Guides · 19 in the set
What to know before you buy
Plain guidance on replacing windows and doors in England and Wales: what building regulations require, when you need planning permission, what the numbers on a quote mean, and how to avoid losing a deposit. Written to be useful whoever you end up buying from.
We are an introducer, so we have no product to defend. These are written to help you judge any quote, including one from an installer we matched you with.
Series · 08
Regulations
What the law requires of a replacement window or door in England and Wales, who certifies it, and where planning rules add a second layer.
- 01
FENSA or CERTASS: what is the difference?
FENSA and CERTASS are both government-authorised competent person schemes. Either lets an installer self-certify that your replacement windows meet building regulations and issue you a certificate. Neither is better than the other, and which one an installer belongs to matters far less than whether they belong to one at all.
2 min read · 3 questions
- 02
Do I need building regulations approval for new windows?
Yes. Replacing a window or an external door in England and Wales is notifiable building work. In practice a FENSA, CERTASS or Assure registered installer self-certifies it and sends you a certificate, so you do nothing. If your installer is not registered, you have to apply to building control yourself.
2 min read · 3 questions
- 03
Do new windows have to have trickle vents?
In most cases yes. Since the 2021 edition of Approved Document F, replacement windows in England generally have to provide background ventilation no worse than what they replace, and in practice that means trickle vents. An installer offering to leave them off is offering to make the work non-compliant.
2 min read · 3 questions
- 04
Replacing windows in a conservation area
In a conservation area you may still need planning permission for replacement windows, particularly where an Article 4 direction has removed permitted development rights. Many authorities refuse uPVC on front elevations. Ask the conservation officer what they will accept before you order anything.
2 min read · 3 questions
- 05
Windows in a listed building
Altering windows in a listed building needs listed building consent, and that applies inside as well as out. Consent for uPVC is very rarely granted. Repairing original windows and adding secondary glazing is usually the realistic route, and doing work without consent is a criminal offence.
2 min read · 3 questions
- 06
U-values and window energy ratings explained
A U-value measures how fast heat escapes, so lower is better. Replacement windows in England and Wales must achieve 1.4 W/m²K or better, or Window Energy Rating band B. A rating counts the solar gain a window lets in as well as the heat it loses, which is why the two measures can disagree.
2 min read · 3 questions
- 07
Where does a window legally need safety glass?
Approved Document K defines critical locations where glazing must be safety glass: anywhere below 800mm from the floor in a wall or window, and anywhere below 1500mm in a door or in the panels immediately beside one. Safety glass in these positions is your installer’s responsibility, not something you have to specify, but it is worth knowing because it is the most common thing a cheap quote quietly leaves out.
3 min read · 3 questions
- 08
Which windows have to open wide enough to escape from?
If a room relies on a window as its means of escape, a replacement must provide at least an equivalent escape. Approved Document B gives the benchmark as an unobstructed openable area of at least 0.33 square metres, at least 450mm high and at least 450mm wide, with the bottom of the opening no more than 1100mm above the floor.
3 min read · 3 questions
Series · 06
Buying well
Reading a quote, protecting a deposit, and knowing when the cheap repair is the right answer.
- 09
How to spot a bad window installer
The reliable warning signs are pressure to sign today, a discount that expires when the salesperson leaves, a large deposit demanded up front, no competent person scheme registration, and a quote that will not itemise the specification. Any one of them is reason to slow down.
2 min read · 3 questions
- 10
How much deposit should I pay for new windows?
A deposit of around ten to twenty-five per cent is normal, covering materials ordered to your sizes. Paying most of the price before work starts is not normal. Pay by credit card where you can, because Section 75 can make the card provider jointly liable if things go wrong.
2 min read · 3 questions
- 11
What is an insurance-backed guarantee?
An insurance-backed guarantee is a separate policy that honours your installer’s written guarantee if the installer stops trading. A guarantee from a company that no longer exists is worth nothing, which is exactly when you are most likely to need it.
2 min read · 3 questions
- 12
What a good window quote should contain
A quote you can rely on names the profile system, the glass specification, the spacer type, the hardware and the colour, and states explicitly whether removing the old frames, disposal, making good and the compliance certificate are included. A single line and a total is not a quote you can compare.
2 min read · 3 questions
- 13
What does an A++ window rating actually mean?
A window energy rating is a single letter summarising a calculation that combines heat lost through the window, heat gained from sunlight through it, and air leakage around it. Building regulations are not satisfied by that letter. They are satisfied by the U-value, which measures heat loss alone, so a rating and a compliance figure are two different numbers and a quote should give you both.
2 min read · 3 questions
- 14
What does a ten-year window guarantee actually cover?
A headline ten-year guarantee is normally several separate guarantees of different lengths: the frame from the manufacturer, the sealed units from the glass maker, the hardware from its own maker, and the installation from the installer. The installation part is the one that matters most and the one most likely to be short, and it is worthless if the installer stops trading unless it is insurance-backed.
3 min read · 3 questions
Series · 05
Living with them
Something is wrong with a window you already have. These say plainly whether that is a repair or a replacement, and several of them will talk you out of buying.
- 15
When is it actually time to replace your windows?
Replace when the frames themselves have failed: timber that has gone soft, uPVC that has distorted or cracked, or a system whose hinges and mechanisms are no longer made. Misted glass, a broken handle, a dropped sash and a draughty seal are all repairs, and each costs a small fraction of a replacement window.
3 min read · 3 questions
- 16
Why your windows are draughty, and what actually fixes it
A draught from a window is nearly always one of four things: a perished rubber gasket, hinges and a locking mechanism that have stopped pulling the sash up tight, a gap between the frame and the wall hidden behind the plaster or render, or a trickle vent doing exactly what it was fitted to do. Only the third, and the worst cases of the second, point to replacing the window.
3 min read · 3 questions
- 17
Which windows actually reduce noise?
Secondary glazing reduces noise more than replacement double or triple glazing, because what blocks sound is a wide air gap and a secondary pane sits 100mm or more behind the original rather than the 16mm or 20mm inside a sealed unit. If you are replacing the window anyway, the specification that matters is asymmetric acoustic laminated glass, not triple glazing.
3 min read · 3 questions
- 18
What makes a window or door actually secure?
Two things to put in writing: PAS 24 for the window or doorset as a whole, and a TS007 3-star cylinder, or a 1-star cylinder paired with 2-star handles. Part Q of the building regulations requires PAS 24 on new dwellings only, not on a replacement in an existing home, so on a replacement nobody will specify it unless you ask.
3 min read · 3 questions
- 19
Condensation on windows: what it tells you
Condensation inside on the room face means humid air meeting cold glass, which is a ventilation issue rather than a faulty window. Condensation between the panes means the sealed unit has failed. Condensation outside on the glass means the window is insulating well and is nothing to worry about.
2 min read · 3 questions