Read more about when, why and how to use deck screws when building or repairing an outdoor deck Click Here!
Definition of a Deck Screw
Deck screws are specialized fasteners designed to resist corrosion in adverse outdoor environmental conditions. The deck screw should drive easily into the deck boards, and - once set - the head should lay smoothly against the deck surface.
Designed for easy and quick installation and outdoor use, deck screws are typically self-drilling, self-countersinking and either plated or coated in order to resist corrosion.
Deck screws are manufactured in a variety of lengths and widths as well as drive systems (Phillips and square drive being the most common). Phillips drive screws are easier to load onto the drive bit, but the phillips drive bit has a tendancy to cam out of the recess in the head of the screw. The square drive on the other hand may be slightly more difficult to load onto the drive bit, it will stay on better and not cam out as easily. For additional information about the square drive recess including dimensions and technical specifications, click here.
One of the most important features of deck screws is its point, designed to facilitiate easy installation. This sharp, narrow point permits fastening without pre-drilling a pilot hole (self tapping) which is ideal for soft deck wood like cedar. Some deck Screws also offer speciaized points to improve penetration of the fastener. For example the type 17 point offers a sharper point and a slot cut out of the point (shank slotted) that improves drilling and displaces the wood chips when being drilled into wood.
Deck screws fasten themselves into place because of their unique shank and thread design that offers an increased number of threads along the length of the screw. Consequently less effort is required to insert the screw eventhough it remains tightly in place and difficult to pull out.
For technical specifications of deck screw head and recess dimensions click here.
Material and Coating Properties - Corrosion Resistance
A vital deck screw characteristic is its resistance to corrosion. This is determined by the type of metal or coating used. For example, stainless steel and dacrotized screws are appropriate for exterior use on decks or fences because they resist corrosion exceptionally well and won't stain the lumber. A very clear and concise review on dacrotized screws can be found on Fastener Experts. Galvanized screws are also commonly available and offer corrosion resistance, but may cause staining with certain types of cedar. Unfortunately the new preservatives used in pressure treated lumber, primarily ACQ (Alkaline Copper Quaternary) and CBA (Copper Boron Azole) have been shown to accelerate the corrosion of the galvanized coating. For this reason stainless steel screws or dacrotized screws might be a safer choice.
Considerations for Use
There are a number of good reasons for choosing deck screws over nails. Deck screws typically offer more holding power than nails, can pull a bowed plank down flat better than nails, and elliminate damage that hammering often produces in the wood. They can also be removed much easier than nails and without damaging the wood if and when a deck board needs to be removed.
Whatever fastener you decide to use, a good rule of thumb for determining the proper length of fastener to use is: the fastener's penetration into the underlying material should be equal to or greater than twice the thickness of the actual deck board. So, for example, when installing 1-1/2" boards, you should use 3" to 3-1/2" fasteners.