cutting through the top plates on gable end

[astidham]

Is there a prescribed way to cut through the top plates? The uptairs gable end of my cabin has a window that we would like to make a doorway out of.
The gable end is a gable truss, and the bottom of the window sits on the top plate.
I would like to cut through the plates, and down to the top of the loft floor.

Thanks,
Todd

[rick91351]

WOW if I am reading this correctly I don't think that is doable.  Remembering back we had to talk to the truss company to establish if we could even cut the verticals to put in the windows.  We knew we could but the engineer at the truss plant had to tell us how he wanted it done per the build inspector.   

[akwoodchuck]

I'm not understanding....is the bottom chord of the truss already cut out to accommodate the window? If so, the damage is already done...I'd make sure the truss and wall below it are well-tied with sheathing.

[astidham]

Thanks Rick.
Woodchuck, the bottom chord is already cut for the existing window.
Because of having scissor trusses, we also had to frame the gabe wall next to the truss, since the truss was only 1 1/2 wide sitting on a 2x6 wall we 2x4 framed it to furr out the wall

[Don_P]

A gable truss isn't a truss, it's a frame. No different structurally than a stud wall. If continuously supported by a wall, as is typical for a gable truss, there is no tension in the "bottom chord" of that frame.  Rick's spanning situation is a bit unorthodox but the advice to consult the manufacturer is sound whenever modifying an engineered product.

After my latest rants  you know that a top plate in the middle of a wall is not prescriptive, so we're outside of a prescribed way of doing it. Actually scissors and gable end trusses give inspectors and design engineers heartburn from the get go, scissors should be done with balloon frame ends, again to avoid a hinge in the gable wall. They do not seem to give truss engineers proper heartburn and can cause problems at framing inspections.

All that said,  I would propose cutting 6" wider than the rough opening overall. Run a pair of king studs from floor to roof sheathing notching around the top chord of the gable truss. Use a framing angle or blocking to attach the king to the top chord and end nail through the king into the top plates, a block on the sole plate to back up the king at the bottom and nail it well, again a framing angle there wouldn't hurt. Then nail a jack stud to the king, header, and install any cripples needed. My thinking is that if all three connection points are good you've strengthened the hinge created by the midheight top plate by inserting columns, the kings, secured to the rigid diaphragms of the roof and floor.

[astidham]

Thanks Don...
One issue I would run into is that there is a window that will also be opened into a 3 foot doorway below the upstairs window that is  about 18 inches off center of the one above it.

[Don_P]

I hope I'm visualizing correctly, but as long as it's properly king, jacked and headered and then the wall is well tied to the floor diaphragm I don't see a problem.

[astidham]

Here is a pic

[astidham]

[Don_P]

Aaargh, that's another problem with this framing style, but this isn't a load bearing wall. I'm not sure what the access is like in your framing. I'd do the lower door and try to drop the king stud of the upper door down onto the header of the lower door and secure it. The other side, left side in your interior shot, good luck, best you can do is tie to the floor rim I imagine. If the wall is covered don't forget that recepticle wire under the window.

[astidham]

Thanks Don,
And thanks for pointing out that electrical.
I will have to pull all the interior wall covering under the loft to demo plumbing and some electrical (moving laundry out to addition) I can get a better look then..
We dont absolutely have to have a door there, my wife wants a bridge or catwalk over to the 2nd floor of the addition.
Mainly for another access to the cabin. Ive thought about leaving the opening just the size of the window with a step on the loft side going up...

[UK4X4]

We did similar, adding windows into what was a bare wall on design 1....a bed room , then with design 2 a great room..

we added the uprights more for stiffening that wall than for the windows

Before


after

[Don_P]

To avoid having just a carpenter's opinion, I found an article from a reliable source. I've copied a couple of snips from the article but the entire thing is worth reading. For an explanation of the forces within this particular situation, a scissor truss with a level gable end frame, scroll about 3/4 of the way down the article till you see the graphic with the red circle that has a slash through it.
http://www.structuremag.org/article.aspx?articleID=360

The gable end frame is a prime example of how trusses and other components can simplify the framing process. Gable end frames are most often used directly above the non-truss-bearing end walls of a building, and save the contractor the time and expense of field framing the end wall to match the roof slope. However, it is imperative to remember that a gable end frame is an integral structural element of the gable end wall and must be incorporated into the wall design in order to function properly. Confusion sometimes exists as to how much of this "incorporation" is provided by the truss manufacturer and how much must be provided by the building designer. This article reviews the basic design considerations used by the truss industry for gable end frames, and discusses several items that must be considered by the building designer to ensure the successful integration of the gable end frame into the building structure.

................................

Some building codes and construction standards include general prescriptive requirements concerning gable end wall bracing. For example, Section 2304.3.4 of the 2004 Florida Building Code (FBC) states the following:

2304.3.4.1 General. Gable endwalls shall be structurally continuous between points of lateral support.

2304.3.4.2 Cathedral endwalls. Gable endwalls adjacent to cathedral ceiling shall be structurally continuous from the uppermost floor to the ceiling diaphragm or to the roof diaphragm.

2304.3.4.3 Full height studs. Full height studs may be sized using the bracing at a ceiling diaphragm for determining stud length requirements.

A similar provision is provided in Section 3.4.1.1.2 of the 2001 Wood Frame Construction Manual (WFCM), which is referenced in Section R301.2.1.1 of the 2006 International Residential Code®.

3.4.1.1.2 Stud Continuity. Studs shall be continuous between horizontal supports, including but not limited to girders, floor diaphragm assemblies, ceiling diaphragm assemblies, and roof diaphragm assemblies...

This is one of those problems when using engineered products and relying on the manufacturer's in-house engineering without either understanding everything involved yourself or having a project engineer overseeing the entire structure. The manufacturer's engineer will design his part of the project without reviewing how it works within the entire structure. Three of you have posted pics of gable truss frames used incorrectly, and I think 2 of you even had a project engineer overseeing the project. I guess the only real solution is for us to know what they are supposed to know. That's pretty much why I started learning this stuff for myself.  The take away here is, don't order a level gable end truss with a scissor trussed roof, stick frame the gable with unbroken studs from floor to roof or at least from floor to ceiling plane. Don't forget to have them drop the gable frame for lookouts... by the time you've messed with all that, it's usually better to just balloon frame it in the field.

[UK4X4]

The wall and trusses were engineered signed and checked

The modification was passed by the truss engineer before it was done, I had sized the windows to keep the horizontals in one piece, but the GO wanted more verticals to stiffen the wall.

I have a double truss in that wall and a triple 16" from that, balloon framed,

is it right ...nope I'm not sure but the truss company ok'd the changes

And there will be some steel straps installed across those joints, and others where air ducts meant we had to cut out the plates quite deep

[akwoodchuck]

Three of you have posted pics of gable truss frames used incorrectly......

I don't know, Rick's looks pretty skookum....drop-chord gable truss with lookouts on edge, attached at ceiling level.....the other two are questionable but definitely within Alaska tolerances....lol. I've cut a lot of gable truss top chords to let in flat 2x4 lookouts....I doubt the engineers like it but it's standard practice up here....most houses you see are done like that.

[Don_P]

Rick's should probably have been a structural gable truss since it is not continuously supported. Notice the size of the chords supporting the span as simple beams rather than as a truss. Once sheathed I'm not worried but it probably should have been designed differently. Critique is less important, getting to best practice for those in design is more what I'm driving at.

I've certainly seen them all and have notched top chords as well... but none of that is the way it should be done. It really isn't much harder to do it right and if the labor is your own, the out of pocket is lower to build it correctly. The truss industry is sort of doing a disservice by allowing people to think that a cobbled together blend of stick and truss framing is somehow the way that gable should be framed. When stick framed it is cleaner, stronger and probably has less wood in it.

[akwoodchuck]

Yeah gable roofs are considered the simplest but they still can get complicated in a hurry when dealing with PPP....(piss-poor planning )....here's a pretty informative article on the subject:  http://www.structuremag.org/article.aspx?articleID=360

[astidham]

Thanks everyone.... I wish I would have balloon framed it to start.

[Don_P]

That doesn't mean you can't put a door up there though and in fact it will stiffen the wall just as the jacks and chimney in UK4x4's stiffened that wall, you'll have jack's and an intersecting roof plane. My belaboring it was aimed at helping with the immediate situation but also towards getting people away from framing that hinge into the wall in the future.

If you remember my "plant shelf" remedy when this happens on a tall cathedral wall it is covered in this section of the article ak and I linked to... its the girder mentioned here;

Stud Continuity. Studs shall be continuous between horizontal supports, including but not limited to girders, floor diaphragm assemblies, ceiling diaphragm assemblies, and roof diaphragm assemblies

[astidham]

Good info Don,
I might be able to get some 2x4s stuffed down the wall after the wall covering is removed, but I would have to put it in, in sections because the loft joist and the roof would keep me from installing anything full length, which might lead me back to the same condition.
Maybe laminate some 2x4s?
I got plenty of planning to do on this door.
The addition on this end of the house has a matching scissor truss, except it is 4 foot longer on the front side, and 4 foot shorter on the back side.
This roof only spans 10 feet until it connects to the 2 story addition.

[Don_P]

This section really becomes an interior wall with a pretty low vertical load. I'd remove the 2x6 fireblocking at the floor level and drive a 6x6, or whatever dimension the gap is x 6" tall, into the gap between the sheathing and rim, level to the floor. Then from the garage side run 4 ledgerlock or timberlock screws thru the sheathing, the block, and into the rim joist. Then attach the bottom of your king and jack stud to that blocking.

I'm unclear what you mean by a 10' roof span between existing and the garage roof. I am envisioning a lapping of the roof overhangs somewhere forming a short section of level valley up top. I've built a cricket in that situation to shed water to each side.

[astidham]

this is the 10' section between the 2 structures.
my trusses match the cabin scissor truss for this 10" width.

[grover]

Wouldn't the floor of the loft stiffen that hinged wall pretty well?  That is assuming you have the floor joists of the loft tied into the wall securely such as timberlok screws?  The floor is not at the hinge point but it is close.