Understanding the Foundation of Your Floors

Posted by Brett McCutcheon on May 4, 2019 9:22:00 AM

Foundation of Your Floors - Subfloors

When asked to describe a floor, most would comment on the surface visible to the eye. For example, they’d say, “It’s a wood floor” or “It’s a tile floor”. But the surface is the icing on the cake. The surface has very little impact on the soundness of the structure. It’s what’s below the surface that determines the longevity and stability of construction. Here we talk about what builds the foundation of your floor.


The lowest floor of a building is supported by the foundation, this may be wood or a concrete slab. If you’re on the first level, your first wooden structures are joists, which we’ll discuss in a moment. If you’re on a higher story, or there’s an in-ground basement, your joists are supported by beams, or “vertical supporting members”. These are the big supports that carry the weight of the floor to the foundation and can be metal or wood. The beam material and sizing are determined by the load to be carried. There are a variety of options for beams including wooden simple, flitch, box, or laminated and steel I-beams. Steel is favored when there is a longer span needed, but the ideal beam materials varies case by case.


Joists are horizontal structural members that span the open space between beams that transfer the load to the vertical beams. Typically, these are constructed of 2x4's, but there are a variety of arrangements based on the load bearing demands the floor will be under and the span they’ll need to cover. The three most commonly used styles are dimensional lumber, I-Joists, and open-web trusses.

While dimensional lumber has been used for a long time, it does create issues as it tends to have higher moisture content than its counterparts, leading to drying which can result in squeaks, unevenness, and ultimately call backs. I-joists do a great job of incorporating sustainable materials via the OSB component but can add complications for duct work. Finally, the open-web trusses are built with narrow dimensional lumber and metal webbing. They can be designed to work efficiently with duct work and use more available materials than dimensional lumber alone.


Now that we have support structures in place, it’s time to add a critical layer that joins your supporting members with your aesthetic ones – the subfloor. This is typically a plywood or OSB product that is laid in sheets across your joists. The keys to quality subfloor installation are laid out thoroughly in our post How to Reduce Callbacks and Costs for Subfloor Installations. But, the most important takeaway is that the bond between joist and subfloor must be secure to avoid most common flooring issues.

We suggest using a fastener designed for the job—SubLoc® PRO SCRAIL® from FASCO America®. These combination fasteners are applied with force and precision using a pneumatic gun. They go in like a nail but with the holding power of a screw. The SubLoc® PRO SCRAIL® was developed to avoid subfloor squeaks. The upper threads grab into the deck board and prevent micro movement of the wood even in the event of wood shrinkage. The aggressive double threads are designed for squeak-less floors because they prevent board movement that can lead to unwanted noises.

Construct your floors right the first time.

By gaining a thorough understanding of the elements that support your flooring, you can understand how to build ones that last. A great floor is never just the surface you see, but the foundational elements supporting it that make it last. We understand quality and produce the tools and the fasteners that can help you get the quality results you want.

Download the Whitepaper: 3 Steps to Ensure a Squeakless Floor

Topics: Deck Fasteners, invisideck


10% Discount on Your First SCRAIL® Fastener Order

SCRAIL®, Fast like a Nail, Strong like a Screw, are incredibly versatile collated fasteners that can be driven with a pneumatic nailer at a rate twice as fast as collated screws and eight times faster than bulk screws. You can rely upon SCRAIL® fasteners to hold strong, without callbacks to fix a squeak or a nail pop.

Give SCRAIL® a try, and enjoy 10% off your first order.

  • Use SCRAIL® almost anywhere ordinary screws are used
  • Save time and labor costs 
  • Twice as fast as collated screws, eight times faster than bulk screws
  • Easily adjusted, quickly removed
  • Dramatically increased holding power vs. nails
  • Making projects easier since 1998

Subscribe to this blog

Recent Posts