Help identifying framing issues? Photo and 3D imagery available 1

[adlib13]

Hey all! I'm a mechanical/structural engineer from the aerospace world that's new to building structural and don't have a strong intuition yet. Perhaps you can help me!

I'm currently under contract for this new construction house and it caught my eye that the roof rafters aren't stacked/aligned with the studs. Is this a structural issue given our heavy 225 psf Tahoe roof snow loads? Or will the doubled top plate and sheathing adequately redistribute the load into the studs without issue?

Anyone see any other issues? There's a full detailed high res 3D Matterport scan if you want to fly around!

https://my.matterport.com/show/?m=rE3i8zh6gfw&brand=0

 

[OldDawgNewTricks]

You could check the double top plate capacity to see if it's OK. Consider if there are any locations where one of the plates is spliced in between studs and so you might only have a single top plate to carry the load.

Another potential issue that I see is providing a continuous load path for wind uplift. There are hurricane ties from the rafters to the top plate, but where does the load go after that? Are there ties to the studs, etc. to form a continuous load path to the foundations?

Is this a ground floor story or upper story? I don't see any hold-downs, but maybe there are strap ties on the exterior face that are not visible.

When you say you are "under contract for this new construction", what is your role? Are you the EOR responsible for the design? Might be a good idea to find a more experienced engineer to review things.

 

[BAretired]

I prefer to see the rafters aligned with studs, but in your case, it has been built without aligning them. For normal snow load, I don't think there would be a problem, but 225 psf, if valid, is an extremely large snow load, so you must check the top plate, because it could very well be a structural issue. The contractor used poor judgment in failing to align the rafters and studs.

Conservatively, consider the double top plate as two separate members, one sliding freely on the other, unless special care has been taken to glue and screw them together. Also, check to see where each member is spliced. And check penetrations such as the one beside the window to the right.

Other issues: Check whether solid blocking is required between studs. I believe they should be provided at 4'-0 spacing.

 

[SWComposites]

Presumably the OP is under contract to buy the house.

To the OP - have you discussed this with the engineer that sealed the structural drawings? And have you reviewed those drawings?

 

[jhnblgr]

Looking at the photos it’s a relatively short span to the next beam support so based on that there likely isn’t a tremendous amount of load on the wall, what’s the slope and type of roof system would be needed to determine the roof snow load. I have ran calcs where the studs were crushing the bottom plate causing the need to change framing methods. What did you use for the photos they are handy looking.

 

[adlib13]

To clarify: i am under contract to buy (not engineer!) the home. Sorry for being unclear about that. what I wrote was indeed confusing.

You could check the double top plate capacity to see if it's OK. Consider if there are any locations where one of the plates is spliced in between studs and so you might only have a single top plate to carry the load.

Smart! I'll look closely for top plate splices and see where/how they're reinforced.

Another potential issue that I see is providing a continuous load path for wind uplift. There are hurricane ties from the rafters to the top plate, but where does the load go after that? Are there ties to the studs, etc. to form a continuous load path to the foundations? Is this a ground floor story or upper story? I don't see any hold-downs, but maybe there are strap ties on the exterior face that are not visible.

Here I was entirely focused on compression, but great point about tension load path! I'll look into this and ask the builder + structural engineer. This is upper story.

When you say you are "under contract for this new construction", what is your role? Are you the EOR responsible for the design? Might be a good idea to find a more experienced engineer to review things.

Mwahaha definitely not the EOR for this. I'm under contract to buy the house and just happen to be a mechanical engineer with enough structural engineering understanding to ask dumb questions + get myself in trouble but not enough understanding to know what i'm doing.

I prefer to see the rafters aligned with studs, but in your case, it has been built without aligning them. For normal snow load, I don't think there would be a problem, but 225 psf, if valid, is an extremely large snow load, so you must check the top plate, because it could very well be a structural issue. The contractor used poor judgment in failing to align the rafters and studs. Conservatively, consider the double top plate as two separate members, one sliding freely on the other, unless special care has been taken to glue and screw them together. Also, check to see where each member is spliced. And check penetrations such as the one beside the window to the right.

I'll run some calcs and ask the structural engineer to do the same.

Other issues: Check whether solid blocking is required between studs. I believe they should be provided at 4'-0 spacing.

Maybe someone else can weigh in on this, but reading up on this briefly it seems that horizontal fireblocking in stud walls tends to be required every 10 ft - but our walls are only 9 ft, so perhaps that's why there's no blocking.

To the OP - have you discussed this with the engineer that sealed the structural drawings? And have you reviewed those drawings?

I've gotten in touch with them and they're worried about this, but they don't have the bandwidth to support right now : ( So i'm getting second opinions and taking matters into my own hands? Not really sure what to do. Only a few days the GC says before insulation goes in and drywall goes on. As for the drawings... I need a crash course in how to do structural engineering for homes and how to read these drawings. Any tips?

Looking at the photos it’s a relatively short span to the next beam support so based on that there likely isn’t a tremendous amount of load on the wall, what’s the slope and type of roof system would be needed to determine the roof snow load. I have ran calcs where the studs were crushing the bottom plate causing the need to change framing methods. What did you use for the photos they are handy looking.

The design criteria for ground load is 321 psf, roof load is 225 psf, the slope is 5 in 12, and it is composite shingle. The 3D imagery was a proper Mattterport scan that a local realtor did for me for $200 so that I could know what is behind any given wall in case of future changes or issues.

 

[dik]

I'm not into wood construction very much. Is that a continuous dimensioned lumber 'band' (strip at the end of the joists) and are the joists connected to it? Does the exterior sheathing extend past the band to tie everything into the wall construction? For heavy loading, I would assume that this is the construction.

If those are hurricane ties, it would be far better if the joists lined up with the wall studs.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JoelTXCive]

Building code only requires the joists to line up directly above the studs if there is a single layer top plate.

Your house has a double layer top plate, so the studs and joist do not need to line up. The double top plate serves as a beam to direct the joist load into the studs.

 

[dik]

This was the only one I was aware of...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[OldDawgNewTricks]

Building code only requires the joists to line up directly above the studs if there is a single layer top plate.

The prescriptive IRC Chapter 6 provisions that you cited do not appear to apply in this case because the snow loads are too high.

OP said the ground snow load is 321 psf.

 

[JAE]

OldDawgNewTricks is correct. The stated snow load sends you OUT of the IRC and into the IBC where you can't use traditional prescriptive rules of framing - and must design them accordingly.

 

[JoelTXCive]

OldDawg - Thank you for pointing that out! We don't even know what snow is in South East Texas, so I was not even thinking about it.

So, yes, if the accepted engineering practice is that the studs line up; then they definitely need to. (or if the engineered drawings say they need to line up)