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Residential Window Walls

Residential Window Walls

Residential Window Walls

(OP)
Yet another window wall, these things seem to love me, I don't love them. A couple issues with this window wall:



1. I've got 24" of wall at the corners and about 18" between the central door/window and side windows. I've also got a 7' to 8' pony wall underneath this window wall. Obviously I can't get any traditional shearwalls into the main window wall so my first thought was to use Simpson's (Wood) Strong-Wall (catalog C-L-WSW16) product which can be field trimmed to match the pitch of the roof and also is available in mult-story kits. Looking at the literature on the product it appears that it is always intended to bear on a concrete foundation and not other wood structures or members, hence the need to possibly use a multi-story kit or just balloon frame all the way up from the foundation to the inclined double top plate (ie. use a 20' strongwall).

The other option possibly would be to ignore the window wall entirely (as a shearwall) and do a three wall analysis treating the diaphragm as rigid and ignoring the window wall shear resistance. Section 4.2.5.1.1 of the SDPWS 2008 appears to allow for this since the great room is 25' wide and 16' deep with an L/W ratio of 0.64 and the diaphragm length (L) is less than 25'. Has anyone ever used this methodology in this type of circumstance?

2. The second issue appears to be a design flaw. The ridge beam needs to be supported at the gable end with a small beam that spans the polygon window above the door. How does one fit a beam in the space provided? I'm thinking we will probably just need to drop the window height until an appropriate size header can be inserted.

For reference the site criteria on this job is:

Roof Snow Load: 50 psf
Wind Speed: 85 MPH (110 MPH Ult.)
Exp. C
SDS: .739

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Is there a way to eliminate the ridge beam via going the scissor truss route? Saves you having to fight with that one aspect.

As for the lateral, I think 3 sided may be the only way to go.

RE: Residential Window Walls

If you need a ridge beam and support at the exterior wall you can weld a kinked steel beam together.

Scissor trusses cut the interior pitch of the ceiling a bit. You may be able to use a parallel chord truss if you can tolerate 14-16" of roof framing thickness.

RE: Residential Window Walls

(OP)
As I was jogging on the treadmill that thought came to me, support the ridge beam with a small parallel chord truss that then is hangered from the two PSL posts each side of the door.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

You could also probably design the rim over the wall on either side of the ridge as cantilevered beams to support the ridge. It looks like you have reasonable back span to cantilever distances. You'd want to review the hanger closely as you'll be near the edge of the beams.

RE: Residential Window Walls

I usually just do site built moment frames on these if I cannot get a three sided building to work.
That takes care of the lateral and support of the ridge.
If you did not have the lateral problem, I have supported ridges like that on cantilevered LVL's running up the rake. They are tied to the low corner and cantilever off the main window king studs.

RE: Residential Window Walls

Another option with the ridge beam is to replace it with two beams -- one at each post location -- and cantilever / two span the roof joists over those. It may be an easy sell as, in my opinion, that's the traditional framing look for this arrangement anyhow.

That pony wall's going to be pretty robust. As long as the detailing is complete and you're not violating any code limitations, I'd have no problem using the Simpson wall on top of the wood pony wall. Alternately, if the cost is tolerable, you could do the pony wall in concrete.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Residential Window Walls

Quite a few years ago, I ran into a similar construction, with the window wall vibrating during high wind gusting. Interior was not yet finished and the solution was to place 1 LVL (horizontal) above the door/lower window set header from wall end to wall end. As the LVL protruded into the room, beyond the final finishes, It was covered and turned into a high shelf.

RE: Residential Window Walls

(OP)
I like the idea of the site built moment frame (portal frame). I will sketch up a rough detail and post it. My concern is how to connect the ridge beam to the two cantilevered (glulam,LVL) beams at the ridge where they meet, never tried this before. Also the connection between the PSL posts at the sides of the door and the cantilevered beam that is now on an incline. I appreciate all of the input, I thought I was stuck but I can now see there might be a few ways to skin this cat.

On the previous most recent window wall I extended my PSL posts through the rim joist and double top plate of the pony wall to the concrete stemwall. Then applied a strap across the cut double top plate. Not sure if this is the optimal way to do that...

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Steel frame. We do it all the time.
The 3 sided box will not work. They have a ridge vent...aka a big slice down the center of your diaphragm severing all of its ability.
Also, a 3 sided boxed analogy on a sloping roof. Good luck with that. Again, the ridge is a discontinuity in your diaphragm.

RE: Residential Window Walls

(OP)
Here is a first draft at the site built moment frame idea with cantilevered rake beams:



Note that I have have not sized any of the members, straps, or holdowns just yet, the indicated sizes are my best guesses for now until I get the lateral and vertical calcs going. At this stage it is purely conceptual. The wall is symmetric so I only drew the one side.

My big question is the connection detail of the ridge beam to rake beams and the rake beam to PSL column connection at an incline (I may be worrying about nothing on that).

I mentioned steel to the designer and they gave me some very worried looks, that ended that conversation.

I also missed adding the horizontal straps connecting the headers.

The (2) 2x6 king studs next to the PSL column may need to be upgrades to something more stout as well I have to look at the out of plane bending on those and the rest of the wall studs and columns. My suspicion is that the wall may need to be 2x8.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
I also don't want the two cantilevered beams to separate so either a strap over the tops of them (ie. MSTA30, LSTA30 Page 87 Simpson Catalog) at the peak or perhaps a horizontal strap on the exterior side opposite the ridge beam hanger.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
It may also be helpful to create a nailed moment connection at the peak with 8d nails on a 3" x 3" grid, connecting the two rake beams. This may be something to put into RISA or build my own calculator for it. My current PFH calculator doesn't consider the inclined header and potential pinned or rigid joint at its center.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Quote (Bigmig)

The 3 sided box will not work. They have a ridge vent...aka a big slice down the center of your diaphragm severing all of its ability.
Also, a 3 sided boxed analogy on a sloping roof. Good luck with that. Again, the ridge is a discontinuity in your diaphragm.

I have never considered diaphragm continuity in a residential job of this scale. It is something that just seems to work.
I guess you could go with a ventless roof and screw bent sheet metal to the peak if you are worried about it.

RE: Residential Window Walls

(OP)
For the connection from beam to PSL I'm wondering if it might be possible to take a stock CCQ44 and bend the straps 30 degrees, you end up with a width of about 4.75" which can be made to fit a 5-1/4" wide PSL column with some minor notching. One could always order the CCOQ which is without the straps and field weld some on but then you would need a certified welder to make the connection. If the straps were heated (hand held propane torch) and then bent I don't think it would compromise the integrity of the column cap in any significant manner.

The main concern I have is the post slipping up along the beam without a positive connection, but looking at my detail the 2x6 blocking below the rake beam at the peak should help provide this stabilization in compression.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

We have done a handful of steel moment frames for this type of thing but the contractors up here are getting really used to having lots of steel in high-end homes.

RE: Residential Window Walls

(OP)
The other option as suggested is to go with steel (red iron) on the wall. I've actually never done one of those before so any examples that I could potentially use a starting point would be greatly appreciated. I've seen a number of high end homes with window walls done this way but I've never had the chance to get up close and personal on one and really look it over.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

I usually go with steel. FWIW, you could mortise the kings into the rake LVL a little w/o compromising them too much to prevent sliding.
Plywood on the outside and maybe some sheet metal on the inside would also likely work. Kinda depends on your roof slope and the angle of friction.

RE: Residential Window Walls

(OP)
The thickest LVL beam is 1-3/4", I want a minimum thickness of at least 3-1/2" and I'm not into nail lamming beams together. Wouldn't a 3-1/2" x 11-7/8" LSL beam work fine? I notice that a lot of engineers choose the LVL over the LSL, pound for pound the LVL is generally stronger in bending but LSL is usually more economical.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Why are you against nail-lamming? It's so ridiculously common that I never give it a second thought.

RE: Residential Window Walls

Why don't you want to nail the laminations together?
I never spec LSL beams except as bands. I have enough problems with way over-designed LVL's sagging on me. Don't wan't another animal to deal with.
Also, they simply don't stock them at the local yards.

RE: Residential Window Walls

(OP)
I always worry about the side loading if you have to hanger a beam from another nail-lammed beam. A single beam eliminates this problem. I'm probably worrying about nothing.

Here are a few numbers so far.

I have a 50 psf flat roof snow load -> sloped roof snow load of 50 psf

My glulam beam spans 16' and a 5-1/2 x 15 beam seems adequate for the job. My end reaction is 7464 lbs (2194 D + 5270 S).

Half of this reaction is picked up by each cantilevered beam, 3732 lbs.

With the cantilever beam the deflection and the bending control. I end up with a 3 ply (5-1/4" thick) LVL beam with the down force at the PSL column of 7179 lbs and an uplift at the end of the wall of 810 lbs.

I'm very nervous about the hanger at the rake beams. My SDS 1/4" screws attaching my HGU5.62 hanger are going to be quite closely spaced with 18 per rake beam and about 3" from the end of these beams, splitting may be an issue. It might be better to cut the inner ply at a scarf and then splice the two rake beams together and then hanger from this section. I probably need to draw a diagram to illustrate the point.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

As for the side loading. There are published calculations for LVL with side loads to determine what type of fastener and spacing is required

RE: Residential Window Walls

(OP)
I know I've got my copy of TJ-9000 open right now, looking at this page. I'm not saying it can't be done its just one more thing to hassle with and then spec out on the drawing so that the contractor doesn't mess it up. A single ply beam is more convenient.

Simpson calls for 2-1/2" SDS screws for the HGU hanger series this will really only penetrate the first LVL ply.

My idea might not have any merit but below is a quick sketch of the two rake beams spliced together and then the hanger attached to the splice:

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
I'm actually starting to think Kootk's idea of running two beams instead of one would be a much better solution. I've already spent way too much time mauling this whole thing over today but I'm still not satisfied with the solution.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Sounds like a better idea. I would not try that connection with that kind of load. Mine ridge reactions typically max out at about 2500 lbs. when I use that system.

RE: Residential Window Walls

(OP)
So the architect likes the idea of the dual beam design with cantilevered roof joists, time to rerun all my numbers. I am still going to keep the LVL rakebeam (1 ply only) to use as part of my moment frame, however it will no longer be carrying any significant gravity loads and I will use a 14" deep LVL to match the I-Joists of the vaulted roof.

The one issue now is the architect wants the PSL post centered in the 18" wall section, how exactly the additional studs and trimmers frame out around it is a bit of a mystery...

I've also never encountered a cantilevered roof joist system like this before. I'm planning on installing a strap across each joist to the opposing side but beyond that is there anything else to look out for?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
I think I am going to go ahead with the wood moment frame system on this wall. The wind loads are fairly low as are the seismic (comparatively speaking) so I think I can make the numbers work. However, I am interested in broadening my horizons so that I can do a window wall design in steel in the future. What are some resources for doing this type of residential design with steel? I have a number of steel text books and the code books already but these really don't provide much direction as far as what a typical design should look like.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

If you go steel you can go with an ordinary moment frame and then the detailing is easier but you have to take a hit on the R value and that will carry over to your wood shear walls too unfortunately so we usually go with a SMF. The problem with the special is that there are requirements for lateral bracing of the top and bottom flanges of the beam and this isn't very possible with wood framing. It seems to be conveniently ignored to some extent around here. Here we would probably have a two story moment frame with a bolted flange plate (BFP) connection at the upper sloped beam and a reduced beam section connection (RBS) at the lower horizontal beam.

RE: Residential Window Walls

(OP)
I understand the terms OMG and SMF but the rest is Greek to me, I might as well stick with wood for now, at least I understand what I'm dealing with.

With the two beam design the 14" deep TJI Joists will be resting on the glulam at a 7:12 pitch. Based on the TJI documentation you cannot birdsmouth cut I-joists on the upper bearing points, only lower bearing. What do you typically see done in this situation, beveled glulam, beveled bearing plate, variable slope seat connector?

Based on TJ-4000 I will also need to nail (2) 8D nails from the I-joist bottom flange into the glulam and also install a backer block and twist strap (slope greater than 3:12).

The architect also wants to use flat 2x4 outlookers (gable overhang of 18") however I don't see how one can notch around the flange if they are oriented this way (detail O, page 30).



A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Quote (medeek)


With the two beam design the 14" deep TJI Joists will be resting on the glulam at a 7:12 pitch. Based on the TJI documentation you cannot birdsmouth cut I-joists on the upper bearing points, only lower bearing. What do you typically see done in this situation, beveled glulam, beveled bearing plate, variable slope seat connector?


Quit using those god-awful TJI's and your problem is solved!

RE: Residential Window Walls

(OP)
What's wrong with TJI's? I like their product better than LP or BCI, in my opinion its a better product. How else are you going to span these floors and roofs? Floor trusses are too expensive and in my opinion are not stiff enough, the joints have a miniscule amount of play in them but it all adds up so floor performance suffers.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

I also prefer trusses like xr250. I've seen too many rotten tji joists from minor water infiltration.

My hands are tied a lot of the time.

RE: Residential Window Walls

(OP)
Here is what I have so far. I think I have all my load paths covered but I will maul it over during the weekend and gladly consider any feedback from the board. Somewhat of a non-standard portal frame (moment frame) going on, I'm still figuring out how to analyze it fully. My strap and holdowns are still pending my final lateral numbers. The ambiguity is caused by assuming a rigid diaphragm so the lateral load to this wall is somewhat governed by its rigidity compared to the other three walls of the room. How to assign a rigidity to this construct is where I'm scratching my head at the moment. More rigidity will attract more load which will drive up my straps and holdowns...

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
Forgot to add the pad footings for the PSL posts

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
I created a simple moment frame model in RISA2D, to look at the forces involved. The worst case scenario is only about 1,500 lbs lateral from wind with a flexible diaphragm, rigid diaphragm gives a much smaller lateral load. The results are shown below:

Axial Loads:



Shear:



Bending:



Numbers:



The problem with the model is that it is a little to simplistic. I don't have a member type that I can use to simulate the shear wall panels (RISA's wall panel aspect ratio limitation did not let me use a high aspect ratio wall panel), so I just used the same 3.5 x 11.875 LVL for all the members. Varying the stiffness of the shear panel will affect the moment distribution at the top and bottom of the shear panels.

One interesting thing that popped out was the zero moment at the peak. If the load from the diaphragm is balanced this is the case and there is really no need for a moment resisting connection at the peak. Granted the wind loading will not be balanced but overall the moment at the peak will probably not be significant.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
The largest moments are at the shear panel base as expected. I have 24" of width at my shear panels so my worst overturning force will be: 2376 lbs + 385 lbs = 2,761 lbs

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
I've created a SketchUp model to help identify any further problems with the design. I just realized that the floor joists will not span the 25' of the room and a floor beam will be required at mid-span.



View model and download SketchUp model here:

https://3dwarehouse.sketchup.com/model.html?id=cb4...

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Quote (medeek)

What's wrong with TJI's? I like their product better than LP or BCI, in my opinion its a better product. How else are you going to span these floors and roofs? Floor trusses are too expensive and in my opinion are not stiff enough, the joints have a miniscule amount of play in them but it all adds up so floor performance suffers.

I actually meant I-joists in general. We use 2x10's and 2x12's here for most roofs . I-joists if we have to. The framers and contractors prefer the dimensional lumber.

For floors, I use mainly 2x10's or 2x12's with steel I-beams or LVL beams if needed.
Sometimes I-joists and floor trusses, if there is no other practical option.
Here is my problem with i-joists (based on my field experience)

1) difficult to frame with if sloped or skewed
2) The flimsy OSB bands suck for point loads and do not like water. Deck attachment is sketchy at best. I usually spec LVL bands behind decks.
3) Make renovations difficult as they are difficult to modify
4) They don't hold up well in fires (this is anecdotal but believable)
5) Blocking point loads thru them is difficult and is rarely done well or at all. I have seen numerous I-joists buckled from point loads. Never seen a 2x10 do that.
6) The loads from the long spans joists and their skinny profile cause them to dig into dropped beams. The blocking between them does not, so it causes a hump in the floor and will pop floor tiles
7) They do not hold up to water (as Jayrod said)
8) I have seen too many instances of them sagging alot more than they should under sustained loads - such as heavy kitchen islands.
9) They are expensive! - which is why tract builders try to span them out in length and spacing.
10) They are not designed to be used in typical roofs without structural ridge beams. This requires the expense of the beam and the expensive hangers.
11) Cannot notch them and use ledger strips - like dimensional lumber (further adds to the cost)
12) Another source of off-gassing in a house (I am guessing)
13) They seem to shrink in length just as much as dimensional lumber.

I could go on and on, but I am tired.

RE: Residential Window Walls

(OP)
Added the pad footings and a few more straps:



A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

(OP)
The designers here are starting to go with 14" I-Joists on the mid floor levels so that all of the central air ducting can live inside the floor. In some cases they remove most of the web (about 12" holes in height) in strategic locations. I haven't evaluated those situations in the detail but the I-Joist manufacturers and their software has given them a green light on it. I think if large holes are in the central portion of the span where the shear values are minimal then everything should be fine, similar to a rect. chase through a typical floor truss.

I've read quite a bit on the fire resistance of I-Joists and I would tend to agree traditional 2x10 and 2x12 lumber is hard to beat. Similar problem with plated trusses though. I think the building industry (residential) tends to turn a blind eye to this issue, otherwise costs of building homes would become exorbitant.

I've never really encountered any water damage to I-Joist floors but I've seen some issues with roofs where there is no venting, granted the 2x10s would probably not have fairly very well either, but major mold and drywall damage was more the issue than structural damage on that particular job.

Agreed on the point loads. Squash blocking is a must, the flimsy OSB webs will simply collapse.

They are supposed to be more dimensionally stable than regular lumber, less shrinkage, warping and twisting. I do think this is where they beat out the traditional lumber. In my opinion I think they are stiffer than typical plate floor truss but some studies may prove me wrong, just my gut and anecdotal evidence on that one.

The I-beam shaped profile should theoretically give a more efficient structural shape, so less weight and cost for the same performance. On the positive side what is driving I-Joists versus other solutions?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Quote (medeek)

On the positive side what is driving I-Joists versus other solutions?
Dunno. Good marketing and misinformed Arch/Engineers IMHO. Many builders love these things (mostly tract builders), so if they request them, I guess ya might as well specify them.
Most of the custom builders I work with prefer dimensional lumber if it makes sense.


RE: Residential Window Walls

(OP)
How does the price compare between dimensional lumber and I-joists in your market?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Quote (medeek)

What do you typically see done in this situation, beveled glulam, beveled bearing plate, variable slope seat connector?

I've seen a few beveled bearing plate conditions.

Quote (medeek)

Varying the stiffness of the shear panel will affect the moment distribution at the top and bottom of the shear panels.

If it's at all possible to do so, I would design the moment frame as though it were taking a load consistent with a simple diaphragm assumption. It will be overkill for the moment frame but, given the inaccuracies involved in estimating the share going to the moment frame, I feel that this approach is prudent.

Quote (medeek)

One interesting thing that popped out was the zero moment at the peak.

I would model that joint as pinned in your analysis for the simple fact that it would be rather difficult/expensive to attempt to create a moment connection there anyhow.

Quote (medeek)

The largest moments are at the shear panel base as expected.

I might model the interior PSL column into the moment frame as vertical pins / horizontal rollers at the underside of the rafters. Whatever overturning winds up being resisted by the axial loads in those posts will be overturning that doesn't have to be resisted by the base connections of the moment frames. It should improve matters some and be a better reflection of reality.

Quote (medeek)

I understand the terms OMG and SMF but the rest is Greek to me

Yeah, I hear 'ya. As rn14 intimated, the trouble with using steel special moment frames in wood is getting the requisite beam bracing somehow. I believe that's fundamentally why the Simpson moment frame offering exists: it's been tested without the bracing. Whether you go with a special moment frame or an ordinary moment frame, I won't bullshit you, the design of the first couple of frames will be painful fee burners. If you go that route, I'd recommend trying to more or less mimic the Simpson frames as they were developed with wood frame constructability in mind. Include things such as:

1) Beam and column sizes that you use repeatedly so that you can use template calcs and details that you'll develop.
2) Bolted end plate moment connections.
3) Allowance for top and bottom plates in wood.

As for figuring out what's going on with steel moment frame design, I'd recommend these resources:

- AISC Steel Design Guide 28: Stability Design of Steel Buildings
- AISC Steel Design Guide 4: Extended End-Plate Moment Connections Seismic and Wind Applications
- AISC Seismic Design Manual

It's no harder than the wood moment frame systems that you've already mastered but it is a new beast with some different claws and fangs.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Residential Window Walls

Quote (medeek)

How does the price compare between dimensional lumber and I-joists in your market?

In my market, dimensional lumber is pretty much dead for horizontal applications other than decks. All TJI, all the time except for pitched roofs. This is especially the case for taller wood buildings where shrinkage is the name of the game. When I worked for the Wood Truss Council of America, I was continually shocked at the degree of regional differences present in the use of pre-engineered wood products. Some places in Florida and Texas, the truss fabricators will ship out entire neighborhoods prefabbed. In other markets, even floor trusses are shunned and you still get guys wanting to frame pitched roof with 2x. Even where I'm at now, floor trusses are very rare despite the widespread adoption of TJI and roof trusses.

I don't sweat any of the fire issues these days other than following code. The research that I've seen in recent years all points to fire safety being almost exclusively a function of sprinkler system and alarm system performance. Statistically, it seems that that the materials of construction aren't really even very influential any more with respect to fire safety.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Residential Window Walls

Quote (KootK)

I don't sweat any of the fire issues these days other than following code. The research that I've seen in recent years all points to fire safety being almost exclusively a function of sprinkler system and alarm system performance. Statistically, it seems that that the materials of construction aren't really even very influential any more with respect to fire safety.

Makes sense as long as the structure has sprinklers. Most single family homes do not.

RE: Residential Window Walls

Quote (Medeek)

How does the price compare between dimensional lumber and I-joists in your market?
Last job I checked was 2x12 versus 14" i-joist (base grade BCI).
The i-joists were 65% more. That did not include all the additional hangers etc required.

RE: Residential Window Walls

(OP)
Western Washington and Oregon are also pretty much I-Joist floors with manufactured truss roofs. The occasional custom home or old timer wanting to do something different. Floor trusses are rarely used in residential applications and solid sawn is for walls and pressure treated for deck joists. In the immediate area the small builders like to use solid headers 6x6, 6x8, 6x10 and the larger builders go for the LSL headers 1-3/4, 3-1/2 etc... It interesting how certain areas build certain ways and tend to stick with it. Utah on the other hand likes to use (2) 2x10 headers, at least the plans I've seen.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Quote (XR250)

Makes sense as long as the structure has sprinklers. Most single family homes do not.

Good point. To counter:

1) travel time to safety in a single family home is usually pretty minimal too.

2) It tends to be finishes and contents that contribute to fire load during the fire rating period more than skeletal structure.

3) joists are subject to the same fire testing requirements as everything else. If one wishes to go beyond what society deems "good enough", then I suppose that is another matter.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Residential Window Walls

Kootk,

I evaluate a few fire damaged structures a year. The sheetrock does a damn good job of protecting the joists. When it gets into an attic, the dimensional lumber will typically char a bit but then no more damage occurs unless the fire goes un-checked. Many times, repairs are not required. I imagine an i-joist in that situation would be toast - literally and figuratively.

RE: Residential Window Walls

Quote (XR250)

I imagine an i-joist in that situation would be toast - literally and figuratively.

I don't disagree. And if the goal is extra-code fire performance, then I'd also agree that solid sawn joists would have a leg up. I guess my point is that, as with most things engineering, I feel that it's generally the client's prerogative to decide whether or not they want extra-code performance. I know just enough about fire science engineering to know that it's actually pretty complicated and I've got little business practicing it other than to follow the basic rules. In my market, the great minds of fire engineering science have decided that TJI's are good enough to provide the socially agreed upon level of fire protection. I wouldn't insist upon more unless I'd sold it to the client ahead of time as a value add.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Residential Window Walls

(OP)
As and add on I've come up with a detail for the cantilevered I-Joist roof:

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

Looks good. However, it further bolsters my case on how difficult it is to work with I-joists. That detail would be much easier with dimensional lumber if it worked out spanwise etc.

RE: Residential Window Walls

(OP)
Good point, the detail in the manufacturers called out for a twist strap at the bearing point on the beam, but I didn't want little tabs sticking down that would be visible so I had to devise a different method to make the connection between the beam and the I-Joist, bit of a pain

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Residential Window Walls

One could install a non-structural ridge board and some variable slope hangers for, perhaps, more conventional detailing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Residential Window Walls

Good point. I just checked the price on them and they are only about $5.00 a piece online. (Probably $10.00 from a lumber supplier) Much cheaper than I expected.

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