Should You Lay Plywood Over Plank Sub Floor?

When it comes to installing new wood flooring, the success of your project will depend to a large extent on the preparation.  Preparation takes into account making the right decisions when ordering your wood flooring, but also means making sure your sub floor is well prepared for receiving your new floor.

If you’ve got a plank sub floor and are looking to install a new wooden floor, then you’re highly to be debating the pros and cons of laying your new floor directly on the old plank sub floor, or introducing a layer of ply.  As any regular reader of this blog will know, if you’re laying a new wood floor over an old plank sub floor, there are several things you need to take into consideration.

The first is that the sub floor planks are stable, well fixed and in reasonable condition.  When it comes to laying your new boards over the old, there will be no scope for negotiation when it comes to direction ie.  you must lay the new boards perpendicular (at 90 degrees) to the old ones.

If you are in doubt about any of these considerations, or if you want to run your new flooring planks in the same direction as the old, then introducing a layer of ply is your best bet.  Here’s why:

Your existing boards more than likely run perpendicular to the joists in your home.  Unless you want to run your new planks perpendicular to the original boards, you have no option but to introduce a layer of ply.

The existing planks that make up your floor have strength that runs in one direction only, and it is now recognised that ideally, subfloors should have strength that runs in both directions.

Introducing a layer of ply will stop squeaks in your floor if it is done properly (see below).

Things to take into account when laying ply over plank subfloors:

Take time to make sure your existing planks are well secured in place.

Repair any broken planks.

Install a layer of at least ½” or preferably 5/8” ply over the existing planks.  This is particularly important if your old sub floor has lumps and bumps in it.  If you don’t respect this thickness of ply, then you’re highly likely to see rises and falls in your new flooring.   If at all possible, aim to sand your existing planks if they are showing significant signs of old glue or materials that need to be removed.

When you fix the ply to the old floor, you should avoid fixing it to the joists.  Working this way creates what is called a “slip” between the two flooring materials and is recommended.

By working this way, there will be no need to introduce any form of liner between the old planks and the ply.

Working with full sheets of ply will make your job easier and will improve the end result.

Like all wooden flooring products, it’s a good idea to acclimatise your plywood before laying it.

Once your ply is neatly in place, you’ll have a great surface on which to install your new floor.  The method of installation you choose will depend on a whole host of factors but will be one of these:  glue down, nail or staple down or floating.  Again, you can find an article debating the pros and cons of each method here.  Two of the most important things to bear in mind, whichever method you use are: to acclimatise your new flooring well and secondly to allow for expansion and contraction of your new flooring by leaving an expansion gap of 10-15mm around your whole room.

If you follow these general guidelines, you shouldn’t go wrong when installing your new wood flooring, but if you’d like specific help for your project, simply get in touch.  At Wood and Beyond, we have a great team, all of whom are passionate about wood flooring and we’ll happily share our years of experience with you if you’d like us to.

FAQ

Q: Should I lay my new wood floor directly on the old plank subfloor or introduce a layer of ply?

A: If you have doubts about the stability, condition, or direction of the old subfloor, or if you want to run your new flooring planks in the same direction as the old, it’s recommended to introduce a layer of ply over the plank subfloor.

Q: Why should I introduce a layer of ply over the plank subfloor?

A: Introducing a layer of ply is beneficial because it allows you to run your new planks in any direction, strengthens the subfloor in both directions, and helps eliminate squeaks if done properly.

Q: What should I consider when laying ply over plank subfloors?

A: When laying ply over plank subfloors, ensure that the existing planks are well secured and repair any broken ones. Use a layer of at least ½” or preferably 5/8″ ply, especially if the old subfloor has lumps or bumps. Avoid fixing the ply to the joists to create a “slip” between the flooring materials. Acclimatize the plywood before installation and work with full sheets for better results.

Q: How should I install my new wood flooring over the ply?

A: The method of installation depends on various factors, such as glue down, nail or staple down, or floating. Regardless of the method, remember to acclimatize the new flooring and leave an expansion gap of 10-15mm around the entire room to accommodate for expansion and contraction.

Q: Can I get specific help for my wood flooring installation project?

A: Yes, if you need specific help for your project, you can reach out to the team at Wood and Beyond. Their experienced team is passionate about wood flooring and can provide guidance based on years of experience.

Jonathan Sapir

Jonathan Sapir has over 17 years in the flooring industry. As an authority on flooring, he infuses his extensive knowledge and passion for quality products into every article. Jonathan's expertise helps readers make informed decisions for elegant and durable flooring solutions.