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Old 03-21-2012, 07:01 PM   #1
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Siding job coming up


Circumstances have moved the residing of the house to the front of the project list. The first floor is brick so all the siding will be on the second floor of the story and a half craftsman. There are four sections. There are side gables (north and south) and a front and rear dormer. The gables are stuccoed. I will remove the stucco (it's really rough and crumbling) before putting up hardiplank. Then I thought, "Hey, I can put foam over the sheathing and increase insulation!". Then I thought, "Hey, I can remove the sheathing and put the foamboard directly on the studs and not cause a big bump out above the brick!" And then I thought, "Hey, I can remove the old mineral wool insulation, cover the inside of the wall with 6 mil vapor barrier, add ROXUL, foamboard, tape, and then side it and it will be about as tight as an old hovel can reasonably get!" (Can you spell 'Requirements Creep'?)

It is my understanding that the foamboard can be installed without sheathing if the structure is crossbraced. Do the roof rafters that make it a gable qualify as the crossbracing? The entire surface is triangular. The wall studs are connected directly to the rafter and the rafters go from the top ridge down to the brick first floor.

The reason for eliminating the sheathing is to prevent from creating a big step where the brick first floor and siding second floor meet. 3/4" planks become 1" foamboard. Purely cosmetic. This isn't an issue on the dormers because they don't tie into a vertical wall. I can use sheathing and foamboard. I guess the question there is is it better to put the foamboard on the outside of the sheathing or put the sheathing on the outside to provide better backing for the siding? Oh, yeah. The dormers are covered with 84 year old asbestos shingles. Joy. But the county has already said it's OK for homeowners to remove them. They don't recommend it. But it's legal.

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Old 03-21-2012, 07:22 PM   #2
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The old shingles are not friable... that is why it is safe and allowed for you to remove them.

Sheathing should not be removed. You want it there for sheath strength.

Foam board goes on over the tyvek which goes over the sheathing. Then 3/4" strapping to provide a rainscreen which will allow your paint to last much longer.

foam board will help address thermal bridging and will be code as local departments adapt the new codes 2" is much better. depending on your location poly is not a good idea at all.

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Old 03-21-2012, 11:11 PM   #3
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I'm in St. Louis. Cold Zone 4 I believe.

Here's the house.

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There used to be an awning on the side window. A wind storm tore it up a couple weeks ago. When I went up to finish removing it, I saw the condition of the stucco up close. The picture doesn't show the broken stucco on the carport roof. The dormer siding has issues too. The leaky flashing is courtesy of the contractor who shingled the roof about 10 years ago. I think the leak is from cracks in the shingles that extend above the flashing. It leaks when snow is piled up against the dormer. That will be fixed with the residing.

The practice wall is a little section that's relatively low without any obstructions. I'll use it to practice with the pump jacks. It will need sheathing because I don't think there are enough studs to ensure a stable plank. It has an attic space behind it. I had considered using 1" to 2" foamboard on the attic side of the interior walls.

There's a trim board between the stucco and brick. That will go away and the siding will go all the way down to the brick. This is balloon construction and the studs go all the way down to the sill plate on top of the brick wall. The second floor does not touch the gable wall. But that is where I didn't want to have a big step out.

Now, Bob said keep the sheathing for sheath strength. That was the intent of my question about whether the roof rafters that frame the gable provide sufficient bracing to skip the sheathing. Also Hardie doesn't talk kindly about 2" foamboard and only grudgingly accepts 1". I don't remember seeing them reference use of strapping at all. It's late. I'm not going to look it up now.

The dormer does need bracing. The current structure is vertical studs with horizontal plank sheathing. I described elsewhere on this site how a microburst that hit the south side of the dormer caused a bunch of diagonal cracks in the plaster because the dormer flexed sideways. So I will replace the old sheathing with plywood to stiffen the structure.
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Old 03-22-2012, 06:21 AM   #4
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there should be a big ''bump out'' above the brick
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Old 03-22-2012, 11:49 AM   #5
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Got a chance to look at the Hardie installation instructions:

They specify using foam board no more than 1" thick. I can only use 2" foam in the attic spaces.

They do not show the use of furring strips, although they do show planks applied directly to studs which would imply that there is no need for a solid backing behind the siding (mounting on furring strips should be OK)

They do show the planks applied directly to studs without sheathing on a cross raced structure...which brings me back to my original question: is a gable wall considered cross raced by the roof rafters?

Other issue Bob brought up. Why would I want to put the weather barrier behind the foam? I understand the controversy about taping the foam and then the foam shrinks and the tape comes off. But wouldn't it be better to have the weather barrier over the foam to reduce air infiltration around it?

Also unresolved. Do I need/should I use a vapor barrier in St Louis, MO?
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Old 03-22-2012, 01:55 PM   #6
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local code may require a vapor barrier on the warm side of the wall. But you should not have one since in reality you are still in a mixed climate. Moisture will travel by diffusion into the wall and the wall must be able to dry to one side or the other. This barrier is placed inside in cold climates (Canada), outside in warm climates (NC) and should be omitted in mixed climates.

Those directions are not using the strapping (1X3's vertically on every stud) mounted with long screws. It is the proper way to go. For zero energy homes we use hardi planks over 6" of foam and never had to touch up anything yet. One house had the hardie installed with no extra insulation or stapping. The movement between joints is very noticeable. On my work there it is not. As a result the new addition to this other house is now being done by my crews. research rainscreens... this is what the strapping is doing as well as a better nailing surface for the hardie planks. Moisture is completely removed with this system.

Vapor barrier goes on the plywood, not the foam. You need to think of where the dew point can be reached and protect the wall from condensation at that point.
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Old 03-22-2012, 02:53 PM   #7
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wrb goes on the drainage plane which may or may not be the sheathing,i don't see your point as far as dew point and where the wrb is or how effective it is sandwhiched between the foam and sheathing
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Old 03-22-2012, 03:53 PM   #8
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I have to join Tom and go, "Huh?" thermal breaks and condensation layers are vapor barrier parameters which you said I should leave off.
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Old 03-22-2012, 04:21 PM   #9
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the gable end typically is not load bearing so i don't think the sheathing is serving any structural benefits,but...where as fc can be directly stud nailed all too often the are not enough imo i bet there is only 1 stud on each side of the upper gable window
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Old 03-22-2012, 05:06 PM   #10
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The sheathing is all about shear strength (so the walls wont rack) and nothing to do about load bearing in general. I know in many parts of the country not sheathing the walls is acceptable but Id never do it. Id pass on the job if they told me to apply siding directly to the studs (other than T-111).
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Old 03-22-2012, 05:18 PM   #11
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Which is what I said... shear strength to fight from twisting or racking from wind loads.

a vapor barrier is not the same a a weather barrier.

read up on how to build a perfect energy efficient wall. John Straube (SP?) said the tyvek goes on the sheathing. I agreed and have been doing it this way for years now.

Condensation is to be considered when insulation is not only on the warm side of a wall. For example: A basement wall with 1" foamboard. The concrete wall will reach dew point and condense when warmer moist air hits it. The 1" foam is not enough to keep the concrete warm enough in New England climate. You need 2" foam

Thermal Bridging???? where is this mentioned? Foam is used on the outside of a wall to stop and address thermal bridging. This is a heat transfer that is greater than the average of the wall. About 25% of the effective R-Value is lost in a 2X4 wall due to the thermal bridging of the studs. This is why two things are done in an energy efficient wall. 1: Foam is placed on the outside of the studs. 1" will only give you a R-6 or less. So thermal bridging is not addressed. 2" will give you the same average r-value of the wall. 2: advanced framing allows room at the corners and between headers for foam. Also walls are at 24" OC to lower the heat loss average on the wall.
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Old 03-22-2012, 08:33 PM   #12
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again wrb goes on the drainage plane,wherever that may be and that is determined by where the windows are positioned,sandwhiched between foam pretty much negates it's permiability and ultimate water resistance

the structural issue ill defer too the pro's
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Old 03-22-2012, 10:21 PM   #13
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Quote:
Originally Posted by Bob Mariani View Post
Which is what I said... shear strength to fight from twisting or racking from wind loads.

a vapor barrier is not the same a a weather barrier.

read up on how to build a perfect energy efficient wall. John Straube (SP?) said the tyvek goes on the sheathing. I agreed and have been doing it this way for years now.

Condensation is to be considered when insulation is not only on the warm side of a wall. For example: A basement wall with 1" foamboard. The concrete wall will reach dew point and condense when warmer moist air hits it. The 1" foam is not enough to keep the concrete warm enough in New England climate. You need 2" foam

Thermal Bridging???? where is this mentioned? Foam is used on the outside of a wall to stop and address thermal bridging. This is a heat transfer that is greater than the average of the wall. About 25% of the effective R-Value is lost in a 2X4 wall due to the thermal bridging of the studs. This is why two things are done in an energy efficient wall. 1: Foam is placed on the outside of the studs. 1" will only give you a R-6 or less. So thermal bridging is not addressed. 2" will give you the same average r-value of the wall. 2: advanced framing allows room at the corners and between headers for foam. Also walls are at 24" OC to lower the heat loss average on the wall.

sorry Bob but i just don't understand this postand you brought up vb in post 6 which is maybe what the op was responding to
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Old 03-22-2012, 10:25 PM   #14
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Quote:
Originally Posted by kwikfishron View Post
The sheathing is all about shear strength (so the walls wont rack) and nothing to do about load bearing in general. I know in many parts of the country not sheathing the walls is acceptable but Id never do it. Id pass on the job if they told me to apply siding directly to the studs (other than T-111).

that shear could be replaced with diagonal bracing?
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Old 03-22-2012, 11:24 PM   #15
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Like the roof rafters on a gAble wall?

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