Technical Specifications

Here you can read in more detail about the technical details of the windows we produce and the materials we use within our repair and upgrade services.

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Repair Care

Decoration Protocol

Sashcraft’s Advanced Sealing System

Heritage Glazing

Vacuum Glazing


Sustainable Hardwood

Accoya wood

Stained Glass

Noise Reduction

Thermal Performance

Repair Care

Sashcraft is an accredited user of the Repair Care International system, which is used in combination with traditional joinery methods. It offers a total solution for sustainable timber restoration and maintenance. The DRY FIX®/DRY FLEX® primer and repair system is the only durable solution for decayed and damaged joinery. DRY FIX® primers penetrate deep into the fibres of the wood ensuring that DRY FLEX® bonds permanently. Based on a unique epoxy resin formula, DRY FLEX® remains elastic so that it accommodates any movement.

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Decoration Protocol

  • To comprehensively rub down all joinery
  • Areas of defective paint will be burned/sanded back to bare timber
  • The external side of retained existing sashes will be burned back to bare timber in most cases
  • All rotten wood to be cut out and restored using the Repair Care International system and traditional joinery methods
  • Conservation joints will be created appropriately to allow for movement to the windows and any other external joinery in preparation for decoration
  • Any new wood to be primed with micro-porous paint
  • Internal and external joinery will be finished with up to three coats of high-quality, water-based, micro-porous paint. Please note that all mouldings associated with the windows internally will be fully decorated.
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Sashcraft’s Advanced Sealing System

Cambridge Sashcraft’s patented Advanced Sealing System ensures optimum operational, acoustic and thermal efficiency on all period windows we work on.

The Sashcraft Advanced Sealing System is protected under UK Patent No. 2580028, and European Patent No. EP3670809.

Our in-house system utilises an optimal arrangement of Schlegel weather seals that are built into sash and casement windows to eliminate thermal and acoustic ingress.

Unlike brush draughtproofing systems which fail when brushes are exposed to moisture or paint, our sealing system is highly durable and effective, with our system benefitting from the following properties of Schlegel seals:

  • Excellent memory – returns to original shape after compression
  • Stability – low/no stretch gained by glass fibre internal cord or insert
  • Easily compressed – low compression forces, unaffected by temperature variance
  • Acoustics – outstanding acoustic performance – independently tested
  • Thermal conductivity – unrivalled thermal performance – independently tested
  • Paint and Stain Proof – properties unaffected by standard paints and stains
  • Stabilised – unaffected by rot, fungi, UV light or ozone
  • Patented – Schlegel has been innovating seals for over a century
  • Temperatures – the widest operating range +70ºC to -65ºC
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Heritage Glazing

Developed by CN Glazing.

CN Heritage Double Glazed Units Offer the Perfect Replacement for those with Historical Significance.

CN Heritage double glazed units have the appearance of single glazing, therefore, retaining the character, charm and heritage of the building. Only a very close inspection will reveal the glass to be a double glazed unit.

When glazed traditionally into sash/casement window frames the units are virtually undetectable because the units do not have the double reflection or the distorted reflection that is seen when you sometimes look at standard double glazing, making them suitable for period properties.

By also using the technical glasses available today and by filling the space between the two panes of glass with krypton gas, a homeowner may gain all the thermal and sound benefits of normal double glazing without compromising the appearance or the value of their property.

Key features:

  • Slim Sightlines
  • Use Planitherm Low E Glass for a warmer house in winter and cooler in summer
  • Use Toughened Glass
  • Krypton filled cavity for improved performance
  • Low U-Values
  • Edgetec Super Spacer bar, in Black, giving appearance of a shadow gap

To produce our CN Heritage Double Glazed Units we use Edgetec Super Spacer bar. Edgetec Super Spacer bar introduces no-metal, pre-desiccated, structural foam spacer system that is a warm edge technology to suit all sealed glass unit applications helping to deliver windows of the highest standards. Its award-winning, patented Thermal Set Spacer (TSS) technology gives the ultimate in high-performance spacer systems. Super Spacer has 100% memory and allows for expansion and contraction, a major cause of fractures in conventional sealed units.

With Super Spacer® thermal bridging is all but eliminated, resulting in a massive 70% reduction in condensation.

Most of the heat loss through a window occurs at the edge of the unit, Super Spacer® blocks this escape route.

Values (the term used to measure thermal efficiency)
A U value is a measure of heat loss in a building element, therefore, it is the measurement of the whole window and not just the glass. It can also be referred to as an ‘overall heat transfer coefficient’ and measures how well parts of a building transfer heat. This means that the higher the U value the less efficient the thermal performance of the building element. A low U value usually indicates higher levels of insulation.

The thermal efficiency benefits of C N Slim Heritage Double Glazed Units over single glass can be seen below:

Single Glass – U-Value is approx. 5.6 W/m2K

Glass 1 (External) Cavity Glass 2 (Internal) Centre Pane U-Value
4mm Float/Toughened 6mm Krypton Filled 4mm Planitherm Total Plus Low E 1.5W/m2K
4mm Float/Toughened 8mm Krypton Filled 4mm Planitherm Total Plus Low E 1.1W/m2K

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Vacuum Glazing

We are accredited suppliers of FINEO Vacuum Glazing and LandVac Heritage Vacuum Glazing.

Vacuum Glazing, with its unrivalled thinness, provides optimal thermal and acoustic comfort.

Vacuum Glazing offers exceptionally low U values (0.4 – 0.7 W/m2K), in line with Triple Glazing and eight times better than the existing float glass in Sash or Casement windows. When used in combination with Accoya which has a 40% thermal conductivity improvement over hardwood and the Sashcraft patented Advanced Sealing System, a traditional window can be transformed into an exceptionally efficient unit.

Both variants of Vacuum Glazing achieve Weighted Sound Reduction Index (Rw) ratings of >39 Db. A 10 Db reduction corresponds to a 50% reduction in the perceived volume of sound. Vacuum Glazing provides acoustic insulation corresponding to approximately a 16 x, or 93.75%, decrease in the perceived volume of sound. Residential traffic typically generates noise in the range of 50-70dB, which is reduced by Vacuum Glazing to an intensity equivalent to a person whispering.

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For sliding sash windows, we supply and fit new high-quality window accessories: brass/chrome pulley wheels, sash lifts and a lockable heritage fitch fastener – which has been approved as a  Secured By Design Official Police Security Initiative.

For casement windows, we supply and fit high-quality fasteners and stays: solid brass or chrome as preferred with lockable options.

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Sustainable Hardwood

Cambridge Sashcraft work hand in hand with Rosewood Joinery to develop replacement sashes, windows and doors.

We use Utile hardwood from Latham Timber  to construct our sashes for both our renovate and sash replacement and complete replacement services.

The sashes are made in our local joiners workshop, Rosewood Joinery. Owned and managed by Paul Bailey, Rosewood Joinery use traditional methods with meticulous attention to detail to create superior replacement sashes, windows and doors.

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Accoya wood

We are also approved suppliers and manufacturers of Accoya wood. Accoya turns everything you know about wood on its head. It is timber that has been modified via a process called ‘acetylation’, which increases its durability, enabling it to resist rot, defy the elements and stay strong and resilient for decades to come, without effecting its natural appearance.

The treated wood is thoroughly tested for dimensional stability, durability, paint retention and in-ground conditions, ensuring it achieves the optimal performance.

From a sustainability perspective, while other types of durable woods tend to be slower growing species, Accoya is made using fast growing, sustainably forested radiata pine.

Accoya offers outstanding durability, meaning it is long lasting and also easy to machine, sand and paint and its incredible dimensional stability means it will not swell or contract with temperature and humidity changes – which makes it ideal for windows and doors.

Great stability

Dimensional stability is the degree to which a material maintains its original dimensions when subjected to environmental changes. With Accoya, swelling and shrinkage is reduced by 75% or more, which means doors and windows will open effortlessly all year round.


Accoya offers the best level of durability possible in wood. Lasting 50 years above ground, and 25 years in ground or freshwater, it has Class 1 durability. This surpasses even teak. It forms an effective barrier to insect attack, being indigestible to microorganisms and insects and therefore more durable to wood-destroying fungi, and is virtually rot-proof.


The process used on the timber increases the wood’s strength and hardness. Its high strength-to-weight ratio makes it suitable for even the most challenging applications.

Accoya works well with all known coatings systems. The wood is easy to coat as it requires less preparation and sanding that others. Its improved stability also means coatings last up to two times longer, which reduces the need for maintenance. And the less time spent maintaining the wood, means less money being spent on coatings and the less coating used during the life time of the wood.

Superior insulation

In comparison to other commonly used hardwood and softwood species, Accoya wood offers superior thermal insulation. This provides energy conservation advantages such as when used in applications including window frames and doors.


The modification process does not compromise the wood’s natural beauty. It remains comparable in colour to the original source species, allowing for a natural look to be created in a property. Alternatively, it can easily be coated in a wide range of colour finishes.


Accoya is sourced from FSC® and other regionally certified woods, meaning it is a naturally renewable material. Only abundantly available, fast growing source species, such as Radiata pine, are used in its creation.


Accoya wood provides compelling environmental advantages over slow-growing hardwoods, woods treated with toxic chemicals and non-renewable carbon intensive materials such as plastics, metals and concrete.

The manufacturing process is also non-toxic and adds nothing to the wood that does not already naturally occur in it. It protects the environment from the harmful effects of common treatments and may be safely reused, recycled and incinerated.

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Stained Glass

Cambridge Sashcraft work with local Stained and Leaded Glass Specialist Damon McDonald to offer sympathetic restoration of stained and leaded windows using traditional methods. Glass can be repaired and professionally cleaned and we can create bespoke glass panels for windows and doors.

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Noise Reduction

The Sashcraft Advanced Sealing System significantly reduces the amount of noise ingress; noise travels in a similar way to air and will find a route into a building through any gaps. Sashcraft’s memory foam based sealing system minimises the gaps and improves noise resistance.

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Thermal Performance

The use of the Repair Care system in combination with traditional joinery methods and a professional decorating service ensures that there are no gaps in or around timber to facilitate air ingress.

The Sashcraft Advanced Sealing System uses memory foam seals that are independently tested showing unrivalled thermal performance. Air permeability is significantly reduced keeping draughts out.

The low u-value of our conservation approved glazing greatly reduces the amount of heat loss through the glass.

As a whole, our service options contribute to a reduced u-value and a more energy efficient building.

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