We are currently tackling a renovation project for a 1910 three-wythe brick home with embedded joists in Climate Zone 4A. Unfortunately, our small bathroom renovation revealed mold issues when the walls, ceilings and floors were opened. Now that everything has been remediated and dried out, we want to make sure we are insulating/sealing properly moving forward. Due to budget and logistical constraints, we are approaching this work piecewise rather than demolishing and renovating all at once since we are living here during the remodel.

As I plan the sealing and insulating of walls, floors, and roof/attic, I want to ensure that this phased approach will not cause interim moisture management issues. We are in a historic neighborhood, so exterior insulation is not an option, and we are trying to avoid using spray foam due to cost and the lack of practicality for our piecemeal renovation.  I was hoping to get your expert advice on a few key considerations:

1. Sequencing: Is there an ideal order to tackle sealing and insulation between walls, floors, and the roof to avoid performance gaps or unintended consequences?
2. Integration: How can I ensure the different phases integrate seamlessly, especially when connecting new insulation or air barriers to existing materials?
3. Moisture Management: What precautions should I take to prevent moisture issues when sealing and insulating piecemeal?
4. Material Selection: Are there specific insulation materials or sealing products you would recommend for this type of incremental work?

Any insights you could share or resources you might recommend would be greatly appreciated. Your expertise would be invaluable in helping me navigate this process effectively. Much of our planning is taken from combinations of Avoiding Mass Failures, Unvented Roof Systems, and  Internal Insulation of Masonry Walls: Final Measure Guidelines.  
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Roof: Generally, we plan to install Rockwool R23 insulation between the rafter cavities that we can access. Under that (between the rafters and the drywall or backerboard), we plan to apply Sika Majrex 200 to allow unidirectional drying inward but not allowing as much vapor permeance from bedrooms and bathrooms to enter the insulated spaces as readily. Sometime in the next couple years when budget allows, we plan to add two layers (4″) of continuous polyiso above the roof deck to get us where we need to be for code and to mitigate winter condensation concerns. We have a complex roofline with 5 dormers perpendicular to one main roof ridge, so a properly vented roofline/attic assembly isn’t an option. Unfortunately, the ceilings of several rooms on the 2nd and 3rd floors already follow the roofline in a cathedral style ceiling, most without ventilation or insulation and will need to be demo-ed as the renovation progresses (hopefully after the rigid foam insulation is installed on the roof).

Roof Questions: Is this plan feasible? If so, how do we temporarily airseal the portion of the insulated roof from the uninsulated? Do we use a vertical piece of foam board and spray foam around the edges to block off that area until we get to the next part of the roof? Or do we allow air to pass through from the other parts of the roof to access the unidirectional vapor retarder?
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Walls: For each masonry wall covered in plaster, we plan to leave it as-is. Our understanding is that while the mass masonry assembly is very air permeable, the plaster walls with paint are very air impermeable while still allowing vapor transfer.

For the exposed portions of our masonry walls, like the one behind where our tub/shower will go, the plan is to follow Wall Aproach Three listed in Avoiding Mass Failures: https://buildingscience.com/documents/building-science-insights-newsletters/bsi-105-avoiding-mass-failures

1. Brick wall — 2. interior parge coat on brick wall to create an even surface — 3. fluid-applied air- and water- control layer (vapor permeable) — 4. A layer of 2″ Rockwool — 5. Wood frame non-load-bearing wall attached to rafters above and subfloor below (avoiding thermal bridge with masonry wall) — 6A(?). Sika Majrex Unidirectional vapor control layer — 6B. concrete board/drywall. Unfortunately, there is a wood-framed stained-glass window on the exterior wall that shares the tub surround that also needs to be sealed (historic, so we cannot remove). The plan is to continue the bathtub tile to the wooden frame of the window and seal with caulk. Much of the wall space around the window is empty (perhaps where there was once additional brick). Can I simply frame out this area, securing it from the embedded wood blocking or do I need to fill the cavities completely with mineral wool, etc.?

Wall questions: The Insight Avoiding Mass Failures specifies using a vapor semi-permeable WRB, while multiple other sources specify using a WRB that is highly vapor permeable. Which should be used? Do I need the Unidirectional vapor control layer between the wood frame and the drywall/concrete board?

The bathtub comes with a built-in layer of styrofoam around the based, which acts as both an insulator and a level support for the tub, but this leaves a lot of open space between the styrofoam and the tub/wall exterior. Should I fill that space with rockwool? Leave as-is? Just make sure the vapor retarner extends from the adjacent wall  the to the floor before installing tub?

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Roof-Wall junctions: The main rooflines start at the 2nd floor subfloor level. Immediately under the subfloor, there is a small gap between the subfloor and the brick wall below. Should these gaps be sealed with canned spray foam or would that create an issue where the subfloor and brick wall are somehow connected in a bad way?

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Thank you in advance for reading this far and for your time and guidance. 

Wishing you all the best,
Mel