So they've run out? So now they can run over and buy a roll of Tyvek at the nearest building supply. (Even if you're out in the countryside and it's 50 miles away.) The OSB needs protection from water even if there's no living space behind it.

Not wrapping gables with housewrap is a common error, so at least your framers are in good company. (See link.)

Here is a link that might be useful: Wrapping the House: Do's and Don'ts

I also can't imagine why it wouldn't be necessary. The Tyvek isn't insulation, it's waterproofing. Especially if you have any lights in the porch ceiling, it seems crazy to go without, particularly just because they 'ran out'.

I wouldn't accept this.

tyvek should be installed.

also the windows should be taped in this order

sides first
top second covering tape from sides
this will divert water from entering the window
the bottom is left untaped to allow for drainage.

best of luck.

In most cases, nail fin type windows should be installed in conjunction with the housewrap/self adhering flashing.

Here is a link that might be useful: prper install wrap/flashing/window

This isn't a porch roof; it's a wall with a window in it and it needs a weather/air barrier.

A good window installation should have flashing or a pan over the rough sill and turned up the jambs before the window is installed. This has become the industry standard and is defined by ASTM E2112-07 "Standard Practice for Installation of Exterior Windows, Doors and Skylights".

The Integrity site provides elaborately illustrated installation instructions and your contractor should offer you a very convincing reason for deviating from them. Go to the link below and look for INSTALLATION INSTRUCTIONS. Then click on the last PDF listed entitled, "Wood-Ultrex Window Installation".

The Integrity instructions provide an approach for a window installed after a housewrap/air barrier and another approach for a window installed before asphalt felt building paper. You may need to adapt the latter approach since your windows is already installed.

Note that the nailing fin overlaps at the upper corners are carefully sealed to the frame (a common water penetration point), the flashing tape at the jambs rolls up onto the frame to seal the continuous joint (another common water penetration route), and there is a carefully integrated sill flashing/pan installed before the window.

Here are similar instructions from WR Grace for their Vycor Plus flashing tape:

Here is a link that might be useful: Integrity installation instructions

Since it is not a conditioned, habitable space, the gable end does not require housewrap or any other type air barrier.

And depending upon your building code and the siding material you are installing over the gable end, you may not be required to have any weather barrier on this gable end either.

That does not mean you should not install a weather barrier under the siding....just that you may not be required to install one.

That said, your builders do not need to install an entire roll of Tyvek (unless the contract specifically states that Tyvek will be used) and instead could use some left over roof-felt paper...which could actually be the superior weather barrier product in this case.

The IRC defines an exterior wall as enclosing conditioned space but says nothing about it being habitable.

However to use that definition to void the code requirement for a weather barrier over an exterior wall envelope is clearly contrary to the intent of the code since a leak in an unconditioned space is no more desirable than in a conditioned one, not to suggest a building code would even be relevant for this situation.

A builder once told me he didn't want to put building paper under asphalt shingles and I simply told him if he did it he would get paid so he did it without further discussion. Just tell the builder to put the Tyvek up as the contract requires if he wants to be paid. And never rely on a building inspector to enforce the building code; he might be related to the builder or worse. But first read the contract documents.

A good rain will show you why you want to install a housewrap.

Just because it is above code does not mean it shouldn't be done.
I would think that any homeowner who understood that you want to cover the wood with a barrier before covering
with siding would agree to pay the added cost of the material and labor to insall.

Code is the legal minimum..it doesn't cost much more to
do a little better.

best of luck.

instead could use some left over roof-felt paper...which could actually be the superior weather barrier product in this case.

Indeed. (See link below.) I've noticed a number of high-end homes here that are going back to the old "standard" under masonry veneers. But only as long as it's 30 lb. felt.

Here is a link that might be useful: Leaky Housewraps

"The IRC defines an exterior wall as enclosing conditioned space but says nothing about it being habitable.
However to use that definition to void the code requirement for a weather barrier over an exterior wall envelope is clearly contrary to the intent of the code since a leak in an unconditioned space is no more desirable than in a conditioned one, not to suggest a building code would even be relevant for this situation."

1) Just because a wall is on the exterior of a house does not mean it encloses conditioned space or is part of the thermal envelope.

In the above case, the wall shown is not part of the thermal envelope and does not enclose conditioned space.

Therefore, an 'air barrier' like Tyvek would not be required.

2) Only since 2006 has the IRC required a weatherbarrier under most common siding materials, and there are still plenty of jurisdictions across the US that still use 2003 versions of that code. For them, placing a weatherbarrier under the siding would not be required or even enforceable.
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That said, and for the record, if you go back to my original comments you will find I did not endorse nor even recommend that this area should have no protection.

I said just the opposite:

That a weatherbarrier should be installed even if there was no code requirement for it to be there, but that the weather barrier could be any type approved material, like felt paper.... and did not have to be an air barrier like Tyvek.

If you're going to quote the 2003 IRC you need to look at it more closely. It says:

"The exterior wall envelope shall be designed to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer ..."

That membrane is required to be either asphalt saturated felt or "other approved weather-resistant material". Of course, there are exceptions for certain types of siding.

This requirement goes all the way back to the 1986 One and Two Family Dwelling Code published by CABO, which was made up of the same member organizations as the current IRC (ie CABO changed it's name to the IRC in 1999) so this requirement has remained essentially unchanged for at least 24 years and probably 27 or 30 since the 1986 version has vertical revision lines in the margins and the code publishing cycle was every 3 years as it is now.

macv:

The day you stop trying to make readers "see better" by not poking them in their eyes is going to be the day you finally become a positive contributor in this forum.
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Under the 2003 Code, section R703.1 indeed does say: the "wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the veneer..."

However, taking one section of the Code out of context to prove your point is not making any point at all.

Section R703.1 is supplemented by TableR704.4 which lists all common siding types as you well know, and that Table, as you well know, fully excludes the requirement for a weather-proof barrier of any type at all behind sidings materials like:

-horizontal aluminum
-steel
-some particle boards
-T1-11
-And most wood clapboard

So my comments stand as true and right and correct, and your attempts to convolute my words in order to make yourself look good by trying to make me look bad has not gone unnoticed by the intelligent readers of this forum.

Sheesh.

Grow up already.

Fiber-cement lap siding is required by the 2003 IRC to have a weather-resistant material behind it.

The OP asked for advice about how to weatherproof an exterior wall. Why do you disrupt the discussion with nitpicking irrelevant building code issues and personal attacks? If you don't know how to detail an exterior wall listen and learn or go away.

Thanks, guys. I've sent this link to my DH so he can check further into details on other parts of the house. I do know we'll go ahead w/ the Tyvek on that gable.