I have been reading what I can about wrapping a house with exterior foam. As I embark on this task on my own new home I would love some feedback as to the process I am leaning towards.
The order is as follows….
-2×6 wood frame (OVE, 24″ centers, no crips, etc.)
-7/16″ osb
-tyvek house wrap
-vinyl windows with sticky flashing on edges
-1″ styrofoam
-beveled cedar siding (back primed)
-interior insulation to be R-21 paper-faced batts
..heating system is a mitsubishi minisplit ductless heatpump
..ventilation is through a slot-vent window in each room and 24 hr timer fans in the bathrooms (2)
I am liking the insulation value of this setup but have some concerns about air exchange and mold potential.
My climate (southern oregon) is not incredibly wet so hoping to skip the time and expense of a rainscreen over the foam.
Thanks for any thoughts or concerns as to this system!
Replies
2 words - Mooney Wall.
http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm
http://builditsolar.com/Projects/Conservation/MooneyWall/MoreMooney.htm
Use the advanced search at the top of the column for more information.
William the Geezer, the sequel to Billy the Kid - Shoe
I love the mooney wall idea. Wish Id known about it during the design phase...I suppose i need to spend even more time lurking!but,
I already purchased all the exterior foam for a great deal on Craigslist. Also in my small house (1350sf) I cant lose the floor space at this point in the game (interior wall layout more or less set)
I'm sure others will address this as I'm only going to pose another question. For a while the mo of a lot of builders was that sticky Tyvek wrapping the whole house and they did indeed run into issues of the house breathing or, rather, not breathing.
What Tyvek product are you wrapping the house with? I build to Archi spec's and am just learning how much I have to learn in regards to the exterior wrap and how it affects the quality of virtually everything else in the house. I do know that several builders had problems with overly tight houses, along with the breathing issue, was around openings where there might be a small break in the envelope a vacuume affect was created and water getting behind the siding would travel side ways for something like 6' and get sucked in.
Any way, the calvary and all their more informative response are on the way. Mostly I just wanted to say Hi being from Ashland.
You can still ditch the FG and use DP cellulose.
Lot more insulation for the buck.
What kind of foam did you buy?
Joe H
I hope that someone else will agree with me that you should not skip the rain screen. I live in Nebraska and paint just doesn't last on my house. It blisters and peels. I truely believe that cedar needs a rain screen to liet the backside dry.
In his climate a rain scree plan would be worth while
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
The rain screen makes sense for sure. Any experience with the tyvek rainscreen. Im sure its not near as good as the real thing but perhaps in a relatively dry climate it would suffice? I admit I am skeptical as it seems like the easy way out (and therefore not fine homebuilding.)I'll skip the paperfaced batts for unfaced friction fit. Wish I could afford cellulose or some other blown in but the budget is real tight.
Did you back prime the cedar? Just curious because there are many many houses around here that have cedar siding without rainscreens. Perhaps it is different in an old leaky house with at most tarpaper under the siding (as opposed to a modern, airtight barrier.)
Thanks for the advice.
I didn't build it. My late FIL built it in 1950.
skip the paper face or any other VB on the interior face of the studs
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
You should be thinking about a heat recovery ventilation system. Hopefully you are also focusing on airtightness as well as insulation.
Windows and bath fans are not the way to properly vent a tight home. Not sure what a slot-vent window is, can you explain?
Is this house constructed yet?
a slot vent window is as it sounds ...a small operable slot at the top of the window to allow ventilation. Recommended by Earth Advantage for venting.
The house is in the framing stage now. Should be dried in by this wkend!
I'm a proponent of humidistatically controlled heat recovery ventilation systems. The bath fans on timers is one approach, but it requires someone to manually turn the thing on. The slot vent window system would require that someone manually opens them when the fans are venting, and to close them when the fans are not operating. If someone leaves the vent slots open when the fans are not in operation, that's a direct opening to the outside through which conditioned air will escape.If someone turns the bath fans on when the vented slots are not open, you are creating a negative pressure situation in the house. The makeup air will need to come from somewhere.With the HRV system, everything is automatic including fresh air intake, and you will be recovering some heat on the exhaust side rather than just dumping conditioned air via the bath vents.If you are still in the framing stage, there is plenty of time to have the system sized and installed.Just my 2 cents
<If someone turns the bath fans on when the vented slots are not open, you are creating a negative pressure situation in the house. The makeup air will need to come from somewhere.>thats a good point, the bath fans will be on 24 hr timers so they will go on automatically but the slot vents are of course manual.
This certainly is a weak point in the system. Ill talk to my air guy about the HRV. -I know the initial cost is going to scare me though!
Thanks
There are some passive inlets that can be used.Can't remember the name. Some are one way fabric "flapper".They act something like the damper on exhaust fans, but take almost no pressure to open..
William the Geezer, the sequel to Billy the Kid - Shoe
Yeah, these up front costs always make folks nervous, but I'm guessing that in the long run it might be less expensive not to be dumping heated (or cooled) air straight out through the bath vents.I can't begin to tell you how to run those calcs, maybe someone else here can.Be careful with the HRV during the construction process. I understand that solvent vapors (e.g. floor/wall finishes) can cook the material on the fan blades.
jp
you should skip the fg.
go with dp cellulose.
get your house tested for air sealing.
check your caz readings.
and vent with timed fans.
did it myself, it works
good luck
thomas