Can Regular Carbon Steel Screws be Used in Sheltered, Outdoor Applications?

Regular ASSY® carbon steel screws are intended for use in dry service conditions only, while corrosion-free ASSY® A2 stainless steel screws are suitable for wet service conditions.
Normal over Regular ASSY® carbon steel screws are intended for use in dry service conditions only, while corrosion-free ASSY® A2 stainless steel screws are suitable for wet service conditions. Dry service conditions are met when the average equilibrium moisture content of wood remains below 15% over a year without exceeding 19% at any given time. For the majority of regions in Canada and the USA, (especially inland), timber used for sheltered outdoor applications generally meets these criteria. The wood must be protected from direct wetting and be allowed to dry effectively in case of accidental wetting.
Even in sheltered outdoor applications, wind-driven rain, splashing, or poor air circulation leading to high moisture content in the air may cause corrosion issues.  Additionally, a location such as the underside of a bridge may be initially protected from direct wetting, but cracks formed in the deck over the service life of the structure may allow rainwater to penetrate through later on. Engineering judgment and careful consideration of both the surrounding conditions and structural detailing is required when specifying screw types.

Revised December 20, 2018


Relevant Technical Resources

Gallery moisture content changes stress predictions cover Timber Moisture Content Changes and Associated Stress Predictions on Structural Wood Screws

Products Covered in this Article

Gallery eco a2 ASSY Eco Stainless Steel
Gallery kombi a2 ASSY Kombi Stainless Steel
Gallery sk a2 ASSY SK Stainless Steel

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