Housewrap under vinyl siding
Ok, I’m getting educated and made some decisions. To recap, I’m residing with vinyl after stripping down to plywood sheathing (1/2″ plywood over 2×4 studs, fiberglass batt, poly vapor barrier, sheetrock, zone 5). I’ve decided to go with 3/4″ rigid foam over the plywood and under the vinyl which is R3 and very water vapor permeable. Can only fit 3/4″ thickness insulation board (long story). Probably going to use Progressive Foam HalfBack H2O with water management system (grooves toward sheathing to drain any leaked in water). Want to add house wrap (Tyvek or Typar). Confused as to where/how to apply and which product is best. Tyvek video states apply after rigid insulation board goes up. Typar video states apply directly to sheathing before rigid board goes up. Can you help by advising which product to use and how/where to install? Once again, thanks in advance for your help!!! Very much appreciated. [email protected]
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George,
The housewrap is your water-resistive barrier (WRB). You need to integrate all of your window flashing, door flashing, and flashing for penetrations like hose bibs and electrical boxes with your WRB.
Your WRB can either go under the rigid foam or over the rigid foam, as long as you have developed details that allow you to integrate your flashing with the housewrap.
For more information, see Where Does the Housewrap Go?
Martin Holladay, thanks for the quick response. Got it and understand. Any preference of product between the two I mentioned? Looks like the perf spec of one is slightly better than the other...Thx, again...
George,
Does it matter whether you choose Tyvek or Typar? No. What matters is careful installation: getting the laps right, and not putting unnecessary rips in the membrane when you install it.
Your plan seems risky. Code-minimum R-value for rigid insulation outboard of the sheathing for a 2x4 wall in zone 5 is R-5. The product you've selected looks like EPS foam, and 3/4" of it only gives you R-3. That may not be enough to keep your sheathing warm enough to avoid its temperature dipping below the dew point. If you go through with this, you will have to make your bulk water management detailing perfect. And, of course, if this is a permitted and inspected project, the building inspector won't sign off on it if he's any good at his job.
To Nathaniel, thanks for the response, first off. I hear you loud and clear but I don't have a choice of thickness to work with. I have 3/4" due to rake and roof construction. I'm not reroofing so building out the rake to meet a thicker insulating board is not possible. So I see 2 choices, both involving 3/4" material. Go water vapor permeable for a little less R value (R3 to be exact) or go non permeable for a little more R value (R3.75 as best as I can find with no foil). I'm pulling off R4 (fiberglass impregnated styrofoam coated with plastic resin - looks like barn board from 1980). Don't know permeability of current material which is now falling apart. If you have other suggestions given the constraints I have to deal with please let me know. Don't know what to expect from building official, but I want to do the right thing. Again, thanks!
I agree with Nat's observation and would add that if you put EPS or XPS on top of your sheathing (outboard of the envelope), you will hamper drying to the outside. That means you need to plan/ structure your HVAC and interior walls systems accordingly:
- drying to the inside
- don't use airtight drywall methods
- use permeable primers and paints on walls
- seal the openings between the wall plane and the attic (at top plates, and heads of wall cavities)
- no penetrations in the ceiling below the attic; use an impermeable ceiling treatment
- any systems or mechanicals in the attic space need to be completely isolated from the conditioned space below
- consider use ERV/HRV with moisture removal feature
- use an active (exhaust fan) ventilation solution for fresh air in and stale moist air out
I hear you on the weak overhangs. Those suck. Given that constraint, if energy savings is your goal (or your code official forces you), perhaps you could remove the 1/2" plywood and replace it with diagonal bracing and 1 1/4" foam. Dunno if that would fly; depends on the wind and hurricane codes in your locality. That would get you to R-6.25 for XPS (not sure if they'd allow EPS as sheathing), and R-7 for polyiso when it's hot out (R-5.5 or so when it's cold, which is enough).
Doing it this way makes the foam your weather barrier if the seams are scrupulously taped with the best tape, especially if it has a smooth, impermeable facer of some sort. You could/should put housewrap over it anyway, but at that point, it's cheap insurance, not a total non-negotiable necessity.
Alternatively, if you need to re-roof sometime soon, perhaps you could batch up the two jobs. A long shot, I know.