question about home renovations

[Lion06]

I am sure many of you watch all of the home improvement shows (either by choice or force). I often see people just adding sliding patio doors or french doors out onto a new deck where there was only exterior wall.
Obviously a header is sized for this application.
The question I have is regarding the lateral resistance of the house. I have never seen any of these shows make any mention of the lateral system. How does one go about determining if the wall you are about to cut a 6'x8' hole in is a shearwall?? I would expect that whoever designed the house would have used every exterior wall of the house (solid walls, and solid panels between walls) as a shearwall in an effort to get the unit shear on each wall as low as possible.
That being said, if you start cutting holes in those shearwalls and making them essentially worthless, it seems to me that someone should be verifying this is acceptable rather than simply sizing a header for vertical loads.
Can someone tell me if I am missing something?

 

[DWHA]

CJSchwartz
Glass is not the best material to use to resist shear, but that does not mean that is does not have some shear capacity. I am just saying that having a patio door will not make the wall worthless. And a properly framed in patio door will not significantly reduce the shear capacity, unless you have a very small house and a very large door.

 

[Lion06]

DWHA-
If you have a 30' wide x 9' high shearwall (assume an entire wall is available). Now you cut a 7' x 7' hole in the middle of that wall. How will you transfer shear across that opening to make this act as "one" wall? If you assume (2) shearwalls (which is perfectly reasonable), the unit shear will increase only marginally, but you have such a smaller "d" now that I would be amazed if a hold-down wasn't needed.
I don't think you can just cut an opening that size in the wall and assume that it will not significantly affect the lateral resistance of the building. Even if you look in Breyer's book, the shear on perforated shearwalls is considerably higher around the openings and is accounted for in the original design. Unless you tear off the siding and take the steps necessary to achieve this extra shear capacity, the segmented shearwall is the way to go. That being said, the "d" is getting cut down immensely as stated above and this has real consequences that can't be rationalized away, IMHO.

 

[DWHA]

So are you ignoring any and all strength of the door? If you are ignoring that then I will agree with you. But, the door itself does have shear strength and forces will be transfered thru it. You can neglect it, and that is a conservative approach. But that does not mean that is wrong to say that the door does have some capacity.

Do you think that everytime that a patio door is added the contractor takes measures to prevent this. No, it does not happen. That being said, Have you seen a house that has failed in this way prior to other significant failure?

 

[csd72]

DWHA,

Structural items are required to be ductile, something glass is not.

 

[UcfSE]

DWHA, what exactly is the capacity of the door? Is it connected correctly to transfer load? Has the manufacturer designed the door for the racking load you are requiring or accounting for? There is also csd's point about ductility.

I don't agree that it's ok to do what you want because something else will fail first anyway. That only means that more than one member or system was incorrectly designed.

 

[Lion06]

DWHA-
I agree that the door may have some shear resistance, but it is not something that can be counted on (there is no way to quantify it). Also, as csd72 points out, the glass is not ductile.
No, I don't think a contractor takes measures to account for this - that was the whole point of my initial post.
Also, I am not sure that just because I personally haven't seen this result in a catastrophic failure makes it "right". It is quite possible that there has been enough redundancy in the system to make up for it, or maybe the building hasn't experienced its design loads... either way, I don't think we, as engineers, can just say it is ok without investigation.
I have seen houses with cracks (in the drywall) radiating from the corners of the doors in situations like this. This may or may not be directly attributable to what we are talking about, but......
That being said, I was trying to figure out if these guys are doing something behind the scenes that we are not seeing or if this is a nightmare waiting to happen. If the first is true, I was curious as to what went in to checking this kind of thing (as you can see from some of my previous posts in this thread).

 

[DarthSoilsGuy]

sounds to me like this may be one of the main reasons it is not required. Because, engineers don't want to touch it (or at least not for the crappy sum that the contractor or homeowner is Begrudgingly willing to pay for the piece of paper).

all the time, I get cold calls to look at existing residential foundations to sign-off on them for loan approvals. Our competition is rushing to shmooze me for all the "referrals" i give them.

 

[Tomfh]

I think it's pretty safe to say that lateral stability isn't checked for your average door installation.

 

[SnTMan]

I think in this part of the world (mid USA) all you need to build houses is a pickup and a circular saw

regards,

Mike

 

[unclesyd]

The only show that routinely refers to permits, architectural, and engineering help is the show "Holmes on Homes" with MIke Holmes. He always comments if the builder or remodeler didn't get permits or engineering help and that is part of the problem the homeowners have.

Another emphisis he has that the code is only the minimum requirements and may not completely fill the bill.

One of his latest shows he had Weyerhaeuser come in and design a beam for the first floor that carried the load bearing wall for the second floor.

 

[skier1578]

StructuralEIT,

I have often wondered the same thing. I practice in Southern California and if we have a project that only moves a window/door even 6" within a wall that could possibly be a shear wall, we have to look at the lateral system that "might" be there. If we don't - the building official will ask us to. You never know when that 6" made the holdown that was there obsolete. The homeowner is always happy about this process but it is often less expensive than stripping down the whole house to verify for sure where the existing shear walls are (or if there are any, depending on the age of the house).

I'm sure that if these shows do look at the lateral system, it is just not shown. After all, the parts that would be very interesting to us, just isn't to everyone else.

 

[Lion06]

I guess my concluding question is, "What would you do if you were doing a renovation to your own house?" Would you size the header for gravity and not give a second thought to the lateral implications, or would you start trying to check out the capacities and how exactly would you go about it? Would this change if you were doing a 30' opening on a 40' wall into a new addition (what was a lean-to with no lateral system of its own) compared to a 7' wide opening for patio doors?

 

[csd72]

Looks to me like it is a simple 3 step process.

1. calculate the load on the wall ignoring any contribution from internal walls.

2. Calculate the strength of the remaining wall using typical wall sheathing (note assumptions on sketch to be confirmed).

3. Calculate and specify the additional tie downs needed on either side of the opening. Also note edge nailing required to double studs.

csd

 

[UcfSE]

Another thing to keep in mind is a lot of jurisdictions don't require a structural engineer for single family homes less than a certain size.