Instead of sheathing, we have double-layered 9″ wide (tall?) shiplap (the green-painted boards outlined by the green boxes in the attached picture) under our cedar shingle cladding, and it is very likely to have had lead paint applied to it in the time between it’s 1910 construction and when it received cedar shingles sometime in the 80s or 90s. A bunch of the cedar is in bad shape, so we’re replacing it with cement fiber board.

The gaps between cladding (Where in good shape) are between ~ 1/16″ – 1/4″, and I’d love to properly air seal these without having to manually treat each seam, so I am considering a spray-applied or SA WRB between this shiplap and the eventual cement fiber plank cladding we’ll use. We cannot, unfortunately, add anything over the shiplap due to exceedingly strict setback laws and a non-conforming nature of much of this 110 year old house.

I’m trying to understand if I should encapsulate the lead paint with a proper encapsulate (are there any with good vapor permeability?) or if a spray or SA WRB might do the trick well-enough to prevent deterioration, chipping, aerosolization/dust formation as the house experiences its next 110 years of life? 

Right now, I am thinking alkalinity/pH of whatever goes over it (paint or WRB) will affect lead ion mobility — e.g. Prosoco Spray WRB MVP has a pH of 8.5-9.5, which may indicate some ability to mobilize the lead in the paint to which it will be applied.

I’d be very grateful if anyone has thoughts on or experience with this.