When buying quantities of standard fasteners, such as screws or bolts, buy a full box anytime you will need close to a half box or more. The second half of the box will be virtually free. For example, 45 individual screws will usually cost about the same as a box of 100 screws.
It’s possible to retrofit insulation into an existing home, even without the access provided by remodeling. The choices, however, are much more limited. There are some retrofit insulation products that are designed for minimal disruption to finished wall or ceiling surfaces. Significant gains in R-value, however, may mean hiring a professional to assess your needs and devise an energy savings plan. Small or large, insulation projects can yield substantial gains in R-value and in comfort.