Rising moisture is a huge issue for many people.  If you’re planning to install either a solid wood or engineered wood floor, one of the most important preparatory actions you need to take is to measure the moisture in your sub floor. There is a whole host of ways that you can do this yourself, or if you choose to get the professionals in, they’ll do it for you.  If you do it yourself, you need to be confident that you have achieved an accurate reading.

In the ideal world, the moisture content of your sub floor should be 2% or less.  The importance of getting this part of your installation process right can’t be stressed enough.  At the end of the day, you can kid yourself that you don’t have a damp issue and forge ahead and install your floor if you want.  However, there’s no getting away from the fact that if you do this, then sooner or later, the problem is going to raise its ugly head and potentially cause significant problems.

So, in short, if there is significant moisture in your sub floor you owe it to yourself to take the right course of action before installing your new wood floor.  There are two key remedial actions that are commonly used in a rising moisture situation and they are vapour barriers and damp proof membranes.  There is much confusion between the purposes and pros and cons of each option, so in this article, we’ll explain the differences between the two and how they might be used.

Damp Proof Membranes (DPMs)


A Damp Proof Membrane or DPM is a waterproof barrier that’s introduced between your sub floor and your wood floor.  Effectively a thick plastic sheet, a damp proof membrane (DPM) is used to create a barrier between a concrete (or screed) subfloor and a wood floor.  This barrier is intended to stop moisture passing from one to the other.

Damp proof membranes (DPMs) can be used to help resolve damp issues that already exist or as a preventative measure to avoid damp or moisture problems in the future.  The thickness and quality of the DPM you choose will affect how efficient it is and how long it will last.  Commonly used in the foundations of new builds, it is only reasonable to accept and expect that DPMs have a limited lifespan.  That said, this way of blocking moisture should be effective for a lengthy period.

Vapour Barriers


A vapour barrier is a damp proofing product that is attached to a wood floor underlay and is intended to reduce the passage of moisture.  It is important to state that vapour barriers are not Damp Proof Membranes and shouldn’t be considered as such.  Although vapour barriers may make appealing claims, it’s well worth remembering that they will only be effective in situations where moisture levels are slight.

How Do You Choose?

When you know the moisture level of your sub floor you’ll be better equipped to decide the best way ahead.  However, it is also important to think about your installation method when it comes to choosing the right way to keep moisture at bay.  Although it sounds obvious, many people forget that if they choose a moisture barrier of any sort and then choose a nail-down or staple-down installation, they could be undoing all their hard work and investment.

If you imagine the setting; you’re nailing down or stapling down your boards directly on top of your moisture barrier.  What are you doing?  You’re effectively creating a sieve structure in the moisture barrier you’ve paid dearly for.  Each and every hole you make will create a route for the moisture to pass from your sub floor to your new wood floor.

As a result, if you’re going to opt for any form of moisture barrier together with a nail-down installation, it’s essential that you introduce a ply subfloor between the barrier and the floor boards that is sufficiently thick to make sure your nails or staples don’t come into contact with the barrier.


In order to choose the right way of blocking moisture from rising into your new wood floor, first and foremost, you need to know the extent of the problem you’re dealing with.  If you have a deep-rooted problem then there’s no doubt that a DPM, plus a vapour barrier will afford you the best protection.  However, if your moisture issue is hovering around the acceptable limits ie. less than 2%, it may well be that a vapour barrier alone will do the trick.

The very best advice we can give on this subject is “if in doubt”, either seek advice or take a belt and braces approach.  A wood floor is an investment for the long term and it would be a crying shame to shorten your investment’s life expectancy by ignoring a problem that you know exists.

If you’re in any doubt about the decisions you’re about to make for your wood floor, why not get in touch?  At Wood and Beyond we have a wealth of experience and expertise on hand to help you.