory repel water from the surface rather than create a cup that will withhold water. Shedding water is the key to extending deck life.
9) Deck-to wall connections: this is where most jobs go sour. Either build a deck that is completely independent of the building (with Sonotubes near the wall connection), or go through the proper steps to not create a gaping hole in your building envelope that welcomes water, air, and carpenter ants, just to name a few of the unwanted invasions.
Once the exterior cladding has been trimmed away at the joint with the deck, there should be metal drip cap tucked under the original weather barrier that carries water clean over the edge of the rim joist that is bolted into the wall. Squares of self-sealing elastomeric membrane can be placed behind the joist in contact with the wall in order to avoid wicking of water through the hole created by the bolt.
10) Last but not least: Don't forget to factor a 2% slope away from other structures in order to drain water in the right direction. The base structure should set the slope, and the decking will simply follow the same angle.