Sash Window Replacement, Renovation and Upgrade FAQs

Listed below are questions we are often asked. Please take some time to look over these before submitting a general enquiry. We have answered here as concisely as we can to cover more topics without too much reading, with many of the questions covered in greater detail in the relevant areas of our website. There is also a customer service section at the bottom of the site with more detailed information.

Questions About Services

Newly manufactured sashes, pre-installed with double glazed units (IGU’s), made to fit your existing window case (surround). Typically, we make these to match the format of the existing windows.

A complete replacement comprises new sashes AND case (window surround). Replacing your whole window is usually only required when the existing case (surround) is beyond repair or if none is currently in situ.

You can replace your windows if your local council give permission. To receive consent, a Listed Building Application must be submitted. You can do this yourself or, we can do this on your behalf as part of your quotation.
With a simplex system, the lower sash can swing inward and allow access to clean and paint a window. This system is standard in sash and case windows on the first floor and above.
Yes, although we recommend you have your windows painted by professional tradespeople. If you wish to go down this route, it will need to be discussed at the time of your quotation and may affect your guarantee.
We usually require a minimum of six weeks lead-time for manufacturing, although there may be some flexibility depending on our schedule. Typically, manufacturing works are booked eight to ten weeks before fitting and refurbishments a bit sooner, depending on our planner.
We will try to match the colour of your interior woodwork as closely as we can. However, please be aware that it can be difficult to achieve an exact match. Through time, pine will darken when exposed to sunlight, so it’s often the case that it will appear lighter at first.
As part of the draught-proofing process, we replace the existing parting beads and baton rods with new timbers integrated with brush strips. We also install a strip into the meeting rails in the centre of the window. While installing this system will show a large improvement over windows without, draughts will not be stopped completely.

Questions On Glazing

As a general rule, they do not. Slimline units are typically either 14mm 4/6/4 or 12mm 4/4/4 and allow for installation to historic windows. They are seen as a compromise for local authorities so that double glazing does not affect the character of the building. Most councils will allow the installation of slimline units in conservation areas and listed buildings.

Our argon filled, warm edge spacer units have a u value of:

14mm (4/6/4) Units – U Value 2.0

16mm (4/8/4) Units – U Value 1.6

18mm (4/10/4) Units – U Value 1.4


Low E or low emissivity glass has a film on one side of the glass that improves thermal retention when used in a double glazed unit.

  • Low E glass helps reduce Energy Costs
  • Low E glass blocks infrared light from penetrating the glass from the outside
  • Low E Windows Reduce Destructive UV Rays. These coatings help reduce ultraviolet (UV) light
  • Low E glass has a slight blue/green tint to it
  • Low E Windows Do Not Block All Natural Light

Fineo is a new type of vacuum-sealed unit manufactured in Belgium, which offers a better U Value than standard units while retaining a thin profile. It has a better lifespan than conventional units and also improves accoustic dampening. These units are ideal for Georgian style multi-pane windows.

Fineo 8 (7.7mm thick) has a U Value of 0.7

Any units which are less than 800mm from floor to glass are required to be toughened glass. Toughened Fineo is available however this comes with a visible vaccuum port on the corner of each individual unit. As this can be unsightly particularly in multi-paned windows, we can apply a clear safety film if requested. 

Fineo also offers better sound reduction than triple glazing and significantly reduces noise compared to standard IGU’s. Please see glazing industry figures for noise reduction below: 

  • Single glazing reduces sound by 29DB
  • Double glazing (up to 28mm) reduces sound by 31DB
  • Triple Glazing reduce sound by 32DB
  • Fineo vaccuum units reduce sound by 35DB.

Please see the Energlaze website here:

Not necessarily however it will reduce it significantly. Several factors cause condensation, and while double glazing will help, it may not eliminate it entirely. The ambient moisture levels in the property and outside temperature extremes are governing factors here. When possible, rooms should be well ventilated to allow air circulation.

Yes, although it depends on the dimensions of the existing sashes, primarily the astragals on multi-pane windows. The process can be quite destructive to the existing timbers and, the overall finish is usually not as neat as with new sashes.

Toughened, also known as safety glass, has been heat-treated in a furnace to give it extra strength against impact. If any portion of a pane of glass is below 800mm from floor level, toughened glass is a requirement.

Double glazed units are deemed to be failed if there is water or condensation visible inside the unit. A slight haze can sometimes appear on the glass in certain temperatures however this does not mean the unit has failed.

External condensation is a natural phenomenon and predictable event caused by the outer pane of the glazing being colder than the glass that it replaced. Fitting modern low-emissivity (low-e) glazing can increase the chances of external condensation but this is not a fault in the glass or the windows. With single glazing and older style double glazing a larger proportion of heat was lost to the outside through the glass but nowadays, modern low-e glazed windows help to keep more of the heat inside and the outer pane is not heated as much. 

Now for the science part; moisture condenses out of the air onto a cold surface that is said to be below the dew point. The dew point varies with the air temperature and the amount of moisture it contains. In Spring and Autumn in particular, the glass temperature can fall to a low level during the night and the dew point can be comparatively high in these seasons. The glass is more often likely to be below the dew point in these conditions and the moisture condenses onto the surface. 

In order to comply with the latest Building Regulations we are all obliged to fit more thermally efficient windows in our homes. (There are only a few exceptions to the regulations and they tend to apply to unheated spaces or listed buildings that would suffer external condensation to the same extent anyway). The trend is to use a glass product that has lower U-values and provides better thermal insulation; the lower the U-value, the lower the outer pane temperature is likely to be but the bigger the risk of condensation is on the external surface. In northern European countries where they use triple glazing with very low U-values, the phenomenon is understood and accepted. The householders are focused on saving energy and maintaining a comfortable internal environment.  Overall though, in many cases the condensation does not last long and a little heat from the sun warms the outer glass enough to evaporate the moisture, a gentle breeze or wind will also do the same job.

You may notice that not all the panes are affected by early morning condensation even in the same window.  Even subtle differences in orientation and the position of objects outside the window can change the surface temperature of the glass to the point that one pane suffers, and another does not.  Any object (be it an overhang, canopy, tree etc.) blocking off the window to a clear night sky may also have the effect of reducing the occurrences.

A plus point to this phenomenon, is the knowledge that your windows are keeping the heat in as they are designed to do thus proving that you have a superior insulating glass product! The presence of external condensation in a particular season does not mean that the glass will suffer the same throughout the year. Any occurrence is beyond the control of the window supplier and is a natural result of the environmental conditions.  

Questions On Works

Yes! Our fitters and painters will do their best to keep disruption to a minimum during works and allow access as needed.

If our fitters finish up at the end of the day and with a window incomplete, they will temporarily secure either the old windows or the replacements in position before leaving.

As a rule of thumb, windows take a little more than one day per fitter, and we usually have two fitters per job, depending on staffing levels. Painting usually takes slightly less time than fitting but can be impacted by inclement weather.