New Rafter Connection into Existing - Different Roof Pitches

[Redacted]

Hi there I am working with an architect on a few building renovations. The architect would like to put a small shed ~5x5’ outside with a mono-pitched roof that ties into the existing building rafters.

I was wondering if any of you have any experience with connection details for new rafters tying into an existing for a situation like this with different roof pitches (see attached).

Or any documentation/references on best practice for this connection detail would be helpful as well.

I know it’s not a big load only being a 5’ roof extension but I would like to follow best practice with the connection type.

At this point, I was considering a bolted connection.

 

[jayrod12]

Yeah bolts or nails or screws. My preference would be one of the two latter as opposed to bolts. I just find that if you don't have to force the contractor to drill holes, the less that can go wrong.

 

[Harbringer]

Something like below. Of course you have to check the existing framing for stresses and deflection. You also should check wind uplift on the connection to the existing rafters. If you have trouble making it work you could switch the nails for Simpson SDS screws or slot the existing sheathing and provide a strap from new to existing rafter.

 

[Redacted]

Thanks all for the responses so far. The reason I was inclined toward the bolted connection is that the local building code recommends 1x 3/8” bolt for new rafters of this span to connect to existing.

Both rafters (new and existing) are timber 2x6’s.

Although the code only calls for one bolt I was considering 2 to add in redundancy.

Harbringer, I like that your proposed solution is a connection through the centroid of the rafters. However, the rafters are only 2” thick. Would you be able to provide more information (a front view) of the connection detail?

The way I was initially thinking was just to have the rafters side by side and do a through bolt connection (pretty simple for the contractor to do, see attached). Although if this can be changed into a bolted connection through the centroid that would be cleaner.

Can your proposed configuration be used with the two bolt scenario?

 

[jayrod12]

Can't bolt through the narrow face of a rafter.

I'm not a huge fan of bolts in this scenario. And trying to fit two bolts into that mating surface area will be even harder.

In Harbringer's detail, you would be using wood screws/nails (I'd use screws if the uplift is signficant) to fasten the 2x8 on flat down to each existing rafter. Then connecting the new rafters to that 2x8 with light gauge angle clips or something like that.

 

[dauwerda]

I like Harbringer's detail (or something similar) as it avoids any demo into the existing roof to make the connection.

 

[gte447f]

Harbringer's detail is the way to go. His detail is self explanatory as is; a front view is not necessary. I would not overlap the rafters as you are showing, because, to do so, you will have to remove the existing roof deck, as others have pointed out. If you were going to overlap the rafters as you are showing, then through bolts are completely unnecessary for for such a lightly loaded connection, when, theoretically, a single 16d face nail could do the job for 20 psf dead load and 20 psf live load. I never use 3/8 bolts for anything. I use 1/2 bolts minimum. In practice, I would use 2 or 3 clinched 16d nails if I were going to do it your way.

 

[Redacted]

Ah, I think I see where my confusion lied regarding Harbringer’s detail. He is nailing directly into the sheathing and not the existing rafter itself (or am I misinterpreting this). I had initially thought it was a rafter to rafter connection.

For clarity the existing roof is a slate roof (see attached general slate roof detail). Based on what I have seen of the existing roof it appears that the slate just rests on the laths, there is no sheathing - just laths (see attached image). The building is also in a hurricane prone country (150mph wind speeds), so the uplift is pretty high. We typically tie rafters down with hurricane clips at the ends.

I would prefer a solution where I didn’t have to remove the slate to secure the connection but the rafter appear to be the strongest structural element to tie to? Are there other better options? Any advice would be greatly appreciated.

 

[gte447f]

In that case (i.e. no existing roof deck sheathing), then I would overlap the new rafters with the existing as you were planning. Personally, I would use 16d face nails, the number of which to be determined by the magnitudes of the applicable loads, but you could use through bolts if you prefer.

 

[jayrod12]

Agreed that without sheathing, fastening to the face is a better option. Removal of the slate is unavoidable unfortunately.

 

[EdStainless]

How far above the collar tie and pitch kick will your new rafters be landing?
You are going to have to strip the tile/slate back anyway, Placing a 2x8 across the existing rafters and then clipping the new ones down looks strong and like it would easy to get right.
Just went through a similar process on my daughters house in S FL.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Harbringer]

The detail I posted would be nailed through the sheathing into the rafter below as noted. The flat 2x would act as a sleeper and span between existing rafters.

If there is no existing sheathing, I'd use the same detail but add vertical blocking under the flat 2x to provide some lateral bracing to the existing rafters. Why rely on a nailed or bolted connection through the face of the existing rafter when you can rely on direct bearing?

I'd also at least require real sheathing at the new part of the roof.

 

[gte447f]

KISS (keep it simple stupid) method. With existing sheathing in place, I would go with Harbringer's detail. I have used same/similar in this situation several times in the past. Without existing sheathing in place, it could not be simpler to face nail to existing rafters. The capacity and reliability of laterally loaded (shear) dowel type fasteners (nails) for wood to wood connections is well established and I see no reason to second guess or shy away from face nails. Harbringer's detail also relies on nails loaded laterally for wind uplift. I realize it is short term vs long term loading, but there is no reason to shy away from face nails is my point. I would not hesitate to use Harbringer's detail (over existing roof sheathing) with toe nails instead of the A35 clips; again, no reason to second guess nails.