Vinyl Waterproof Deck Membranes


Up until about the 1980's, it was nearly completely unheard of to install a balcony or deck overtop of the living space of the home. The biggest reason for this was the great difficulty in keeping the surface waterproof and properly drained so water could not penetrate the surface below.

Many solutions were tried to keep balcony and deck floor waterproof such as fiberglass flooring (like a boat hull), and various waterproof roll-on products, however the development of modern vinyl flooring products revolutionized options for home designers.

Vinyl flooring presented home designers with an affordable, and reasonably reliable waterproof surface which could allow balconies and decks to be built over interior spaces of the home. As a result, building designs by the late 1980's and into the early 2000's included new placements of decks and balconies around the home as well as typically more of them.

However, like all 'miracle' building products, there often comes a shadow side of these products. In the case of vinyl flooring, home inspectors need to watch for some important problems for clients:


Waterproofing is only effective if it can keep out 100% of the water trying to penetrate. A correctly installed vinyl system has sealed edges and should drain water away from the surface but like any plastic, vinyl will remain waterproof right up until it gets a hole in it. Deck and balcony surfaces can take a lot of abuse with people coming and going, BBQ's and furniture being dragged across, and even UV rays from the sun beating down on the material. One small hole in the 'waterproof' layer, and water will be able to penetrate and cause hidden damages below.

Vapour Barrier

Vinyl materials are a very good vapour barrier in addition to a moisture barrier. This means that humidity in the air cannot easily pass through the floor. This sounds like a good thing for a waterproof surface but in some cases, it can cause problems. A common area problems can be observed is when a deck is over a finished garage. The paint on the finished garage ceiling is typically a latex (plastic) paint and with a vinyl floor on the decking above, there are effectively two vapour barriers trapping humidity in the wood joists between the ceiling and the floor. In the humid seasons, some moisture gets into the hidden areas and it cannot escape fast enough to prevent molds and other hidden damages to grow.

For home inspectors, if you see 'organic growth' on the garage ceiling or walls (usually around windows and the garage doors where condensation occurs in the cooler areas), consider if there is a deck above that may have a vinyl floor helping trap in the moisture. Fixing this issue requires finding a way to ventilate the space between the two vapour barrier surfaces.

UV Rays

Even if a vinyl floor is perfectly installed and never walked on, it will still lose its waterproofing in time. UV rays from the sun make the flooring brittle and cause cracking which eventually can let in water, plus, it is more susceptible to damage from occupant activities. While many manufactures say this material can last up to 20 years, in high sun exposure areas and depending on install quality, it can require replacement in even as early as 6-8 years.

Door Sealant Plasticizers

Every now and then as a home inspector, I would come across a gummy black substance on an otherwise good looking vinyl deck surface. In hind sight, the balcony door had often also been replaced. When doors are installed in renovations, a sticky plastic membrane is applied at the bottom of the door system to the wood framing to help with waterproofing. It turns out that the plasticizers in vinyl deck materials are incompatible with this waterproofing door seal material and it will cause the door seal to partially liquify leaving the black tar-like material. There does not seem to be any easy way to clean this tar-like substance off the vinyl and its impact to the life span of the vinyl is unknown.

What Do Home Inspectors Need to Look for with Vinyl Flooring?

First, home inspection is a visual inspection so we are only able to look for visible clues of flooring damages. Home inspectors should be looking for:

  • Signs of cracks, holes, or other mechanical damages which may allow water through the system
  • Check seams in materials to ensure they are well attached (seams 'fish mouthing' is typically a sign of age and failure of the system)
  • Look at connections at walls, pillars, guardrails, and edges for appropriate design to resist water coming in at edges
  • Check for signs of correct slope and drainage
  • Observe material for general condition and deterioration

For home inspectors that carry a non-invasive moisture meter, it is possible to do some sample testing on the deck surface for signs of water penetration below. However, be cautious with interpreting readings as higher moisture levels are common in all exterior areas in unconditioned spaces during the rainy seasons. A moisture meter should be adding additional information to your other visual clues. 

Final Thoughts

Replacing vinyl flooring is a regular maintenance item for homeowners. This material is not very expensive and installation can be done quite quickly if there are no major hidden damage repairs needed or repairs needed to fix drainage or other problems. Home inspectors should identify any repairs needed or replacement that should be considered by clients with vinyl flooring systems while reminding clients that these systems are intended to be replaced during the home life cycle.

By James Bell - Owner Solid State Inspections Inc.