It really doesn’t matter which type of anchor you use
or what type of shim. The key is to be able to make
the adjustment before you anchor the windows and
provide solid support between the frame and the
opening behind the anchors.
The most common type are tapered wood shims.
These are better versions of the wood shake cut-offs
improperly used by poor installers. Pre-cut wood
shims have a consistent taper and fit in smaller
places. The downside is that they are tapered and
must be used in pairs. Also, to effectively use a
tapered shim, it often needs to go beyond the depth
of the window frame, and that is not possible for
many replacement applications.
A better solution is stackable plastic shims These can
be “U” shaped or “horse shoe” shaped with snap off
length adjustment so they fit. The “handle” can then
be broken off when final trim is applied. Also, plastic
shims will not deteriorate in moist conditions which
can be a real plus.
Win-Bag is an inflating bag that when placed
between the window frame and the rough opening,
allows minute adjustments before anchoring and
before final, solid shims are added. The product has
wide use in the U.S. as a method to pry open car
doors to unlock them, Win-Bag™ and other similar
products are used extensively in Europe to center
windows and doors in their openings. Many profes-
sional window and door installers use them because
they are simple, precise, and can fit in the smallest
spaces.
Once the window frame is plumb, level and square,
anchors are installed with wood or plastic shims
added for support behind the anchors and the airbag
shims are deflated and removed.
Types of Shims
Window Fitters Guide to Window Installation 
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SAMPLE MANUAL

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