Lag bolts splitting rafters?

I have started pricing systems in my area. The last installer I spoke to says he WILL NOT use traditional racking. He has had issues with splitting the 2x4 rafters with the lag bolts. Instead he, if given the job, wants to screw each panel directly to plywood with large L-feet.
I inquired about the next time I have to shingle. His reply was "that would be the shingler's problem". This is a Canada wide Chain of independant operators under a common name.
I'm a little stirred up.
Has ANYONE had the splitting rafters problem?

Comments

  • dreesdrees Posts: 481Solar Expert ✭✭✭
    Re: Lag bolts splitting rafters?

    The rafters should be pre-drilled prior to inserting rafters - I've never heard of rafters splitting when installed properly - maybe if the rafters were marginal to begin with!

    Most certainly L-feet "secured" to plywood is not actually secure. It would not pass inspection!
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    actually, i'm surprised they allow 2x4s in the first place, especially with the snow loads up there you guys can get.
  • toppertopper Posts: 113Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    Drees:That was my thoughts as well. 1)Place the standoffs 2)Drill pilot holes (from underside if need be to center on 2x4 rafters) 3)Bolt down standoffs 4)Install flashings 5)Install racks 6)Install PV's wiring, etc.
    Niel: These are "self supporting" truss rafters rated for all applicable loading. Standoffs are acceptable @ 4ft On Center according to engineering.
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    FYI, Engineered trusses often have a 2x4 top chord. One could (assuming attic access, add blocking between the rafters/trusses, bolt or nail those through the side of the top chord, then bolt to the blocking,, even use through machine bolts.

    Tony
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?
    niel wrote: »
    actually, i'm surprised they allow 2x4s in the first place, especially with the snow loads up there you guys can get.

    These would not be traditional rafters, rather "engineered" truss type construction with lots of bracing. www.trulinetruss.com/html/roof_truss.html
    Like others have said, if the installer had pre-drilled for the lag bolts, there would be no splitting. Sounds like he needs to be educated on a bunch of things:cry:
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    i still don't like the method as that transfers any stresses or weight to the 2x4 bottom horizontal section. i forget what mine are, but i believe they are either 2x8 or 2x10 and we're talking real time and not smaller due to shrinkage in the drying process. i might say it's shaky even going with 2x6, but 2x4 is crazy to me.:roll:
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Lag bolts splitting rafters?

    It isn't the size of the boards but the shape of the structure. Wood in compression has amazing strength. The biggest problem is when you get leverage action increasing the deflection - to the point of fracture. That's why single board spans need to be thick, and placed arc upwards.

    They make 'I' beams out of OSB and clear wood that can take twice the weight load of the equivalent solid wood, weighs half as much, and almost no deflection.

    Yes, I have a little bit of experience with this stuff. :cool:
  • icarusicarus Posts: 5,108Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    YOu may not like it Niel, but engineered trusses have been around for generations. If you actually look at the engineering specs, and the test to failure point, truss systems (floors/roofs/bridges etc are very efficient structures, pound for pound.

    I have also installed some flat truss systems that had no bottom chord connection to the bearing point. It looked like it couldn't support it's own weight much less the weight of the roof and the loads on it, and yet it was an amazing structure.

    Roof trusses can be engineered in all kinds of configurations to meet all kinds of application. For example, and attic type truss can be built with a significant open span to allow useable space, all while being strong enough for both the floor load of a living space, as well as designed roof loads, all with smaller lumber sizes, and less total lumber.

    The other advantage of truss applications is that they can handle much longer spans without needing intermediate bearing points.

    Enough about that for now,,,back to the OP. Have them predrill the top chord!

    Tony
  • toppertopper Posts: 113Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    Thank you all for your input.

    Bottom line from what I understand is, Don't be a meat head, Predrill with your good eye, and follow engineering specs.

    That guy Will NOT be doing the instalation of the PV's. I think I will opt to install the racking and PV's myself. Unfortunately, SaskPower now requires that only a qualified electrician do the electrical work Plus side: I work with a lot of electricians on a daily basis. Should be able to do a lot of the bull work myself and save some cash.
    Thank-you all again for clearing this up.
  • 65DegN65DegN Posts: 106Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    You might consider using Timberlock screws. They are slimmer to allow less displacement and splitting of the wood but tougher than a 3/8" lag screw.
    Also of course predrilling is worthwhile.
  • westbranchwestbranch Posts: 5,024Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    just to add a bit more info on truss construction. Most , if not all, engineered truss manufacturers will use MSR ( Mechanically Stress Rated) wood. the reason is that the wood arrives at the plant with a deflection value marked on it so there is no question about its strength. NOTE, this is NOT the same as and does not relate to the old visual defect based, Standard or '#2 and better' lumber grades most people are familiar with. I have seen 2 x 4 's that , in my opinion , would have been a #3 or reject and had a top MSR rating.

    If you get a chance to tour a lumber mill that has an MSR machine it will boggle the mind when you see how fast the test can be done... about 2 seconds per piece.

    http://www.msrlumber.org/designmsrlumber.htm

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge, Hughes1100 Sat Modem
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • solarixsolarix Posts: 713Solar Expert ✭✭
    Re: Lag bolts splitting rafters?

    We have switched to using the SDS screws made by Simpson and available at Home Depot. 1/4" engineered screw with tip designed to drill the wood rather than split it and rated for 260 lb pullout. Still want to predrill, but much better system than a lagbolt. However, my struct. engr still wants to go to installing blocking (2x4 nailed onto trusses) to avoid screwing into the trusses. Doesn't make sense to me though. Anybody else have to use blocking?
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?
    solarix wrote: »
    However, my struct. engr still wants to go to installing blocking (2x4 nailed onto trusses) to avoid screwing into the trusses. Doesn't make sense to me though. Anybody else have to use blocking?

    Still penetrations in the trusses, only several penetrations now to hold the blocking, rather than one down through the top. Interesting.
  • WindsunWindsun Posts: 1,164Solar Expert ✭✭
    Re: Lag bolts splitting rafters?
    solarix wrote: »
    We have switched to using the SDS screws made by Simpson and available at Home Depot. 1/4" engineered screw with tip designed to drill the wood rather than split it and rated for 260 lb pullout. Still want to predrill, but much better system than a lagbolt. However, my struct. engr still wants to go to installing blocking (2x4 nailed onto trusses) to avoid screwing into the trusses. Doesn't make sense to me though. Anybody else have to use blocking?

    As noted, the SDS screws are much better for mounting than the traditional lag bolts. Spec sheet here.

    If using regular lag bolts, predrilling a pilot hole is advisable to avoid sp[litting in 2x's. Pilot drill should be around 1/2 the diameter of the screw - that is, 3/16" pilot for a 3/8" lag bolt.
  • westbranchwestbranch Posts: 5,024Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    Solarix, is that just a 2x4 block nailed to the side of the truss or a 2x4 that spans the distance between the trusses?

    If the latter it will transfer/spread some of the forces (compression & tension) to 2 trusses rather than just into one truss
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge, Hughes1100 Sat Modem
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • solarixsolarix Posts: 713Solar Expert ✭✭
    Re: Lag bolts splitting rafters?

    My structural PE wants just a 12" 2x4 scabbed on the top chord. Can't talk him out of it. Going to be a real pain for us to mess around in the attic for a no good reason. Maybe I can talk to the AHJ to see if they will nix this. Really annoys me to have these people that have no skin in the game to be in authority over it.
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?
    solarix wrote: »
    My structural PE wants just a 12" 2x4 scabbed on the top chord. Can't talk him out of it. Going to be a real pain for us to mess around in the attic for a no good reason. .

    A 12 inch long piece or 2X4 with a bunch of nails and a screw through it ain't gonna be all that strong. Think your rafters might split with one screw? Ha! Don't be surprised to see some of the little pieces of 2X4 split to the point of practically falling apart. Sad how the power of authority goes to some peoples heads:cry:
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Lag bolts splitting rafters?

    Oh good grief! :cry:

    If it's necessary to reinforce the structure (thin sheathing, for instance) you would cut 2x4 (or 2x6) to fit flat against the sheathing in-between the trusses at the point where the panel mounts will screw down. These should be fastened with PL premium & screws, not nails.

    This will not only spread the load between trusses but also reinforce the trusses at the potential stress points (especially with 2x6).
  • westbranchwestbranch Posts: 5,024Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    making the assumption that you are paying for the PEng 's services,

    he should be giving you a full explanation and 'signed /sealed ' diagram of what you are to do and how to do it...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge, Hughes1100 Sat Modem
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?
    westbranch wrote: »
    making the assumption that you are paying for the PEng 's services,

    he should be giving you a full explanation and 'signed /sealed ' diagram of what you are to do and how to do it...

    Definitely agree! Then when parts of your PV system comes loose because the little scabs fall apart etc, perhaps he'll pay to have the PV system properly mounted. Methinks he may have never built any part of a real building. Book smart, but common sense poor. Unfortunately all too common in these modern times.:cry:
    Thank god, living in the back woods, I don't have to deal with people like that.
  • aj164aj164 Posts: 109Solar Expert ✭✭✭
    Re: Lag bolts splitting rafters?

    It is worth mentioning that squirting caulking or sealant into the pre-drilled hole can cause the wood to split. If you're using sealant, make sure the drill goes all the way through the rafter. This gives the excess sealant somewhere to go as it gets compressed by the screw. Otherwise, you're hydraulic fracking all over your customer's roof.
  • VicVic Posts: 2,878Solar Expert ✭✭✭✭
    Re: Lag bolts splitting rafters?

    Well, aj, have nexr seen this. As most sealants do not expand while curing. Because Lags have a spiral thread, excess sealant is pushed out, to the head of the lag (in my experience). It could be wiped off with a rag, or just left in place. Just my experience. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
Sign In or Register to comment.