Where is the home?

 

Is this for your house in northeastern NJ? If so, R-5 (1" XPS) is plenty to stop condensation--- IF there is FG in cavity; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=New%20Jersey Without it and only R-10 exterior, you wouldn't meet code minimum energy requirements, BUT the empty cavity could be warmed by the house HVAC system and would be safe against condensation on sheathing boards (need your nearest city). I'd pull the window/door trim to air-seal there. Long as there is no poly under drywall/plaster, check at outlet/switch boxes.

Gary
PS. WoW, the OP at "moisture sandwich" is waiting for your reply. Ops, forgot the site already notified you...

 

I don't see the nails staying put without support for 2" and only 3/4" into wood. I don't think the foam, long term, will do the job.

 

It is NE-NJ. The general rule is r13 in 2x4 wall. The house was closed yesterday, and I haven't done much except look at it.:laughing: I am trying to get some experience/been-there info about exterior insulation and siding. It is true that exterior insulation hasn't been around for long for diys. I'm sure commercial situation has costly solutions. BTW, I'm not putting on stucco.
Blown in cellulose or FG seem to be the solution, then use 1" xps. I have no idea what'll happen to the roofing nails standing out 2". I also don't know what happens to the r-value with nails holes all over the boards. I just wondered if this is one way to insulate.
I wondered if the town inspector will allow r10 - because studs are also insulated and air infiltration is stopped a lot better than stud bay insulation. I expect the inspector probably will reject this idea since there is not much evidence base.

Gary in WA - I have to thank you especially for all the links to the info. Initially I was going to insulate from inside and put 1" xps to prevent condensation.

Building Science did not mention one thing. What happens to the r value when I put nail holes all over the xps. It does say that little tears and holes in under slab vapor barrier doesn't cost its performance, but is this same for xps boards? Does Building science assume tyvek type of wrap to control air movement (therefore better r value performance)? I was just going to use 30 lb tar paper. I think I read that 30 lb tarpaper does pretty good job of sealing around the nails. Air movement would have been handled with xps sealed around the sheathing.

 

I wouldn't use nails when it comes to 2" foam board.

More is more in this case but 1" should do the trick when it comes to a 2x4 insulated walls for the purposes of condensation as Gary pointed out.

We have hung siding on home that we put 2" foam but we strapped them first.

I would also use foam washers and screws if it were me. Better holding and spreads out the clamping force.

As far as the R-Value, it makes little different. If you added up all the square footage of all the screws/nails in a piece of 4' by 8' foam, you might have the size of about 1/2 a business card.

Envelope issues as a result of a bunch of poorly punched holes, broken sections, etc. would be far more disastrous to overall efficiency.

Gary...thanks for the heads up. I do most of the posting as I am in a car or at a jobsite. What sort of notification are you talking about?

 

All good points. I'm still worried about that 4 square inches hole that ruins the r value with the draft.
All in all, if the inspector allows the plan, 2" xps and strapping looks good to me.
1. Nailers around the corners, windows, doors.
2. xps and seal the joint with can foam. I don't trust tape. I may use gorilla tape, but can foam may be cheaper.
3. 30 lb felt.
4. Strapping every 12" o.c. (or less?). Will check with the manufacture manual but following the 16 o.c. studs feels too wide for vinyl.
With this kind of drainage plane, I may go wild with the vinyl and stop worrying about flashing.:laughing:

 

Again, the 4 square inches, vs. the 4600 square inches (i.e. 1/1000 of the board size) will only amount to that 1/1000 R-Value downgrade.

The envelope implications with the nails are the far greater concern.

Are you buying the foam? If so, op for the T&G stuff if you can get it. Makes for sealing it much easier and I prefer foam compliant sealants as compared to foams if the gaps are tight.

I would check on the chemical compatibility between whatever foam you use and the felt. The "Tyveks" will have great tear resistance when fastened with an appropriate fastener, come in larger rolls (less seams), and a higher perm rate in lower humidity conditions. You have all the vapor tightness you need at the foam. I would want my WRB to be more open than 5 or less (in the case of felt).

I do like the variability of the felt but I just don't think you need anything close to a 5 on that side after the foam. If any water gets behind the WRB, I would want it to dry readily to the outside. That's kind of picayune but check that the foam is okay against the felt. There are plenty of volatiles in felt already.

12" strapping is probably still a bit wide for vinyl. If it were my home, I would go tighter than than.

 

This is what I call Totally Acceptable Advice.:laughing: Many thanks.

If the plan inspector is ok, I'll try xps and felt - and I will check for compatibility. Straps will be on studs and one midway. I think I remember the nail spacing as 8" for vinyl. That works great.

 

Just as a reminder to others and me, I'll be checking for compatibility between any stick on flashing and caulk (or such). That post about a goo dripping from the window side was something new.

 

http://www.inspectionnews.net/home_...pe-home-inspection-and-commercial-inspection/27063-melting-window-flashing.html

Sorry, I don't know how to post a linkable address. Or just google "goo dripping from window frame". I may have linked there from a post in this forum.

Problem may be plasticizers in caulks reacting with asphalt based flashing?

Is this corrected somehow by the industry by now, or is this something I have to remember when buying the material?

 

All the Tyvek flashing tapes are butyl based for these reasons amongst others.