I am building a brick home in Houston.
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Is this wall construction plan sound? I have a 5 1/2″ brick ledge with the following plan: Brick -> Air Space -> Tyvek -> Osb -> 2″ by 4″ frame -> Blown Cellulose -> Dry Wall -> Paint. I am concerned about solar [vapor drive].
Home Details:
Location Houston
Ventillated Crawl Space
Ventillated Attic
Large 2nd floor space over driveway
Living area over detached garage
Brick Veneer
Asphalt Shingles
Cellulose Insulation
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Replies
Robert,
Since OSB is a vapor retarder, your wall will probably work. However, considering your climate and the fact that you are using a reservoir siding (brick), your wall would be much better protected against inward solar vapor drive if you substituted 1-inch foil-faced polyisocyanurate for the OSB. Of course, your wall needs a bracing plan to provide racking resistance.
Would it be possible to use 1-inch foil-faced polyisocyanurate over the OSB?
The reason I'm asking is that the structure is engineered to have OSB/Plywood and that can not be changed at this point. So my option is to continue with Tyvek and OSB or some other combination of material with OSB. I'm just trying to cover all options before making the final choice with my builder.
Robert,
Yes, you can install foil-faced polyisocyanurate on top of your OSB sheathing. Remember that you should never install interior polyethylene or vinyl wallpaper if you have foam sheathing.
Martin,
Thank you for your help. I have one last question is an acceptable strategy to use a double sided non-perforated foil radiant barrier house wrap with OSB? Or does the insulation of the polyisocyanurate play a critical role in decoupling the OSB sheathing from the foil? It would seem that any moisture on the interior side of the OSB will be removed via AC or de-humidifier.
The solar vapor drive of the brick has me pretty concerned. Houston gets wet, sunny, and hot!
Robert,
I wouldn't substitute radiant barrier foil for the polyiso. The foil-faced polyiso does several things: in summer, it stops inward solar vapor drive. In winter, it raises the temperature of the OSB sheathing, lowering the chance that interior moisture will condense against the cold sheathing.
Radiant barrier foil doesn't raise the temperature of the sheathing. If you use radiant barrier foil, your wall risks winter condensation problems.
It's been an interesting week. We could only find 1/2" Foil Polyiso in Houston. We looked at two large building suppliers that are listed on the Johns Manville website. It would cost about $2,500 more to go with the 1/2" Polyiso vs. Tyvek. We start framing on tomorrow so at this point it seems Tyvek is in the lead. We briefly considered Tyvek Thermawrap but then noticed Martin's Top Ten list. lol
We did decide to use the 1/2" JM Foil Polyiso in the open crawl space. This was one of two methods detailed in Joe L. article about crawl spaces.
Am I missing anything? Should I think about a Radiant Barrier over the Tyvek? http://www.radiantguard.com/ultima-radiant-barrier-1000sf.aspx Since I am using 1/2" in the CS, should I add more foam insulation? Should I be thinking about the JM product under the second floor that is over open space? or the space over the garage?
Any other advise for someone who is just about to start framing?
I have a pic blog if anyone is interested.
Thanks,
Robert
Taped XPS would also be good for stopping the vapor drive and warming the wall cavity to promote drying to the interior in winter. Foil is better but if it's not in the budget maybe second best will do.
I found a diagram on Building Science of the Perfect Wall - Residential. http://www.buildingscience.com/documents/insights/bsi-001-the-perfect-wall/
I think this is possible for my build using the following materials: Brick -> Air Space 1" -> XPS Foam 3/4" to 1" -> Smooth Foil Wrap -> OSB -> Wood Insulated Cavity -> Dry Wall Taped -> Paint. My builder is pricing the materials and we should know by the end of the day.
Making these decisions is hard and more complicated given that my family could live/ grow up in this house for 50+ years. Certainly makes one want to get it right the first time.
Kind Regards,
Robert
Robert,
I question your use of "foil" between the OSB and XPS.
There is no benefit from the foil without an air space.
A recent Lstiburek Article reccomends "crinkled" building wrap between OSB and Foam sheathings.....the purpose is for hygric redistribution.
I was thinking the foil would simply act as the vapor barrier that is present in the Perfect Wall -Residential. http://www.buildingscience.com/documents/insights/bsi-001-the-perfect-wall/
In Joe L Houston Profile designs that work. He states that the House Wrap/OSB will work with 1". I have 2" so maybe I should just stick with that.
In Joes Stucco Woes Perfect Storm he says "The gap allows redistribution of the moisture in both the stucco and the OSB sheathing. The gap also does something else—if it is wide enough it becomes a ventilated space making the “Goldilocks” vapor curve argument moot. Once we have a ventilated space (with meaningful air movement) the permeability of the traditional building papers and plastic building papers almost does not matter. Anything between the “low perm” and “high perm” materials can be shown to work. In fact, an insulated semi-permeable sheathing does the best job of controlling inward vapor drives in all climate zones."
This seems to suggest anything I do with that size air space and good ventilation should work.
Hi ... another issue ... if you're using a 2x4 with blown cellulose that will be 4" of insulation. I think that will be about R10 or 12 ... don't you need to have R20 in Texas? And even if you don't need R20 ... why wouldn't you have it considering A/C load demands in Texas?
"It would seem that any moisture on the interior side of the OSB will be removed via AC or de-humidifier. "
Boy o boy A/C 24/7/52 ..... I guess at this point it's too late to drop the brick and go for a double stud R40 wall instead.
Yes too late on the brick it is paid for! Interesting enough 2x4 is standard construction here in Texas.
It looks like I can get 3/4" Foil Faced Polyiso. Dow Tuff Stuff. It has an R Value of 5.0. The blown in Cellulose has an R Value of 14. Not exactly balanced as Joe would suggest. I'm pretty sure he would want 3" Polyiso.
So the question is how would you guys build this wall?
Brick -> Air Space ~1 1/2" -> Foil faced Polyso 3/4"-> OSB -> 2"X4" Wood Cellulose Insulated Cavity -> Dry Wall Taped -> Paint? Is this a good plan??? Better than Tyvek???
The clock is ticking... We started framing yesterday.
Thanks for everyones help.
Robert,
Your latest plan will work. I wouldn't worry about any moisture issues, as long as the mason does a good job keeping the air space free of mortar droppings, and as long as your brick includes above-grade weep holes. Be sure that the flashings are properly integrated with your foil-faced polyiso, which will be your WRB.
Martin,
Have you seen Joe's very new article "Mind the Gap, Eh?"
He seems to be saying that the "crinkly stuff" would be a good idea between foam sheathing and OSB.
John,
ASHRAE gave me an ID number and PIN a while ago to log onto their protected Web site, but it isn't working today, so I have no access to the article. If you have relevant advice for Robert, though, go ahead and give it. It sounds like he's running out of time to finalize his details.
Martin,
I will email you...after my meeting
John,
Thanks for sending me the scan of the "Mind the Gap" article. The way I read it, the gap between OSB and rigid foam sheathing -- e.g., "crinkly stuff" -- is only required if the cavity insulation is closed-cell spray polyurethane foam. If you use cellulose, any incidental moisture that reaches the OSB -- there shouldn't be much -- can dry to the interior.
Yes, Martin... I agree
I was reading between the lines and being over conservative.(as usual)
There will be hundreds (or thousands) of brick ties with fasteners penetrating the sheathing and the OSB......but hey I know I am conservative
How can I research what "Crinkly Stuff" is?
Robert,
It probably is overkill
all of these layers .....material and labor costs can get out of hand
The article only calls it "crinkled" building wrap
no trade names or products are mentioned
Examples of crinkled housewrap designed to promote drainage include StuccoWrap and PinkWrap Plus.
Hello everyone. Progress has been good. I finally secured a source for 3/4" Poliso which was amazingly difficult. Call manufacture, call distributer, distributer told me to call wholesalers until I found one that carried it. I thought wouldn't it be easier if you could give me a few names??? Anyway I got it ordered.
At this point I'm wondering if I should go ahead and do a wrap over the OSB. I think it is maybe $1k more to do. This is my forever house... Thoughts?
We are framing the second floor today!!! Whohoo... Here is a link http://picasaweb.google.com/cozart/HomeBuild# for those who like visuals.
Does anyone have any ideas for insulating under the 2nd floor space over the driveway? If you look at the pics you can see how this is all tied together with large steel beams. http://picasaweb.google.com/cozart/HomeBuild#
Robert,
Here in Vermont, we've learned that you can't use fiberglass batts to insulate a floor exposed to the weather (for example, a bonus room over a garage). It's hard to do a good job here without closed-cell spray polyurethane foam, although dense-packed cellulose would probably work. In Houston, you don't have to worry as much about frozen pipes, so you may be able to get away with sloppier insulation practices than we can in Vermont.
Those steel beams worry me. It's hard to see the bearing posts for the steel beams in the photos. Obviously, those steel beams are terrible thermal bridges, since they extend outdoors. The ends of the beams must be carefully insulated from the interior of the house with thick insulation. If that's impossible, you have no choice but to bring the steel beams inside the home's thermal envelope. That would mean insulating them entirely, including the outdoor portions.
Martin,
I was thinking you would say something to that effect. This is one application that I think spray foam is the clear winner. The total area is about ~250 sqft. I'm going to see about getting some quotes on it. I assume if you use the foam that I will not need the Poliso foam in that area. I can take that extra and use it in the garage.
Robert,
Wow...it looks like that beam is going to carry a brick veneer wall too!
Is that right?
That column is taking a serious load....
Even without the weight of the brick veneer
I just don't see how you are going to insulate ALL of "the outdoor portions" of that beam as Martin has suggested.
Yes thats right we have brick veneers on both exterior walls. It is hard to to tell in the picture but the garage is spaced 3 feet from the garage and the steel beams support brick veneered walls on all sides. This being our forever house we have 100% brick everywhere.
I told the engineer that we would be living in this house until we pass away god willing in about ~60 years. I think he took my comments to heart as everything is designed pretty stout. The piers are all atleast 10ft deep. We got lucky in the worst drought in memory we hit the water table at 10ft.
It is in the 100 year flood plain and that is why we are going up. Although I somewhat doubt the maps as the previous house which was atleat 50yrs old never flooded. We made it through tropical storm Allison which was bad for Houston. Think 20" of rain in two days. Since then our watershed has had tremendous work done to it. It's a pretty interesting project thus far.
I think we spray foam that area over the driveway and that should be able to decouple the steal from the living spaces???
My builder and I meet with the foam insulation company today. We decided to spay foam in that area over the driveway and spray all the interior surfaces of the steel beams. In addition to that, I got him to agree to spray the stemwall floor joist conection. I figured the Polyso that we are putting under the house has a much better chance of working if we foam that area of the crawls space.
The major changes that I have made thus far are:
Replacing Tykek wrap with Stucco Tyvek
Adding 3/4" Polyso Foam to the exterior walls and under the garage
Spray foam the area above the driveway
Spray foam the stemwall floor joist connection and add 3/4" Polyso to the crawspace
I think these have been wise changes and I would like to thank everyone here for their help and comment on how much of a valuable tool the internet has been in learning what questions to ask.
Can you all think of any small projects that could make a difference at this stage?
Hello,
In place of Tyvek, you may want to look at the reflective insulation housewrap product at http://www.EcoFoil.com
Well at least he got the cellulose part right...
There are a number of different Radiant Barrier companies out there, but this one seems to have been around the longest (over 25 years) and they have one of the thickest and strongest products. Seems like they would be a good choice.