Thinking About Joists

One of the challenges I’ve been mulling over in my brain for quite some time is how we’ll tackle the floor joists. The good news is that we’re not there yet, so we have time to figure it out. First, let me explain a bit how the floors are built and why I’m thinking about it.

Balloon Framing

The house is balloon construction. If you don’t know what that is, check out the link for details, but in short we have studs running the entire height of the house. A ribbon is notched into the inside perimeter of the studs at the height of the floor joists, which then rest on top of it and are nailed to the studs. The floor joists for the first floor are 2x10s, so they’re decently strong and the floor is nice and stable. The second floor, on the other hand, has 2x6s. Being so much smaller means two things: the floor has a lot of bounce (known in engineering terms as deflection) and it can’t span as far. Both of those are issues because we want to make the floor plan on the first floor more open and we want to have stable floors upstairs, especially since we’re planning a second floor laundry.

So what to do about it? Well there are a few options. The simplest option is to sister additional 2×6 joists to the existing ones. That means we can’t increase any spans, though, so we’d need to define a floor plans that is either more enclosed or has support beams below the joists to carry the load. I’m not a fan of support beams visually, but we could integrate them into a coffered ceiling or archways between rooms.

A more involved option is to add new joists that are either I Joists or Open Web Trusses. These could be installed throughout the floor or only in areas with larger spans. They would lower the ceiling by at least six inches. The I Joists in particular are capable of spanning the full width of the house with minimal deflection. Installing these isn’t a simple matter, though. For one, we’d have to do a lot of load calculations to ensure the structure was stable. More importantly, we’d have to cut out the walls that were still holding up the existing floor joists in order to fit the new, taller joists in. We’d also have to build new framing structure into the outside walls to carry the increased load to the foundation. All of this gets very complicated and guarantees we have to bring in a structural engineer.

This is pushing me back toward the simpler option, but there’s an added wrinkle: HVAC. Even if we have radiant floor heating, we still need ducts for air conditioning or even just air circulation. We want to have a whole house air filter, especially once we’ve sealed all the walls, windows, and doors up tight. Without forced air heat, there still needs to be a system to bring in fresh air from outside or at least filter the indoor air. How we run the duct work depends on the system we get. One of the reasons we’re looking at high velocity forced air is that it uses smaller diameter ducts, but even so we need a main trunk, plus we can’t exactly cut big holes through the 2x6s when they’re already so small.

The plan is to run the HVAC from above and below, meaning the first floor ducts will be in the basement and the second floor ducts will be in the attic. Unfortunately, with the ceiling in the basement being so low I can’t help but think this isn’t the best plan. We hope to lower the basement floor to gain some inches, but even so it won’t be all that high. I’m wondering if some creative ceiling designs might solve these problems. If we can use a combination of coffers in the living room and strategically placed bulkheads in the kitchen and dining room, we may be able to work out a solution that lets us keep the joist height as it is and still reinforce the floor.