Timber Dutch barn conversion cost
Timber Dutch barns convert at £1,650 to £2,180/m² mid spec on our indicative Q2 2026 model. They are the cheapest of the three archetypes when the curved roof is retained and the timber frame is sound.
The frame and the roof
A traditional Dutch barn is a five-bay open structure with a curved (often corrugated steel) roof. The frame is the asset; if it is sound, the conversion is essentially a new envelope hung within the frame. Replacement of the corrugated roof with insulated standing-seam metal (typically aluzinc or zinc) costs £160 to £240 per m² of roof area.
Insulation and Part L
Achieving the Part L elemental U-values on a timber Dutch barn typically uses warm-roof PIR (140-180mm) and an inner stud wall with mineral wool plus PIR plasterboard. Airtightness is the bigger challenge than U-value; expect the design team to specify a wraparound membrane.
Class Q on Dutch barns
Many Dutch barns fail Class Q on the "permanent and substantial construction" test, particularly older corrugated examples. The 21 May 2024 amendment did not relax that test. Allow for a 30% to 40% refusal probability on first submission unless the building is exceptionally well-preserved.