Sunroom Part 3 – Floor Trusses or How to Replace a Floor Joist

Now that we have most (not all) of the foundation issues resolved,it’s time to start building something!

This is a long post because I wanted to show just how easy it is to replace those rotted out floor joists.

Materials arrive for the build. I specified open web trusses for the floor. You have three common choices for a wood floor system – dimensional lumber like 2X10″ floor joists, “I” joists which is a strandboard panel capped by 2X lumber on edge or the open web truss pictured. I selected these because I want to run all of the HVAC pipes and other mechanicals through the truss, not under, so that I have maximum space in the crawl area.

Here’s the start of setting the trusses. I used a carpentry crew for the rough build. I built the mudroom by myself and it took about two months – too much time to be without a roof on this structure. These guys will be here for a week and get it under roof.

The trusses are in place and the Solid Start rim boards are attached. Engineered rim boards were used because I had custom trusses made to a specific height to match the existing floor levels. This was to keep the sunroom’s floor on the same plane as the existing floor. You’ll see why that’s important (at least to me) in a latter post.

We’re finally going jackless! The front foundation was framed and the pour is underway.

Final pour for the front foundation is in. No more concrete trucks – for now.

Now we can turn our attention to those rotten and termite eaten floor joists. I’ve replaced 20 or so of these, so I did develop a system that seemed to work for me. You see in the above photo that the existing floor joists don’t line up with the new floor trusses. This is a bad thing, and a good thing. Bad because they don’t line up – good, because we have to replace them anyway.

To remove the joist just cut it 3/4 the way up towards the top of the floor joist from below. I will say that you don’t need to jack up the floor unless it’s on the exterior wall, but you must do one at a time from start to finish. If you do have excessive sagging a temporary support wall will do the trick.

Then get a small sledge and beat the crap out of it. Split the bottom off and continue to pound away. The red chalk lines you see in the picture is where the new joist will go.

Once you get to this stage you can pry the remaining wood away from the flooring nails.

Take your trusty angle grinder and grind them off flush to the floor. In this step it’s important that you take care not to burn your house down.

Use some PL glue in the proper place and get ready to beat the wood a little more.

Since I install these by myself it’s good to have a clamp on one end to apply pressure – this way when you’re working on the other end it won’t bounce out of position. Here the clamp is putting pressure to the new floor joist. You just work it by hammering the joist until it is upright.

This is how the floor trusses are tied to the new floor joists. They are both sitting on the new poured wall foundation. The old floor level will have a 1/2″ plywood overlay before the hardwood floors are installed. The trusses will only have a 3/4″ subfloor and the hardwood will be applied over that. This will give a seamless floor transition from the kitchen into the sunroom. Once the floor joists are in place I fasten construction screws through the floor into the joist  from the top every 4-6″ the length of the joists.

So we’ll just keep moving along. Stay with me – one day I’ll get to paint something.

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14 thoughts on “Sunroom Part 3 – Floor Trusses or How to Replace a Floor Joist

  1. “Get a small sledge and beat the crap out of it”…..yeah. Love it. Hope it was fun! Photos were great, and I learned something about floor joists! Congrats on the departure of the concrete trucks.

  2. Thanks Janet! Sometimes you just gotta bang on something. The good thing about rotten floor joists is that – they’re rotten! Makes beating them up a little easier. I’m sure the concrete trucks will be back sooner or later.

  3. The picture of the grinder is cool, but yes, I’d be worried about something catching on fire! Looks really great, good thing you were able to replace the termite damaged areas.

    • Bob – you would be the one to feel my pain – but it was pretty easy because of the basement – if it was a crawl space – man, that would be a different animal altogether.

  4. “In this step it’s important that you take care not to burn your house down”. So many times you don;\’t know how I struggled with wishing my house would burn down to when something happened where it could actually burn down and I was praying it doesn’t burn down. LOL

    I have to get the joists in my barn replaced. I don’t see all this happening though. I envy you.

    • Mz Jay –
      Don’t you know I’ve felt the same way. We just think we want to be out of our misery – when we get a chance we decide we can live with the pain after all. 🙂

    • You know, really none of it is too hard once you get in the middle of it. If you just think about it, it gives me a headache. But once you’re in – you have an accelerated learning curve. I’m also enjoying your blog as well.

  5. I used to work reconstruction 60 years ago when I was in college. Seeing all your projects brings back lots of memories. I want to thank you for liking my, “It’s Easy to Love Mud” on papermudandme.wordpress.com. I just started a new series on a boat my wife and I built. I know my remodeling work gave me the basics for building our boat. – Aloha – pjs.

    • Thanks so much Paul – I hope the memories were good ones! Being in the gallery business I just love pottery. Many years ago I was fascinated with the St. Ives potters and have collected Bernard Leach and his circle ever since. I’ll be looking for those boat posts!

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