Building components · Openings & Frames
Window Frame
Explains the frame as the structural and control element of a window, distinct from the glazing it holds.
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 window frame is
The frame is the fixed part of a window: the surround that sits in the opening, holds the glazing, and carries whatever moving parts the window has. Wind pressure on the glass is delivered through the frame into the wall.
It is also where the building's control layers have to be continued. The air barrier and the water control layer both have to connect to the frame, because otherwise there is a hole in each of them at every window.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not the glazing. Insulated glass units and glass types are published material entries; the frame is what holds them.
- It is not the opening. The opening is the hole in the wall; the frame is the element installed into it, and the space between the two is where most window problems live.
- It is not a mullion or transom in a curtain wall. Those are the framing members of a facade system spanning between floors; a window frame sits within a wall opening.
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.
- window frames
- frame
- casement frame
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- How it is fixed into the opening, since it has to transfer wind loads without being distorted by the fixings.
- The gap around it and how that gap is filled, insulated and sealed.
- How the wall's air and water control layers are connected to it.
- Whether it can move relative to the wall, since frame and wall have different movement behaviour.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
The frame is commonly the least insulating part of a window, and where it sits relative to the wall insulation affects the whole opening's thermal behaviour.
Water reaching the perimeter gap has to be directed out rather than in, which is a function of the surrounding arrangement rather than of the frame itself.
Frame and wall respond differently to temperature, so the perimeter joint has to accommodate movement rather than resist it.
The perimeter gap exists precisely because the opening cannot be built to the frame's tolerance, and it is that gap that must be sealed and insulated.
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.
Materials
Commonly incorporates
Materials this element commonly contains as a distinct constituent part, rather than being made of.
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.
Junctions
Interfaces this element takes part in
Junctions where the condition between this element and another governs how the construction behaves. These name the junction and the subjects it raises; they are not details, arrangements or approved ways of building.
Cavity Closer to Frame
Where the element closing the cavity meets the frame, and where the opening's thermal perimeter is either continuous or not.
Raises: Thermal continuity · Moisture · Air leakage · Fire continuity
Frame to Jamb
Where a frame meets the vertical edge of an opening, and where the wall's every layer must be closed onto it.
Raises: Thermal continuity · Air leakage · Moisture · Movement
Frame to Opening Head
Where a frame meets the top of an opening, beneath a structural element that deflects and above which water collects.
Raises: Structural transfer · Moisture · Thermal continuity · Movement
Reveal to Frame
Where the internal finish returns into an opening and meets the frame, on the coldest internal surface near a window.
Raises: Thermal continuity · Moisture · Movement · Air leakage
Sill to Frame
Where a frame meets the sill, at the point a window's whole collected water arrives.
Raises: Moisture · Weathering · Movement · Buildability
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
Related elements
Neighbouring components
Typed relationships to other elements. There is deliberately no generic “related” category: an edge that cannot be classified does not exist.
Clarifications
Commonly misunderstood
- That fitting a window is a matter of getting it into the hole. The perimeter arrangement — insulation, air seal, water management — is where performance is won or lost.
- That a well-rated window guarantees a well-performing opening. The installation determines whether the rating is achieved in place.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- How is the frame fixed, and does that fixing avoid distorting it?
- How are the wall's air and water control layers continued onto the frame?
- Where does the frame sit relative to the wall insulation line?
- How is the perimeter gap insulated and sealed, and how does it accommodate movement?
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 dimension, fixing, sealing arrangement, U-value or air permeability is stated here.
- Window installation performance depends on the opening arrangement as much as on the window, and both are design matters.
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 →