Subfloor Ramps

I like to monitor the online social media flooring chat groups and other groups whose subjects interest me not just for my own purposes but because it is impossible to predict where and when helpful information might be gleaned and passed on to aid someone else. I’m often amazed by the wisdom filled nuggets offered so generously and without hesitation.

There’s a subreddit called r/flooring that has over 3000 redditors comprised of an eclectic make-up of consumers, professional floor guys and do-it-yourselfers. As a long-time consumer advocate I take particular interest in individuals that come forth with unique flooring challenges, problems and concerns that more-or-less has them stuck in the mud. Problem solving is what makes the floor covering trade interesting to me.

Recently a redditor described a subfloor anomaly they were dealing with in a one-story house where the subfloor was constructed at two different elevations. A ³/₄” difference from one section to another; created more likely on accident as opposed to some grand design. What this person wanted to achieve was to have a hardwood floor flow from the higher elevation to the lower elevation without a reducer or other type of transition. The original reddit thread is embedded directly below if you’d like to read the feedback.

Smooth Transitions

Over the course of four decades installing flooring I’ve built-up many subfloors in order to create smooth, flush transitions to other floor coverings. Thereby eliminating T-moldings and reducers so that the transition is not only aesthetically pleasing but is functional when put into service.

Transition moldings are designed to cover and accommodate both expansion gaps and changes in elevation. The challenge with doing away with these often expensive accessories means creating a system that allows different floors to meet at the same elevation, but more importantly permits the floors to move, as building materials are prone to do, both independently and without affecting the point of unison, or handshake if you will.

This situation is unique in that it isn’t about raising one type of floor covering to create a handshake with another entirely different type of floor covering. What needs to be accomplished in this circumstance is to integrate the higher subfloor into the lower subfloor by building a gradually sloping ramp, utilizing subfloor underlayment materials, a decent imagination and some floor guy ingenuity. The flatness of the ramp must meet industry accepted flatness tolerances outlined in the National Wood Floor Association (NWFA) and the flooring manufacturer’s installation guidelines.

The NWFA is the flooring industry’s default source for everything you need to know about wood flooring and it’s installation. The latest revised version of the NWFA installation guidelines are oddly silent about slope. The word isn’t so much as mentioned, though the word level is used twice in relation to both wood and concrete subfloors. Personally, I’m a bit surprised that within 180 pages of a very comprehensive guide, the slope of a subfloor isn’t given more attention. To be fair, I have seen individual specifications written by floor manufacturers who dictate that slope should not exceed one-inch in six feet. I don’t know if that qualifies as the industry standard but it seems like a reasonable expectation for wood flooring. Any steeper and we’d need to post a brake check sign.

Making the Grade

Installing a wood floor on a slope that measures at a 1.4% grade (Slope=Elevation/Distance)(1.4%=1/72*100) can be a risky proposition. While it’s most likely safe to do so, my personal preference is to have any change in elevation be undetectable to the naked foot. I know of floor installers that can easily detect minor subfloor irregularities simply by walking across the room in work boots. I don’t have that particular super power, thankfully my layman mortality makes me aware that traversing a 1.4% grade slope feels like I’m making an obvious change in elevation. What might the percentage grade of a ramp be that mere mortals find undetectable? Based on much trial and error I found that a quarter inch elevation in a three foot run is a good rule of thumb, a 0.7% grade or better. Strive to achieve better when possible.

Fortunately for the redditor, he came to the right place to ask if someone had experience doing something he had envisioned could possibly be done. I had recently built a ramp on a concrete subfloor that began at an elevation of approximately one inch above the later addition of a master bedroom suite. It’s bewildering as to why someone would construct an addition with a lower subfloor that met the existing subfloor in a common hall. To make matters worse the new addition was finished without ever raising the height of the subfloor to match the original. Some hokey ceramic tile floor patch job was implemented where the slabs met in the middle of the hall. There’s no accounting for taste but this was just wrong on so many levels.

If You Build it They Will Come

The creative solution here was to build a ramp that goes from point A to point B, starts at an elevation of about one inch and runs approximately sixteen feet down the length of the hallway. This would make for a 0.5% grade and in my experience an elevation change that would be undetectable under foot.

Ramps present a challenge to build because they utilize a lot of material that needs to be placed not only on an angle but must also adhere to strict subfloor flatness tolerances. This project required about 700 lbs. of underlayment, Mapei surface prep products were used. A combination of self-leveling cement (SLC), cement floor patch and cement skim coat material.

The SLC was applied first in increments using dams to pour sections at progressively lower elevations.

After building the foundation in a stair-step fashion a mason’s line and aluminium screed were used to measure required flatness before and after hand troweling in the other cementitious materials to achieve flatness specs. The slope was further lessened by back grinding the higher elevation concrete to a taper and extended the feather edge into the room another three feet bringing the grade down to 0.4%.

Embedded below is a YouTube slideshow to give you a visual aid of the steps that were taken to build the ramp. It’s not a high tech video but I think it will provide a good understanding on how integrating elevations can be accomplished. The master bedroom floor was to be the same floating cork plank floor that was installed throughout the remainder of the house.

With a Floor Guy's ingenuity
all things become possible.
 ~FindaFloorGuy 

Let me not neglect to mention that it’s important to adhere to floor manufacturer installation guidelines to maintain flooring warranties and more importantly the safety of the user. Especially when applying creative problem solving techniques.