Browse Forums DIY, Home Maintenance & Repair 1 Aug 26, 2018 5:39 pm My home is about 12 years old and was built on bearers and joists. The downstairs (subfloor) joists are HJ200-47 hybeams, with yellow tongue flooring and genuine, polished T&G hardwood flooring on top of that. Subfloor clearance is approximately 2 metres above the ground. Being T&G flooring, some deflections in the floor are more noticeable and annoying (max 10 mm deflection over a 3.6 metre span). The deflection has been there since the house was built and hasn't worsened since then. I'm in the process of repairing these and would love some expert opinion/ advice. I'm happy to go to the trouble of "sistering" these joists with similar size Hyspan timbers. If I did this, what is the correct method of doing so in terms of gluing, nailing, screwing, web stiffening etc. I've also been advised that I could just use construction grade plywood (instead of sistering with hyspan timbers) to stiffen both the web's and flanges to remove the deflection. In both cases, I'll be firstly propping the joists to remove the deflection beforehand. I've also included some photo's, including how the joists are attached to the bearers at each end. Please let me know if you believe this may be contributing to the problem. Please also let me know which method, or alternative you'd recommend. Many thanks. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Re: Correct deflection in floor - hybeam joists 2Aug 27, 2018 10:54 am Have you checked that the builder has used correct beams and spacing as per engineering design? What is the span of your joists? Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Correct deflection in floor - hybeam joists 3Aug 27, 2018 10:58 am building-expert Have you checked that the builder has used correct beams and spacing as per engineering design? What is the span of your joists? The span is approximatey 3.6 metres, which appears to be within the allowable range. Again, the deflection is minimal, however I do want to correct it and simply need to know the correct way to go about this. Many thanks. Re: Correct deflection in floor - hybeam joists 4Aug 27, 2018 1:55 pm You have not answered the question I have asked the question because every building problem is a jig saw puzzle and you have provided only half of the pieces. What is causing the deflection? It must be a load to have caused deflection or otherwise beams with no loadings will be straight.(unless they are crooked) Your proposed method of stiffening is misdirected. Deflection occurs when resistance to bending stresses is inadequate and the resistance to bending stresses is provided by top and bottom flanges. Forget plywood to web, additional beams will be more effective and I would go for F17 KDHW because they also help eliminate bounce. I have hj300 14m long continuous over 3 spans @450crs. and never had any issues but I used 2 rows of herringbone bracing at each span to stiffen the beams. Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Correct deflection in floor - hybeam joists 5Aug 27, 2018 5:38 pm Thanks for your assistance with this. Would you recommend "sistering" the joists with the new beams, or placing the new joists in between the existing ones (bring the spacing down from 400mm to 200mm centres ? Also, please take a look at the way the flange was notched out on one side (in the pic). Could this be causing the deflection experienced (remember, it's only aproximately 10mm over 3.6 metres)? Thanks again. Re: Correct deflection in floor - hybeam joists 6Aug 28, 2018 6:38 am Notching at joist bearing will have no effect on deflection as the bending stresses are maximum at middle of the beam or at concentrated loads. As I pointed out before, you have presented half of the picture puzzle. No one in their right mind will give you useful advice based on that. Do yourself a service and engage a structural engineer to review the cause of the deflection and recommend a cure. Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Correct deflection in floor - hybeam joists 7Aug 28, 2018 8:41 am I'm pretty sure I've provided all of the information you've asked for. The joist sizes, their spacings and spans, as well as the flooring material used above the joists. The correct beams and spacings were applied per the engineering designs and these were independently certified. Please let me know what other information you need. Thanks again. Re: Correct deflection in floor - hybeam joists 8Aug 29, 2018 6:44 am No there is insufficient information, what is needed is site inspection to verify the deflection, diagnose its cause (review documentation) and then recommend a remedy. Despite certification how do we know that the builder followed plans and detailing. How do we know that the owner has not altered something post construction? On this forum I provide guidance and general advice to assist owners in the right direction, I do not provide project specific free advice. That type of advice is fee for service and my question is why are you not asking your engineer? Remember this Free advice is worth money you pay for -nothing. The best advice is the advice you pay for because it should be the best option of the available alternatives and should save you more money (hopefully much more) than you pay for the advice and make your life easier. However you might get lucky, PM StructuralBIMGuy, he seems to offer structural free advice on this forum. Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Correct deflection in floor - hybeam joists 9Aug 29, 2018 5:50 pm With all due respect, we're talking about a 10mm deflection over 3.6 metres that hasn't moved in almost 12 years. Most people wouldn't even worry about it. However being a perfectionist I want to correct it and enjoy walking across a truly level polished timber floor. There is a heap of information on Youtube regarding how to correct deflections such as this by using simple "sistering" techniques. Perhaps someone else on this forum who actually knows the correct way to "sister" Hybeams in these situations could provide some simple advice. The key thing I need to understand is where to nail/ screw correctly into the actual Hybeam. If this site is the wrong place to seek such advice, then just let me know and I'll be on my way. 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 14651 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 16842 Hi All, about to commence a bathroom renovation and need some advice on subfloor works. Current subfloor is hardwood T&G floorboards on 90x45 joists, but intention is to… 0 5849 |