There are probably more bad practices carried out in historic renovations in the name of insulation and ventilation than any other aspect of the renovation process. We have strong opinions on what works and what doesn't.
Your insulation system needs to do two things. First, it must provide resistance to convective heat loss. This resistance is measured by the R-value listed in the product literature. The second major component of weatherization is air sealing. Air sealing stops the movement of air through a wall, roof, or floor cavity. Without effective air sealing most insulation materials do not perform very well. Batts, in particular, perform terribly if they are subjected to air movement. Air sealing can be achieved though the use of materials such as caulking, plastic sheeting, drywall, etc., but it is difficult to do and few even attempt it.
For this reason we advocate for two alternatives to batts: spray foam and dense-pack cellulose. Spray foam insulation air seals as it insulates so it is an excellent choice for old houses. By expanding to fill the cavity- even around pipes, wires, and other obstacles- foam insulation prevents air movement. We've been using spray foams for almost 15 years with tremendous success.
Dense-pack cellulose also fills the cavities and does a very good job of air sealing. Not as versatile as foam, and more subject to air movement and moisture, nevertheless, cellulose is a very good product and we've used it with success on many renovation projects (and even additions).
The important thing for owners of historic buildings to keep in mind is that the "accepted" practices most commonly in use (e.g. batts) are not the best practices for insulating and ventilating old buildings. We've been renovating historic houses, barns, and churches for twenty years and know what work and what does not. For a more detailed look at these issues, please download our free whitepaper below. For a free consultation, click the button at the left.