Why Wood Expansion Gaps are Necessary when you are Installing Hardwood Floors and flooring

What is an expansion gap and is it really necessary to leave the recommended 3/4" gaps around the perimeter of the room to protect against hardwood floor expansion? First of all, an expansion gap is nothing more than a space that is left between the wood planks and the walls, columns, baseboards, thresholds, or any other spots that are part of your house. The reason why you need expansion gaps is because of how wood reacts with moisture and humidity as well as dryer climates. When the environment is humid, the wood will expand, absorbing the moisture in the air. When it is dry, the wood will contract or shrink. When expansion happens, you risk the possibility of buckled hardwood floors. When it contracts, cracking occurs.

Different types of hardwood will react differently. For example, solid hardwood flooring is going to contract and expand far more easily than engineered wood. How much it reacts to moisture or dryness will largely depend on the wood species you selected, the humidity in the room and finally, the cut of the hard wood.

That Quarter inch gap may be too much though....

How much of an expansion gap you will need will largely depend on the size of the room. In smaller rooms, such as the typical bedroom, you could leave as little as a 3/8" gap. On the other hand, if the rooms are large, like by a couple thousand square feet, a 3/4" gap would most likely be recommended. The larger the room, the more space will be needed in the case of expanding hardwood.

What is a Spine?

A spline is a long thin strip of wood that will go between planks. This "splice" will between two wood planks and you can face the wood grain in opposite directions. This will help with expansion issues for wood floors.

Wood Splines are also used as an alternative to T-molding when transitioning between rooms. Unlike the typical T-molding, adding a spline makes for a continuous flow from room to room because the spline is set between the wood on the groove side of the plank.

Typically, because expansion of the hardwood flooring will occur in the direction of the tongue, there are several things that you can do to offset expanding wood.

First of all, depending on the size of the room, you may want to start at the center to help offset initial expansion as the wood gets acclimated to the room.

You can also use slip tongues or wood splines to help prevent overexpansion. Slip tongues help to reverse the direction of expanding wood. Another option is to install the flooring with the tongue facing out in both directions, away from the center of the room.

Expansion on Glue Down Floors

In most cases, flooring that requires to be glued down is not used on solid hardwood (most are nailed down) and therefore expansion with glue down floors rarely happens because most glue down flooring uses engineered wood. However, if you have problems with expansion on glued down floors, then these tips may help you with your install. First all, while a slip tongue could be used, it isn't really necessary. Start your installation with the groove facing out. This will make for a cleaner install. Before you begin, you will want to figure out where the most logical place will be to start laying as this will help to minimize the areas in the home that will require you to back fill.

Engineered Wood and expansion and contraction

Unlike solid wood, engineered wood is not as likely to expand and if it does, the expansion won't be as intense. This is largely thanks to the fact that engineered hard wood is built in layers or plies. The ply layers help to limit the expanding properties, with the exception of the floating hardwood floors. With the floating floor, the entire floor will expand and contract as opposed to glued-down or nailed floors in which individual planks or rows will create the problem.

Moisture levels, the way the wood is cut and species all play a part in expanding and contracting wood...

As if this wasn't enough, how much a hardwood floor will expand and contract depends greatly on the specie of wood as well as the humidity in the environment of the home. And to make things even harder, depending on the species of wood, moisture level changes in the home may not factor in the equation at all. The x factor in this is how the timber was cut before it became hardwood. For example, hardwood today is typically cut flat or plain sawn. When it is cut this way, the expanding wood expands across the grain. In older homes, you will find three quarter sawn cuts and rift sawn floors. A quarter sawn cut typically will expand in a vertical direction as opposed to across the grain making the expansion gaps easier to plan. Quarter sawn hardwoods are the most stable but also the most expensive.

Moisture levels, the way the wood is cut and species all play a part in expanding and contracting wood

As if this wasn't enough, how much a hardwood floor will expand and contract depends greatly on the specie of wood as well as the humidity in the environment of the home. And to make things even harder, depending on the species of wood, moisture level changes in the home may not factor in the equation at all. The x factor in this is how the timber was cut before it became hardwood. For example, hardwood today is typically cut flat or plain sawn. When it is cut this way, the expanding wood expands across the grain. In older homes, you will find three quarter sawn cuts and rift sawn floors. A quarter sawn cut typically will expand in a vertical direction as opposed to across the grain making the expansion gaps easier to plan. Quarter sawn hardwoods are the most stable but also the most expensive.

Some wood species will expand more than others....

For instance Hickory hard wood will expand more than Oak. Bamboo flooring can be a better alternative in climates with higher humidity.

Heartwood will expand less

The most stable of all is hardwood made from the heart of the timber. This is largely due to the growth rooms in heartwood which are tighter and less likely to expand or contract. Most heartwood is clear grade and not used in homes as it is more expensive although there are fewer flaws in the wood.

How Wide Your Planks are will determine expansion

Another factor is how wide your wood planks are. The wider the width of the wood, the more likely it will expand. If you decide to go with wide width hardwood, you should probably go with straight grain hardwood.

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Comments 2 comments

paul thorogood 5 years ago

we have had a teak floor laid no problem with the floor it is a very large area but we have been left with a large gap round the edge aprox3/4 of an inch to large to hide with a skirting any sugestions as what to fill with

paul thorogood


mchid 4 years ago

If the wood is nailed down to a wooden subfloor (victorian floorboards plus plywood), then how can you see 2cm of expansion? Surely if the old subfloor doesn't expand (a 100yr old house and 18mm plywood won't expand??) then that would infer the nails magically move by 2cm. Pretty unlikely but am I the only person to spot this?? Confused!

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