Browse Forums General Discussion 1 Apr 28, 2013 3:13 pm I've a quick question about floor joists and maximum spans. I've read the span tables but also interested in real-world and long-term experience from framers/builders. Got a second-floor lounge room. The floor is a single span of 4.8m. The joists are 200x45 LVL15 (equivalent to F17) with 450mm on centre. There's plywood sheeting on top, nailed and glued, nothing below, no further bracing. There are mid-span blocks between joists. There is minimal load on this floor; a few couches and a coffee table. Flooring will be wood, nailed and glued. According to the tables the maximum span is 4.5m. Builder reckons it's OK for strength and I trust him, but I can't get a clear handle on what this means for bounciness and sagging, especially in the long-term. Bounciness at the moment is noticeable. What are the opinions from experts in the trade? Re: newbie question about floor joists, maximum spans 2Apr 29, 2013 8:29 am The joists are overspanned,it won't sag,but you will feel bounce,especially if you are seated and someone walks into the room. Will the building inspector pass this?what was on the plan? Re: newbie question about floor joists, maximum spans 3Apr 29, 2013 10:02 am oldchippy The joists are overspanned,it won't sag,but you will feel bounce,especially if you are seated and someone walks into the room. Will the building inspector pass this?what was on the plan? I'm relieved you say sagging wont be a concern. That's a silver lining. The engineering plan had the joists oriented 90 degrees so the span was only 4.2m. The builder made an honest mistake, but by the time the mistake was noticed the upper floor had been framed and roofed. The engineer thinks it is still structural but bouncy. The inspector hasn't seen it yet. The builder thinks its acceptable. I'm concerned about being disappointed with the result. The engineer mentioned sister joists to reduce bounce, but there's a lot of structure in the way that would make full length sister joists very difficult to install. Would some joist stiffeners be a suitable workaround? Either bridges, or metal straps, or something along those lines? I have no idea how effective that would be, if at all. Re: newbie question about floor joists, maximum spans 4Apr 29, 2013 5:01 pm Quote: The builder made an honest mistake, but by the time the mistake was noticed the upper floor had been framed and roofed. A friend of mine once described someone saying they had made an "honest mistake' as " yeah I screwed up bigtime and made a monumental mistake and honestly I have no idea nor the inclination of how to fix it" According to my span tables ( NSW Timber Framing Manual ) 4500mm span @ 450crs should be an F17 240 x 45mm joist not 200 ( single span not continuous). The joist is undersized to start with ( 4500) then he has gone 300mm more. Stewie Re: newbie question about floor joists, maximum spans 6Apr 29, 2013 5:46 pm Ok, it sounds like I should press the builder to strengthen the floor. Probably by sistering the joists to make them strong enough to handle 4.8m spans. Thanks for the advice. Re: newbie question about floor joists, maximum spans 7Apr 29, 2013 11:03 pm The Hyspan LVL tables indicate 4.4m span for a single span 200x45 @ 450 centres. At 300 centres you can achieve a 5m span so your builder is going to have to basically work out some way of retro fitting another lvl in between the existing lvl's in order to meet the spec's. Let us know how it works out. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: newbie question about floor joists, maximum spans 8Apr 30, 2013 3:08 pm OK, lets throw the rule book out the window. If you fixed another one of the same size next to every second one it would probably sort out any bounce problems.The additional one wouldn't even have to be sitting on the top plate,as long as it was within 50mm of the plates and glued and gunned to the existing one.2 rows of blocking in-between would also help. Along the same lines,I have found when doing decks,single span deep joists,clients have told me that it feels springy, when they have had a party,some 20-30 people on it,and although it is built to code still gives a bit. I have fixed this by getting underneath and batten screwing a piece of 90x45 on its flat across the underside of the joists, long batten screws,sort of tying all the joists together,so for one to go down it has to pull the both each side with it. Works well. Re: newbie question about floor joists, maximum spans 9Apr 30, 2013 8:54 pm oldchippy OK, lets throw the rule book out the window. If you fixed another one of the same size next to every second one it would probably sort out any bounce problems.The additional one wouldn't even have to be sitting on the top plate,as long as it was within 50mm of the plates and glued and gunned to the existing one.2 rows of blocking in-between would also help. Along the same lines,I have found when doing decks,single span deep joists,clients have told me that it feels springy, when they have had a party,some 20-30 people on it,and although it is built to code still gives a bit. I have fixed this by getting underneath and batten screwing a piece of 90x45 on its flat across the underside of the joists, long batten screws,sort of tying all the joists together,so for one to go down it has to pull the both each side with it. Works well. Thanks oldchippy. This is excellent stuff and exactly what I hoped to get from this forum; real-world advice from the experts. I've asked the builder to double up the joists as you've suggested. He might grumble about it, but it seems like a good idea to do it now while everything is still open, rather than risk any problems later. Re: newbie question about floor joists, maximum spans 10May 01, 2013 1:14 am There are many things you can do to reduce bounce. You could simply glue and screw another layer of flooring at right angles to the existing flooring and it will stiffen the floor up substantially. The problem isn't bounce, the problem is that you have a house not built to engineers specification. As you mentioned, you have a set of approved plans that include engineered drawings for the sub-floor, these haven't been followed. Whatever the builder does make sure he gets it approved by your engineer or clearly demonstrates that it meets the required span tables for the product used. Anyone on this forum or even your builder can recommend a solution that may well fix the problem but unless it is certified by an engineer then it really doesn't matter. I'm not trying to be alarmist but your builder has already made a very basic stuff up, you need to make sure that any rectification work is more than just window dressing to make you happy. And old chippy, that is in no way a shot at you. Your idea is fine (I'd probably do something similar myself) but for piece of mind, and for certification purposes the OP should make sure it is signed off by an engineer or demonstrate that it meets the relevant span tables for products used. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: newbie question about floor joists, maximum spans 11May 02, 2013 12:13 pm chippy There are many things you can do to reduce bounce. You could simply glue and screw another layer of flooring at right angles to the existing flooring and it will stiffen the floor up substantially. The problem isn't bounce, the problem is that you have a house not built to engineers specification. As you mentioned, you have a set of approved plans that include engineered drawings for the sub-floor, these haven't been followed. Whatever the builder does make sure he gets it approved by your engineer or clearly demonstrates that it meets the required span tables for the product used. Anyone on this forum or even your builder can recommend a solution that may well fix the problem but unless it is certified by an engineer then it really doesn't matter. I'm not trying to be alarmist but your builder has already made a very basic stuff up, you need to make sure that any rectification work is more than just window dressing to make you happy. And old chippy, that is in no way a shot at you. Your idea is fine (I'd probably do something similar myself) but for piece of mind, and for certification purposes the OP should make sure it is signed off by an engineer or demonstrate that it meets the relevant span tables for products used. Chippy, I am in no way having a go at you, but an engineer doesnt need to sign off any framing member changes. If it was steel, then yes, the certifier would ask for for an engineers stamp, but timber can simply be assesed against the 1684 code or against the manufacturer of the LVL's. The engineers stamp counts for nothing at the end of the day and he probably wont even be interested in assesing the timber structure. The certifier can and should do this. There are allowable deflections limits, but as already stated, the sizing hasnt even been met. I find with deck joists that the minimum size esp single span usually has too much deflection, i always go one size up Re: newbie question about floor joists, maximum spans 12May 02, 2013 5:24 pm I agree, that is why I said the builder needs to demonstrate that it meets the required span tables for the product used. As I said in a previous post, for that size LVL you would need to go to 300 centres to get the required span. If this cant be achieved (which the OP said couldn't) then you need to get an engineer to approve whatever other non traditional way the builder is attempting to rectify the problem. My response was largely to Old Chippy. He had recommended a method that would definitely work to beef up the floor, but unless it is a defined method of construction in the code or from the manufactures of the products then it still technically isn't compliant unless approved by an engineer. Realistically, if the builder did what Old Chippy said and then just sheeted it all no one would be any the wiser. The floor isn't going to collapse and the deflection issue would have been addressed. Maybe things are different over here in the West, but plans will always have engineering plans that show size and location of all structural elements (Beams, LVL's, Lintels etc) these plans have been approved by the local council. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: newbie question about floor joists, maximum spans 13May 02, 2013 5:48 pm Hi again Chippy, My point is an engineer wont touch it. He will simply refer you back to the manufacturer of the LVL's. Yes, plans over here spec sizes of beams and lintels etc, but it isnt the engineer that specifies or even signs off on them, that is the certifier. The engineer is responsible once steel and footing designs are needed which is why steel and footing details can usually be on a seperate page for something like an extension Re: newbie question about floor joists, maximum spans 14May 02, 2013 5:57 pm So what does the OP do? The floor isn't and can't be retrofitted to meet the code or span tables. Does the builder have to pull it all down, and start again? My point is there must be some way of getting it certified, and to do that, who decides if it is capable of meeting structural requirements? Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: newbie question about floor joists, maximum spans 16May 02, 2013 7:21 pm tjilpi So ultimately, the engineer needs to approve any changes to the design, and the building surveyor needs to be sign it off, if the house is to be constructed legally to minimum standards Thanks tjilpi, that is exactly the point I was trying to make. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: newbie question about floor joists, maximum spans 17May 03, 2013 9:19 am Things must be different over in the west Chippy. Any changes to timber sizes can be assesed against the code or the manufacturer. Any Cert 3 qualified or above person should be competant enough to make this assesment The engineer doesnt sign off on the timber aspects of a house, and any size or member can be changed without referral to an engineer. 200x45 LVL's can span 4.9 @ 300 centres so if an intermediate joist was thrown in it would be compliant. The builder could prove his point to the certifier (or as you call them Surveyor) and it cant be knocked back. Re: newbie question about floor joists, maximum spans 18May 03, 2013 9:30 am Excuse me if I'm wrong,but aren't these beams already engineered,so whats it got to do with an engineer again.? In most tables I've seen over the past 45 years,doubling up of beams to increase their span is an approved method,provided they are fixed together appropriately,and a look into the span tables by the relevant building surveyor who granted the permit,and who is now inspecting the works,would confirm this.Sure there would have to be an amement noted but as far as getting an engineer to approve it -I don't think so. Thanks for all replies. I just noticed now the pictures I added to post right on top of page were wrong. I attached pictures showing "current" and my "suggested" floor… 9 14635 Houses have been framed on floor joists since settlement, chipboard flooring is only around for 50 years or so, so why would it not be satisfactory? However exercise skill… 3 16834 The distance between my DEBs varies from 4.1m at the narrowest to 8.1m at the widest. 5 27305 |