Are the TJIs in trouble? Deflection Sets In.
“It’s just par for the course” they say. I never realized that building on a golf course would share so many similarities with the game itself. As soon as we start moving again on the project, not only do we get a thunderstorm “when it rains it pours”, but there are concerns with the TJIs that support the second floor.
This morning started with a builder meeting to go over some modifications to the master suite - primarily extending the bedroom wall by a foot. When I walked the space on Friday I just felt the bedroom was too tight and extending the wall into the master closet, bath and laundry room would be the right call to make. The framers were onsite so the changes shouldn’t be too big of an issue. I snapped some pictures of the progress and headed into the office.
Shortly after getting to work an email arrived from our builder expressing some concerns with the span of the first floor ceiling joists (16″ TJIs).
I was talking with my framer and he mentioned a few items that we need to look at and perhaps address.
1. The ceiling joists in the family room appear to be overspanned, per his opinion. I wouldn’t worry about this so much, until we realized that it is carrying the entire second floor load and the roof system as well. The second floor ceiling joists have a girder running down the center to support them, which sits directly above the middle of the 1st floor ceiling joists.
2. We’ve already got 3/8″ deflection (sagging) in the middle of the 1st floor ceiling joists. Some deflection is going to be natural, but we haven’t added furniture and the roof yet.
{Reference to Structural Engineer on the project removed}. Chances are, the spans are adequate, but I don’t want to take any chances. I highly recommend that we get a field engineer to look at the spans and load calculations just to be safe. If we have to add a few girders or LVL’s, it’s a whole lot cheaper now than later.
I’m not concerned or overly worried. I just want to make absolutely sure that we’re either adequate with framing, or preferentially, a little over engineered. Let me know what you think. A visit from my engineer is going to cost XX bucks to have him look at a few things.
Fair enough. I appreciate the fact that concerns are communicated to the team and possible solutions are offered up. Everyone seems to agree that if the framing is undersized then we should do something about it sooner rather than later. Our architect offers to forward these concerns onto the structural engineer (on the plans) for comments and suggests we wait to hear back from him first. A few hours pass and our architect replies back with some details.
I just got off the phone with my engineer and he said that if the 14” TJI 560 or the 16” TJI 230 were installed as shown on the framing plans there should be no cause for concern. They are designed for L/480 deflection which means that they should have up to .26” deflection under dead load conditions and up to .52” deflection under live loading conditions (dead load is just the weight of the structure and live load is that of furniture and people,etc). He also said the joists are designed to span up to 24’-1” and maintain this deflection.
1. I have not measured the as-built dimensions, but the span should be 23’-1” according to our plans and therefore the joists should be adequately sized.
2. I am not sure how the deflection was measured, but if it is in excess of .26” even before the second floor walls, then we should look at the installation of the joists themselves.
3. As a point of clarification, the roof load is carried by the exterior walls and not by the second floor system… so the floor system is only carrying the walls and ceiling for the second floor.
So at this point he does not see any cause for concern given the information as it has been stated. If it is determined that any of these factors vary from what is stated, then he would want to examine to situation more closely.
And there you have it… So, what should we do? It seems as if we need to meet on Thursday as a team to measure, discuss and get some answers so that the Barter House can move onward & upward.
Comment: lamidesign.com/plans
These engineered floor joists are prone to this. The problem is their charts are optimistic. They use the same deflection standards - L/240, L/360, L/480 - these were invented for solid lumber joists which did not span as far. As L increases, which it does for these joists, much further than you can span with 2x lumber, what do you know, you suddenly have a very noticeable amount of deflection in the middle of your floor. It still meets the deflection standard, but the math bears it out - you now have a sagging floor. You have to ignore their charts and shorten the spans or beef up the floors with their stronger series joists, or closer spacing.
Follow-up comment which disagrees with the previous statement:
The I-joist tables are perfectly valid, and if anybody thinks there is a problem with ¼” deflection (or even 3/8” if that is really what it is) in 23’ span, they are *mistaken*. L/240, L/360, etc. standards were not “invented for solid lumber joists”. Steel trusses spanning 120’ use the same deflection criteria.
Rebuttal:
Steel trusses spaning 120 ft are not commonly used for floors, perhaps roofs - the comparison is irrelevant. The fact remains that as the span increases the resultant deflection allowed by the manufacturer’s span charts increases. At some point depending on the individual’s perception, the floor goes from feeling solid to feeling springy even though it meets the L/xxx criteria. That is solely a condition of the longer spans and one that experience informs you to anticipate.
Additional:
I don’t want to alarm you - this is not going to fall down. What it comes down to is your comfort level with the sensation of the floor. I’ve done enough projects to experience a range of reactions to this. Some people could care less, but others have complained that the perfume bottles on dresser top are “tinkling” (vibrating) when somebody walks across the room. Do you have light fixtures hanging from the ceiling below - are they jiggling when somebody is upstairs? If the light shade throws a shadow line across the room it can feel like the whole house is shaking. I’ve learned that relying on the manufacturer’s span charts for longer spans is perilous. L/480 is fine for a 15ft 2×10. It is often not enough for a 24ft TJI over a modern living space. The standard does not serve well with these longer span joists.
I want to thank the LiveModern community for offering their input and suggestions on this issue. Keep the comments coming.
