retrofit/remodel insulating a partial cathedral ceiling and walls
I am in Wisconsin zone 6 and have completely stripped a 100+ year old balloon framed farmhouse to the studs. Failing UFFI and a woefully inadequate wiring, knowing there was some historical water damage plus some changing of house layout, it was time to do a complete gut job and make it right for the long term future.
The second story is an interesting mess of framing where there are knee walls and dormers in some places and a few spots where the solution to concern about strength was to keep scabbing on more 2×4’s until it looked solid. The roof is a 9:12 made up of asphalt shingles, 1″ board decking, 2×4 (rough cut 2″x3 5/8″ actual) rafters. All rooflines have a ceiling joist attached 5′ down the rafter from the peak. Every other rafter also has a collar tie near the peak. Some rafters then have no attachment to them for another 9′ of run to the exterior wall while others have a knee wall 4′ of run from the ceiling joist. Surprisingly, this roof doesn’t have a visual droop to it, but it was certainly “springy” when I was inspecting the roof a couple summers ago when above the section without the knee wall. The knee walls do not have structural walls directly underneath. Not surprisingly, this house normally grew gigantic icicles with marginal fiberglass stapled in the space behind the knee wall and failing UFFI in the cathedral section.
Walls are the same 2″x3 5/8″ rough cut where they generally attempted to hold 16″oc spacing, but it isn’t terribly precise and there are some spliced studs when one section of the house was apparently made taller. Walls have 1″ board sheathing, wood siding, tar paper and steel siding on the exterior.
Obviously, I’d like to improve this situation. This project is for interior only right now as the roof has some life left which we intend on replacing in ~5 years when adding an attached garage. The new roof will be standing seam steel or some other “forever/longer lasting than me” type material. Right now, my thoughts are to dense pack cellulose the walls besides potentially using up some on-hand roll fiberglass if I find a wall that has good enough stud spacing to accommodate.
The roof obviously isn’t so simple and where I’m mostly looking for the gut check. It obviously held up fine for over 100 years, probably because it kept itself mostly melted off limiting snow loads, but I’d rather make it stronger and give it some actual insulation. My initial thought has been to add depth and rigidity by plywood plating on a second 2×4 under the rafter as well as plating the birds mouth with 3/4″ plywood. This would add stiffness and protect the birds mouth from blowing out with the potentially higher snow load than the roof is used to. I’d likely put a knee wall under the roof that doesn’t currently have one. Regarding insulation, I want to heat the space behind the knee walls as it is a fairly decent amount of space to use as built in shelves/hanger racking. For the partial cathedral ceiling, I’m thinking foam board to create a vent baffle, cellulose or fiberglass filling the cavity and iso under the rafter, furring strip and plasterboard. I like that because of my apprehension about non-vented and spray foam under an older than newer (but currently non-leaking) asphalt roof BUT its non-vented soffit and tiny gable vents and adding vents would be a lot of work versus making a phone call for someone to spray 4-6″ of foam up there and then add fluffy stuff between the spray foam and plasterboard.
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Replies
Your project to update and insulate a 100+ year old balloon-framed farmhouse in Wisconsin zone 6 is ambitious and thoughtful, especially given the home's unique construction challenges and your desire to preserve its integrity while improving efficiency and structure. Your approach to the walls and roof sounds well-considered, but here are a few additional points and suggestions for your consideration:
Wall Insulation
Dense Pack Cellulose: This is an excellent choice for the walls, as it provides good thermal performance, air sealing capabilities, and is environmentally friendly. The irregular stud spacing and historical construction quirks of balloon framing might actually benefit from the flexibility and fill capability of dense pack cellulose.
Roll Fiberglass: Utilizing on-hand materials for walls with suitable stud spacing is practical. Ensure any gaps or irregularities are addressed to avoid thermal bridging and air leakage.
Roof Insulation and Structural Support
Adding Depth and Rigidity: Your idea to reinforce the rafters with plywood and an additional 2×4 is sound, particularly given the "springy" nature of the roof and the history of inadequate support. This will not only add stiffness but also improve the roof's load-bearing capacity, essential for your planned standing seam steel roof.
Insulation Strategy: Creating a vented baffle with foam board is a smart move, especially in older homes where maintaining a dry roof assembly is critical. Your plan to use cellulose or fiberglass in the cavity and then applying rigid foam insulation below the rafters is a good balance between improving insulation values and managing moisture.
Ventilation Concerns: It's crucial to ensure that the roof assembly can dry out, particularly with non-vented soffits and minimal gable venting. While adding vents can be labor-intensive, it might be worth exploring less invasive options or consulting with a building science professional to design an effective roof ventilation strategy that works with your home's existing features.
Considerations for the Knee Walls and Cathedral Ceiling
Knee Wall Insulation: Heating the space behind the knee walls and using it efficiently is a great idea. Ensure that the knee walls and the floor of the attic space behind them are well-insulated to prevent thermal bridging and heat loss.
Partial Cathedral Ceiling: Your apprehension about non-vented and spray foam applications is understandable. Your proposed method provides a balance between insulation, ventilation, and preserving the roof's integrity. However, given the complexities of insulating cathedral ceilings and the potential for moisture issues, consulting with a professional to ensure that the assembly is correctly designed to manage moisture and provide adequate insulation is advisable.
Additional Thoughts
Professional Input: Given the complexities involved in insulating and reinforcing an older home, especially one with unique framing and historical water damage, seeking advice from a structural engineer or a building science expert could provide peace of mind and ensure that your solutions are both effective and safe.
Future Roof Replacement: Planning for a "forever" roof material is wise. Incorporate strategies now that will complement the future roof, such as ensuring any structural reinforcements are compatible with the weight and installation requirements of standing seam steel or similar materials.
Your approach to preserving and updating your home respects its historical character while making it more energy-efficient and comfortable for the long term. Careful planning, along with professional advice, will help you navigate the challenges unique to renovating older homes and ensure that your improvements are successful and sustainable.