Horizontal vs. vertical furring and installing house wrap on interior of exterior walls
pauldonis
| Posted in Construction Techniques on
I am retrofitting an exterior 2×4 wall with extra wood to accommodate 5 1/2″ of Roxul R24, then adding a complete coverage of 1″ extruded polystyrene to add R5. To include an airspace and to accommodate drywall I’ll be adding 2×3 on the flat at 16″ centers.
Questions:
- Where should the super 6 vapor barrier go?
- Can I run the furring vertically to align with the stud spacing? I’d prefer to avoid running it horizontally for convenience of mounting, etc. and am using 2x to have a stronger mounting surface than 3/4″ strapping.
- I cannot access the outside and the 1911 red brick is just fine; Should I install house wrap (Tyvek) to the interior of the plank sheathing before I insulate?
Thoughts?
Replies
I think it would be easier to just add another 2x4 stud wall on the inside, and drywall conventionally.
Replace the old insulation, if any, with regular 3 1/2" insulation. Seal up any air leakage with caulk or foam before insulation. I would not bother with the Tyvek on the inside.
Add new 2x4 wall, 24"OC on the inside, staggering studs so that the new and old studs DO NOT line up. This will provide a thermal break for the wood. Window and door frame are exception. The new wall in not structural, so headers or king/jack studs are not required. Move any electrical boxes to the new wall, with proper vapor barrier boxes or wrap.
Insulate new wall with regular 3 1/2" insulation.
Apply vapour barrier to inside wall, and seal.
Apply drywall normally.
This will give you R28 for the Roxul, and an additional R1 for the drywall and existing sheathing. Total R29. Same as what you are trying to acomplish, but without much fuss.
If you want more insulation, add a layer between the two stud walls. You can add as much as space and budget allow, but there are diminishing returns on investment as you go thicker.
Much better solution!
Thanks for this! I've been overthinking this I think so this kind of insight helps a lot!
I was shying away from 24" centers on the interior for stability but perhaps this isn't really an issue. This solution is also a lot easier if the walls need plumbing and straightening and is, of course, more cost effective as the foam is more expensive.
The only question is that of the Tyvek, responded to separately. The old insulation was actually sawdust mixed with mortar poured into the wall and kept in place by a rather labour-intensive batten and plank form in between the studs. Quite ingenious for 1911.
Should have mentioned this, but we are in the Ottawa Valley in Ontario, so below -40 Celsius is not unusual in the winter.
As to installing Tyvek, the primary purpose of that is to seal the exterior surface against air infiltration. The brick should do a pretty good job of this generally (unless the mortar is beginning to deteriorate), so the only areas needing sealing would be around windows, doors, and other "penetrations". You can probably do this just as well, if not better, using caulk, spray foam, etc (though there are a few scenarios where the Tyvek would be worth it).
With respect to Tyvek...
Thanks so much to both of you for the input.
With respect to Tyvek, yes, the brick is in good shape and there appears to be a clear, appropriate airspace between the exterior sheathing and the brick. There are a number of gaps between the planking of the exterior and the thinking of the Tyvek would be that it would be cheaper and easier to cover completely than to try to caulk every gap, which would result in a tremendous amount of caulking (roughly 62' of a 9' insulated wall). Unless it is unnecessary to seal this area for air infiltration to this degree, but I'm under the impression that it is.
Yeah, in that case Tyvek may be a good idea. You'd fasten it to the inside of the outer sheathng, wrapping around the existing studs.