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Helpful? 3

To Install Stucco Right, Include an Air Gap

How should stucco be installed to avoid the wall-rot problems plaguing thousands of U.S. houses?

Posted on Nov 12 2010 by Martin Holladay, GBA Advisor

In many areas of the country, hundreds of stucco-clad homes have suffered wall rot. Although building scientists are still researching the causes of wall rot behind stucco, it’s clear that all of these walls got wet and were unable to dry.

Among the reasons that have been proposed for the recent epidemic of stucco-clad homes with wall rot:

  • Many of the houses had OSB sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , which is more susceptible to rot than plywood or board sheathing.
  • Many of the houses had only one layer of Grade D paper or asphalt felt under the stucco rather than two.
  • The homes lacked a ventilated air gap between the stucco and the sheathing.
  • In many of the homes, interior polyethylene prevented the walls from drying to the interior.
  • Many of the homes had flashing errors.
  • Some of the homes had high indoor humidity coupled with an imperfect air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both..

If you’re planning to install stucco on a wood-framed wall, you can benefit from the many lessons learned from all of the failed stucco installations of the last twenty years. Before we tackle the question of how to avoid such failures, however, let’s delve into some stories from the recent wall-rot plague.

A failure rate of 51%

I wrote a special report on rotting stucco-clad walls in Minnesota for the May 2006 issue of Energy Design Update. The article began, “In Minnesota, home inspectors have discovered that hundreds of recently built homes — especially stucco-clad homes — have rotting walls. In spite of years of efforts by construction experts to educate builders on improved water-management details, wet walls continue to take a staggering toll on builders and insurance companies.

“According to Ron Glubka, the chief building official in Woodbury, Minnesota, the city’s wet walls represent ‘the largest construction defect problem in local history.’ … Glubka [reports that] the building department has issued permits for wall repair work for 344 out of the 670 stucco-clad homes built in Woodbury in the 1990s — a failure rate of 51%. … In most of the Minnesota cases, the necessary wall repair work has not been minor or cheap. In one case discussed in the November 19, 2005 issue of the Star Tribune, a Minneapolis newspaper, the stucco walls at the Woodbury home of Steve and Debbie Long required $174,860 of repairs; the total bill was paid by their builder’s insurance company. ‘The costs incurred boggle my mind,’ says Paul Ellringer, an engineer and building consultant in St. Paul, Minnesota. ‘The worst case I’ve seen is one where the repairs cost $700,000. Just in Minnesota, the problems have been costing hundreds of millions of dollars a year.’ ”

Builders called to fix failed stucco often flub the repair

Unfortunately, the expensive repairs made to rotting stucco houses have themselves proved faulty. The Energy Design Update article noted, “As further evidence that some Minnesota wall repairs have been based on faulty diagnosis, experts note that some rebuilt houses are beginning to fail for a second time. According to [building consultant MacGregor] Pearce, ‘In a significant number of houses, the repairs to the stucco have failed too.’

“Among those who have seen ‘failed rebuilds’ is Paul Ellringer. ‘I’ve had two clients where their house was rebuilt twice,’ said Ellringer. ‘With one client, we are on the third rebuild. The earlier rebuilds failed because they keep redoing them the same way. Most rebuilds are feeble — for example, they will just tape the window fins with four strips of tape rather than using a pan flashing.’

“[Building diagnostician Steve] Klossner blames the failed rebuilds on bad diagnosis. ‘Some of these buildings have had major fixes, and they are already failing a second time, because the first time around they didn’t catch all the causative issues,’ says Klossner. ‘At one house I saw, they blamed the windows, so they pan-flashed the windows. The first time, they put it all back together and ignored a major problem — elevated indoor humidity. Now the walls are wet again.’

“Ellringer has seen so many rotting walls that he is prone to glum predictions. ‘I think that eventually the failure rate for stucco homes will turn out to be 80 percent,’ says Ellringer. ‘I also think the rebuilds will fail at the same rate as the original houses.’ ”

A nationwide problem

Although the article focused on problems in Minnesota, similar clusters of wall-rot problems have occurred throughout the country, wherever builders have installed stucco over wood-framed walls.

Although rot problems have occurred in walls with differing details, the most risky wall type appears to have the following layers: stucco, one or two layers of building paperTypically referring to Grade D building paper, this product is an asphalt-impregnated kraft paper that looks a lot like a lightweight asphalt felt. The Grade D designation has come to mean that the building paper passes ASTM D779 (minimum 10-minute rating with the “boat test”) and different products are called out as “30-minute” or even “60-minute” based on D779 results. At times confused with roofing felt, roofing felts and building paper differ in two ways: felts are made of recycled-content paper, building papers of virgin paper; felts are made of a heavier stock paper; building papers a lighter stock. See also roofing felt., OSB, fiberglass-filled studs, polyethylene, and drywall. While it always helps to have two layers of building paper instead of one, or to use plywood instead of OSB, or to omit the polyethylene, switching just one of these details is not enough to prevent a wall from being damaged by moisture.

So — what’s the best way to detail a stucco-clad wall to avoid these problems?

Lesson one: Install at least two layers of building wrap under the stucco

The evidence is overwhelming: one layer of asphalt felt or Grade D building paper is not enough protection under stucco. This fact is now reflected in most building codes. For example, section R703.6.3 of the International Residential Code requires that “exterior plaster” (stucco) be installed over “a water-resistive vapor-permeable barrier with a performance at least equivalent to two layers of Grade D paper.”

Lesson two: Install a ventilated rainscreen gap

Many stucco installers believe that two layers of Grade D paper or asphalt felt creates a “drainage gap” between the two layers of paper. The idea is that when the wet stucco mixture is troweled onto the metal lath, the stucco soaks the outermost layer of paper, which wrinkles when it dries. These wrinkles are said to create a drainage gap.

Although the theory has some merit, thousands of failed walls have shown that two layers of paper aren't enough to prevent OSB from rotting. Whatever wrinkles exist in the paper are not enough to allow water to drain or to allow the stucco wall to dry faster than it gets wet.

Stucco absorbs water every time it rains, and it dries very slowly. To prevent wet-wall problems, it’s essential to include a true ventilated rainscreen gap behind stucco. The gap needs to measure at least 3/8 inch.

If you’re installing stucco over OSB or plywood, here’s how to create a ventilated rainscreen gap:

If you’re installing stucco over foam, here’s how to create a ventilated rainscreen gap:

  • Install 1x3 or 1x4 vertical strapping on top of the foam, screwed through the foam into the studs.
  • Fasten paper-backed metal lath to the strapping, and proceed with a standard installation of three-coat stucco.

If your local building inspector raises questions about the number and size of the screws you plan to use to fasten your 1x4 strapping, you may need to get an engineer to review your details. As long as you have an engineer’s stamp, your local building department should be happy.

Lesson three: Follow best practices for moisture management

It should be obvious that any house needs adequate flashing and moisture management details. However, such details are often missing or installed backwards. If your house has wide roof overhangs, your walls may survive such errors. If roof overhangs are stingy, however, and if your siding is a slow-drying siding like stucco, your walls may be in trouble.

So, here are the basics:

  • Asphalt felt, building paper, or housewrap must be lapped shingle-fashion, so that upper courses lap over lower courses. Any window flashings or door flashings must be integrated with the water-resistive barrier in a way that respects these laps.
  • Windows and doors need pan flashing at sills and Z-flashing at heads. Ideally, the Z-flashing will include end dams.
  • Roof rakes that intersect walls (as when a single-story garage is attached to a two-story house) need kick-out flashing to prevent water dripping off the roof from soaking the wall below.
  • Roof overhangs should be generous, not stingy.

Lesson four: Don't raise the grade around your house

Since stucco siding is made from Portland cement and sand, many homeowners confuse stucco with concrete. That's why it's fairly common for homeowners to raise the grade around their house until the grade is above the home's wood framing. After all, the homeowner thinks, the stucco looks similar to the foundation — so why can't I backfill against it?

Home inspectors often find raised flower beds or deep mulch around the perimeter of a house. Behind the soil or mulch is soaking wet stucco. And behind the stucco is wet OSB.

Some readers are now thinking, "Oh, come on now — no one's that stupid." But home inspectors are just nodding their heads and thinking, "Yup. I've seen that many times."

What about one-coat stucco or EIFS?

The details suggested above apply to traditional Portland-cement-based three-coat stucco. Some builders have switched to more modern versions of stucco — either “one-coat” stucco (a stucco method that actually requires two coats) or an exterior insulation and finish system (EIFS).

One-coat stucco consists of a 3/8 or 1/2-inch-thick layer of “enhanced” Portland-cement based stucco covered with a thin finish coat. Most one-coat stucco formulations include glass or polypropylene fibers and plastic additives (polymers). One-coat stucco can be installed over OSB, plywood, or 1-inch-thick expanded polystyrene.

An EIFS installation always includes a layer of rigid foam. A plastic mesh is laid over the foam, and a synthetic stucco mixture (that is, a stucco formulation that is not based on Portland cement) is troweled or sprayed directly over the rigid foam.

Some builders (and most insurance companies) associate EIFS with a well-publicized cluster of wall-rot failures in North Carolina. After suffering a serious black eye, the EIFS industry came up with new installation details (“water-managed EIFS”) that include a drainage layer between the rigid foam and the wall sheathing. Newer EIFS-clad homes with water-managed details have experienced very few wall-rot problems.

Regardless of which system you choose — traditional three-coat stucco, modern one-coat stucco, or EIFS — any installation that lacks a drainage gap between the stucco and the wall sheathing is risky.

Last week’s blog: “How Risky Is Cold OSB Wall Sheathing?”


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Image Credits:

  1. Energy Design Update

1.
Fri, 11/12/2010 - 08:25

Interesting Photo
by John Brooks

Helpful? 0

Martin,
It looks to me like the "moisture" is coming from the interior.
Not from wet stucco
Notice there is almost no damage above each floor-line.


2.
Fri, 11/12/2010 - 08:28

the first photo
by John Brooks

Helpful? 0

my comment was about the first photo not the second


3.
Fri, 11/12/2010 - 09:46

Response to John Brooks
by Martin Holladay, GBA Advisor

Helpful? 1

John,
Your hunch about the house in the first photo may well be right, although I have learned over the years how difficult accurate diagnosis is without a site visit.

After interviewing a great many people for my report on the Minnesota problems, I came away convinced that there was no single smoking gun -- no single cause that explained all of the failures. In many homes, more than one factor contributed to the sheathing rot.

Stucco gets wet, like all types of siding. But stucco holds much more water than vinyl siding, and stucco dries slowly. Although you may be right that most of the moisture that damaged the OSB came from the interior, the stucco may have contributed the problem, since stucco slows drying.

Any time you have damp OSB, whether due to interior moisture accumulating during cold weather or due to flashing leaks or saturated siding, the most important thing you can do is encourage fast drying. That's why houses with vinyl siding have far fewer wet-wall problems than houses with stucco.


4.
Fri, 11/12/2010 - 11:00

EIFS
by Vic

Helpful? 0

Martin, we are using EIFS on one of our projects. Our contractor did install a drainage layer over our sheathing, and then applied the rigid foam. He also left a 1" gap around the edges of the foam. For example, over our front porch the EIFS does not run all the way down to the roof, instead there is a 1" gap between the foam and the porch roof. When I asked why he left a gap, he didn't give me a clear answer, just that it was how they always do it. Is it to allow ventilation? I'm concerned about water entering the wall system through those gaps and have been considering flashing those areas again. We are in the DC area and are using an R-3 SIS exterior wall.


5.
Fri, 11/12/2010 - 11:04

Response to Vic
by Martin Holladay, GBA Advisor

Helpful? 1

Vic,
I think it is appropriate to leave a 1" gap between the porch roof sheathing and the bottom of the foam sheathing on the wall above the porch.

My guess is that there is an air gap between the foam and the WRB. I hope that's what you mean by "drainage layer." If so, it's appropriate to have an air inlet at the bottom, to encourage ventilation drying.


6.
Fri, 11/12/2010 - 13:38

3/8" actual or nominal?
by Doug

Helpful? 0

Great article as usual Martin!
I notice that almost every drain gap manufacturer sells both a 3/8" thick version and also a thinner version, usually around 1/4".
Around our area (the DC area, Zone 4 with 4000 HDD and 1200 CDD) only the thinner material is typically available. When I've contacted the manufacturers, they say the 3/8" version is a Canadian spec that is not needed except in very cold climates. I noticed that all your examples are from places with about twice the HDD as we experience here. Do you suppose 1/4" is adequate in some parts of the country? Do you know of anywhere it has failed?
I would also like to add Masonry Technology ( www.mtidry.com ) to your list of suppliers. Their gap material is pretty neat, and they have useful accessories and good support to boot.


7.
Fri, 11/12/2010 - 13:45

1/4 inch will work
by Martin Holladay, GBA Advisor

Helpful? 1

Doug,
I wouldn't sweat the difference between 1/4 in. and 3/8 in., especially if you are finding it hard to locate products with a 3/8-inch gap. By including a 1/4-inch gap, you are providing a much better detail that the failing houses I mention in the blog.


8.
Fri, 11/12/2010 - 17:35

in the older neighborhoods
by J Chesnut

Helpful? 0

There are many examples in my neck of Minnesota of older homes (1900-1930s) which had stucco placed over the original lap siding. I took some photos of one over-stuccoed home where the owners were tearing the stucco off to reside. The metal lathe on this home was applied right on the original wood siding (no building paper.) The original wood siding was in surprisingly good shape. (This same house had evidence of being filled with insulation from the outside before the over stuccoing.)

There are many over stuccoed homes in this area. You can tell because the stucco comes out past the window casings and a band of wood is typically applied on the casing to flush out with the stucco. Judging from the exterior these applications seemed to have been performing just fine over the years.

I always wonder why I don't see more evidence of rot where the stucco butts up to the old wood window casings. I would think the stucco drys slow enough where this intersection would have common recurring rot.


9.
Fri, 11/12/2010 - 18:41

Response to J Chesnut
by Martin Holladay, GBA Advisor

Helpful? 2

J Chesnut,
These are among the differences between older homes and homes built in the 1990s:
1. Older homes have board sheathing and wood lap siding, with no OSB.
2. Older homes never have interior polyethylene.
3. Because older stucco formulations never had additives that reduce the drying potential, older stucco dries faster than new stucco.
4. Older homes have less insulation than newer homes. If walls have less insulation, the stucco stays warmer and therefore dryer.


10.
Fri, 11/12/2010 - 19:19

Just curious
by Garth Sproule

Helpful? -1

Do these failures favor any particular orientation?


11.
Sat, 11/13/2010 - 07:21

Response to Garth Sproule
by Martin Holladay, GBA Advisor

Helpful? 1

Garth,
As far as I know, no. But I'd be happy to hear more failure stories from any readers who have some to share.


12.
Sat, 11/13/2010 - 08:17

Failure Photos
by John Brooks

Helpful? -2

Martin,
I would love to see a blog with lots of "failure photos" and or links to such photos and stories.


13.
Sat, 11/13/2010 - 12:31

Manufactured Stone
by John Zito

Helpful? 0

I've repaired a few walls with the same problem that had manufactured stone. All had the same issues: No drainage plane, grading issues (in one case the grade was above the sill plate), flashing issues. Since manufactured stone gets applied essentially the same as stucco (lath and scratch coat), I always include a rain screen behind it.


14.
Sun, 11/14/2010 - 06:41

It's just bumpy stucco
by Martin Holladay, GBA Advisor

Helpful? 0

John Zito,
You are absolutely right -- the same catalog of problems occurs with adhered manufactured stone veneer. That's why John Straube and Joe Lstiburek call stone veneer "bumpy stucco."


15.
Tue, 11/16/2010 - 11:35

@ J Chestnut: older stucco is
by Alsatian

Helpful? 0

@ J Chestnut: older stucco is LIME and sand, with almost no portland. Old lime plasters allow water vapor to pass through. Portland does not. Modern stucco has too much Portland in it. Portland doesn't "get wet" so much as it traps moisture. Too much Portland is the problem. In the historic districts I work, when we take non-original Lime stucco off a house with original lap siding, the lap siding and board sheathing is in very good condition 9 out of 10 times.


16.
Wed, 11/17/2010 - 22:49

Waterproof Your Stucco ****
by Glenn Summers

Helpful? 0

Seems like it would be a LOT easier to merely waterproof a Portland Cement based stucco that has been properly applied, knowing full well there is no more moisture transfer in - out - or through your stucco. Then you can concentrate on the Real source of the moisture that is causing these problems.
Rotting substrate that is getting wet won't be blamed on a waterproofed stucco material. You'll then be looking for other points of entry that breach the stucco cladding through penetrations other than the stucco surface itself.
A wind driven event will put enough water through a wall surface at an improperly sealed window or other opening to drench OSB and watch it explode! Enough moisture and time will swell the OSB to give the appearance that the stucco is falling off. In actuality, you have a substrate that will not support a stucco finish because it is wet and not suitable to have had the stucco put on it in the first place!
Easy to waterproof the stucco, the bigger challenge is to eliminate other sources of moisture from getting behind the stucco to compromise a material that your Hoping will qualify as a adequate substrate to begin with!


17.
Wed, 11/17/2010 - 23:43

sheathing rot
by greg

Helpful? 1

lets see here.... we now apply plastic to the interior walls. do you really think the old timers waterproofed a wall much better than the current workers? they did not install window sill pans. usually one layer of felt. usually short overhangs. how much heating energy could these homeowners have puchased for the price of the fix its that also aren't working because the vapor barrier is still there. also during the 90's we found out the need for and developed elatomeric paint for stucco as the housing style was short overhangs.


18.
Thu, 11/18/2010 - 01:17

Stucco Rainscreen Using Furring Strips?
by Keyan Mizani

Helpful? 1

Thanks for the informative article Martin. You note several drainage mat solutions for creating a rainscreen behind stucco, but I'm considering using furring strips (vertical) instead. I've seen this done for stucco, and would prefer it, but am wondering if the lack of a substrate behind the mesh will cause problems for the stucco (3 part/traditional stucco). Can you share any information and/or details for this?


19.
Thu, 11/18/2010 - 05:09

Response to Glenn Summers
by Martin Holladay, GBA Advisor

Helpful? 1

Glenn Summers,
I agree with you that the inherent problems of OSB are a significant element in these wall failures. However, I strongly disagree that "waterproofing" stucco makes a wall more robust. There is plenty of evidence that such waterproofing makes the situation worse.

Waterproofing -- achieved by using additives in the stucco mix or by applying a waterproofing coating to cured stucco -- is a way to reduce the tendency of the stucco to absorb water when it rains. But waterproofing also reduces the ability of the wall to dry to the exterior. As a result, once the wall gets wet, the water is trapped.

Old fashioned stuccos, whether lime-based stuccos or Portland-cement-based stuccos, dry quickly when the sun comes out or a breeze is blowing. Modern stucco mixtures with waterproofing additives dry very slowly, if at all.

There are many ways that water can saturate OSB. It can leak into the wall around windows, as you point out. It can also originate in the home's interior, piggybacking on exfiltrating air. Once the OSB is wet, you definitely want it to dry quickly -- which means you don't want waterproofed stucco.


20.
Thu, 11/18/2010 - 05:13

Response to Greg
by Martin Holladay, GBA Advisor

Helpful? 1

Greg,
You wrote, "Do you really think the old timers waterproofed a wall much better than the current workers?"

No, I don't. Old-fashioned walls were often leaky. However, these walls dried quickly. As long as the wall's drying potential exceeded the annual wetting, the walls did not fail.

You also wrote, "During the 90's we found out the need for and developed elastomeric paint for stucco as the housing style was short overhangs."

I don't believe that modern stucco formulations or elastomeric paint are a good substitute for skimpy roof overhangs. As I explained in my answer to Glenn Summers, elastomeric coatings just slow down drying, and that's not what you want.


21.
Thu, 11/18/2010 - 05:17

Response to Keyan Mizani
by Martin Holladay, GBA Advisor

Helpful? 0

Keyan Mizani,
You can definitely install stucco on top of furring strips. In my article, I suggested the technique:

"If you’re installing stucco over foam, here’s how to create a ventilated rainscreen gap:
* Install 1x3 or 1x4 vertical strapping on top of the foam, screwed through the foam into the studs.
* Fasten paper-backed metal lath to the strapping, and proceed with a standard installation of three-coat stucco."

For many decades in California, stucco was installed directly over the studs, without any sheathing whatsoever. Asphalt felt, then metal lath, then stucco -- that was all.

These days, it makes more sense to start with wall sheathing: rigid foam, diagonal boards, or plywood. Then feel free to install vertical strapping and stucco.


22.
Tue, 11/23/2010 - 10:58

stucco over other than wood framed walls
by Joseph

Helpful? 1

I'm designing a house using AAC block and intending to cover it with 1" to 2" rigid foam and then stucco over it. Would you recommend a drainage plane either under the rigid or on top of strapping? Or is this necessary at all with the AAC as the wall?


23.
Tue, 11/23/2010 - 11:03

Response to Joseph
by Martin Holladay, GBA Advisor

Helpful? 1

Joseph,
The wall assembly you describe is robust and is not subject to rot, so I don't think you need an air gap under your stucco. Just be sure that you have good fastening details for your rigid foam and your stucco lath.


24.
Tue, 11/23/2010 - 22:44

Stucco issues
by Anonymous

Helpful? 1

If you substituted marine ply for OSB would this help?


25.
Wed, 11/24/2010 - 05:28

Response to Anonymous
by Martin Holladay, GBA Advisor

Helpful? 2

Anonymous,
Many studies have shown that plywood responds much better than OSB to repeated cycles of wetting and drying. Plywood is more robust and durable than OSB.

I'm not familiar with the properties of marine plywood, except that I assume it is expensive. I imagine that few builders or homeowners are able to afford to build their homes from boat-building materials. I imagine that other solutions are more affordable.


26.
Fri, 11/26/2010 - 15:53

protecting existing stucco
by Paul Marshall

Helpful? 0

Quite an interesting...and scary article.

My question is: What can a homeowner do to prevent rot to an existing stucco home. My house was built 12 years ago and stuccoed using the one coat method of 1/2 inch Portland cement substrate topped with a synthetic stucco product. The walls is a 2x6 filled with faced fiberglass but no polyethylene. Thankfully, the sheathing is 1/2 inch CDX and not OSB. No special admixtures (latex, fibers) were put in the substrate. And only one layer of asphalt paper was installed. In one room I've noticed that water must be getting behind the stucco because the mdf baseboard has swollen in places. I thought that it must be coming around the windows so I renewed the caulking even though it looked to be in pretty good shape. There are a few cracks in the stucco field but I didn't think these to be a problem since the building paper should prevent water entry. After reading the article, I'm now having serious second thoughts.

Besides caulking all cracks is there something else I can do to ensure the maximum longevity for the stucco? I live in Missouri where I get about 45 inches of rain per year (and lots of humidity).


27.
Sat, 11/27/2010 - 06:31

Response to Paul Marshall
by Martin Holladay, GBA Advisor

Helpful? 2

Paul Marshall,
You wrote, "In one room I've noticed that water must be getting behind the stucco because the MDF baseboard has swollen in places."

You have no choice but to open up the wall behind the swollen MDF. Most homeowners find it is easier to open up the wall from the interior, but you could also open up the wall from the exterior.

If your windows were poorly flashed -- for example, if there is no pan flashing on your rough sills -- and if water is leaking in at your windows, you really have no choice but to remove your windows are do the job right.

I would start with the windows that are most exposed to the weather.

Before you jump to any conclusions, however, you much do a thorough investigation to be sure you have properly diagnosed the source of the moisture. This takes a home performance contractor or a home inspector with wide experience, building science knowledge, and a good brain. In many parts of the country, it's hard to find people like that.

Good luck.


28.
Sat, 11/27/2010 - 06:33

One more thought for Paul Marshall
by Martin Holladay, GBA Advisor

Helpful? 0

Paul,
Installing stucco over only a single layer of asphalt felt is probably a code violation and is certainly a violation of best practices in the industry. That means that it's possible that the contractor who installed your stucco is liable for damages to your house, so you may want to talk to a lawyer familiar with construction defect cases.


29.
Sat, 11/27/2010 - 13:22

Thanks for the advise
by Paul Marshall

Helpful? 0

I was afraid of that (having to open up wall). I'm sure there is a rather nice mold culture thriving there that needs to be dealt with even if the sheathing is sound. The only wall that shows any leakage is an east wall that doesn't show problems unless the rain is coming from that direction, which is about 10% of the time. This leads me to believe it is not due to the porous nature of stucco but to free water that is penetrating cracks. I guess I put too much faith in the asphalt paper and should assume it to be essentially worthless. Is it a safe conclusion that making sure the cracks are well sealed should be the line of first defense?

The windows are well flashed at the top, but at the bottom the only protection is the asphalt felt. The mdf baseboard is swollen at one of the windows and at a spot about halfway between the two windows in the room. In fact, I noticed last summer that a picture that was hanging right between the 5 ft space between the windows was discolored behind the glass. It was not wet but I theorized that water vapor had moved through the wall and then through the picture back. This could indicate the cracks in the field are contributing to the problem. I'm sure it will all be obvious when the wall comes off.

Unfortunately, I doubt there is any legal recourse. I didn't watch the contractor that closely when he installed the building paper, but it seemed like it was only one layer. My bad memory is not the only problem however. It's quite possible that contractor is now deceased as he was getting up in years, but my biggest problem is that at the time the house was built, there was no code in my county. I designed the house in conformance with the extant UBC at the time, but left the stucco details to the contractor as I trusted him as a professional.

This sounds like a warm weather project where I can leave the walls open for a couple of rain events to see where the problem is. If the sheathing is still sound and I'm able to stop the leaking from the inside is there a product I can coat the exterior with that will help repel the water? Or would you even recommend that?

Thanks for all your help.


30.
Sat, 11/27/2010 - 15:27

Forget caulks and coatings
by Martin Holladay, GBA Advisor

Helpful? 2

Paul,
Forget caulks and coatings. You're barking up the wrong tree there.

Open up your wall on the inside, and get a friend to spray the wall and the window with a garden hose. You don't have to wait for rain.


31.
Wed, 12/01/2010 - 14:35

how to match (E) stucco
by Anonymous

Helpful? 0

Thanks for the article.

You mentioned that often a 2nd or 3rd rebuild is still done wrong.
Do you have any advice on how to patch stucco in a remodel situation? For instance, where you are extending an existing stucco wall that never had a drainage material in it? How to deal with the added thickness of the rainscreen?

If a typical 3-coat system is 7/8" thick, what do you find to be the added thickness of a 3-coat system with a rainscreen layer once the whole 3-coal system is completed?


32.
Wed, 12/01/2010 - 15:11

Response to Anonymous
by Martin Holladay, GBA Advisor

Helpful? 2

Anonymous,
Q. "Do you have any advice on how to patch stucco in a remodel situation?"

A. Here's a good article from JLC:
http://www.jlconline.com/cgi-bin/jlconline.storefront/4cf69cb80973a9cf27...

Q. "How to deal with the added thickness of the rainscreen?"

A. If you intend to rebuild a portion of a wall with a rainscreen, while leaving an adjacent portion of the wall without a rainscreen, there will be no way to disguise the transition. You will have a bump. Finish the bump with your choice of trim board.

Q. "If a typical 3-coat system is 7/8" thick, what do you find to be the added thickness of a 3-coat system with a rainscreen layer once the whole 3-coat system is completed?"

A. If you include a rainscreen gap, then the depth of the gap represents the added thickness of your system. In general, most rainscreen gaps vary from 3/8 in. to 1 in.


33.
Thu, 12/02/2010 - 16:53

3 part stucco application to residential bldg The Falcon Theo
by Dr. T

Helpful? 0

I have applied 3 part stucco to my two story with suscess over 5 years ago. I have studied the issue and here is a few suggestions.

1. Consider the sheathing: 1/2 " plywood is he best use 5/8" if you can afford it. If you choose to use OSB, do not apply it within 2 feet of window and door openings or 4 feet from the bldg. corners. Instead, use plywood. This is a critical issue to the strength and indurance of your bldg.

2. Wrap your bldg with a fiber web based bldg house wrap. Do not use the continious film type here. That paper will cause issues by trapping moisture in the walls from the interior sources.

3. Cover the house with 1/2 to 1 1/2 " extruded polystrene foam board. A product like Owen's Corning is excellent. Prior to, furr out the boards to 1/4 to 3/8 gaps from the walls. I suggest a 1/4" Owen's Corning Fan Fold strips (1 1/2") will do. No need to go and buy lumber for this, keep it simple.

4. Cover the foam board with 30 lb building paper. The heck with kraft D paper. It should be outlawed, scrapped and buried and sprinkled with iron so that it does not come back. After covering with 30 lb building paper coat the paper with black asphalt foundation or roof grade moisture barrier. This will make the paper 100 lb or better and you can make more than one application. This coat when cured will survive direct element exposure 10 year after application, so you will have plenty of time to finish your bldg.

5. Apply your self furring lathe. Do not use none the furring lathe, your are asking for trouble if you do that. The self furring lathe will channel and drain water better. However, you must apply weep screeds and proper flashing with this lathe in order for it to work properly. The application of the lathe is a art and individuals will vary in their mehod. I choose to be traditional and adherent o the old school of live and learn. I will say that it is extremely important that one flashes windows, door and corners properly.

6. Last, the type of finish coat is important. I use a hand trowel smooth with a faux texure o creat shadows. I feel that it is the best way, you may not agree. However, I find it easy to water proof the stucco with a smooth finish. By the way, If you don't want rain water adsorpion coa you finished walls with a sealer, use the industrial srength mixtures. Semi gloss works well.

I hope that this helps. If you want more info concerning my study and results including pictures contact me here and I will respond.

Note: a bone to pick with the bone heads: Stucco 3 parts should be 2 parts portland and 1 part masonary cement. You can increase the masonary cement to increase flow and adhesion. One shold be concerned with the aggregates, in your first coat use concrete sand and in subsequent coats use mason sand. You won't regret it.


34.
Tue, 11/13/2012 - 00:18

how should that building wrap lap?
by Robert Mace

Helpful? 0

Building a house and the stucco sub is putting on two layers of building paper (Super JumboTex); however, I'm concerned about how he's lapping the paper. Rather than lapping each layer independently to create a drainage plane between the two layers, he's lapping the upper two layers over the bottom two layers. By my eyes, if the stucco bonds, he's created truncated drainage planes. He disagrees.

I've pointed him to R703.6.3 of the International Residential Code which suggests that each layer lap itself, but he says that doesn't apply to our case because we have the Zip System underneath it all.

I find lots of posts about using two layers of building paper but very little about how the layers should lap.

How should that building wrap lap?


35.
Tue, 11/13/2012 - 08:14

Response to Robert Mace
by Martin Holladay, GBA Advisor

Helpful? 0

Robert,
I think that your proposed lapping method is better than the contractor's lapping method.

However, as my article makes clear, the key element of a long-lived stucco installation is the air gap between the stucco and the sheathing. If you don't include an air gap, no amount of lapping will be enough to let you sleep well at night.


36.
Tue, 03/12/2013 - 09:11

EIFS
by damian mast

Helpful? 0

I am wondering if it is still necessary to have a drainage plane behind the rigid foam layer of an EIFS system if the the foam is designed to be thick enough to prevent the dew point from reaching the exterior sheathing(For my project in Climate zone 6 this would be R-11.5). This is assuming that the exterior flashing details are correct. I am also planning to use plywood sheathing, no interior vapor barrier and an HRV to control interior moisture.

Also, If you use foam with the a pre-manufactured drainage plane don't you loose any added R-Value that could be gain by the added foam layer.


37.
Tue, 03/12/2013 - 15:56

Response to Damian Mast
by Martin Holladay, GBA Advisor

Helpful? 0

Damian,
If you are specifying EIFS, the system (a) should be installed by an EIFS contractor who has been trained and certified by the EIFS system manufacturer, and (b) every detail of the system should exactly follow the recommendations of the EIFS manufacturer (for example, Sto Corp.).

That way, if something goes wrong, you call negotiate with Sto's insurance company.


38.
Tue, 04/09/2013 - 12:22

rainscreen behind stucco & brick
by Marsha Broquedis

Helpful? 0

I am doing a remodel & 2nd floor addition and live in zone 3 (Oakland Ca. area). The first floor exterior walls will have stucco with brick pilaster corners. The walls will be 2x6 with dense pack cellulose and an inch of rigid on the exterior. If there is 1/2" of plywood then the polyiso and the vertical strapping is there need for any wrb anywhere? What vertical strapping do you suggest behind both the brick (old clinker bricks) and 3 part stucco? I plan on sealing the foam seams with dow weathermate ,should I place two 1/2" layers of foam to stagger the seams? Can I tape the plywood seams with dow weathermate or should I use 3m all weather? Thank You.

DSC_4609.JPG


39.
Tue, 04/09/2013 - 12:41

Response to Marsha Broquedis
by Martin Holladay, GBA Advisor

Helpful? 0

Marsha,
Q. "If there is 1/2 inch of plywood then the polyiso and the vertical strapping, is there need for any WRB anywhere?"

A. Every wall needs a WRB. In fact, a WRB is required by code. The WRB can be housewrap, rigid foam, or one of several other materials. For more information, see:

All About Water-Resistive Barriers

Using Rigid Foam As a Water-Resistive Barrier

Q. "What vertical strapping do you suggest behind both the brick (old clinker bricks) and 3-part stucco?"

A. You don't need any strapping behind brick. If your mason is suggesting the use of vertical strapping behind bricks, I would choose another mason. If you want to have an air gap between your stucco and the rigid foam, use vertical 1x4 strapping screwed through the rigid foam into the studs. Then fasten paper-backed metal lath to the strapping.

Q. "I plan on sealing the foam seams with Dow Weathermate. Should I place two 1/2-inch layers of foam to stagger the seams?"

A. Two layers of rigid foam with staggered seams are always preferable to a single layer of rigid foam.

Q. "Can I tape the plywood seams with Dow Weathermate or should I use 3M All Weather?"

A. When I tested a variety of tapes on plywood, Dow Weathermate failed the test, while 3M All Weather was one of the winners. More information here: Backyard Tape Test.


40.
Sat, 06/22/2013 - 10:43

Edited Sat, 06/22/2013 - 10:47.

moiture barier and codes and location
by patrick lymard

Helpful? 0

On the one hand this problem of moisture barier and mold has created employment in the repair construction industry. Thats good. However i am hoping each state will create laws allowing home builders to choose to aliminate the inside plastic moisture barier which traps moisture. Any home built in a wet season or frozen ice on stud will be traped. This is certainly true with vinyl sideing and most likely a factor in stuco applications.
Also most rural areas and small towns do not have these codes and allow the builder to decide. One idea is for the lumber industry to treat the lumber with a mold preventitive treatment. Or sealant. My guess is its already been invented but like so many great ideas are blocked by a stuborn political and industry that work hand and hand for there own benifit.
Black mold is dangerus and has killed people and causes many illnesses. Its not to be used to profit from.
Same is true for fiberglass insulation which has been proven to be less insulating qith moisture in it.


41.
Sat, 06/22/2013 - 14:28

Response to Patrick Lymard
by Martin Holladay, GBA Advisor

Helpful? 0

Patrick,
Vinyl siding does not trap moisture. In fact, of all the common types of siding, vinyl siding is probably the best ventilated, and most likely to encourage drying to the exterior. Vinyl siding is far less likely to trap moisture in a wall than stucco.


42.
Mon, 07/01/2013 - 19:00

Stucco drainage details
by Sal Lombardo

Helpful? 0

Great article, have read it many times over. I am considering stucco/EIFS exterior finish for a new home construction (wall assembly being debated for, cost, thermal performance, durability etc..), in the event of 2x6 stick framing with a plywood exterior wall, I get the detail described for all the good reasons you point out. However, in the event of an ICF wall, no drainage plane is needed correct? I've looked at some sources, have yet to consult a local EIFS contractor:
http://www.stucoflex.com/wall_assembies.htm
http://www.icfmag.com/how-to/ht_great_stucco.html
It seems the thinner, elastomeric EIFS system goes right over the ICF (after a base coat, screen and case coat) is directly applied as the wall is not considered to "breathe", (http://www.cement.org/stucco/faq_icf.asp). You agree? If so, the lower cost to finish an ICF wall should be considered as part of the "wall cost" since a plywood wall would need the requisite moisture gap and application system to put it together whereas with ICF it ready to apply.
Thanks


43.
Tue, 07/02/2013 - 05:38

Response to Sal Lombardo
by Martin Holladay, GBA Advisor

Helpful? 0

Sal,
You are correct that when EIFS (synthetic stucco) is applied over ICFs, you don't need an air gap between the synthetic stucco and the EPS foam. Of course, your EIFS contractor is the one providing the warranty -- so the installation must follow all of the recommendations of the EIFS manufacturer, and you shouldn't attempt to direct the EIFS contractor concerning installation details.


44.
Thu, 07/25/2013 - 05:47

Edited Thu, 07/25/2013 - 05:49.

Another subdivision plagued by stucco failure
by Martin Holladay, GBA Advisor

Helpful? 0

Here is a link to an online news article about a residential subdivision in Ottawa with houses that are less than 10 years old -- houses with leaking stucco and rot.

Repairs to these houses are costing between $25,000 and $40,000 per house. The only people who are happy are the lawyers: Stucco leaves Ottawa homeowners stuck with repair bills.

[Thanks to Andrew Henry for letting me know about this particular cluster of failures.]


45.
Sun, 06/22/2014 - 00:22

stucco and airgap question
by joel kauffman

Helpful? 0

Thanks for the article. I have a question I cant seem to find the answer too.I am remodeling my house down to the studs. Put In cellulose insulation and OSB. Going with stucco on bottom half. I forked out the bucks and bought Homeslicker stone and stuccoto to create a 1/4 inch air gap. We have installed standard tyvek on the OSB and have the home slicker stone and stucco over it. So my big question is do we need another layer of felt down on the outside of the homeslicker or is the layer of stucco blocking fabric that comes with the product good enough ?

To be more explicit. Code requires two layers of felt due to the fact that stucco binds to the first layer leaving the second an intact weather barrier. Is this kind of protection needed with homeslicker stone and stucco product? Would adding a layer of felt on the outside of the homeslicker air gap creat some kind of unintended consequences?


46.
Sun, 06/22/2014 - 05:30

Edited Sun, 06/22/2014 - 05:32.

Response to Joel Kauffman
by Martin Holladay, GBA Advisor

Helpful? 0

Joel,
There are really three questions here:

1. What does the manufacturer of Home Slicker Stone and Stucco require?

2. What will your local building inspector require?

3. How much risk are you willing to accept?

For the answer to question 1, see this document: Home Slicker Stone and Stucco Installation Instructions. That document recommends that lath and stucco can be installed on top of the product in question, as long as there is a WRB between the wall sheathing and the Home Slicker. (See illustration below.)

For the answer to question 2, contact your local building department. Your inspector may want to see an additional layer of building paper or asphalt felt on the exterior side of the Home Slicker Stone and Stucco, because the wording of the building code gives your inspector that latitude.

The answer to question 3 is hard to pin down. However, after researching stucco failures, which are very common, I would include a layer of asphalt felt (or use paper-backed lath) on the exterior side of the Home Slicker product if I were building a home with stucco. Asphalt felt is cheap, and the insurance is worth it.

.

Home Slicker Stone and Stucco.jpg


47.
Sun, 06/22/2014 - 10:26

follow up question about home slicker
by joel kauffman

Helpful? 0

That all makes sense. I was just worried about creating some kind of unanticipated problem by having a 1/4 inch air gap with WRB on both sides. Is there any concern in that regards as felt and tyvek has different permeability properties. The felt inside of the stucco would not be flashed so lots of water would be entering the air gap.


48.
Mon, 06/23/2014 - 05:13

Edited Mon, 06/23/2014 - 05:14.

Second response to Joel Kauffman
by Martin Holladay, GBA Advisor

Helpful? 0

Joel,
Q. "I was just worried about creating some kind of unanticipated problem by having a 1/4 inch air gap with WRB on both sides. Is there any concern in that regards as felt and Tyvek has different permeability properties. The felt inside of the stucco would not be flashed so lots of water would be entering the air gap."

A. Installing one or two layers of asphalt felt on the exterior side of the air gap will not cause any problems, even if there is a WRB on the interior side of the air gap.

That said, flashing details are crucial, and must be carefully thought out. I'm not sure why you anticipate that "lots of water will be entering the air gap." Hopefully, your meticulous flashing plan will prevent that.


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