Question on roof eave blocking with Simpson A35 clips
My plans call for A35 clips on the eave blocking (2×6). Typical eave space is 22 1/2″ inches between rafters (2×8) with a 3 1/2″ x 5 1/2″ (actual) ceiling joist (this is a remodel – flat roof to gable) with new rafter nailed to it. Each rafter is tied down with Simpson H2.5A tie nailed to the wall douple plate (2×4’s). Single story home. The blocking will have three 2″ round vents in each one and the roof sheeting has to be nailed to the blocking. The plans do not detail where the A35’s go, or if one or two is needed per block. My engineer (plan maker) moved back east before the project was started. The plans state to nail (or screw) the clips to the top wall plate – should they be nailed to the top of the wall plate or to the side ? One or two clips per block ? Any help here? Is this overkill because I live in an earthquake state? Orignial plan was to just nail the blocks in as was typical years ago.
Replies
how about more rafter detail?
What's the after pitch and what does the bird's mouth cut look like?
Seems to me that if the blocking has to be nailed to the roof sheathing, then the bottom edge of your 2x6 cross blocking might be shy of the top plate (if fastened plumb). At any rate, with H2.5A rafter ties at each rafter, the A35's do seem redundant. I guess your engineer is really expecting the worst.
Another point to consider: If your blocking pitched perpendicular to the roof pitch that that will obviously set it at an angle to the wall top plate. That makes the A35 more cumbersome to install because of the primary 90 degree factory bend. There are bending slots for a section of each leg, but I don't see how you'd make use of them for the blocking to top plate connection. So it seems to me that if your blocking was pitched to the plate-- and you can hold blocking just to the outside edge plane of top plate--, then you'd want your engineer to consider replacing hte A35's with a TJC37 jack truss connectors. Maybe install two in each bay so that you can miss the 3 vent holes. Another plus is that each leg of the TJC37 are 3.5 inches tall, so they'd most likely reach your blocking if it has to be held off the plate in order to reach your roof sheathing.
Shear transfer.
The A-35s transfer shear from the roof diaphram to the walls. It is important that the roof sheathing be nailed to the blocks. You need one per bay. Locate them so that they miss the vent holes. Try to space them as evenly as possible, but the exact location is not critical. This is not just something your engineer thought up, it's code in many places. You can't have a gap between the block and the sheathing. The gap at the bottom due to the angle doesn't matter much unless the roof pitch is excessive. Put them on top of the wall plate If you nail the A-35s with a plam nailer they'll get sucked up to the block. Alternatively you can use an LPT-4 on the side of the plate and the face of the block. Your inspector will want to see them.
I (not surprisingly) disagree
IMO the blocking specifed here is intended for lateral bracing of the rafters. In fact, contrary to what this engineer is calling for, I believe this can be best achieved (and usually is) with a continous 2x sub fascia. Most residential framing does not transfer roof panel shear (minimal) to walls and there usually is no added blocking between rafters that is metal clipped to wall plates. If this is code, Mike, please cite it. Roof assemblies and wall assemblies are largely structurally independent. As for roof shear loads, they are usually resolved within trusses themselves or, in the case of rafters, resolved in ceiling joists or collar ties. I believe any code required connection is going to come from a hold down (tension for uplift) straps like the A35's. Further, any roof "diaphragm" action Mike refers to is going to come from the connection (usually nailed per code) between the rafters and the sheathing; same as floor framing diaphragms.
so, when someone has a question on this forum your default answer is always get an engineer...
when someone post a question here when an engineer design is in play you still seem to manage to show your true colors and either belittle the op by critiquing the fact that they have a question, or seem to know better than an engineer.
you do know that there are multiple ways of achieve a goal and your way is not the only way...
ref get an engineer
mark122 wrote:
so, when someone has a question on this forum your default answer is always get an engineer...
when someone post a question here when an engineer design is in play you still seem to manage to show your true colors and either belittle the op by critiquing the fact that they have a question, or seem to know better than an engineer.
you do know that there are multiple ways of achieve a goal and your way is not the only way...
In Florida you do not have a choice. All structural plans need to be stamped. In that case, if you need answers, call the engineer who stamped the plan. You already paid for him.
In the case of those A35s, depending on how you bend up those tails, they can be installed several ways so the guy who spec'ed them should have given you a detail.
I think deadnuts likes plastic?
Yes?
I'm sure the engineer in this case specified according to local code. The attached is from the City of Los Angeles, but is typical of all codes that have shear transfer requirements for horizontal diaphrams. The blocking and clips are required at floor diaphrams as well. Note the nailing requirements for sheathing at the blocking.
The attached pdf clearly shows the shear load transfer paths from roof to foundation. it includes code references.
That is a different clip
Eave Blocking A35 clips
Little late getting back - but the engineer (back east now) agreed I could use Simpson LS50's - they have just about the correct angle to mount just fine on the top wall plate and back side of the angled Eave Blocking. That way they won't interfere with the other required rafter ties. It took longer to order these from local hardware store - two weeks, rather then the normal "order monday get thursday" . Rain came back by the time I got the ties. So will wait for Spring to finish (unless I have a few more weeks of dry weather).
The engineer still wants them set at 16" o.c. - which she said would mean some blocks would have one and some two ties. So it will work for me - the angle can be adjusted where needed and would only be a slight adjustment. Total run is 56' on one side and 41' on the other - so lots of ties to install (and not cheap doing that many). I can only guess that it's for earthquake reasons (it's California) - too far from the coast for hurricanes and to narrow a valley for tornados. I will still nail the block ends from the rafter sides; then add the ties.
All in all I think I'll have as much metal as I have wood on the roof.
Thanks for everyone's comments. I'll post more pictures when I get the first two blocks or so done.
In addition to agreeing that this is now common in earthquake zones for sheer transfer along the top plate, I'd just say to not be shy about predrilling holes for the hanger nails in areas that are prone to splitting like near vent holes. Also installing clips at 16" oc does not neccessarily mean they have to be exactly at 16" - it's much better to be a few inches off one way or the other if it means the clip's nails are in solid wood rather than right on the edge of the block.
Mounting Eave Ties
Eave Blocking - Simpson LS57 ties
Thanks - quite correct - will get as close to 16 O.C. as I can with location of other ties, wood edges and other nailing taken into consideration and yes, I have the time to predrill all nail and screw holes [ OwnerBuilt(ing) ]. Time consumming ? yes - but better than split wood.
Have predrilled what seems like a thousand holes so far for all the rafter ties and hangers - makes for long day - but no splits. I have rafter hangers at ridge board and strap ties from one side to the other at the top - if not predrilled I would have had some splits by now.
Can't always get the best wood. Ordered over length and extra boards (16 footers) in order to cut (split) ends off. A couple so far will be cut up and used for eave blocking due to extremely warped boards and split ends.
Thanks for the input everyone.