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Building components · Roof Carcass & Edges

Dormer Cheek

Explains the cheek as a wall in a roof position — carried by roof framing, thin, exposed on both sides of a corner, and required to continue the roof's layers around a change of plane.

Form:Unit or moduleRoles:StructureWeather controlInsulation

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 dormer cheek is

A dormer cheek is the side of a dormer: the vertical surface running from the main roof slope up to the dormer roof, closing the space between the dormer's front face and the slope it emerges from. There are two of them on a conventional dormer, one at each side.

It behaves like a wall but lives in a roof. It is carried on roof framing rather than on a foundation, it is commonly far thinner than any wall below it, and it is the piece that has to bring the roof's insulation, air and water control layers around a change of plane and then meet the covering along a sloping junction at its base. Those three conditions together are why a small area of construction takes a disproportionate amount of detailing.

Boundaries

How it differs from nearby elements

The distinctions that keep this entry from being a restatement of its neighbours.

  • It is not a verge. A verge is the edge of a main roof slope at a gable, where the governing problem is holding the covering down against uplift at an exposed edge; a cheek is a vertical enclosing surface on a projection, and its governing problem is the sloping junction it makes with the roof it stands on.
  • It is not a trimmer. The trimmer is the structural member framing the opening in the roof that the dormer occupies; the cheek is the enclosure standing on that framing, and the two are commonly confused because the trimmer is what makes the dormer possible.
  • It is not a wall leaf. An inner or outer leaf rises from a foundation and carries the build-up of a wall through its height; a cheek is supported by roof structure, is built far thinner, and has to reconcile its insulation with the roof's rather than the wall's.

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.

  • dormer side
  • dormer flank
  • cheek wall

Dependencies

What it depends on

What has to be right elsewhere for this element to do its job.

  • What it is framed from and what carries it, since it stands on the roof structure rather than on anything below the roof.
  • How the covering, soakers and flashings return along its base on both sides, which is a sloping junction running the full depth of the dormer.
  • How the insulation and control layers of the roof are continued around it without a break at either corner.
  • The depth available within it, because a cheek is commonly the thinnest part of an otherwise generous build-up and is a recognised position for a cold path.

Considerations

Topics that genuinely apply here

Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.

Moisture

The base of the cheek is a long sloping junction between a vertical surface and a roof covering, which is the kind of junction where water is directed rather than excluded, and where the direction of every lap matters.

Thermal

The cheek is commonly much thinner than the roof and the wall it connects, so insulation continuity around it is a design problem rather than a matter of filling the space available.

Weathering

A dormer stands proud of the slope, so its sides are exposed to driven rain on two faces meeting at a corner, and water shed from the dormer roof arrives at the top of the cheek.

Buildability

The whole element is small, high up and made of junctions, which means the amount of detailing is concentrated in an area that looks trivial on a drawing.

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 LibraryStructural softwood →Studwork framing is the most commonly encountered way the cheek is formed.Materials LibraryOriented strand board →Sheathing over the framing gives the cheek a face to carry the outer layers.Materials LibraryNatural slate roofing →Slate-hung cheeks are long established, taking the roof material down the vertical face.Materials LibraryZinc sheet →Sheet metal cheeks are common where the dormer is treated as a single wrapped form.

Materials

Commonly incorporates

Materials this element commonly contains as a distinct constituent part, rather than being made of.

Materials LibraryMineral wool insulation →Insulation is contained within the cheek framing, where the depth available is set by the framing rather than by the build-up either side of it.

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.

Edge and terminationCold Pitched Roof →Interrupts the slope and the ventilation path through it, both of which have to be continued past the dormer.Thermal layerEdge and terminationWarm Pitched Roof →The point at which the rafter-line insulation has to turn through a vertical plane and back again.Edge and terminationAbutment Detail →Its base is an abutment between a vertical surface and a sloping covering, running the depth of the dormer.

Clarifications

Commonly misunderstood

  • That the cheek is a minor piece of cladding hung on the side of the dormer. It is a full envelope build-up in miniature, and it carries the same control layers as the surfaces either side of it.
  • That it can simply be insulated to the same depth as the roof. The space available is set by the framing and by how far the dormer may project, which is why the cheek is treated as a thermal detail in its own right.

Conversations

Questions for qualified professionals

Questions worth asking someone with the project in front of them. This page cannot answer them.

  • What carries the dormer cheeks, and how is that framing connected into the existing roof structure?
  • How do the roof's insulation and control layers continue around the cheek at both corners?
  • How is the junction between the cheek and the roof covering formed along its full length?
  • What is the intended finish to the cheek, and how does it shed water arriving from the dormer roof above it?

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

  • This entry describes an element and its junctions. It states no framing size, spacing, insulation thickness, projection or fixing arrangement, and none can be inferred from it.
  • Forming or altering a dormer changes roof structure and commonly engages planning and building control processes; both are matters for qualified professionals and local requirements rather than a reference entry.

Roof Carcass & Edges

The battens, boards and edge elements that finish a roof structure and prepare it to receive a covering.

Browse all roof carcass & edges entries →