Illustration of a brick house with white windows and a green front door with one pull handle

Advice & Guides

The Cii Double Glazing Blog

Practical guides to choosing windows, doors and roof glazing, planning upgrades and understanding repairs.

Anthracite grey uPVC casement bay window with angled side returns, a lead-covered bay roof and a stone sill on a red brick terraced house

Window Guides16 October 2026

Bay Window Double Glazing: Survey and Replacement Guide

How to replace a bay window with double glazing: keep its shape and sightlines, check the support and bay roof, know when permission applies and what to agree.

White uPVC bedroom window seen from inside, with a fixed pane, an opening sash swung inwards and a trickle vent along the frame head, gardens beyond

Planning Guides15 October 2026

Replacement Window Building Regulations in England: A Homeowner's Checklist

A checklist for replacement window building regulations in England: planning, heat loss, ventilation, safety glass, escape openings and who certifies the work.

White double glazed sliding sash window with a two-over-two pane layout set back in the brick reveal of a yellow brick terraced house

Window Guides14 October 2026

Sash Window Installation: Double Glazing That Fits

How to replace sash windows with double glazing and keep their character: what to record, which details to agree, permission checks and what fitting involves.

Old white-painted timber bay window seen from inside a living room, with a survey folder, pencil and tape measure on the window board

Planning Guides13 October 2026

What Happens at a Window and Door Replacement Survey?

What a window and door replacement survey covers: how to prepare, what the surveyor checks at each opening, and what the written quote should then include.

An anthracite grey composite front door beside a white half-glazed uPVC front door on a pair of pebble-dashed semi-detached houses

Door Guides10 October 2026

Composite vs uPVC Front Doors: Which Fits Your Home?

Composite vs uPVC front doors compared on looks, glazing, security, thermal performance and fitting, plus the questions to ask at your home survey in Essex.

Replacement friction hinges, a window handle, rubber gasket and a screwdriver on the window board in front of a white uPVC casement window

Repair Guides9 October 2026

Double Glazing Repair: 7 Fixes Before Full Replacement

Seven double glazing repairs to check before you replace a window or door: misted units, cracked glass, handles, hinges, seals, door locks and patio rollers.

Window Guides8 October 2026

Double Glazed Windows: uPVC vs Aluminium Quotes

Compare uPVC and aluminium window quotes like for like: sizes, opening layout, glass, whole-window U-value and fitting, and when a new sealed unit is enough.

Illustration of an anthracite hipped roof lantern on the flat roof of a brick extension

Roof Glazing Guides7 October 2026

Roof Lanterns for Extensions: What to Plan First

Plan roof lanterns for a flat-roof extension: compare lower-profile rooflights, size the opening, choose glazing and coordinate fitting and approvals.

Illustrated comparison of open aluminium bi-fold doors on the left and sliding patio doors on the right

Door Guides6 October 2026

Bi-fold vs Sliding Doors for an Extension

Compare bi-fold and sliding doors for your extension: clear opening space, garden views, everyday access, thresholds and the questions to ask at a survey.