Sill Plates, Floor Joists, and Subfloor

Were you to label our tiny cabin with a catchy title, I believe you could use “The house without nails.” The nails that are used are oak pegs. Amazingly, the subframe only called for 4 oak pegs. It’s amazing how solid a structure can be when it’s designed a certain way. But before I get into the details of the subframe timbers, I’ll share with you my “termite barrier”.

Although the only certain effective prevention against termites is chemical warfare, I’ve taken some building efforts to avoid problems. I layed down a layer of aluminum flashing that separated the timbers from the concrete. On the outside of the wall, the flashing was lipped over so that if any termites were to create tunnels to the top of my wall, the lip on the flashing should discourage them from going any further. I’m not sure how incredibly effective it is, but I read it somewhere.

I’ve had countless people recommend to me that I should use a pressure treated sill plate underneath my timbers to discourage pests and avoid moisture damage. The reasons I didn’t go for that approach are two-fold: 1. Pressure treated lumber maintains it’s resistance to pests such as termites for up to 4 or 5 years. While 4 or 5 years of pest prevention is nice, I plan for my house to be standing much longer than 4 to 5 years. Unless I could pressure treat the lumber in place once the house was built, there wouldn’t be much use for the stuff. 2. These sill members should not be getting wet. If they are getting wet, I have a problem and no amount of pressure treating will keep wood from disintegrating over time. The best method for protecting these timbers is to keep them dry with proper flashing and siding techniques.

These timbers were also left unfinished. Since they were covered up by the floor and will be covered up from underneath with insulation, I didn’t see the point. The timbers for the upstairs frame will be finished on 3 sides.

Placing my timbers up on the wall and connecting them together was one heck of a task. If it weren’t for Pa’s tractor, some extra hands, and a very large sledge hammer, I doubt I would have made it very far. But the timbers made it to their respective spots slowly but surely and the joints actually fit. I was overly relieved to see how well they fit together.

Here’s proof that the whole thing came out almost dead level. I can’t believe I managed it.

The sill members along the outside edge are 8″ x 8″. On the long side of the house, they’re 20′ long and on the gable side they’re 16′ long. They are heavy. The floor joists are 4″ x 6″ and just over 15′ long. The floor joists taper to 4″ x 4″ where they meet the sill members.

Red oak has a decent resistance to decay from moisture, so I made sure that I used it on the sill plates and on a majority of the floor joists for better quality.

Next, I set out to put down a subfloor. I debated on whether to go with the tongue and groove stuff from lowes that come in 4′ x 8′ sheets but decided to go with rough cut lumber run at a 45 degree pattern. A friend of mine labelled me as a purist and I wanted to stick to that reputation. Plus these boards were just beautiful and I cut them myself on the sawmill about a year ago. They still have some drying yet to do but seemed pretty dry when I went to install them.

I screwed them down with decking screws and trimmed the edges when they were finished… Remember, I said it was the house without nails, not without screws.

I left openings where the posts drop in when the frame is put in place. I was sure to make the opening about a half inch oversize to give myself some wiggle room when I go to install them.

Once it was all said and done, I covered the entire floor with 2 layers of 6 mil plastic, a layer of tarp and then another layer of 6 mil plastic on top of that. Needless to say, there wasn’t a single leak when the rain came.

And here’s proof that I’m actually doing this work and not hiring it out. I apologize for the creepy-ness.

Next step, build the basement door, and work on the frame pieces over Winter to be installed in the Spring!


6 thoughts on “Sill Plates, Floor Joists, and Subfloor

  1. Nick December 22, 2015 / 9:40 pm

    Random technical question regarding the 8×8 sill plates….how were these attached to the concrete foundation walls?

    • jlough8788 December 23, 2015 / 4:22 pm

      Traditionally, the sill timbers were never attached to the foundation for multiple reasons.

      1. There wasn’t hardware to accommodate such a task.
      2. A timber frame is occasionally moved in its life to a new foundation. When folks would take them apart, the only thing they had to remove was the siding and the pegs.
      3. The sheer weight of these timbers are more than enough to keep them from moving. One 8×8 of oak weighs approximately 800 pounds. Compound that with many other timbers above them and you have a house that any amount strapping wouldn’t contribute to.

      I didn’t strap mine but that’s not to say you couldn’t. A simple large L-bracket on the inside face of the timber attaching to the top of the block would work fine, but it really would only serve to appease one’s own mind more than be effective.

      Hope that helps!

  2. mrchickadee April 21, 2016 / 1:52 am

    So have you found the 4X8 joist to be sufficient for your span? What were your cabin dimensions exactly? Looks like we are building a similar size house to yours this year and Im debating whether I need a support beam down the middle of 16′ joists, or not…went over to the forestry forum and someone told me i needed something more stout than a 6×8, which just seems silly…Id appreciate your thoughts on the matter!

    • jlough8788 April 21, 2016 / 12:34 pm

      Great comment and I had wanted to make an update on this matter. My floor joists were actually 4″ x 6″ of oak and poplar (I should have used specifically oak). IF I had done 4″ x 8″, I believe that would have been sufficient. However, there was a decent bit of bounce in the floor once everything was loaded on it.

      I ran a large double laminated 2×8 beam running the length of the house (16′ in the basement) supported by a metal jack post. After that the floor has been solid enough for many a dancing jig after successful projects. This post here has a picture of the basement with the support beam in place:

      I think you would be fine with 4″ x 8″ joists of oak and I think I remember seeing an engineering chart stating that it would suffice. I think my 4″ x 6″ joists didn’t make the cut (no pun intended) when it came to that chart. The 6″ x 8″ thing seems like ridiculous overkill, but then again, too stout never hurt anything but a bad back.

      The dimensions of the timber frame section of our house, not including the loft on the front is 16 x 20. With the loft, it is 16 x 28. Hope this helps!

      • mrchickadee May 4, 2016 / 12:42 am

        Thanks for replying, I was wandering about this, and think I will add a central “summer” type beam down the middle of the bottom floor.

      • jlough8788 May 6, 2016 / 12:10 pm

        Summer beam is the term I was looking for. Good luck!

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