What to agree before ordering
Before the windows are ordered, five things must be agreed for every opening: how it opens, the final dimensions from an on-site survey, the glazing and shading, the junctions with the wall, sill and floor, and who signs off each of these. Then the logistics: when they arrive, where they are stored and when they go in.
Once the frames are made, almost nothing can be fixed. A window that opens the wrong way is not altered; it is reordered, with weeks of waiting. So it is worth going through this list on the house plan, opening by opening, before signing the specification. Which profile and material to choose is covered in our article on exterior joinery; here we deal with the checks before ordering.
Opening: the window in the life of the room
A window can look perfect on the façade and get in the way inside. A tilt-and-turn sash over the kitchen sink hits the tap. The bedroom sash opens onto the bedside table. A large upper-floor window with a fixed pane cannot be cleaned from outside without a ladder or a lift. Check every opening with the furniture drawn on the plan: where the sash swings, where the handle sits, how you will ventilate at night.
Garden and pool exits are a separate matter. A sliding system takes no space when open, but large panels are heavy, and the threshold has to be designed together with the indoor and outdoor floor levels. If you want a step-free exit, that decision also affects the terrace drainage, so it is made at design stage.
Dimensions: measure on site, not from the drawing
Order dimensions are taken from the actual opening on site, not from the architect's plan. There are always deviations between drawing and masonry, and for a window they matter. Decide in advance who takes the final measurement, usually the window supplier, and who checks and signs it off for the site.
If the house is built with installation subframes (premarcos), they are set during the wall construction, which fixes the opening sizes early and lets you order the windows sooner, without waiting for the reveals to be finished. It saves time in the programme, but the insulation and façade cladding thicknesses must be known before the subframes go in.
Glazing and shading
Glass is chosen by orientation and by risk. Large west-facing glazing in Castelldefels heats a room on summer afternoons more than any air conditioner can offset, so it needs solar-control glass or external shading, ideally both. How orientation affects the whole house is covered in a separate article. Glazing in doors and close to the floor must be safety glass: the CTE requirements for those zones are confirmed by the project technician.
Roller shutters, external blinds or awnings are decided before ordering, because the box can be built into the frame or hidden in the wall. If they are motorised, a power point for each window is set out at first-fix electrics, before plastering. Insect screens are also best ordered with the windows, in matching profiles.
Junctions: where the window meets the house
Most window problems are not in the windows but in the junctions. The external sill needs a fall and a drip so water does not run down the façade. Under the terrace door threshold, waterproofing has to be taken under the frame, otherwise water eventually gets into the screed. The façade insulation must meet the frame without a gap, or a cold bridge and condensation will appear in the reveal.
Inside, you need to decide how the reveals are finished, with plaster, plasterboard or cladding, and how the internal sill meets the frame. For every detail, record in writing who carries it out: the window installer or the building crew. A detail that "both are responsible for" usually gets done by no one.
What the order must contain and how to receive it
The order should list, for each opening and with a number matching the plan: profile series, outside and inside colour (they can differ), opening scheme, hardware and handles, locks, glazing make-up, shading boxes and motors, insect screens. Ask for the manufacturer's shop drawings and sign them only after checking them against the plan. That signature is the last moment when a change costs nothing.
The indicative delivery date is not the date the house is finished. Check how oversized panels will get onto the plot, where they will be stored away from dust and knocks, and at what point in the programme they are installed. At delivery, check each window against the order and record any defects in writing the same day: scratches and chips are hard to attribute once installation is done. In a house built as a full-cycle project, windows are among the items with the longest lead times, so this list is worked through early, not once the openings are ready.