Attic flooring & roof carpentry technical glossary.
Plain-English definitions of Loft Legs, P5 moisture-resistant tongue-and-groove chipboard, fink trusses, EN 14975 stairs.
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Key terms in Irish attic boarding & insulation
18mm P5 T&G Loft Board
Moisture-resistant structural grade particleboard (EN 312 P5) machined in 1220×320mm or 2400×600mm tongue-and-groove panels so boards fit cleanly through an attic hatch and lock together into a rigid load-spreading diaphragm.
Cold Roof Space
The standard Irish domestic roof build where 300mm mineral wool insulation lies horizontally at ceiling joist level, leaving the attic void above it cold and cross-ventilated at the eaves.
Counter-Battening (Cross-Battening)
Fixing treated C16 structural timber battens (typically 150×44mm or 175×44mm) perpendicular across existing ceiling joists to raise the attic floor above deep quilt insulation and stiffen the ceiling.
Cut Roof
A traditional roof framed on site by a carpenter using heavier 100×50mm or 150×50mm ceiling joists, rafters and purlins, giving a wide open central attic bay without internal timber web diagonals.
Eaves Ventilation Tray (Rafter Roll)
Corrugated plastic baffles fitted between rafters at the wall plate to prevent 300mm mineral wool insulation from blocking the 10mm–25mm soffit airflow gap that keeps the roof timber dry.
EN 14975 Loft Ladder Standard
The European safety standard for domestic folding attic stairs, requiring a minimum 150 kg test load, slip-resistant treads, spring-assisted counterbalancing and safe locking hardware.
Fink Truss (Gang-Nail W-Truss)
Factory-made triangular roof trusses using 35×75mm or 35×95mm timbers joined with stamped steel nail plates at 600mm centres, found in over 80% of Irish housing estates built since 1975.
Airtight Insulated Attic Hatch
A draught-stripped, multi-point latching trapdoor insulated with 50mm–100mm PIR or EPS board to achieve a U-value of 0.55–0.85 W/m²K and stop warm indoor air escaping into the cold roof void.
Loft Legs / XL Loft Risers
Engineered polypropylene support pillars (175mm standard or 270mm–300mm XL) screwed to ceiling joists or truss chords to carry an 18mm T&G chipboard deck above 300mm mineral wool without thermal bridging.
Joist Trimmer
A doubled-up structural timber header spiked perpendicular across cut ceiling joists when enlarging or relocating an attic hatch opening so load is safely transferred to adjacent uncut joists.
Thermal Bridging
Heat loss through conductive materials (such as solid timber battens or compressed wool) that bypass the main insulation layer. Point-contact polypropylene Loft Legs reduce thermal bridging to under 1%.
U-Value 0.16 W/m²K
The SEAI Better Energy Homes and Irish Building Regulations Part L target thermal transmittance for ceiling-level attic insulation, achieved with 300mm of mineral wool or glass wool roll.
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