Wrong rafter hanger used in framing - thoughts? 2

[cb1331]

Good morning all,

I am pretty sure I know how I will be responding to this, but was wondering if anyone has ever seen such a blatant misuse of a simpson hanger? The Building Official requested that an engineer look at a lvl 'ridge beam' as the supplier would not stamp it (i was already going in with eyebrows raised). It turns out that the ridge beam (2-ply 11 3/4" LVL) is okay, but the rafter hangers are hurricane/earthquake ties (Simpson H1 tie) - not rafter hangers. Snow loads in this area are 55 psf and this simply does not bold well for these 'hangers'. Any thoughts?

Much Appreciated.

 

[gte447f]

cb1331,
As some have pointed out, it looks like the rafters have been notched above the collar ties. Why is that? I would be concerned about that.

 

[cb1331]

Thanks for all the responses; some variance on a firm decision on which method is better (toenailing vs. hangers) but hey - welcome to structural engineering.

To clarify, the rafters have not been notched, and are continuous 2x6 rafters from the ridge beam to the supporting walls. Collar ties were strapped to the sides of the rafters with common wire nails (no nail gun). I sketched up a proper hanger detail for him using more preferred methods than hurricane clips as hangers - consequently the supplier provided him with these as hangers (so he says........).

 

[4thorns]

cb,
This might be a little off topic but I was wondering what the 2x8's below the 2x6 rafters are all about. If my attached drawing is somewhat accurate (can't see exterior walls), why not just use stronger rafters all the way to the ridge and save labor? I've seen this design used in trusses but never in my years of building stick framed homes, additions etc. I guess I could see it in an upgrade to an existing building but this appears to be new construction. Just curious.

Doug

 

[jefesdi]

4thorns,
The additional 2x8 framing, from what I can see in the photo provided, is most likely scabbed on undrframing to allow maximum batt insulation to be installed (probably R-38 batts and allowing for a 1" air space for venting) for the volume ceiling built. If it was me, I would be checking the adequacy of the rafter span (2x6's) to make sure that they are not overspanned and with all of the underframing applied, sloped and flat (collar ties). It appears the rafters are 2x6's @ 16" O.C., but I don't think the length of the rafter span was given. 55 psf roof snow load is pretty high.......it does confirm the colder climate application.

I would have liked to see the framed the roof with a larger dimension rafter, forget the scabbed on underframing (because your ceiling wall transition is still at the same height) and treated the whole roof system as a cathedral ceiling, thus rafter span & correct hanger selection for rafter connectors might not be a question?????

Just what I can decifer..........

 

[msquared48]

I agree with jefesdi about the scabbling on for insulation depth, and the fact that the rafters should have been 2X12's in the first place.

The 2X6's, if not overstressed in bending, will surely deflect down at the collar tie connection under full load allowing the deflection to be read outside in the roofing, and will probably become a permanent deflectior, if the snow load is long term. Moreover, lateral spreading of the exterior walls may become an issue with interior sheetrock damage seen.

I strongly suspect that a structural was not involved in the design prior to the picture being taken. Sharp Building Official though in my opinion.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

Also, with the load given, the position of the collar ties, and since the collar ties are a single shear connection with shallow members, I would check the collar tie connection very closely by running the numbers.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

Is it a collar tie or a collar strut? Under gravity load, it should be in compression.

BA

 

[msquared48]

Depends on whether or not the bearing walls can spread.

Good point BA, but with residential construction, I would expect tension.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[jefesdi]

If the roof ridge beam has beem "sized properly" acording to the start of this thread (with a low vertical deflection limit for this cathedral ceiling setup), then the collar tie would be in tension due to the fact that the top of the exterior walls are not restrained (which I assume is the case). That is why the connection at the ridge beam is so important in this instance. I don't know if the inspector even realized that the connection at the ridge could be in tension as well with an unbalanced snow drift. It might very well turn out that the rafters are undersized for loading & deflection, and that sistering new rafter members next to the existing will necessitate new (replacement) connectors at the roof ridge beam. Especially for limiting drywall cracking as msquared48 pointed out above, I would be concerned.......

 

[BAretired]

Whether it is a collar tie or a collar strut is an indeterminate problem which depends on the rafter location and the relative stiffnesses of ridge beam and rafter.

Collar ties located near the end of the ridge beam will tend to compress with snow load because the ridge beam deflection is minimal and the rafter deflection is normal to the roof slope.

BA

 

[unclesyd]

Just for curosity, I noticed that the rafter just left of center has a fairly large wane that goes into the connector. In our area this large of a wane is not permitted. The rafters to the right also appear to be older wood, not the pretty "white wood" again not permitted if the lumber has been in service. You have to cut out the previously nailed portion before you sneak it by.

have you contacted Simpson yet?