I am remodeling a house on the Oregon coast. The west side of the house is exposed to storms coming off the Pacific Ocean and will be subjected to strong wind driven rain. The current exterior wall construction is:
2 X 4 studs
1/2” plywood
15 # felt
5/8” spacer
3” brick
We are going to remove the brick and add a second 2 X 4 insulated stud bay and with plywood sheeting. I then plan to use 30# felt, spacers and Hardi Board. I also plan to use spray in foam to insulate the outer stud bay. My concern is that moisture will become trapped in the outer stud bay because it will have plywood on both sides.
Should I remove the existing 15# felt before I add the second set of studs?
Should I make ventilation holes through the existing plywood sheeting to allow air and moisture to move between the inner and outer stud bays?
Are there any other issues or problems that I should be aware of with this type of construction?
Thank you for your help.
JEG
Replies
That is
an unorthodox wall construction. What are you trying to achieve? High R value? Water resistance?
We want to have a high R value but I do not want to create any long term moisture problems. Being on the Oregon Coast, I want the house as water resistant as possible.
Are the interior walls insulated? If not, I'd just have cellulose blown into them, and do nothing more. You would never recoup the cost of what you propose.
Do you not like the brick exterior? I think it is more resistant to blown rain than hardi planks. The brick could be furred out and hardi planks could then be installed over the brick, with some foam infill to add some measure of additional insulation. This would probably not pay off either, but if you want the hardi planks, it would be worthwhile.
Something that may pay off would be foam panels inside the house with new drywall over them, but even that would probably not pay off for a long time.
Yes, the interior walls are insulated.
The brick is very unattractive so we are removing it for aesthetic reasons. I understand that we may not ever recover the cost of replacing the siding.
By removing the brick and extending the wall we are also able to move and resize windows more easily. We plan to replace all of the windows with vinyl new construction windows. We are also making two small additions that will have 2 X 6 walls.
FYI, The house was build in the 1950's.
How about:
Remove the brick, remove the 15# felt. Change around your windows by reframing the existing stud wall. Add a couple of inches of XPS foam on the exterior. Add a rainscreen. Add your new cladding of choice.
This would be less costly than any new stud wall and still give you a very well insulated and tight house.
Agree
completely. This is a very standard approach, no wheels reinvented.
Less costly alternative would be to remove brick and felt, install new felt, rainscreen and siding, and then install horizontal 2x2 furring on the interior, dense-pack the walls and install drywall. Reduce thermal bridging, pretty good R value, no foam needed.
I think then that Sapwood has the best reply. But if you use foam on the outside you do have to be concerned with termites, mice, carpenter ants and the like invading the foam. Some foam is borate treated I believe, which would be very benificial for such an install.
Then there's the suggestion that a slightly shady contractor friend gave my dad after looking at the farmhouse he'd just bought: "Insure it and then burn it." (It never was clear whether the guy was to any extent serious with that suggestion.)