More than a few owners of old homes have called me concerned about the floors in their old house. They’re shocked to discover that their house doesn’t have a subfloor. They’re thinking someone remuddled the place and somehow removed the subfloor or maybe termites ate the whole thing clear away.
I’ve gotten the question so often that I felt it was high time I wrote a post about it to explain this phenomenon to folks to assuage their fears that their house is about to fall apart.
Prior to WWII most homes were built with a crawlspace or basement foundation. The technique of a monolithic concrete foundation was still a few years away from catching on during the post war building boom.
In these days of pier and beam or stem wall foundations the common technique was to build floor joists from rough lumber supported by a series of masonry piers. Then over top of those floors joists 1×4 to 1×8 sized subfloor was installed (usually diagonally to provide additional racking support). These boards served as the subfloor prior to the integration of the plywood we use today.
These same 1×4, 1×6, 1×8 boards were also commonly used on the exterior walls as sheathing to strengthen and protect the frame. Though depending on your region this step was often skipped completely with the wood siding being installed directly onto the wall framing.
Builders have always been looking for ways to build faster and cheaper, and the old days were no exception. Skipping the wall sheathing created a big savings with only the small downside of a slightly less well insulated and minimally less sturdy structure. At the time the solid wood siding being installed was much stronger than the options we use today and that strengthened the structure sufficiently.
This same mentality was transposed to the subfloor in homes where historic builders would install the finish floor directly onto the floor joists. Then the walls of the home were built and installed on top of that finish floor.
You may think this is shoddy craftsmanship, but in the days of solid 1″ thick tongue and groove heart-pine flooring it was hardly thought to be a problem. The tongue and groove design made the missing subfloor design doable since it effectively blocked air and bugs from entering the home and provided enough strength to support the rest of the structure.
How to Tell If You Have No Subfloor
There are some sure fire signs that your house was built with no subfloor. There are regional differences, but down here in the south I find that homes without subfloors are most commonly smaller homes in historically working-class neighborhoods where budget was a large concern for the structure of the home.
For us in the south that means heart-pine floors rather than the more expensive red or white oak floors found in more affluent homes. The big giveaway is the joint pattern on the floor. If you see long floor boards with joints between boards that often line up in the same plane then you likely have a home with no subfloor. That indicates that the floor boards were nailed onto the floor joists rather than in a house where a subfloor exists which allowed the flooring installer to start and end boards anywhere they chose. Subfloor homes have a more random pattern to the joints placement of floor boards.
What to Do About a Missing Subfloor
First, let me encourage you to not freak out that your subfloor is missing. In a 100-year-old house this is not uncommon and shouldn’t be something you’re concerned about. There are a few things that you may want to thinking about differently if this is the case with your house.
Without a subfloor your floor is going to feel a lot colder in winter. In a crawlspace designed house, that’s not too difficult to fix. Grab some of your preferred insulation (I prefer mineral wool for subfloors) and install it below your floors in between the floor joists. You can use strapping or netting to hold it in place underneath the house.
Do not install spray foam insulation! For new construction I’m a fan of foam insulation, but to retrofit it into old houses it can cause a lot of problems, especially when you have what are likely loose tongue and groove joints on your flooring. You’re likely to get foam squeezing up and into your floors that will make a real mess of your finished floor.
If you need to replace damaged floor boards on a house with no subfloor the work is a bit more difficult. You’ll have to make sure that the boards being replaced are cut to a precise size so that they end on a joist. Also, any boards that run underneath a wall will be almost impossible to fully remove, so you’ll have to make cuts at the wall to get them out leaving a small chunk remaining underneath the wall to support it.
Other than these two small things, an old house with no subfloor should not be a problem for you. Don’t be concerned, don’t run for the hills and skip buying that dream bungalow if you find this to be the case. Just realize that you’re buying a unique style of historic house that comes from a different time before building codes mandated the design of our homes. The fact that it has lasted 100 or more years already means that it has stood the test of time and will continue to stand for decades more in all likelihood.
Founder & Editor-in-Chief
I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.