I live in seattle washington, according to buildingscience.com a “marine” region close to a cold region. What design should my walls be? 2×6 with faced bats sheathed then wraped with siding? Add a layer of hard insulation between the siding and the house wrap? Choose an exterior insulation (some foam sandwiched in foil perhaps) that acts as a vapor barrier and use unfaced bats? Where do I need my vapor barrier? Should it just be vapor semi impermeable? AHHHHGGGGGG!!!!!! Please help. I really want to insulate outside my sheeting because I want more efficiency. I really don’t want mold. Thanks for any and all help.
Jeremy
Replies
EEBA and Building science have books that are specific to your climate. Your area's publications will give you a synopsis of several options for building your wall assembly that work well in you cold marine environment.
I live in a mixed humid zone and my EEBA book gives only what is best for my area, sorry I can't be more informative. Maybe there is a copy at your local library, or order a copy via e-mail.
..............Iron Helix
"EEBA and Building science have books that are specific to your climate."Acutally they don't.But I found this footnote."7 BSC has not yet developed climate-specific building science guidance for the new Marine region. In the interim, guidance provided in the HTW Mixed-Humid climate can be applied."http://www.buildingscience.com/designsthatwork/hygro-thermal.htmThat page also has links to the specifics for the mixed-humid climate.Here are the books.This has lots of information on walls including rain screens.http://www.buildingscience.com/resources/walls/default.htmand moisture.http://www.buildingscience.com/resources/moisture/default.htmHere is the EEBA.http://www.eeba.org/And here is another similar group.http://www.nibs.org/betechm.html
I sit corrected.....
It was my understanding from the EEBA lecture I attended in St. Louis on June 13, 2006 that there were specific sets of references for the described climate zones.
I probably mis-heard or misunderstood what had been said, even with $5000 worth of hearing aids' I still get things screwed up!
......Iron Helix
PS....I have the mixed humid climate version of the EEBA series as it is the region in which I live. Nice reading!
Well, like as not, don't use batts, for one, they leak around the edges and FG just has too many "issues."
I'd be really interested to get RayMoore's take on Marine-Cold.
Given that you may be exposed to very lateral rain, it would seem like an excellent case for PERSIST, as keeping all the moisture, and al lthe water vapor as far out of the structural envelope as possible certainly seems like a net good.
Note that might actually bring your walls 'back' to 2x4, as the insulation envelope is outside of the structural envelope (you may still need to may adjustments for wall thickness at the windows, just not the stock jamb extensions used with 2x6 construction).
My take on marine cold is I could use some about now. We've had over 100 degrees for 20 of the last 22 days. I don't remember what rain looks like and my rainwater tank is almost empty.
I think PERSIST is the way to go in virtually every climate, though I might use something else in a very dry climate, then again, I might not. I've given the system a new acronym. I call it REFORM, which stands for Rigid Exterior Foam Over Rubberized Membrane. Joe Lstiburek likes the new term, though he reminds us that the system is sometimes done with membranes that are not rubberized and with exterior Rockwool instead of Foam. Both of those are inferior options and should not be encouraged, though I see the fire benefit of the Rockwool.
The most important issue in the described climate is bulk water intrusion, so flash flash flash. Rainscreen systems like REFORM can be a big benefit as well.
Other systems have been effective, but the details and the specifics can get you because you will start out closer to the edge of failure in that climate. Water management is just harder to accomplish there.
As for vapor diffusion issues, if you are trying to use typical cavity fill insulations, I would probably not use a vapor barrier. I would let the wall dry to both sides and put my efforts into bulk water management. I would also do more homework about my climate specifics and would consult a psychrometric chart to determine the seasonal vapor pressures. I have no firm answer without more climate data unless you go the REFORM route and then I have no fear.
Send Rain!
My take on marine cold is I could use some about now.
LoL! You are not alone in that <g>.
I'm almost afraid of rain, as it will likely fall hot, and only make it more muggy around here, not less (as if we need it damper and less evaporative <sigh>).
rainwater tank is almost empty.
Ugh, I'm more than some tired of getting monthly average rainfalls, but only on 2 or 3 days of the month.
I call it REFORM ... Joe Lstiburek likes the new term
That's a pretty good recommendation.
The most important issue in the described climate is bulk water intrusion, so flash flash flash. Rainscreen systems like REFORM can be a big benefit as well.
Ok, then, I was not daffy in thinking that what OP really needed was a rain-proof structure first, that was also well insulated. The mental image of just using deeper framing, but still firmly coupled thermally to the outside temperatures (and with all the pesky gaps along the framing members batts provide) just seemed wrong to me.
I'm not entirely comfortable with the "green-ness" of mandating 2x6 exterior walls filled with fg batts anyway--a mooney wall using fast-growth 2x4s instead being closer to my thinking of good practice (though, the need for increased hardwood for jamb extensions jsut to meet an arbitrary AHJ wall-thickness/R value rule also rubs wrong).
For Seattle, especially near the coastal areas, I'm wondering if using the NO buildingscience house as a starting point for rain-proofing makes a certain amount of sense. Separating the house from ponding water, providing under-structure drainage, long overhangs & the like "seem" like a good starting point.
The long overhangs "clang" a bit, mentally, against a desire to grab as much solar gain as the PNWet allows (with some SAD considerations for the residents, too)
But, that's desing, isn't it? It's all compromise of one sort or another.Occupational hazard of my occupation not being around (sorry Bubba)
Wow guys, thanks so much for all the advice. Due to budget and code restraints here is my plan: 2x6 framing with (?bats, ?blown in cellulose?, something else?) covered with sheet rock on the inside. If I am understanding correctly I do not visqueen under the sheet rock, I cover the rock with latex paint and I don't worry about another type of vapor barrier on the inside of the cdx sheeting which I will be covering the outside of the house with. Now, outside we are putting cdx sheeting over the 2x6 studs and covering with (tyvek, which is semi permeable? rubberized membrane which I assume would not be permeable at all, foil also not permeable or something else?). Then a rigid insulation (what would be a good choice? ISO? Styrafoam? faced not faced???). Then we want to put furring strips along the insulation to attach our siding to and to give an airspace behind the siding--so it can dry. We will have 2 foot overhangs with our roof. I am spending alot of energy on drainage of the footings. This house is 2 levels. Ground floor sits on a slab. This is on a sloped lot where the north end of the house is about 5 feet underground and the south end is about 1 foot above grade. we are directing the water around the house and downslope. The roof (roof plan calls for metal we like the look and durability) water will be collected in a tank to the south of the house. Lets see, what else... we get around 35 inches rain/year. Max temp 95 min 28 with mean of 54 all these numbers are very seat of the pants. We spend alot of time with temps about 50ish grey skies and some light misting and rain. Mild climate overall. OK I'll stop there and let me say again thanks so much for advice sorry if some of my questions are boneheaded I am pretty new to this stuff.
Jeremy
PS guys can you define PERSIST for me?
Jeremy
Here's a link to some test structure in Alaska with nice pics of the details: http://www.uas.alaska.edu/ct/whats_new/persist/index.html
Ray Moore will have better links, I just can't find any right now by googling. PERSIST is Pressure Equalized Rain Screen Insulation.Occupational hazard of my occupation not being around (sorry Bubba)
Pressure Equalized Rain Screen Insulated Structure Technique
Here are some links:
http://www.north-rthn.org/newsletters/ABSN-Fall-02.pdf start reading about halfway down.
Here is a great link I just found. Chris and Peter are friends of mine and introduced me to this technique back in 2001. Since then we have improved and perfected the details of this system while cutting insallation costs in many areas.
http://irc.nrc-cnrc.gc.ca/pubs/bsi/2003/docs/PrariesCaseStudies4.pdf
I am posting this again not to be obnoxious but because I really want to make a good choice on the exterior of my house which I am building. The major question in my mind is what do I cover the cdx with? something impermeable or semi-permeable? Please advise. Thanks for all the sage advice.
Due to budget and code restraints here is my plan: 2x6 framing with (?bats, ?blown in cellulose?, something else?) covered with sheet rock on the inside. If I am understanding correctly I do not visqueen under the sheet rock, I cover the rock with latex paint and I don't worry about another type of vapor barrier on the inside of the cdx sheeting which I will be covering the outside of the house with. Now, outside we are putting cdx sheeting over the 2x6 studs and covering with (tyvek, which is semi permeable? rubberized membrane which I assume would not be permeable at all, foil also not permeable or something else?). Then a rigid insulation (what would be a good choice? ISO? Styrafoam? faced not faced???). Then we want to put furring strips along the insulation to attach our siding to and to give an airspace behind the siding--so it can dry. We will have 2 foot overhangs with our roof. I am spending alot of energy on drainage of the footings. This house is 2 levels. Ground floor sits on a slab. This is on a sloped lot where the north end of the house is about 5 feet underground and the south end is about 1 foot above grade. we are directing the water around the house and downslope. The roof (roof plan calls for metal we like the look and durability) water will be collected in a tank to the south of the house. Lets see, what else... we get around 35 inches rain/year. Max temp 95 min 28 with mean of 54 all these numbers are very seat of the pants. We spend alot of time with temps about 50ish grey skies and some light misting and rain. Mild climate overall. OK I'll stop there and let me say again thanks so much for advice sorry if some of my questions are boneheaded I am pretty new to this stuff.
Jeremy
Post #6 expresses my ideas on the subject but if you are unable to use REFORM(PERSIST) and feel you must use cavity fill insulation, then I would opt for cellulose. Let it dry completely before covering up(not just dry on the surface). Pull some out of the wall and check the moisture content behind it next to the OSB. Damp spray cellulose takes up to weeks to thoroughly dry out. Don't trap the water in the wall.
Don't use fiberglass. The only good thing about fiberglass is the cost. That is a poor reason to use a product that will be there for decades.
I dislike Spun bonded Polyolefin (tyvek, typar, etc.) but you can use it if you like. I prefer #30 felt paper to tyvek. I just don't use these methods anymore. I use REFORM on every project.
Flash, flash, flash
Airsealing is very important! Since you won't be using rubberized membrane, you will need to work very hard at air sealing at the level of the drywall and also at the level of the osb. Problem areas will be at the outlets and switches, furrdowns, stairs on exterior walls, wall intersections, tubs and showers on exterior walls, light fixtures, wall plates, wire penetrations, windows and doors, and pulldown stairs. REFORM eliminates all these issues as areas of concern. The cellulose will help a tiny bit with air tightness though the cellulose industry touts this as a strong advantage of their product.
The foam on the outside is a great idea and will also help with the air sealing. With a properly detailed house you can get blower door testing numbers of .75 ACH50 with REFORM or 2 ACH50 with the drywall air barrier approach. Tighter is better. Don't forget to supply mechanical ventilation. That is for another discussion.
For your situation I would use Dow Styrofoam at one inch thickness.
If you use 5.5 inches of cavity fill insulation that will give a center of space R-value of around 19. One inch of styrofoam will give you R-5. Think of this in terms of the temperature of the osb in January. We want to make sure that the temperature of the osb is never cold enough to form condensation from interior moisture deffusing through the wall.
The average temperature in January for Seattle is 40 degrees. This will put the average temperature of the osb in january at about 46.25 degrees. This ignores radiant gains and losses but is still a good thing to consider because the north wall will be the most worrisome in the winter. Under these conditions, condensation should not form within the wall from diffusion unless the indoor RH is maintained at greater than 40% for the month of January. The cellulose will give some forgiveness due to it's ability to act as a hygric buffer(water storage capacity)
You should be fine with this system but I'll take a 2x4 wall with all the insulation outside a rubberized membrane every time. Consider the temperature of the osb in january under those conditions. Room temperature. You can't get much safer than that. You could have an indoor pool and be safe in the winter time with no interior vapor barrier.
I'm really sounding like a fanboy, I know, but it's that good.
THanks thanks thanks!!!!
Since I have already framed (oooppps) could I cover the outside OSB (I am actually planning CDX) with the rubberized membrane(then the styrofoam then furing then siding) and do the cellulose on the inside covered by rock but no plastic? Or should I just go with felt then outside insulation etc....??? Thanks again Ray, really good advice.
Jeremy
It is a difficult climate to deal with. A lot will depend on your heating/cooling practices, and the specific microclimate where you are (as I suspect winter lows can vary by 20 degrees or more from one end of Seattle to the other).
You might want to check with the local building inspector's office, or the state agency responsible for energy conservation and weatherization. They may have some pamphlets designed specifically for the Seattle area.