Mid-century extension in Dublin

How Cora Marshall and Philip Clarke converted their compact 1950s two-up-two-down house into a bright and spacious family home.

In this article Cora and Philip take us through their Dublin extension project, including:

  • Working with an architect and extending at the side of the end-of-terrace concrete house
  • How to extend and maximise garden space with before and after floor plans
  • Moving the internal staircase
  • Details of the external wall insulation work
  • Window replacement
  • Securing a self-build mortgage
  • Redesigning the plans to the budget
  • Construction drawings for the extension project and for future alterations
  • Builder contract details
  • Demolition work, moving out and the need to replumb
  • Snagging


Size before: 55qm
Size after: 100sqm
Total cost: €130,000
BER: F1 upgraded to a B2
Walls: insulated externally with 120mm EPS with silicone silicate render (which is, according to the architect, hydrophobic and has better self-cleaning properties than acrylic renders) onto existing solid concrete walls or on the new build over 215mmm solid concrete blockwork. U-value 0.2 W/sqmK
Roofs: insulated with 50mm PIR insulation fixed to underside of joists with airtightness tape to joints and junctions with walls. Plasterboard and skim plaster finish to ceiling. 200mm fibre insulation between rafters above (sloped sections of roof insulated with 100mm PIR insulation between joists fitted flush to underside of rafter and 50mm PIR insulation to underside of rafter).
Existing solid ground floor: which featured a tar/pitch DPM above the original slab was retained and damp-proofed from above before floor finishes were applied. Conventional insulated concrete slab construction was employed to the new extension.


Written by Astrid Madsen

Astrid Madsen is the editor of the SelfBuild magazine. She previously held the same role in an Irish trade publication, before that she worked at the National Standards Authority of Ireland. She graduated with a BA in Urban Studies from Columbia University in New York and holds an MBA from the Instituto de Estudios Bursatiles in Madrid. France of origin, she now lives in Portarlington, County Laois, where she's taken on the task of renovating a listed building! Email astrid.madsen@selfbuild.ie

Extension built off-site

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