Bouncy manufactured I joist floors

[Bill Anglin]

Could use a little help here. Warranty inspection was performed on a 1 year old 2 story house. Client advised and I experienced that the floors in the kitchen and living room on main level are "bouncy". They had to move a china cabinet from the dining room because it rattled so bad when they walk past it that items would fall off of the shelves. The floor structure is 12 inch manufactured I joists from Boise Cascade. They are spaced 16" OC and they span approx 18.5 feet across the kitchen and dining room. The I joist is in place by Joist hangers nailed into the sill plate at the top of joist. There is only one visible nail on both sides of the joist hanger. My knowledge of I joist span, installation and minimum spans allowed by code is very limited. Any help here is appreciated. Will post photos when I figure out the problem with picture sizing.

[Mark Reinmiller]

Could use a little help here. Warranty inspection was performed on a 1 year old 2 story house. Client advised and I experienced that the floors in the kitchen and living room on main level are "bouncy". They had to move a china cabinet from the dining room because it rattled so bad when they walk past it that items would fall off of the shelves. The floor structure is 12 inch manufactured I joists from Boise Cascade. They are spaced 16" OC and they span approx 18.5 feet across the kitchen and dining room. The I joist is in place by Joist hangers nailed into the sill plate at the top of joist. There is only one visible nail on both sides of the joist hanger. My knowledge of I joist span, installation and minimum spans allowed by code is very limited. Any help here is appreciated. Will post photos when I figure out the problem with picture sizing.

BC makes five different series of I joists in 11-7/8" depth. The allowable spans for 12" o.c. range from about 20 feet to about 26 feet using a live load deflection criteria of L/480. That is 33% stiffer than the code-required minimum of L/360. In the past the L/480 criteria has been widely used to provide stiffer floors with I-joists, but some manufacturers do indicate that the floors may not be stiff enough for some people. BC notes that the L/480 criteria may still be an issue, especially when there is not a drywall ceiling attached to the bottom. They refer to the L/480 criteria as "3 star". They also have a table for a "four star" floor using an L/960 criteria (100% stiffer than 3 star). The allowable spans in that criteria range from 15-1/2 feet for the two lowest strength joists to 16 feet for the middle grade, to 18 and 19 feet for the highest two grades. Assuming you have a mid-grade joist then there are much longer than the 4 star, but shorter than the 3 star. I would not think that they would perform too bad, but it is subjective. Also, moisture can effect performance.

Regarding the joist hangers, you would have to know the make and model to determine the attachment requirements. Some top flange hangers can be installed with as little as two nails.

The link below will give you information on the BC i-joists.

Western US (including Alaska) - Boise Cascade, LLC

[John Kogel]

I-joists in general are springy. If the spans are correct for the size and grade, then strictly speaking there is no defect. Even so, it is not uncommon to see additional supports added under high traffic areas. They are lucky in this case to have a crawlspace under the springy floor.
They should ask the builder to install additional support posts so they can put their china cabinet back where it should be.

Those appear to be a type of hanger that wraps over the top of the ledger, in which case they would be correct.

I-joists do indeed absorb moisture, so it would be a good idea to measure the humidity in that crawl hole.

[Eric Barker]

What's going on with this? Is it suppose to be a supporting beam?

[Jerry Peck]

What's going on with this? Is it suppose to be a supporting beam?

Looks like a load bearing stud knee wall with a header across an opening for pipes and other goodies. Except that the header is only bearing on one jack stud at each end, I would think there would be two jack studs at each end of the header?

That and the lack of a good connection between the header section and the stud knee walls sections on each side - should have run the single top plate across the header and tied it into each stud knee wall on each side.

[Ted Menelly]

Could use a little help here. Warranty inspection was performed on a 1 year old 2 story house. Client advised and I experienced that the floors in the kitchen and living room on main level are "bouncy". They had to move a china cabinet from the dining room because it rattled so bad when they walk past it that items would fall off of the shelves. The floor structure is 12 inch manufactured I joists from . They are spaced 16" OC and they span approx 18.5 feet across the kitchen and dining room. The I joist is in place by Joist hangers nailed into the sill plate at the top of joist. There is only one visible nail on both sides of the joist hanger. My knowledge of I joist span, installation and minimum spans allowed by code is very limited. Any help here is appreciated. Will post photos when I figure out the problem with picture sizing.

16 on center at 18.5 feet lengths is a hell of a lot of span even for heavier graded joists. That being said I used a high grade 2x12 in my home I added a room onto, tiled that floor and then loaded it up with furniture and there was no bounce before loading it up and certainly none after and used 16 inch tiles for the 16 foot wide by 32 feet long room (joists spanned 3 1/2 inches less give or take) and never had a crack in the tiles. I built an 8 foot wide red oak entertainment center 8 feet tall with multiple shelves and door and loaded it up with equipment. It rocked zero amount.

I joists properly sized should be just as good if not better than 2x12s. There is a problem with the size. A Boise Cascade Rep will answer any questions you may have. No matter what tables you are looking at.

[Mark Reinmiller]

16 on center at 18.5 feet lengths is a hell of a lot of span even for heavier graded joists. That being said I used a high grade 2x12 in my home I added a room onto, tiled that floor and then loaded it up with furniture and there was no bounce before loading it up and certainly none after and used 16 inch tiles for the 16 foot wide by 32 feet long room (joists spanned 3 1/2 inches less give or take) and never had a crack in the tiles. I built an 8 foot wide red oak entertainment center 8 feet tall with multiple shelves and door and loaded it up with equipment. It rocked zero amount.

I joists properly sized should be just as good if not better than 2x12s. There is a problem with the size. A Boise Cascade Rep will answer any questions you may have. No matter what tables you are looking at.

Your post made me go back and look at the original post. I had through he wrote 12" o.c. and the spans I posted were for that spacing. At 16" o.s. the allowable spans for L/480 range from 18'-5" to 23'-11". For the L/960 criteria the spans range from 14'-4" to 18'-7". I-joist floors are often bouncy because of the relatively light weight of the joists. You cannot directly compare the performance of solid joists to I-joists. Stiffness of floors is subjective. It appears that the floors meet code. If they are too bouncy for the homeowner then maybe the builder will perform some alterations, but it does not appear that they would be required to do so.

[Stuart Brooks]

Almost all new homes in this area are built with TJIs and I have never felt a bouncy floor in my inspections. I wonder what they used for subflooring? I usually see .720 (23/32") T&G OSB glued and nailed or screwed. Now I did find a house in a pre-drywall inspection where the framing contractor glued the subfloor and tacked each sheet at the corners -- only. They did not nail the edges or the field.

[Ted Menelly]

Your post made me go back and look at the original post. I had through he wrote 12" o.c. and the spans I posted were for that spacing. At 16" o.s. the allowable spans for L/480 range from 18'-5" to 23'-11". For the L/960 criteria the spans range from 14'-4" to 18'-7". I-joist floors are often bouncy because of the relatively light weight of the joists. You cannot directly compare the performance of solid joists to I-joists. Stiffness of floors is subjective. It appears that the floors meet code. If they are too bouncy for the homeowner then maybe the builder will perform some alterations, but it does not appear that they would be required to do so.

Firm good. Bounce bad. He is not building a trampoline even if you can use it for one. Up size the joist to minimal deflection or live with the bounce. Just because it holds weight does not mean it is worth a dam. And yes, the whole idea of these joist is to reduce use of wood and cost (right) and to meet or beet any conventional lumber joist. They use to show an elephant standing on them....So What. Bounce bad. Firm good.

Might all sound stupid or childish but after all those were all the original intents.

A little edit here. If you build any home and the bureau, entertainment cnter, whatever, rocks back and forth? Then there is a problem. The statement from BC that I heard myself directly from their reps in the past , "they maybe not be firm enough or they may bounce/deflect more than some people like"....that is about a foolish a statement as I ever heard. Bouncing/rocking furniture, seriously. That is not to the liking of anybody.

[Dwight Doane]

Not being really familiar with this type of construction (sorry old school) it does bring up the question(s) of what is acceptable deflection ? How do you measure it ? (this goes for all construction)

[Raymond Wand]

If the floor is springy and not built to specs, it leads me to ask what other issues abound in the house that may not be discoverable?

[Stuart Brooks]

If the floor is springy and not built to specs, it leads me to ask what other issues abound in the house that may not be discoverable?

So true. Something like this floor would just make me look for more. I know it's there. It's just taking the time to find it. Blocking? Squash blocks? Was the subfloor installed in the right direction? Full filler between doubled TJIs? I keep an updated PDF from the APA on installation of engineered structural items. I've sent a copy of the file to some clients and have screen captures of details that I can include in the report. We still have lazy or ignorant carpenters installing TJI and trusses.

[james hiatt]

Could use a little help here. Warranty inspection was performed on a 1 year old 2 story house. Client advised and I experienced that the floors in the kitchen and living room on main level are "bouncy". They had to move a china cabinet from the dining room because it rattled so bad when they walk past it that items would fall off of the shelves. The floor structure is 12 inch manufactured I joists from Boise Cascade. They are spaced 16" OC and they span approx 18.5 feet across the kitchen and dining room. The I joist is in place by Joist hangers nailed into the sill plate at the top of joist. There is only one visible nail on both sides of the joist hanger. My knowledge of I joist span, installation and minimum spans allowed by code is very limited. Any help here is appreciated. Will post photos when I figure out the problem with picture sizing.

What ever happen to bracing and blocking? They help spread the load to the neighbors but in this case a thin subfloor is suspect For my info what are the cross dimensions of the top and bottom truss boards? LOL to u and the owners here.

[Jerry Peck]

Not being really familiar with this type of construction (sorry old school) it does bring up the question(s) of what is acceptable deflection ? How do you measure it ? (this goes for all construction)

The answer is not easy, nor real complex, but:
- From the 2012 IRC
- - R502.1.4 Prefabricated wood I-joists.
- - - Structural capacities and design provisions for prefabricated wood I-joists shall be established and monitored in accordance with ASTM D 5055.
- - - (That's for the design of I-joists.)

- - R502.2 Design and construction.
- - - Floors shall be designed and constructed in accordance with the provisions of this chapter, Figure R502.2 and Sections R317 and R318 or in accordance with AF&PA/NDS.
- - - (R317 is protection against decay, R318 is protection against subterranean termites.)

- - R502.3 Allowable joist spans.
- - - Spans for floor joists shall be in accordance with Tables R502.3.1(1) and R502.3.1(2). For other grades and species and for other loading conditions, refer to the AF&PA Span Tables for Joists and Rafters.
- - - R502.3.1 Sleeping areas and attic joists.
- - - - Table R502.3.1(1) shall be used to determine the maximum allowable span of floor joists that support sleeping areas and attics that are accessed by means of a fixed stairway in accordance with Section R311.7 provided that the design live load does not exceed 30 pounds per square foot (1.44 kPa) and the design dead load does not exceed 20 pounds per square foot (0.96 kPa). The allowable span of ceiling joists that support attics used for limited storage or no storage shall be determined in accordance with Section R802.4.
- - - - - TABLE R502.3.1(1) FLOOR JOIST SPANS FOR COMMON LUMBER SPECIES (Residential sleeping areas, live load = 30 psf, L/Δ = 360)a
- - - R502.3.2 Other floor joists. - - - - Table R502.3.1(2) shall be used to determine the maximum allowable span of floor joists that support all other areas of the building, other than sleeping rooms and attics, provided that the design live load does not exceed 40 pounds per square foot (1.92 kPa) and the design dead load does not exceed 20 pounds per square foot (0.96 kPa).


Let's use R502.3.2 as it has a higher live load rating. Let's start with live load of 40 psf, a dead load of 20 psf, and an allowable deflection of L/360.

Go here: http://www.woodbywy.com/document/tj-4000 scroll down to page 4, second table down, right columns, shows L/360, I-joist depth, o.c. spacing and maximum allowable span.

The closer one gets to maximum allowable span for the given sizes/spacings the more deflection one will get.

[Sean Prior]

Bill, in my humble opinion(contractor 18 years) engineered lumber for floor joist and rafter
applications reigns supreme over solid wood. It does not warp, twist, bow, shrink, or split, unlike Doug Fir which does all of those things. Add to that it is significantly lighter that solid wood which makes it really nice to build with. It sounds like the client is unhappy and wants you to "Blow the whistle" on the contractor. Instead of looking at span tables and joist hanger specs just review the plans. They should be engineered by an engineer, and approved by the county building dept. If the floor is not built to plan then its on the contractor. If the floor is built to plan than it goes back to the engineer or county. Either way you don't have to be the expert. If its determined that it has been built correctly than suggest the clients hire a contractor to install a new girder mid span, this should be a simple and economical solution to the problem.

[Mark Reinmiller]

Bill, in my humble opinion(contractor 18 years) engineered lumber for floor joist and rafter
applications reigns supreme over solid wood. It does not warp, twist, bow, shrink, or split, unlike Doug Fir which does all of those things. Add to that it is significantly lighter that solid wood which makes it really nice to build with. It sounds like the client is unhappy and wants you to "Blow the whistle" on the contractor. Instead of looking at span tables and joist hanger specs just review the plans. They should be engineered by an engineer, and approved by the county building dept. If the floor is not built to plan then its on the contractor. If the floor is built to plan than it goes back to the engineer or county. Either way you don't have to be the expert. If its determined that it has been built correctly than suggest the clients hire a contractor to install a new girder mid span, this should be a simple and economical solution to the problem.

Sean, I agree with you. The tricky thing with I-joists is that because they are light (and perhaps because bridging is not used) they can feel bouncy. In my experience they typically meet or exceed code minimums. In fact, for a long time manufacturers have recommended using L/480 live load deflection instead of the L/360 standard specified in codes. The problem is that every floor behaves differently and everybody has a different level of tolerance for vibration. The china cabinet example is one where it does not take much vibration to notice. I have seen this many times with dimensional joists also.

Manufacturers seem to recognize this more now. Boise is recommending L/960 for applications where vibration may be a concern. If anyone wants to learn a little more about this look at the TJI I-joist sizing program. They not specify I-joist size based upon the level of satisfaction. They list the percent of people who find a certain floor performance acceptable. As the floors get stiffer the percent of people who think they are acceptable increases. I suppose they developed this by building different floors and having groups of people rate the performance. The problem with that from my standpoint as an engineer is-how do I specify a floor that I think my client will find acceptable. I have generally used the L/480 criteria or higher in the past and have not had any complaints. But, we have all run across someone out there who would not be satisfied with the performance of a floor even if they tip-toed across the floor.

BTW, I think it is time to stick a fork in this thread.

[Jerry Peck]

BTW, I think it is time to stick a fork in this thread.

If the fork pulls out clean - the thread is done, but if the fork pulls out with residue - the thread needs to heat up a bit.

[Rick Cantrell]

BTW, I think it is time to stick a fork in this thread.

Not faulting you Mark, but since you said it.
Why is it that a thread is "Done" only AFTER one has their say about it?

Again, not picking on Mark, just made me think.

[Mark Reinmiller]

Not faulting you Mark, but since you said it.
Why is it that a thread is "Done" only AFTER one has their say about it?

Again, not picking on Mark, just made me think.

That is a fair question, and I thought about that as I wrote it. My feeling is that it seems the floor in question meets code and that many people have commented about the performance of I-joists. Many of the comments seem to be along the line that if the floor is bouncy, then it must be "wrong". Everybody is entitled to add their opinion, but after awhile, there is not much to add that is relevant.

[Jerry Peck]

*

*BTW, I think it is time to stick a fork in this thread.

If the fork pulls out clean - the thread is done, but if the fork pulls out with residue - the thread needs to heat up a bit.

Not faulting you Mark, but since you said it.
Why is it that a thread is "Done" only AFTER one has their say about it?

Again, not picking on Mark, just made me think.

There's that bit of heat needed to get this thread to finish well done.

[Bernie Peters]

Could use a little help here. Warranty inspection was performed on a 1 year old 2 story house. Client advised and I experienced that the floors in the kitchen and living room on main level are "bouncy". They had to move a china cabinet from the dining room because it rattled so bad when they walk past it that items would fall off of the shelves. The floor structure is 12 inch manufactured I joists from Boise Cascade. They are spaced 16" OC and they span approx 18.5 feet across the kitchen and dining room. The I joist is in place by Joist hangers nailed into the sill plate at the top of joist. There is only one visible nail on both sides of the joist hanger. My knowledge of I joist span, installation and minimum spans allowed by code is very limited. Any help here is appreciated. Will post photos when I figure out the problem with picture sizing.

The bouncy aspect of Engineered Joists in not a new one or surprising. It's in their nature. However any inspector or builder will tell the home owner that "it meets minimum code." Now the homeowner is stuck with it as is the new buyer and so on. Kenkeknem Smart Build manufactures a product called IBS2000 Load Share Connectors for both new construction (so this problem never happens) and for retrofit jobs where the new home owner or new buyer isn't satisfied with "minimum code" floors that bouncy and vibrate. They work by structurally locking floor joists together forcing the floor to act as a system thereby adding strength and rigidity while virtually eliminating bounce and vibration. IBS2000 is used with both I-joists and lumber joists in new construction and is used to retrofit bouncy I-joist and lumber floors in existing construction.
Call me anytime. Bernie 1-778-754-7522www.ibs2000.com

[james hiatt]

What ever happen to bracing and blocking? They help spread the load to the neighbors but in this case a thin subfloor is suspect For my info what are the cross dimensions of the top and bottom truss boards?

My sentiments exactly! I see someone has patented a simple "X' blocking board.
PS: Don't pull the plug until someone with some sense has inspected this floor and can report that the floor was constructed per normal or there is an OOPS! involved.

[Markus Keller]

Hate to continue an ancient thread but for what its worth ...
Yes these types of joists can be bouncy. From my years of installing these as a contractor the amount of bounce comes down to how close that joist size is to its load limits. If the installed joists are rated say for 10' span and 100 pounds and the actual onsite is 9' and 90 pounds then the floor will be really bouncy. Having dealt with this a couple times very early on. I decided to always upsize to the next rated joist, never had another issue.
You can't always trust what the architect spec's out in the drawings. It helps to do a little research on the joists.

[Jerry Peck]

You can't always trust what the architect spec's out in the drawings.

That is most often described in flowery terms such as "Value Engineering" ... which is nothing more than "Engineering the Value OUT" ... especially when you consider that "value" is what is left over after you deduct all necessary requirements (those are not "value", those are "requirements", the "value" is when Markus would upsize to the next I-joist size ... 'value = getting more than what you paid' ... otherwise it is simply a 'fair exchange of goods'

Buy a new Corvette? That's not 'value', you pay dearly for it.

However, if they were to throw in 'bumper to bumper warranty and maintenance for as long as you own the car' - that's 'value'.

[Randy Mayo]

The floor bounce or vibration felt when walking on the floor is related to the frequency of the vibration, which is a function of the floor joist size and span. People are particularly sensitive to frequencies in the 8 to 10 Hz range. At higher frequencies, vibrations are perceived as less annoying. Field investigation performed by the Journal of Light Construction in real homes confirmed that occupants were not bothered once the vibration frequency went above 14 Hz. Currently design standards do not address floor vibration issues.

[Jerry Peck]

The floor bounce or vibration felt when walking on the floor is related to the frequency of the vibration, which is a function of the floor joist size and span. People are particularly sensitive to frequencies in the 8 to 10 Hz range. At higher frequencies, vibrations are perceived as less annoying. Field investigation performed by the Journal of Light Construction in real homes confirmed that occupants were not bothered once the vibration frequency went above 14 Hz. Currently design standards do not address floor vibration issues.

Always keeping in mind that code is minimum, and code results in the crappiest and most unsafe structure legally allowed.

Code is not 'good', 'better', or 'best' methods or practices.

And if code does not even address something, that does NOT make it 'good' or 'okay', that simply makes it 'not even addressed by minimum' standards, which readily results in less than "the crappiest and most unsafe structure legally allowed".

Comes down to how you want to look at it and try to accept it or expose it for what it is.