New Window to a Residential House 6

[Zeeko83]

Hello all,

Is it OK to add a steel frame around a new window to provide vertical and horizontal stability in a townhouse made of wood?

It might be a simple question but I have been hired recently for a renovation department dealing with a wooden house compound built in 1981 in Saudi Arabia as per UBC (see attached photo). I had a wood design course in 2010 and have no working experience in wood.

The exterior walls are made of 2x4 @ 16" covered by 1/4" thick fiber cement board (exterior). and 1/2" thick gypsum board (inside), there is no hold-down.
low seismic zone and ultimate wind speed is 130 mph.

I used the bracing wall method in 2018 IRC for evaluation considering the new window. However, I could not find any mentioning in IRC, NDS of using fiber cement board as a structural panel to provide bracing! Therefore, I considered only the interior gypsum board. The output was the wall is not in compliance with the bracing method in IRC.
2 solution came to my mind:
1- To remove all interior gypsum board in that specific brace line and add new plywood panels and to be covered by type x gypsum board in that entire brace line.
2- To add steel frame around the window.
However, I am not sure if it is ok to insert such a steel moment frame within the wood frame and if there hidden things I need to consider?

Thanks in advance

 

[dik]

Cold transfer?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[r13]

Won't this work, why steel moment frame? You can add infill to the space between the existing and new studs to strengthen the frame too, if necessary.

 

[XR250]

I doubt I would worry about lateral or out-of-plane stability for a window that small.

 

[Ron]

@r13....if you 2x4's on the inside of the existing opening the window probably won't fit. Generally it is going to have to be something with a thickness of 1/4" or less....thus the steel consideration.

Yes, if the numbers work out with the steel insert, it's ok to use that with wood framing.

Why do you have to meet current code for a single window replacement? That generally would not invoke compliance with current code, just the code at the time of construction.

 

[dik]

maybe in Florida...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[r13]

I am not a wood guy, but in this case I think it is rather simple to build-up with wood rather than mix with different materials. You may remove 4 studs instead of 3 that will be 1/4" (say) short of the window dimension, then buildup with additional studs, and adjust the width with gaps. Unless wood is more expansive than the metal frame, I don't think it is justified for this case.

 

[Zeeko83]

@dik
Would you please elaborate? If you asking about the weather, it is hot generally, in winter 60F and in summer it is 113F, and it is high humidity area.
The building paper is added neat to external face (out side) of the wall.

@r13
That would take the gravity load only. How can I improve the bracing?

@Ron
I should have mentioned that it is an additional window to be added in this house and not a replacement as shown in attached photo in the original post.
You raised a good questions “just the code at the time of construction“ I didn’t thought about it. Most probably the design was as per UBC 1979, I just read this code and the requirements for conventional wood construction for wall bracing are nominal, adding the window would not harm the house. But how can I justify using old code to make changes in the house (adding window)? Is there something in international existing building code would support that or it is a common practice?

Also, does fiber cement board used as a structural panels to brace the wall?

Best Regards,
Abdullah

 

[r13]

I would be surprised if the window will subject to significant distortion that the detail couldn't accommodate. You can add braces in the header, and/or make the header wider to act as lintel. The wood is versatile, you should consult with an experienced designer.

 

[dik]

Not an issue... here in winter it is often -40... and metal structure in a wall can cause thermal issues... including frost buildup on the inside...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

@Zeeko83....you have code provisions that back up the premise that you don't have to comply with existing codes. Check the IBC Existing Building Code. The local building official has a lot of leeway in these decisions; however, in my experience they base the decision on a percentage of impact to the structure. As an example, some say that unless the cost of a repair exceeds 25 percent of the value of the building, you only have to meet the original code. Some take that level to 50 percent. It varies.

Check paragraph 101.7 of the International Building Code-Existing Building. Also check with the local building official. I can't imagine that a single window would invoke full compliance with the existing code when none of the rest of the structure would comply....but then, common sense is in short supply.

@dik.....hey, it gets cold down here too! While in most areas 32F is the freezing point, in Florida if it gets below 60F we are frozen!

 

[dik]

@Ron: We don't get earthquakes, hurricanes, volcanoes, droughts, windstorms, fires, etc... only a couple of tornadoes in my lifetime... life is great... only have to contend with the cool winters... and, with climate change it may warm up a tad.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[BAretired]

The exterior walls are made of 2x4 @ 16" covered by 1/4" thick fiber cement board (exterior). and 1/2" thick gypsum board (inside), there is no hold-down.
low seismic zone and ultimate wind speed is 130 mph.

With winds like that, I would be concerned with the existing wall, with or without the new window.

BA

 

[dauwerda]

Wasn't let in bracing much more popular in that time period (than it is today)? Any chance the wall has let in bracing and it isn't counting on either the fiber cement board or the gypsum for lateral stability?

 

[KootK]

Is it OK to add a steel frame around a new window to provide vertical and horizontal stability in a townhouse made of wood?

It's a clever idea in some respects but I vote no.

1) For lateral loads, no reasonable proportioned frame is going to be stiff enough to compete meaningfully with the wood/gypsum panel shear walls.

2) If the interior space is air conditioned, you may get condensation issues where cold steel interacts with warm air at the exterior.

3) The way that a square moment frame thing will want to deform under load will pull your fasteners, and perhaps break you glass, when it rides along with pure racking deformation of wood / gypsum panel shear walls.

Therefore, I considered only the interior gypsum board.

Even with that you have to be a bit careful. Unless specifically detailed to be otherwise, interior gypsum will usually be discontinuous, broken at intersecting interior walls etc.

Also, does fiber cement board used as a structural panels to brace the wall?

There are indeed sheathing products that are not in the NDS/IRC but, none the less, do have shear ratings and ICC reports. To follow this path, you'd need to identify the exact product that's been used and see if you can track down the testing or code report associated with it.

 

[Zeeko83]

Great posts, Thanks all.
@dauwerda actually there are no lit-in breacing found nor hold-down in the existing structure.
The external sheathing is fiber cement panels, a nearby house with the same design has a horizontal board sheathing. it seems it is relaying to the gypsum.

 

[Zeeko83]

Hello, New update.

Wasn't let in bracing much more popular in that time period (than it is today)?

Yes, I just discovered the let-in bracing. Also, have found a portion of the design drawings which has a general note saying "lit-in bracing to be provided at all house corners".
The proposed window will be located at the same location as the lit-in