Building components · Openings & Frames
Frame Packer
Explains packers as load-transfer elements rather than as spacers, which is why their position is specified.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a packer is
A frame is smaller than the opening it goes into, by design. Packers fill that difference at chosen points: they hold the frame square and plumb, and they are where the frame's weight and the loads on it are actually transferred into the surrounding construction.
Because they are load paths rather than fillers, where they go matters. A packer at the wrong place transfers load where the frame cannot take it or where the surrounding construction cannot support it.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not insulation. The rest of the perimeter gap is insulated; packers are discrete load-transfer points within it.
- It is not sealant. Sealant closes the gap against air and water; packers carry load.
- It is not a cavity closer, which closes the cavity at the opening edge rather than positioning the frame.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- packers
- shims
- glazing packers
- setting blocks
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- Position, since packers should be where the frame is stiff enough to accept load and where the surrounding construction can support it.
- Being permanent, because a packer removed after fixing leaves the frame's load path incomplete.
- Material that will not compress, degrade or corrode in a permanently concealed, occasionally damp position.
- The remaining gap being insulated and sealed around them.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
Packers are how the difference between a frame made to fine tolerance and an opening built to coarser tolerance is resolved.
They are the actual points at which frame loads reach the wall, which is why they are specified rather than improvised.
A packer is permanently concealed in a position that can become damp, so material choice matters more than its small size suggests.
Packers interrupt the insulation in the perimeter gap, which is a reason for using few of them in the right places rather than many.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Where it is met
Application contexts
Building contexts where this element is commonly encountered. Association is not recommendation: appearing here does not mean the component suits every instance of that context, or any particular one.
- Opening
Clarifications
Commonly misunderstood
- That packers are temporary aids removed once the frame is fixed. They are the permanent load path.
- That any offcut will do. A compressible or degradable packer means the frame settles later.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- Where are the packers positioned, and does that suit the frame and the surrounding construction?
- Are the packers permanent, and of a material suitable for a concealed and possibly damp position?
- How is the remaining perimeter gap insulated and sealed around them?
- Do the fixings and the packers work together, rather than the fixings carrying the frame alone?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- No packer position, size, material or spacing is stated here.
- Window and door manufacturers specify packer positions for their products, and those requirements govern.
Openings & Frame Elements
The frames, heads, jambs, sills, thresholds and closers that form and finish an opening through a wall.
Browse all openings & frames entries →