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Double Glazing Frequently Asked Questions


Find answers to frequently asked questions about double glazing installations.

Are you FENSA registered?

We are registered with FENSA, which means we can register all our installations.

Since April 2002 it has been a legal requirement that all domestic replacement window and/or door installations are registered with Local Authority Building Control (LABC).

Installers either had to register their installations with LABC or they could self certify these installations with the only self-certification scheme available to them at that time (FENSA).

On behalf of scheme members, FENSA will:

* Register the installation electronically with the relevant Local Authority Building Control Office.

* Issue a Building Regulations Compliance Certificate to you. You will need this certificate should you decide to move house.

FENSA are authorised & regulated by the CLG.

How do I care for my windows, doors and conservatories?
Cleaning uPVC Frames:

Never use anything abrasive, this will scratch the surface, which will trap the dirt. Wash the frames with a mild solution of washing-up liquid. If any stubborn marks remain, lightly rub with Ciff crème cleaner. DO NOT use Ciff on every occasion, as this will remove the shine from the PVC-u.


After a heavy shower of rain, you may find some water laying in the bottom of your door and window frames. This is nothing to worry about as this will drain away through the drainage holes in the base.

Lead Work:

As with any new lead work, when exposed to rain it will start an oxidation process, which shows as white or mottled staining on the lead work. When this process is complete, the lead work will be dark grey in colour and will no longer stain. This process will take a few months to complete.


Twice a year, spray WD40 into all the locks and on to any metal-to-metal contact surfaces around your doors and windows. This will help to keep them operating smoothly.

Building Work - Conservatory Bases:

As with any new building work, a period of 'drying out' is necessary. Please ensure maximum air circulation and ventilation during this time to assist the process. To test if a floor is 'dry' lay a square of carpet on the floor overnight. If the floor is dry when the carpet is lifted, the process is complete. Never be tempted to use electric or gas fires to speed-up the 'drying out', as this is dangerous.


To ensure a draught free door; please remember to keep the door in the locked position. This will achieve a tight fit on to the draught seals.

Why would I want double glazing?

Replacing standard windows with double glazing can halve heat loss and will also provide a marked reduction in outside noise and internal condensation.

It will generally have a beneficial effect on the look of your property as well as its resale value. In the UK it is proposed that house sales will be graded on their energy efficiency and houses with double glazing will score higher than those without.

Additionally, the main entry point for an intruder is via the windows or doors. Modern uPVC double glazed windows provide an extra level of security due to their durability and the built in multi-point locking system.

Can you supply Triple Glazing?

Yes, we can offer triple glazing as an option for both home and businesses. It is ideal for those seeking better sound and heat insulation than that provided by standard double glazing.

Will I be visited by pushy sales people who want to spend hours in my home trying to get me to sign on the dotted line?

No. JC Windows is a salesman free zone. Our home survey will take no more than 45 minutes and your quotation applies for 30 days so you can consider at your leisure.

What about all those "Special Offers" I see on television that are never what they seem. Will you try and sell me something I don’t need or include lots of hidden extras?

No. We will send you a simple quote based on your requirements. We do not waste your time with silly gimmicks, phoney offers or hidden costs.

I have a small house/large house. Will the size be a problem?

No. We can provide double glazing and glass services for all sizes of property in various styles to compliment the building.

Do I need planning permission to fit new windows?

Planning permission is needed for listed buildings, homes in conservation areas, and for flats only.

I have secondary glazing, what further benefits would I get from fitting double glazing in terms of heat loss?

Secondary glazing has far lower insulation levels than that of double glazing, especially those offered by Low'e double glazing.

I have double glazing already but I get a lot of condensation inside my home, will fitting new double glazing help?

By installing standard double glazing with low e glazing, condensation on the inside pane of the window can be greatly reduced.

What is uPVC?

Un-elasticised polyvinyl chloride. It is the cheapest manufacturing option, up to three times cheaper than wooden frames but also the most energy efficient.

I have heard that uPVC can discolour with age, is this true?

Modern higher quality uPVC shouldn't discolour any more, unlike cheaper earlier versions. No discolouration would be expected through its lifespan nowadays.

Can Argon gas escape from my new windows into the home?

Argon gas fillings should last the lifetime of a double glazed unit, they should not leak any more than 5% over a 25 year period.

What are Energy Efficient Windows?

Look for a B.F.R.C. (British Fenestration Ratings Council) energy efficiency index chart. Rated windows help contain and conserve heat within your home by keeping out the wind and rain. They also allow natural energy like the warmth of the sun to heat the home. Frame material can be - timber, aluminium, uPVC, steel or even a combination of mixed materials.

I have single glazed windows at present, how much will I save fitting new double glazing?

Replacing all single-glazed windows with a B-rated double glazed system should save you approximately £165 per year on your energy bills for smaller energy users.

Does fitting new windows benefit our environment?

You will burn less fuel for heating and generate less carbon dioxide that leads to global warming - typically around 680kg per year for smaller households.

Are there any regulations I need to adhere to when buying new windows?

There are several building regulations that have to be adhered to when installing new windows. It is ultimately your responsibility as the homeowner to meet them. Regulations include overall u-value of window, safety glass and safe cleaning.

Is there any benefit in buying timber windows these days?

Timber windows can often achieve lower overall u-values and offer a slimmer alternative to cheaper chunky uPVC window systems. They do require maintenance and can cost considerably more than a uPVC equivalent - sometimes by as much as 50% added purchase cost.


Where we cannot resolve any complaints using our own complaints procedure, as a Which? Trusted trader we use Ombudsman Services Ltd for dispute resolution. In the unlikely event of a complaint arising and you wish to refer the complaint to them please contact Which? Trusted traders in the first instance on 0117 981 2929.


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