I have a two story townhouse built in the late ’80s with a sagging second story floor. I cut a hole in my dining room ceiling to take a look at the joists and noticed the builder cut some large holes in the webbing to run HVAC. Two of these joists support a bathtub and a stand up shower (with a tiled cement floor – heavy).
The joists are 14” i-joists spaced 24” on center and span about 14′. I have found plenty of information on strengthening joists made of dimensional lumber, but not much for i-joists.
So far, my plan is to jack up the floor a little with a couple of shore jacks, then sister join four 2x4s on both sides of the webbing using adhesive and screws (2 2x4s just below the top flange, and 2 above the bottom flange).
Does this sound like a good plan? Any suggestions?
Replies
I am going to stay out of the engineering on this one, but for glue - use PL Premium. Some adhesives cure hard and toehrs will allow "creep" so your fix could sag again due to glue failure.
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Greetings Dylan,
As a first time poster Welcome to Breaktime.
To get the greatest amount of technical merit from the pros who frequent here add as much description of the scenario as you can and if possible some photos of the joists for clarity of the situation.
Cheers
only life affirming platitudes allowed -Doud '07
Would a full cluster of enemies be called an enema? -Piffin
Edited 2/13/2007 7:50 pm ET by rez
just for my own curiosity where are the holes cut,middle third or one third on either end? and what size holes? just been waitin to here of something like this with i-joist.
Thanks for the help. Here is picture of the situation. I know the picture is not the best, but I already put a temporary patch on the ceiling.
dylan,
is this in a house you had built? do you know if there were inspections? are these holes in the middle of the ceiling or off to the side?
-open up the ceiling as much as you can replacing drywall is not a big deal and you will want to spread the new supports as long as possible.
2 x 4 are not great however if you lack space above and below the duct work
increase the 2x4 to 2x6 if possible and as long as possible.
even 2 on each side and use through bolts every 8 inches
George
Just my suggestion.
Find the manufacturers name on the joists. Call them and have them send a tech. out to look at your problem. Might have to fight to get them to do it , but they should be willing to .
Play it safe.
View Image
only life affirming platitudes allowed -Doud '07Would a full cluster of enemies be called an enema? -Piffin
Call the manufacturer and see if a rep can come and survey the damage. They are your best source of advice on how best to fix this problem.
If those wires aren't from a light I would give them some attention too.
Might be intersting to put a long ... like 6 ft or more ... straightedge on the surface of the ceiling and see how much sag there actually is, and if it is where the hole in the joist is.
"Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Is the subfloor sagging in between the joists, or just the joists?
EDIT: Just looked at the picture again, call the manufacturer.
Edited 2/13/2007 7:41 pm ET by Stilletto
I did not have this house built. If I had known this problem existed, I never would have bought it. I have been told by the neighbors that the builder went out of business a while ago (I know, shocking). I would guess from lawsuits. I was not able to determine the manufacturer of the i-joists. There are some stamps, but they are difficult to read and I can't make out who made them. I looked on GP and other companies websites who make i-joists and my 2x4 method of reinforcing them is what they would suggest, as far as I can tell.I just wanted to know if anyone else had experience with this kind of repair.
Also, the holes are about 4 feet from the exterior (load bearing) wall. I have not made any measurements as to the amount of sag.
Here is a PDF file that contains info on allowable holes and locations in Trus Joist products. Should give you a better clue. http://www.ilevel.com/literature/TJ-9001.pdf
You need a structural engineer not civil.
I can see the nails where he ripped out the box for the light.
Edited 2/13/2007 8:25 pm ET by VAVince
I can't imagine any kind of floor joist system that is on 24 inch spacing! Especially that spans 14 feet. I bet the floor would sag and bounce with no pipes cut through. That whole electrical and HVAC job would not meet code, and is pretty much a mess.
Is there any way to put in additional i-joists? You need a lot more support and stiffness than a bunch of 2x4's will ever give. If you could get some 2x6's in there, you might improve it a bit, but if you want to live in the house for a long time, I would rip out the entire ceiling and re-do the job the right way.
ytek,
I can't rip out the whole ceiling, that would require removing the entire 2nd floor! I it has been this way for 15 years, so I don't think I am going that route. Adding new i-joists does not seem possible.I'm not looking to make a perfect, bounce free floor. Just reinforce it so it is more stable without knocking the whole house down.
Also, 24'' on center is not preferred, but ok according to GP website.
There is no quick fix for this one. The hole in the joist doesn't look to be overly large, although at 4' it's definitely too close to the end.
If it's not strong enough to hold up the weight then it needs additional joists and some 2x4s or even 2x6s aren't going to do squat. The way I-joists work I can't imagine, haven't seen, don't know of a way to reinforce just the area around the cutout and make it amount to anything other than a hack repair. I'll bet that's what Piffin wanted to say. :-)
Beer was created so carpenters wouldn't rule the world.
"The hole in the joist doesn't look to be overly large"Look again!There are three of thos flex ducts running same hole. That hole must be at least 8" x 18" - and it is close to other work.
The HACK HVAC guy who did this could easily have made three small holes. Instead he destroyed a joist or three. As far as what I meant to say - I just wanted to stay out on this one because I can't see enough, got soemthing else on mind, and I knew there wouyld be ten different negative opinions going on to confuse. fact is, the only practical solution here short of rebuilding the floor suystem is pretty much just what he is thinking of. As a pro, I might not do that, but for a DIY, it will help if not cure perfectly.
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I made the same mistake with the picture, I saw the plumbing but missed the flex lines. I went back and deleted most of my post before I got tore a new one. Don't know how, they are huge.
HVAC guy needs to have his sawzall taken away. :)
Nah, He can keep his sawsall. Nobody else will want it after he gets it shoved up his ...
ah
tool storage compartment
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>>>tool storage compartment<<<
Thats a good way to sugar coat it.
There are three of thos flex ducts running same hole.
And typical hvac guys, the ducts are crimped where they go throught the hole. They always say flex duct is supposed to do that, but I think it creates a choke point ijn the airflow."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I have re-enforced I-joists with 3/4" plywood, glued and screwed both sides. Cut around obstructions and butt the ply from the other way, lots of glue, lots of surface contact on the ply. I have also re-enforced with 2x8 and 2x10, but with all the piping you have, I'd recommend plywood. The centers being 24" is, well, ... bad. Solid blocking between the joists is the only quick fix I can think of. Good luck.
I have heard the term "solid blocking" before, but what exactly does that mean? That means just reinforcing the web, correct?
BTW, thanks for the reply.
Edited 2/16/2007 11:46 am ET by dylan77
No, solid blocking is similar to and does the same job as bridgeing, which are the 2x2 diaginal pieces used between conventional (2x10) floor joists. I-joists do not require bridgeing. The idea of bridgeing (typically 2 rows run perpendicular to the joists) is to transmit the live load on one joist to the two adjacent joists. In your case, 2 rows of solid blocking would help to stiffen the floor, IF the rows can be installed on a straight line. The photo does not show the entire cieling, but if you can find a path free of obstructions, then go ahead. This will stiffen the floor, going by our code, you are allowed to increase the max. spans of conventional lumber by adding more rows of bridgeing. Your joists look like 110's, which means that 3/4" ply packed out on the webs will bring it flush to the top and bottom cords. That will help when you go to do your blocking detail.
I-joists may not require bridging but I always do it anyway over 12' spans and especially with deeper I-joists.
Jeff
"I'm not looking to make a perfect, bounce free floor. Just reinforce it so it is more stable without knocking the whole house down."
"I looked on GP and other companies websites who make i-joists and my 2x4 method of reinforcing them is what they would suggest, as far as I can tell."
Could you paste those suggestions here?
Sounds like you might have the situation in hand.
Worst scenario might include spanning the length with 1/4" metal plate and bolt thru between the 2x4 and I-joists if necessary.
only life affirming platitudes allowed -Doud '07Would a full cluster of enemies be called an enema? -Piffin
"I looked on GP and other companies websites who make i-joists and my 2x4 method of reinforcing them is what they would suggest, as far as I can tell."
Surely you're joking.
Beer was created so carpenters wouldn't rule the world.
You've received much good information. Since you are looking at a significant project, and want it to last long term, I wouldn't play any guessing games about how the repair should be made. Contact manufacturer or a civil engineer. Yes, wiring too seems to be a problem as splices not made within an accessible splice box are certainly a no-no.
Randy
Structural engineer, not a civil engineer.
To me, the best practical recommendation is to seek out repair information from the I-Joist manufacturer. They have specialized knowledge as well as engineers on staff who design the products. They also have a bias and do not want to see the product fail in use (or misuse).
I made the recommendation of a civil engineer based on my own experiences in industrial, commercial, and residential work as usually there are more civil than structural engineers available to call on. Where I am now living, we don't have any structural engineers, but we do have several civil engineers. They are all using the same references. Heck we're not dealing with an 80 story building with a structural steel skeleton.
Randy
Heck a civil engineer will tell you how to regrade your property to continue the natural run off. The civil engineer will tell you how to take care of your site flooding. On the other hand, a structural engineer will take into account your spanning, the loading, the spacing of your joists, etc. It doesn't have to be an 80 story structure to use a structural engineer. The fact you have a boat load of civil engineers in your area must mean that there is a whole lot of site developing going on. But I do agree that if you can get the joist manufacturer rep out there, their engineers should be able to assist you.
I happen to be a mechanical engineer (not in the construction business) and as far as I know, there is no such thing as a degree in "structural engineering". People who are structural engineers either have degrees in mechanical or civil engineering since both study beam design in school. BTW- I just dug out my beam design book from school and I have some reading to do tonight. Civil engineering, like mechanical, is a broad field that includes many specialties.I will take some pictures when I get home of the stamp on the i-joists and maybe someone can identify the manufacturer (I can't).
Well you are wrong. However, what you want is a licensed structural engineer. Heck, I took strutural, mechanical, and civil engineering courses in school. I always turn to my structural engineer for consultant work, my civil engineer for site work, my mechanical engineer for HVAC, and the subway engineer to drive the subway train.
I would be more concerned about what an engineer specializes in than his title. Engineers aren't automatically skilled at everything.
Human beings hardly ever learn from the experience of others. They learn; when they do, which isn't often, on their own, the hard way. [Robert Heinlein]
"I would be more concerned about what an engineer specializes in than his title. Engineers aren't automatically skilled at everything."Absolutely correct. I was just pointing out that a person could be a civil engineer who specializes in structural engineering, so you both could be correct.
Hey Joe - I've used civil engineers numerous times in residential work involving the design of long steel beams and support columns. There was no site work involved. I like having them involved because there is no guess work or "Hail Mary" practices. They help me sleep well. Hey, even the truss designer (we live in snow country) at a local truss manufacturer is a "civil" engineer.
Randy.
OK, I'll bite. what is a "Hail Mary" practice?
Hail Mary Project: Do the job or make the repair, then pray that it works. These type projects are often preceeded by the words, "We've always done it this way"; "My brother in law........", "I have a friend...........", "The rule of thumb is........."
Randy
As in an end of the game desperate play in football with the Hail Mary pass from the 50yd line into the endzone.
Take yer best shot, shoot it up there and hope for the best.
is today Saturday?
Structural engineer is a civil engineer.
I got a degree in "engineering" through the department of civil engineering. I could have taken classes to specialize in structures, or any of a number of different specialties. All of the basic education is the same, it's just the upper level courses that specialize in one field or the other.
When you take the EIT (engineer in training) exam, you get asked questions in several different areas, but you don't have to answer all of them. At least that's what I understand; I didn't take the exam. Instead of specializing in one field, I took architectural history and design classes. Now I'm a carpenter. It really is your experience in the field that matters.
I have some experience in the truss design field and what you intend to do sounds like a good idea because your situation really doesn't leave much options but as someone else in the forum mentioned you should check with a manufacturer for a engineered drawing (repair detail) for your situation you will need to give them the span, depth, spacing, live and dead load, and location of hole in the joists affected.
It really makes you appreciate the existance of open web joists.
Are you in the truss business?Just curious, since you mentioned truss design...
One worthwhile task carried to a successful conclusion is worth half-a-hundred half-finished tasks. [Malcolm Forbes]
I used to work for a truss manufacturer I designed roof & floor trusses( Metal webbed floor joists with 2x lumber for top & bottom chords.) Im also a certified engineering technologist but that doesn't mean nothing it's the experience you get in field that counts.
By the way floor joists are usually designed to have a deflection of L/360 so by code a 14'-0" floor joist in residential use can deflect up to 15/32" before if fails minimum requirements. But as you may allready know building codes are only minimum standards and when it comes to floor spans if you stretch it to this minimum you are going to have so homeowners who will be complaining of vibration in their floors. Up here in canada the codes are now asking for vibration calculations in order to reduce this problem. When I left the business 3 years ago BOCA was not requiring it yet maybe it has by now.
So Dylan77 your 1/2" deflection is not something to be scarred of but I would still beef up those flanges with the lumber as you mentionned and if you can open up the drywall all the way and do that for the entire span of the joist it would be even better.
I'm a truss designer - Have been basically since 1984. I've been hanging around Breaktime for a long time, so I'm kind of the resident truss guy. Other truss folks have wandered in, but none of them have hung around for long.
Quite a while back, I did a thread on Floor Vibration that might interest you.
I hadn't heard that BOCA had vibration requirements now. But we're under the IBC now, so it doesn't affect us.
Hope you'll hang around and contribute more - I see you don't have many posts yet.
Never fight ugly people - They have nothing to loose.
I read your piece on floor vibrations and found that it was well done and your right more depth is equal to less vibration because there's more weight. im from canada so the software we used (Mitek) has the vibration checks incorporated in the engineering software its code here. We did a lot of those metal webbed floor joists ultra-v span is their brand name. and the method used to brace these joist is to run a strong back through them just like the open webbed wood joists. what I noticed on the engineering drawings was that whenever I hade a type of joist that would be getting close to the limits it can comfortably span the design would ask for deeper strongbacks at closer intervals so instead of the typical 2x6 it would go up to a 2x8 and the thickness of plywood & method fastening of the decking was a factor in the calculations.
FYI there is a lab in the province of quebec, canada that specialises in testing engineered lumber products off all kind their name is FORINTEK if your interested you could probably google them and find their website.
until next time....
Some years back I was told by a TJ rep that one problem that they had and were attempting to deal with was the " harmonic resonance" or vibration in their floor systems. At that time some people still had very sensitive turn tables for stereos and the needles were jumping .
Anyway , he told me that what TJ discovered was that because they used manufactured material all the mass was nearly the same, unlike sawn lumber , and that this contributed to the problem.
He recomended glueing and nailing blocks of differant sizes to some of the joist's webs at random points along the length to "de-tune" the floor because that way not all the joists would have the same mass.
Ever hear of this?
Glueing blocks on I-joists to change the vibration frequency sounds like snake oil to me. I wouldn't expect it to do much of anything.
A bird in the hand is safer than one overhead.
dylan, how high are the ceilings in your first floor?
only life affirming platitudes allowed -Doud '07
Would a full cluster of enemies be called an enema? -Piffin
ceilings are 8' high
those 'I joists ' look as homemade as any I 've seen- not the same as GP I joists strengthwise. it also looks like you got particle board underlayment, again, not as strong as ply.
so without dropping the ceiling significantly for wider joists of some kind, heavy metal strapping may be the only choice.Expert since 10 am.
A while back, Junkhound posted a header reinforcement method supposedly many times superior to the standard sistering of flitchplates or additional dimensional lumber. He even included pics.
A steel plate, not even spanning the entire header, was bolted to the BOTTOM of the offending header. This arangement was an extreme tension addition to the bottom of the header, in your case to the bottom of the joists, augmenting the natural tension of the depth of the original.
Run that idea past your engineer and you'll only add maybe a 3/4 inch or so to the bottom of the joists and you can then sister a 2x2 or 2x4 to the side of the bottom of the web to match the added depth of the steel and the bolts and to pick up the sheetrock screws when you rerock the ceiling.
The joists that you do not have to repair can be matched to the increased depth of the others with a 1x nailed along the bottom of each.
Since you will have a large area of ceiling rock to repair anyway when you make the repairs it would be to your advantage to do the whole thing.
Greetings from Montreal. Perhaps you could tear down more gyprock in that area,shore up the nasty joist,make proper holes on either side of the mess and reroute those flexible ducts.This would allow you enough space to reinforce and sister up the joist with beefier 2x stock.Fill in the web with plywood strips.Glued and screwed(don`t go cheap on the glue).Make a separate hole for each duct and space them apart. Follow the recommended specs.for holes.I believe the max.amount of holes per joist is 3 but I think this can be overlooked given that you are fixing a condition that is seriously defective.Adding a bit more flexible duct might cause some problems with air flow,but you can change the flex. for ridgid if you are so inclined(tape the joints as well). Also, I think the second joist could use the same treatment.Go big or go home!I must go now and prepare for the 30-40 centimeters of snow coming tommorow. Bon Soir.
Edited 2/13/2007 9:34 pm ET by McCliver
I have had very good experience with joist manufacturers by calling them on the phone and explaining the situation. I inherited a project where the plumber butchered joists in 4 different homes (don't ask), all requiring repairs.
I gave the designer/engineer the joist dimensions and series, spacing, span, size of hole and location in relation to the span. In each case it was a simple matter for them to come up with a fix--basically attaching plywood or 2x material of a particular length/thickness to the side of the webbing. They seem to always specify 8d nails rather than screws--perhaps because the shear strength can be figured more readily with nails than screws. Once fiqured, they'd fax the drawing, we'd fix it, the building inspector was happy.
So, I'd tear down more drywall and try to decipher the numbers/letters. Your lumberyard can probably help identify the manufacturer.
i say fix the drywall and sell!!
A 14" I-joist spanning 14' would have to be damaged pretty badly to sag. Are you sure it only spans 14' ???People don't normally go with I-joists that deep unless there's a good reason.
Food has replaced sex in my life. Now I can't even get into my own pants.
Yes, it is a pretty narrow townhouse so it only spans 14'. I did some measuring last night and I estimate the floor is sagging about 1/2''. I'm not sure if 1/2'' is significant or not. The upstairs floor makes some creaking and popping when walked on, but maybe the situation is not as bad as I think. Seeing those giant holes in the webbing kind of freaked me out though.
If they're only spannnig that far and they're sagging, I'd say something is definitely up. And I wouldn't expect that much trouble just from the one picture you posted. I'd almost bet money there's more damage elsewhere.
I think knowing what you cannot do is more important than knowing what you can. [Lucille Ball]
So you think 1/2'' over 14' is significant? Any beam that is holding weight is going to deflect. It is just a matter of how much is acceptable.
Yeah - I think it's significant. I-joists that only span that far shouldn't have much deflection at all. It could be that it will never be a big deal if it's lasted this long. Or it could get worse. No real way to know, unfortunately.
I wonder if Iraq will repay us for their freedom like Germany and France have.
I had to go back to the original picture for another look and wouldn't say the hole is big enough for three 6" ducts, or 18". The ducts are crammed in there tight, so there's barely 12" to 14" and well clear of the bottom and top flanges. With 1/2" of sag over 14' this isn't something that an engineer would necessarily "fix". Sure, he'd recommend something, but you'd still have the same L/360 sag.
Beer was created so carpenters wouldn't rule the world.
Deflecting about 1/2" with the tub empty or full? I bet empty.TFB (Bill)
No one has mentioned center bridging or solid blocking, I believe.
I would think that if you shored the bottom (to take some deflection out) glue-nailed 3/4" exterior grade ply each side of the middle of the span, then blocked solidly (especially at the bottom of the I-joists) down the center you would improve the floor performance a lot.
Jeff
ETA - keep in mind that the deeper the beam the more subject it is to 'overturning' in addition to deflection - thus the importance of center bridging / solid blocking
Edited 2/15/2007 6:32 pm ET by Jeff_Clarke
I read a few but not all of the posts so this may have been said. I can only speak from a structural engineering persective.
First, the further from the center you can get the meat (2x4) the more it will contribute to the i-joists strength and ability to resist deflection. To calculate the moment of inertia which is tied into deflection , the area of the peice added is multiplied by its distance to the center squared. That means attaching the 2x4 at the top and bottom (d=5") vs. attaching where you propose (d=3") would nearly triple the capacity of the member to resist deflection.
Second, the attachment of these members must be sufficient to resist the shear flow. Glue is a good canidate for this. It is important to remember that the most fasteners are required near the ends of the member where shear is the highest. I did no analysis (and recommend you find someone who will), but as an example; you may need 12d nails on 3" centers in from each end, but then can increase that spacing to 12" towards the center. Or, you may need glue and nails/screws at the ends.
Third, you need to make sure the shear capacity is adequate with those big holes. This may mean adding a 14" tall piece of plywood along one side. That means removing the ducts and putting them back in afterwards. If you did this, adding a second joist would be easier.
There are lots of options, find a local structural engineer to look things over. A full bathtub and tiled floor far exceeds the design loads for that floor.
I proposed attaching the 2x4s just above the bottom flange, and just below the top flange. This will maximize the moment of inertia, thus providing the most strength. The center of the i-joist does not do much anyway, so I think my proposed solution will work fine. A single 2x4 in tension (like the 2x4s at the bottom flange in my solution) will support a couple thousand pounds and even more in compression. As far as shear flow, yes, I need to glue and nail the crap out of the 2x4s. Or I could drill holes and put 3/8'' bolts with large washers trough the 2x4s and flange. The bolts would be much more resistant to shear. I will look at this some more before I start hammering.BTW- I just did some quick calcs and the moment of inertia of the beam (no holes) is about 220 in^4. If you add the 4 2x4s in the locations I propose, you add about 320 in^4, for a total of 540 in^4. Thus the solution would more then double the capacity of the beam to resist bending stress.The solution has to be practical, so I want to avoid moving the ducts. The two joists under the tub only have two ducts running through them, not 3 like the picture shows. The picture is of another joist that runs elsewhere. Due to the weight of the bathrooms, the other joists with 2 ducts concern me more.As much as I would like to, hiring a structural engineer is not in the budget. I will have to function as my own engineer to fix this one.Thanks for all of the responses.
Let me explain why the plywood is more effective than your solution.
One of the most important properties of any shape designed to resist bending and deflection is the Section Modulus, which is related to the Moment of Inertia and is expressed as:S = bd2 / 6 (the 2 is 'squared')
The Section modulus of a 2x4 is therefore 1.5"x3.5"x3.5" / 6 = 3.0625 in3 (cubed)
The Section modulus of a piece of 3/4" ply is .75"x14"x14" / 6 = 24.5 in3 (cubed) - 8 times the value.
Also, the plywood, because of it's construction, has a higher 'E' (modulus of Elasticity) than dimension lumber. This is why Microllams are E = 2,000,000 while DFir is maybe E = 1,600,000.
Both are important in the deflection formula where: deflection = 5Wl3 (cubed) / 384 EI
W (total load) and l3 (cubed) are fixed. You can see from the formula that increasing E or I decreases deflection. The plywood does both.
Jeff
Edited 2/15/2007 7:23 pm ET by Jeff_Clarke
Edited 2/16/2007 7:47 am ET by Jeff_Clarke
If I consider a beam with no holes, for simplicity, and I were to sister two 3/4'' plywood pieces to the sides of the web, the moment of inertia would increase by 166 in^4 (total I=390 in^4). The 2x4 solution increases "I" to 540 in^4. "E" for plywood is about the same as a 2x4, according to the info I found:
http://www.fpl.fs.fed.us/rwu4706/mechproperties.html
So I would say the 2x4 method would deflect less.I agree with you on the section modulus point, but I thought (correct me if I am wrong here) section modulus was more of a check to make sure you are not exceeding the maximum bending stress of the material. Once you check that box, the section modulus is no longer considered. In other words, as long as you meet the minimum section modulus (which I should check), you are done.Besides, installing the plywood would be much more difficult. Given that the 2x4 solution is much easier to implement, I think it is the better solution.