Window Fitting glossary of terms & specifications
15 technical terms, material grades and Irish standards explained in plain English so you know exactly what is on a written quote.
Sorted A to Z for quick reference when comparing specifications.
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Key window fitting terms explained
Airtightness Tape vs Expanding PU Foam
A proper three-layer perimeter seal uses low-expansion acoustic/thermal PU foam in the cavity gap, an internal vapour-control airtightness tape bonded to the block reveal before plastering, and a breathable weather seal outside.
Box-Sash Lead / Steel Counterbalance Weights
Traditional Georgian and Victorian timber sliding sash windows balance each sash with cast-iron or lead weights running on braided cords over brass axle pulleys inside the hollow timber box frame; spiral spring balances are used on slimmer uPVC sash frames.
Centre-Pane Ug Value
The thermal transmittance measured through the middle of the glass unit alone (around 1.1 to 1.2 W/m²K for Argon-filled Low-E double glazing and 0.5 to 0.7 W/m²K for triple glazing). Always ask for the whole-window Uw rather than Ug alone.
EPDM External Weather Seal
Synthetic rubber gaskets co-extruded into uPVC and aluminium sashes (and membrane strips used beneath external sills and jambs) that stay flexible for 25+ years without shrinking or cracking in UV and Atlantic salt air.
Lift-and-Slide vs In-Line Patio Door Gear
On large 2.4 m to 4.0 m triple-glazed patio doors, lift-and-slide hardware raises the 150 kg+ door leaf onto twin stainless rollers when the handle turns 180 degrees, gliding effortlessly and dropping down onto continuous compression seals when locked.
PAS 24 / EN 1627 RC2 Multi-Point Locking
High-security window and door hardware combining mushroom-cam espagnolette bolts, shootbolts, hinge-side dog bolts, internal glazing beads and 3-star anti-snap cylinder locks.
Plaster Reveal Making-Good
Removing old timber or uPVC frames often chips 15 mm to 40 mm of internal plaster along the window reveals. A complete fitting quote includes bonding, skimming or insulated plasterboard reveal repair plus internal uPVC or MDF window board trim.
Pressed Aluminium vs Precast Concrete Sill
In Irish masonry walls, replacement windows either sit onto the existing precast concrete sill (cleaned, primed and sealed at the horn ends) or include a 150 mm to 180 mm stub uPVC/pressed-aluminium projection sill with concealed end dams.
TGD Part B Fire Escape Egress Hinge
Side-hung friction stays fitted to bedroom windows that open to a full 90 degrees with a clear openable area of at least 0.33 m² (minimum 450 mm wide by 450 mm high) and a bottom sill 800 mm to 1,100 mm above the floor.
TGD Part F Background Trickle Vent
Slot ventilators integrated into the head of the window frame or over-frame profile providing equivalent open area (typically 4,000 to 5,000 mm² per habitable room) to prevent condensation and mould when airtight replacement frames are fitted.
TGD Part K Toughened / Laminated Safety Glass
EN 12150 toughened or EN 14449 laminated safety glazing required by law in all door panels up to 1,500 mm from floor level, side panels within 300 mm of a door, and any window pane whose bottom edge sits less than 800 mm above the floor.
Thermally Broken Aluminium Profile
Extruded aluminium inner and outer frame sections joined across a polyamide fibreglass thermal strut (typically 24 mm to 38 mm deep) with foam inserts, allowing slim 50 mm sightlines while meeting the 1.4 W/m²K Part L standard.
Two-Thirds VAT Rule (13.5% vs 23%)
Supply-and-fit window and door installation by a VAT-registered fitter is charged at 13.5% VAT when the trade cost of the frames and glass is two-thirds or less of the total ex-VAT price. Supply-only frames bought directly from a factory carry 23% VAT.
Warm-Edge Spacer Bar (Psi Value)
Composite or stainless-polymer spacer bars separating the glass panes around the perimeter of a sealed unit, cutting edge condensation and improving whole-window Uw by 0.1 to 0.15 W/m²K compared with old aluminium spacers.
Whole-Window Uw Value (EN ISO 10077)
The overall heat loss rate of the complete window (glass, frame and spacer bar combined) in W/m²K. Irish Building Regulations TGD Part L (2022) sets a maximum Uw of 1.4 W/m²K for replacement windows; triple glazing typically reaches 0.80 to 1.0 W/m²K.
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Window fitters guides & price breakdowns
Straight answers to what people ask most: itemised costs, specifications, planning or grants, and what to check before you book.
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Questions people ask
How much do new windows cost?
A white uPVC window is €300 to €900 supplied and fitted. A 3-bed semi with 10 to 12 windows is €4,500 to €10,000 in uPVC, €9,000 to €17,000 in aluminium. SEAI's median for grant-aided window jobs on a semi is €7,110. See the price guide.
How long does it take?
The windows are made to measure after the survey, which takes 3 to 4 weeks. Fitting is 1 to 2 days on a typical 3-bed semi and 2 to 3 days on a detached house. See how long it takes.
Is there a grant?
Yes. SEAI pays €4,000 for a detached house, €3,000 for a semi, €1,800 for a mid-terrace and €1,500 for an apartment, plus €800 a door for up to two, for homes built and lived in before 2011. Don't start before the offer. See grants and VAT.
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