Creating air flow behind wood siding when renovating an old house from the interior
I’m working on a two and a half story 1910 farm house with a basement in Iowa. Since we live in the house, I’m tackling the renovation room by room from the inside. I have the lath and plaster all down on the kitchen exterior wall and have removed the insulation that was blown in. The “sheathing layer” is tongue and groove siding (with 2″ holes where the insulation was blown in) and 3″ wood lap siding laid on the outside of that.
My plan is to add a “waffle” barrier in each of the wall cavities against the outside wood and cover that with a WRB to seal each of the cavities while providing an air gap behind the wood. I’ll furr out the walls to get the depth I need, add rockwool for insulation, and finish it with sheetrock.
My struggle is that I need to vent the cavity between the waffle barrier and the wood layers at the top and bottom to provide air flow. Since I am doing this one room at a time, I can’t create a unified air flow that runs from the sill plate to the attic as I’ve seen other people create. Instead, I’ll have to create an air flow within every cavity.
I’m not seeing any products or designs that can provide the air gaps (holes, slots, etc…) at the top and bottom of each cavity. Of course it needs to be aesthetically pleasing and bug proof, since there are lots of cavities in the wall structure to be vented. Has anyone found a solution that they like for creating air movement behind wood “sheathing layer” when tackling the renovation from the inside?
And I’ll always ask — am I solving the wrong problem? is there a different way of sealing the house and allowing my exterior layers to dry when renovating from the inside?
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Replies
Chris,
You are essentially creating an inverted rain-screen. The main attribute of which will be add a capillary break that will keep moisture from getting back into the cavity from the sheathing/cladding layer, and diffuse any water that does get in. I would categorize adding ventilation to that air-space as useful but not necessary - and given the complexity of doing so, unfeasible.
You may find this article useful: https://www.greenbuildingadvisor.com/article/managing-water-and-insulating-walls-without-sheathing
Thanks. I didn't find that article in my search, but that's what I needed.
Chris,
Even most conventional rain-screens aren't open at both the top and bottom for ventilation.
Do you see evidence of bulk water damage?
While the rigid insulation + air gap will allow outward drying potential for infiltrated bulk water, it comes as at a cost- it’ll eliminate outward drying of diffused moisture. And to be truly effective in worst-case situations, the foam would need to be flashed to the exterior.
Do you plan on residing at some point? I would prefer a Bonfiglioli wall with drying potential to both sides versus this option- or interior rigid insulation (which depends on outward drying) if you haven’t seen evidence of bulk water damage.