I’m a HO, building a new house in Seattle, working with a GC that is a good sport and open to suggestions (up to a point :-). i love this forum, as it’s an endless source of great ideas (and prevented me from making mistakes)
The house has plywood sheathing (4 ply), and will have stucco over it. I read a lot of horror stories on EFIS and, even if I’m sure it can be made to work, insurance won’t let me use it anyway, and selling a house with EFIS is next to impossible.
So I’m going with traditional stucco. One of the interesting things of the new EFIS installations is that they use a drainage mat between plywood and the stucco, guaranteeing good drainage. Traditionally, stucco uses 2 layer of building paper (that supposedly swells then shrink, leaving a drainage plane)
Is anyone using a drainage mat behind traditional stucco? Seems to make sense, intuitively…
Is traditional stucco with 2 layers of building paper a safe bet in the wet Pacific NW? Any other way to install stucco?
Thanks, Rob
Edited 2/12/2005 1:00 am ET by robca
Replies
Rob
Traditional stuuco is the sheathing. There is no ply under it. The two layer of paper are allowed plenty of room to seperate form the stucco. With play this won't happen and your drain plane will be compromised.
Putting stucco over sheathing should, IMO, consist of Studs>Sheathing>1/4"|3/8" redwood slats (verticle, 12" to 16"OC)>Expanded Metal Mesh (used for EFIS)>Darbied Brown Coat>Color Coat.
Using the expanded mesh, means that you don't need the stiffening effect of the scratch coat.
The 1/2" ply sheathing eliminates the need for the sheathing effect of the scratch also.
Whenever you do stucco, make sure it gets 28 moist days between coats!
SamT
28 moist days in spring in Seattle. I think we are covered there :-)
Thanks Sam for answering, but I'm struggling a bit to parse your answer, sorry (it's me, not the answer that has problems). I guess we are using "traditional stucco" differently
My house has been framed with standard 2x6 walls, with 1/2" plywood on the outside (I spent extra for plywood instead of OSB, as many threads here pointed out that OSB nail retention under stucco could be sub-optimal)
I might have used some terms improperly, but my understanding was (from inside to the outside):
Drywall, studs with batt insulation, 1/2" plywood, 2 layers of building paper (that separate and create a drainage plane), metal lath (self furring) or chicken wire, scratch coat, brown coat, finish coat
I think you are suggesting a 2 layer stucco system, with the redwood slats aided by the metal lath as the drainage plane, right? No paper or any other water barrier in that installation?
Thanks, Rob
Rob, here in South Texas where almost evrey house is brick, stone or stucco (almost no wood siding except gabel ends), we use the construction you noted ... three coat stucco over expanded metal lath (but not chicken wire). In place of the two layers of building paper we use Tyvek stucco wrap.
The low end tract houses use eifs and it does not hold up well. My guees is thjat they can get away with using it because we are dry most of the time.
I'm sorry, I thought you wanted it done the right way.
Rob,
My Bad.
Definately need the paper. Sorry. Can be inside or outside the redwood/cedar lathe. Outside is a little better. Outside is a must if not using rotproof wood.
Really want the airgap provided by the lathe. That airgap is what makes the drain plane work.Gotta use longer mesh nails, 'cuz the holding power's in the stud.
2 or 3 stucco coats, your stucco guy may insist on 3, no problem.
Ed, I like paper over Tyvec in this case, as paper has better vapor transmission and 2 layers of paper keeps the water away from the wood better, IMHO.
Rob, it's all JustMHO. What has worked for 100 years will work for another 100 years, as long as you don't change anything. You changed the 100 year method of stucco when you added the 1/2" ply. That removed the traditional airgap. Gotta replace that airgap. IMHO.
SamT
Thanks for the links, will read them ASAP
Sam: I love looking at homes under construction (been doing it for 4 years before deciding to build instead of buying an existing home), and I don't think I ever seen a house around here with no plywood or OSB as sheathing material (I'm originally from Italy, and I only lived in Seattle, so my experience is rather limited). I know that plywood was required by the engineer to ensure structural integrity (shear walls), and OSB would have been an approved substitute. I don't think he would have signed on structural plans without plywood (heck, I could have saved a bundle :-). All homes seem to be framed similarly (studs and ply or OSB), then use a different housewrap or siding material as rewuired (lotsa wood up here, hardiplank, stucco, some brick, etc)
Do I understand you correctly? Are you saying that you can build a stick-frame house with just studs and stucco as the shear wall/sheathing material? And would the fiberglass batts be close to the stucco? I'm a bit ocnfused, as you can tell :-)
Rob,
Before plywood as sheathing came to be standard, stickframe and stucco was considered to be the ultimate in earthquakes and winds.
Stucco has an esthetic tradition. Stucco is user friendly. Stucco is a great wind barrior while still passing vapor. Better than Tyvec, IMNSHO.
Stucco needs an airgap behind it to work the way a stucco wall is supposed to. Stick some paper on a sheet of ply, then dump a layer of 'crete on top of the paper. How much room is there between the ply and 'crete for water to flow thru? The paper expands they say? Where does it expand into? The sheathing or the 'crete?
Yes, they stuffed the insulation right up to the paper.
>>Are you saying that you can build a stick-frame house with just studs and stucco as the shear wall/sheathing material
Depends on your local codes.
SamT
Stucco is very common here in San Diego area. My house was built in 1951 with stucco over stick frame, no sheathing, and no cracks. I doubt the city would let me build one that way today, because most engineers do not regard the stucco membrane as a reliable/calculable shear panel. Some guys run ply on the inside of the wall, but this is really awkward to schedule. My house has cut-in blocking running diagonally in all the exterior walls, in opposing runs that form vees or x's.My expert stucco guy prefers to go directly over the studs. I asked him, "What about over plywood?" His reply: "It will crack." I respect his knowledge tremendously, and so I look for ways around it. The earlier suggestion about redwood battens to form a drainage plane might also stop the cracking, by further decoupling the ply from the stucco. A layer of foam would do likewise.Bill
I wish I could fly a crew of stucco folks from southern California :-). When visiting there I was always amazed by the high-quality stucco installations. Seattle is definitely the place for wooden siding, not stucco.
The problem with not using ply, as you say, is that engineers don't want to have to deal with a shearing material that can change its characteristics depending on installation, and they like the predictability of OSB or ply. After reading the posts here, I understand why not having ply would be better, but it's not an option, alas.
I'll ask my GC to consider adding redwood battens and decouple further (hoping that it won't add too much cost, but I'd rather do it properly once than save money and fix it 3 years later)
Bill, could you ask your stucco guy what he thinks of 2 layers of paper with the proper stress joints, to help with cracking? That's how everyone seems to do it here (probably less than 5% of houses are stucco, so it's a limited pool)
Thanks for all the answers
I guess I dont really have much valuable info here but I live just down the road from you (portland OR) and we share the same wet climate.. I know nothing about stucco except for that MANY of them here are crumbling around the corners of windows.. Just make sure that your GC looks very carefully at his guys' flashing jobs so that he is confident that they are done correctly.______________________________________________
--> measure once / scribble several lines / spend some time figuring out wich scribble / cut the wrong line / get mad
robca,I did ask my guy about the double paper over ply method. He told me of a job he did where the owner had it all spec'd out with ply and double paper. It cracked, but less than single paper would have. I think you need a thicker layer of soft stuff so the staple legs can flex as the differential movement occurs. It is rather like how a slip sheet works over a crack in a slab, with the fasteners being the main difference.I stuccoed my own house in Colorado in the mid 80's, with double paper over ply and lots of expansion joints. It did not crack very much. This was in the mountains with low humidity and windy, very tough stucco curing conditions, and lots of stress as the house is changing temperature, and withstanding 100 mph winds in winter. Despite the slight cracks, I loved the stucco. That was a tight, and quiet house.Bill
Stucco's not supposed to crack. But the only way to prevent is is allow enough moist time for each coat to cure before placing the next.
In dry climates, hang burlap and sprinkle twice a day, In Oregon just sprinkle.
SamT
Rob, there are some 'stucco wrap' type products available now... I saw them at the JLC show. One is a Dupont product, and there are a few others. The idea is that the material has a dimpled surface and will create some air space behind the stucco.
http://www.google.com/search?hl=en&q=stucco+wrap
The main thing is that you need to view the wrap/paper you use and the window/door flashing as one system. I've taken stucco off of plenty of houses and the leaks are typically at the windows and doors, not in the field. So, I would say that while the wrap or paper is important, what's most important is how you flash openings and the way it's tied into that flashing. Since you are interested in the construction of your house on the detail level, I'd say you should get acquainted with best practice in flashing and decide how you want the whole thing handled. There are a lot of self-stick flashing materials out there now, but you have to install them correctly. It should be the most seasoned builder on the crew who is overseeing the flashing details.
You might want to look at this article.
http://www.jlconline.com/cgi-bin/jlconline.storefront/420e46fd0015660327197f0000010529/Product/View/0309stuc
If I remember correclty it has lots of good info.
Here are a couple of others, but I don't remember what they have in them.
http://www.jlconline.com/cgi-bin/jlconline.storefront/420e46fd0015660327197f0000010529/Product/View/0009topq
http://www.jlconline.com/cgi-bin/jlconline.storefront/420e46fd0015660327197f0000010529/Product/View/0309stuc
And go over to http://www.buildingscience.com and check House that Work for your climate.
Also do a search over there for STUCCO.
Don't forget that San Diago is much, much different climate than yours.
What works there might be a disaster in your area.