- Roof shape (gable, hipped) affects usable floor area.
- Roof structure (cut timber, trussed) affects the type of structural work required.
- A home survey and, where appropriate, structural input from an engineer are needed to confirm what is possible.
Roof shape versus roof structure
The words used to describe roofs cover two different things. Roof shape refers to the external geometry — how it looks from the road. Roof structure refers to the timbers underneath — how it holds itself up. Both influence a conversion, but in different ways.
Common Irish roof shapes
Gable-ended roof
A gable-ended roof has a triangular wall (the gable) at each end and a pitched surface between them. The full length of the attic is available up to the ridge, so gable roofs usually offer the most usable floor area. Many semi-detached and terraced homes are gable-ended.
Hipped roof
A hipped roof slopes inwards on the sides as well as the front and rear. There is no gable wall — the roof meets the wall plate on all four sides. This looks tidy from the outside but reduces the amount of standing headroom inside. A common design response is a hip-to- gable conversion, which replaces one hipped end with a new gable wall.
Dormer roof (as an existing feature)
Some houses already have small dormers built into the roof. These are useful reference points because they show where the roof was originally opened up to create additional headroom. New dormers typically follow similar principles at a different scale.
Common roof structures
Cut-timber (traditional) roof
A cut roof is built on site from rafters, purlins and, where needed, struts. The internal volume of the attic is largely open, which is why homes built with cut roofs are often the most straightforward to convert — the space is already there and the structural work focuses on the new floor and any openings.
Trussed roof
A trussed roof is prefabricated in a factory as a series of triangular frames spaced at regular intervals. The timbers are smaller than in a cut roof and the internal webs cross the space diagonally. Trussed attics can be converted, but the internal webs cannot simply be removed. New beams are usually engineered to take the loads before any web is cut.
Attic-truss roof
Some newer homes were built with attic trusses — a factory-made frame designed to leave usable room-height space inside. Where an attic truss is present, the framework is largely already in place. A survey confirms whether it was designed and certified for habitable use.
What roof type does not decide on its own
No roof type by itself makes a conversion possible or impossible. Cut roofs with low ridges can be unsuitable; trussed roofs with generous height can convert well after engineered work. Planning conditions, headroom, stair position and services all sit alongside the roof type in the overall picture.
Why we always defer to an engineer
Any change to the roof structure — cutting webs, adding beams, opening the roof for a dormer — needs to be sized by a chartered structural engineer for your specific property. What is standard on one house may not work on the next. We collect the observations; the engineer makes the structural decisions.
What this means for your project
Every home is different. Use this guidance to ask the right questions and to shape your brief — but confirm what applies to your specific property with a home survey and appropriate professional input.
Frequently asked questions
- How do I tell a cut roof from a trussed roof?
- A cut roof usually has large rafters and horizontal purlins with occasional diagonal struts, leaving most of the attic volume clear. A trussed roof is filled with a repeated triangular framework of small timbers, usually joined with metal plates. If you cannot see across the attic without ducking around timbers, it is likely trussed.
- Can trussed roofs be converted?
- Often, yes — but it requires engineered structural work. New load-bearing beams typically replace the internal truss members so that the floor and roof can span without them.
- Are hipped roofs harder to convert?
- Hipped roofs give less usable floor area than gable-ended equivalents because the roof pitches inwards on the sides. A hip-to-gable conversion or a dormer can recover some of that area, subject to planning and design.
- Does the roof shape affect planning?
- Yes — any change to the external roof profile (dormers, hip-to-gable, raised ridge) is a planning consideration. Conversions that stay inside the existing roof shape are typically treated differently.
Start with a quick check of your attic.
Answer a few simple questions about your home and what you would like to create. We’ll give you an early indication of which conversion route may be worth exploring. A home survey is still required before suitability can be confirmed.
Or call +353 85 150 0853