Should you leave gaps in subfloor?

Author: Mathilde Yost  |  Last update: Tuesday, August 5, 2025

To avoid buckling, subfloor panels should be spaced with a 1/8-inch gap at all edges and ends to provide room for naturally occurring expansion. Tongue-and-groove edges on many premium floor panels, such as Weyerhaeuser's Edge Gold® OSB panels, are designed to self-gap.

Is it OK to have gaps in subfloor?

A gap that small with a rigid product being installed on top will never be an issue. I've been installing floors for 20 years and have never ever filled gaps like that before install.

Should I seal seams in the subfloor?

If you are going over the subfloor with cement board and tile there is no reason to ``seal the seams'' of the subfloor. If you insist, just use the siliconzed latex for ease of application.

Should you leave a gap between plywood?

``APA recommends a 1/8-inch space between panel edge and end joints. Plywood and oriented strand board (OSB), like all wood products, will expand or shrink slightly with changes in moisture content. If the wood structural panels are tightly butted, there is no room for expansion and buckling can occur.''

Do you need to space a subfloor?

Don't beat the sheets together tightly, you must leave 1/8” gap at all sides of the panels to allow for swelling. The sledge makes it easy to “persuade” the sheets together, but don't hit it hard. Be very particular about that 1/8” gap. Just lightly tap the sheets together and leave 1/8” gap at all sides of the panel.

Should you FILL GAPS on a timber floor??

How tight should subfloor be?

To avoid buckling, subfloor panels should be spaced with a 1/8-inch gap at all edges and ends to provide room for naturally occurring expansion.

How much clearance does a subfloor need?

Subfloor Ground Clearance Guidelines

A minimum of 400mm clearance is required between the ground surface and the bottom of the bearer. On sloping sites, the clearance can reduce to 150mm within 2 meters of an external wall.

How much space should be between plywood subfloor?

Mistake #2: Not Leaving Proper Spacing

To avoid this, you must leave a proper expansion gap of 1/8” to 1/16” between the subfloor panels. This value may differ depending on the kind and quality of the material you decide on.

How much of a gap should you leave between OSB or plywood sheathing?

As ambient moisture changes, your OSB or plywood panels will expand and contract. When you butt the panels together tightly, there is no room for expansion and this can cause buckling in the panels. Leaving a 1/8-inch gap between panels allows them to expand and contract without buckling.

Does plywood floor need an expansion gap?

where boards abut a rigid upstand, a minimum 10mm expansion gap should be provided; for large areas of boarded floor, a wider expansion gap may be required at upstands, and intermediate expansion gaps of 2mm per linear metre of floor should be provided.

How do you seal a subfloor gap?

Use a backer rod or other infill material when sealing a gap larger than 1/4 inch with caulk. Many types of caulks and sealants will easily span and seal a 1/4-inch gap. Seal over the backer rod to establish the air seal. One-part spray foams can also span up to 3 inches to create an air seal.

Do I need a vapor barrier over wood subfloor?

When moisture penetrates your flooring, it can cause mold, mildew, and the potential for water damage. A moisture barrier helps control the water vapor's movement to help protect your floors. Therefore, if you're installing floors in an area that sees moisture, even a little, a vapor barrier is needed.

Does subfloor need expansion joints?

Yes, we always recommend an expansion joint of 5 mm on all sides so that your floor can expand and shrink as the temperature changes.

Should I seal seams in subfloor?

The gaps between boards of the subfloor represent pathways for air infiltration and sealing these gaps is tedious. If the budget allows, a spray foam approach provides a quick solution with the combined benefit of air sealing and insulation.

Does subfloor need to be perfectly level?

No subfloor is perfectly level, but any signs of unevenness and high or low spots must be remedied. Please follow these requirements: Subfloor unevenness cannot be greater than 3/16 of an inch over a 10-foot span or 1/8 inch over a 6-foot span.

Should I leave gaps between floorboards?

Gaps between floorboards act as a kind of insurance policy, a buffer zone that accommodates the wood's tendency to expand and contract. Without them, you risk a floor that ends up looking warped, uneven, or damaged over time.

Does it matter which side of OSB goes down?

OSB also has stamping that reads “This Side Down”. This directs the worker on the correct orientation of the board when installing. The side with the stamp is the smoother side. When installed smooth side down, the rough surface will then face up and give the worker traction for safety.

What holds up better in weather OSB or plywood?

In most cases, plywood is better. But, when panels are exposed to water and moisture, plywood is barely better than OSB. Both get damaged when exposed to water for long periods.

How much spacing is typically recommended at the edge joints of plywood subfloor?

APA recommends a 1/8-inch space between panel edge and end joints. Plywood and oriented strand board (OSB), like all wood products, will expand or shrink slightly with changes in moisture content. If the wood structural panels are tightly butted, there is no room for expansion and buckling can occur.

How far apart should OSB subfloor be spaced?

Improper Spacing Between Panels

Like any wood product, OSB will expand and contract after installation; without a small gap between panel ends, the expansion could cause buckling. Most manufacturers recommend 1/8 inch at panel ends and edges.

Is 1 2 inch plywood strong enough for subfloor?

The most common plywood thickness used as subflooring, half-inch plywood is a solid choice for most homes with standard-width flooring joists. Because of the difficulty and cost to replace subflooring, however, be sure that half-inch plywood is strong enough for your job before installing it.

Should I use 5 8 or 3 4 plywood for subfloor?

For traditional plywood flooring installations, where the plywood is directly attached to the subfloor, the recommended plywood flooring thickness typically ranges from 5/8-inch (15mm) to 3/4-inch (19mm). While 3/4-inch plywood is standard for most residential subfloors, certain conditions may require thicker plywood.

What are the standards for subflooring?

According to the National Wood Flooring Association's Installation Guidelines, wood subfloors need to be “flat, dry, sound, clean, and free of squeaks and any protruding nails or staples.” The guidelines state that the subfloor should not have height variations exceeding 3/16 of an inch over a 10-foot span.

Does a subfloor need ventilation?

Ground moisture rising into or entering the subfloor space can create a damp environment which encourages timber rot, fungus growth and the potential for termite activity. Subfloor ventilation increases air flow, reducing any damaging water vapour in the subfloor space.

How far apart should screws be in subfloor?

Subfloor. Screw spacing should be 6" o.c. at the boundaries and 12" o.c. in the field, assuming an unblocked diaphragm. For blocked diaphragms increase the numbers of screws by 15%.

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