Refilling blow in insulation in the attic without a vapour barrier.

Unfortunately your fears are correct. Ideally you would need to remove all of existing insulation, ensure soffits are not blocked, install boxes over pot lights and other penetrations, spray foam 2" to form a vapour barrier, install baffles every 4ft if needed, insulate any exhaust vent pipes, then blow in R60 insulation, 22.25". Expensive but will ensure no condensation/moisture issues

I would check into the energy efficiency grants, they will pay for a good portion of the costs involved. then I would remove all the old insulation, vacuum the entire area. then I would ensure soffit venting is not blocked. I would have proper baffles installed every 4ft, box in all pot lights,then spray foam 2" on entire drywall/truss deck area. then blow R60 into the cavity space, definitely worth the cost. 25% of heat loss goes through the roof, when the spray for company is onsite I would also have the rim joists foamed as well.

Your concerns are valid, but the lack of a vapour barrier does not necessarily mean you can't add more attic insulation. In fact, improving attic insulation is often one of the most effective ways to reduce heating and cooling costs in older homes, provided the air leakage issues are addressed first. In homes from the 1930s, the bigger concern is usually not the missing vapour barrier itself but the amount of warm, moist indoor air escaping into the attic through gaps around pot lights, electrical fixtures, plumbing penetrations, ductwork, attic hatches, and wall top plates. When that air reaches cold attic surfaces during winter, condensation and eventually mould can develop. Before adding additional blown insulation, it is generally recommended to perform air sealing work throughout the attic floor. This may include sealing around light fixtures, vent penetrations, wiring holes, and installing proper covers over recessed lighting if required. Once these air leaks are addressed, additional blown insulation can usually be added safely and effectively. Proper attic ventilation is also an important part of the equation. A balanced system of soffit intake ventilation and roof exhaust ventilation helps remove excess heat and moisture that may enter the attic space. Depending on the existing insulation type and condition, many contractors will simply top up the existing material after air sealing is completed. In some situations, spray foam may be used in specific problem areas, but it is not always necessary for the entire attic. An attic assessment or energy audit can identify the major air leakage points and determine whether your ventilation and insulation levels are adequate. In our experience, older homes often see substantial improvements in comfort and heating costs once air sealing and insulation upgrades are completed together rather than treating insulation as a standalone project.