Replies

1. 
   user-6924093 | Sep 24, 2017 10:10pm | #1

   Update, as I did not mention:

   2x6 walls gypsum->poly sheeting->2x6/fiberglass batt->plywood->currently nothing

   Crawlspace is radon vented (despite no radon) for moisture management I assume, under scrim reinforced thick white poly, with EPS under that judging by the sound/movement/feel - against the soil along all the footwalls. The white poly is powder attached to stripping to separate poly running up the concrete walls with a butyl strip, and polyiso over all of that wherever there was concrete. Exterior crawl vents are all closed and polyiso'd. The HVAC system vents into the crawl. The rimjoists, few that there are (its post and 4x10 beam with beam set direct into foundation wall notches) are completely sealed away behind polyiso with canned foam at the edges. Concrete on top of the wall under the rimjoist is bare - insect inspections? Its very interesting and first time Ive ever seen something like it. Brightest cleanest crawl space Ive ever seen, could eat down there.

   I mention it because I know it affects the stack affect and air must move right through the T&G sleepers/finished flooring to the living space, or right out the edges of the T&G to the outside...

   Mr Holliday answered a question here: http://www.finehomebuilding.com/2014/07/09/can-exterior-foam-be-added-to-a-wall-that-has-an-interior-vapor-barrier

   "Although it would be better if the poly weren’t there, the fact is that tens of thousands of Canadian homes with interior poly have been retrofitted with exterior rigid foam, and there haven’t been any reports of widespread problems. According to building scientist John Straube, all indications show that these retrofits aren’t as risky as some people fear, and he believes that these homes likely will be fine."

   Q: When polyiso is added to the exterior of the sheathing, what prevents rain splash from wicking back up the foam and reducing its performance? Can this be flashed with off with SV-5 coravent or some other material?

2. GBA Editor
   Martin Holladay | Sep 25, 2017 04:24am | #2

   User-6924093,
   First, can you tell us your name?

   This post is confusing. At first, I thought that you needed advice on attaching a ledger board for a deck. Although you didn't really tell us, I eventually figured out that you have stripped all of the siding off the house, and you are asking advice on whether it is safe to install rigid foam on the exterior side of the wall sheathing, as part of a siding replacement job.

   In general, as noted in the Fine Homebuilding article you quote -- and as explained in my article, The Exterior Rigid Foam is Too Thin! -- you can add exterior foam to this house, even though there is interior poly, as long as you follow a few common-sense steps (as explained in my article).

   When you install exterior rigid foam, the foam will cover the exposed ends of the 2-inch-thick tongue-and-groove flooring, sealing the air leaks (mostly). If you want to caulk the ends of the exposed flooring before you install the rigid foam, you can. More important: pay attention to airtightness when installing the rigid foam. It can't hurt to install a bead of caulk around the perimeter if each piece of rigid foam, especially toward the bottom of the wall. (The caulk would go between the rigid foam and the sheathing.)

   Plywood sheathing is not a problem. Leave it in place.

   To deal with splashback, the bottom of your wall will have metal flashing protecting the bottom of the rigid foam. To learn more about this flashing, see this video: How to Install Rigid Foam Insulation Outside a House.

3. 
   user-6924093 | Sep 26, 2017 02:14am | #3

   My account name should not be USER-digits, but L. David Loomis. I am not sure why it ended up without my own name attached, which I feel is important on any internet board. It promotes ethical, responsible, and respectful behaviour. I do sincerely apologize for the confusion. My speech therapist suggests I mention that I am diagnosed Autistic, and I think somewhat differently than neurotypicals. I dont know what you know, nor how much you need to know, so give as much information as is reasonable to ensure fluid communication. I think engineers are more used to the way we think and get us eventually!; the difficulty is generally with reactionary thinkers or the impatient. My company is a sole proprietorship, Artistic Concepts. I generally do murals, plaster bas-relief or other handcraft work such as copper, or even acid staining or inset stone patterns. Despite this handicap I do care a great deal and my work is never beneath above standard! I'm just lucky to have found a niche, only 19% of Autistic (ASD) people work in any capacity; generally part time or tech.

   Yes, I was concerned about double vapor barrier, but found your fine homebuilding article after posting.

   Thank you for the video link Martin.

   Would you happen to have any direction on heatloss through her flooring?

   Ext. Wall Diagram:
   Stud 2x6
   Bottomplate 2x6
   Sleepercar 2x6 T&G subfloor under entire structure & perimeter
   Treated Sillplate 2x6

   The Sleepercar T&G has been utilized (post and beam construction) as subfloor and finished floor both. There is no vapor barrier, nor insulation beneath, because the crawl is completely encapsulated with white plastic, very similar to your article. The crawl has ventilated ducting I assume for moisture control and the heat rises directly through the large gapping of the T&G (very much appears to be an old barn floor).

   My concern is the T&G flooring is not tight. Anywhere. At the perimeter it is in locations only halfway onto the sillplate where it laps over perpendicular. There is quite minor moisture or red ant rot on some of the ends. I treated those locations for insect, allowed them to dry out (post sheathing removal) and will fill with bondo as I cannot screw lift and repair such a design! I could replace the bottomplate but there seems to be no great way to address the lower sleeper car sandwich.

   It is installed square and not diagonal so only two sides expose endgrain, but those same gaps permit air exchange and loss right at the sill, which is going to worsen the moisture problem I am seeing here. It must be a large amount of air gap if aggregated. The only barrier against infiltration in winter as the stack pulls cold directly in off the sillplate, is the plywood sheathing, not terribly tight, which I am given to understand I cannot seal at the bottom? But I am guessing I *can* seal off the sleepers. But I do hate guessing.

   I have no idea how to help this situation other than to "can-foam" all of the sleeper ends.

   PS- Do you also have details of windows flashed innie and outie, for subscribers? I have seen the other free pages but as I am a visual thinker drawings are most helpful. I am happy to subscribe especially if there are pictures.

   Thank you very kindly and most respectfully,

4. GBA Editor
   Martin Holladay | Sep 26, 2017 04:31am | #4

   L. David,
   First of all, I'm sorry that the GBA site registration process makes it difficult to attach your name. Here is a link to an article that explains the problem and the solution: How the GBA Site Displays Readers’ Names.

   If you have removed enough of the plywood sheathing to expose the subfloor, you should finish addressing any rot. When you reinstall the plywood sheathing, you should install the plywood in an airtight manner, and trust the plywood to limit air infiltration. The bottom of each sheet of plywood should be caulked -- usually to the mudsill. I assume that this bottom piece of plywood sheathing will cover the exposed ends of the 2x6 subfloor boards. The seams between the plywood sheets should be taped with a high-quality tape. In this way, the plywood sheathing becomes your air barrier.

   For links to GBA details for both innie windows and outie windows, visit this page: Building Details for a Deep-Energy Retrofit.

   For more information and illustrations of window flashing issues, see these three links:

   ‘Innie’ Windows or ‘Outie’ Windows?

   Installing Windows In a Foam-Sheathed Wall

   Video series: Flashing Windows