Casement Windows

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At North London Box Sash Windows, we take great pride in delivering a custom and personalised service to all our clients. Our team of experienced professionals work closely with you to comprehend your specific requirements and preferences. 

We ensure that we fully understand your needs so that we can provide you with replacement box sash windows, casement windows and external doors that meet all your expectations. 

We understand that every client has unique needs, and therefore, we offer a bespoke service to ensure that our windows fit seamlessly into your property's existing design. Our team ensures that your replacement windows and doors will not only look beautiful but also function efficiently. We use only high-quality materials to ensure that the windows last for a long time. 

If you need a quick quote for replacement box sash windows, our team is always ready to help. We understand that replacing windows can be a significant investment, which is why we provide transparent pricing that reflects the quality of our work. Our quick quote service allows you to receive an estimate quickly, without any obligation to proceed. This way, you can make an informed decision about whether our service is right for you. 

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Key Facts

As well as box sash windows we supply and fit new double glazed, casement windows.Our double glazed casement windows are manufactured to compliment and period single glazed traditional Victorian or Edwardian window. Fully focused on period heritage, each timber profile is meticulously designed to not only replicate the Victorian and Edwardian elegance, but to give the modern benefits of keeping your home warm and provide ultimate durability.

Our standard European Redwood casement windows have engineered timbers throughout, with a hardwood Meranti sill for ultimate durability. The casement sashes have a choice of either a multipoint locking system loaded on frictionless, easy clean hinges or a more traditional method of ball bearing butt hinges hinges with a stay and fastener for secure locking. The glass units are internally beaded as all glazing products should be, with a beautiful timber putty replicating sight line to the outside.

At North London Box Sash we supply our windows with the latest glass technology with accompanying products that surpass the UK’s standard building requirements. All windows are finished in our workshop with one of the worlds leading timber paints, with two undercoats and two finishing coats, new windows will repel even the harshest of weathering at any temperature. With a modern addition of draught proofing the Schlegel gaskets that are fitted to our windows keep out gales whilst also insulating

Key Facts

Double Glazed Casement Window in detail

Double Glazed Casement Window in detail

Engineered Timber

Engineered timber is purposely manufactured from smaller selected prime cuts, from knot free Syberian Larch. The timber sections are meticulously finger jointed and laminated together forming one solid piece of timber. This enhances strength, stability, durability, and also has the positive values of minimal shrinkage and expansion, there is also a 30% less wastage that occurs using large form stock timbers that have to be machined to size.

Stock timbers can have natural distortions like knots, warping, and hard grains, which can in time become visible. The window timbers we use are available in various grades, European Redwood that is our standard timber, good enough to withstand any hard weathering conditions. Meranti hardwood, a more dense timber for expectant exposure to extreme weathering, is also available for clients who desire supreme quality.

Key Features

Knot free
Low expansion and shrinkage, preventing seasonal movement
Stability, strength with no cracking
Anti-Fungus with water repellent treatments
Ethical and sustainable with minimal wastage

Engineered Timber


Our glass units are made up of four properties:

Ultra-Clear 4mm Float Glass
90% Argon Gas
Warm Edge Spacer
Warm Edge Spacer Ultra-Clear Low-E

What is Low-E Glass?

Low-emissivity glass (or low-e glass as it is commonly referred to) is a type of energy efficient glass, designed to prevent heat escaping out through your windows to the cold outdoors.

Low-E Glass

Improve Your Window
Energy Ratings

By installing our low-e windows glass units, you can significantly improve your window energy ratings and reduce the amount of energy lost through your windows by up to 75%!

Improve Your Window Energy Ratings


Heat always flows towards the cold, therefore window glass without a low-e coating will absorb the heat from your home and radiate it onto colder outside surface where it is lost. Low-e glass has a special coating which is an inactive radiator of heat, and does not allow heat to be transferred to the outsideInstead the low-e coating actually reflects the heat back into your room, this can eliminate internal condensation that can rest on cold surfaces like glass.Low- E glass also reduces ultraviolet ray penetration by 73% to help keep curtains, rugs and furniture from fading.

Key Features

Improves U-vales
Stops internal heat from escaping rooms
Reflects heat from radiators back into the room
Stops internal condensation
Allows external heat to enter the room
Reduces ultraviolet rays by 73%

Argon Gas

Low E glass comes as standard with argon gas (instead of air) between the panes to increase energy savings even more. Argon is colourless, odourless, non-corrosive, nontoxic and non-flammable. It’s known for its insulating qualities and provides 30% more resistance to thermal conductivity than air.

Argon Gas

Key Features

Improves U-vales
Enhances soundproofing characteristics
Minimizes heat exchange through the window
Reduces the possibility of condensation and frost
Can be used in all climates
Does not corrode window material unlike oxygen
Does not contaminate the environment; non-toxic gas

Warm Edge Spacer

When it comes to building sustainably, high-energy efficiency, durability, and indoor climate are key factors. To achieve this, thermally optimised edge bond solutions for insulating glass are what it takes. With our warm edge spacers between the glass panes, our technoform warm-edge spacer improves the thermal performance of theedge bond and thus guarantees gas tightness at a peak level.

The effects are not only minimised energy losses there is also a visible reduction in external condensation that can form at the edge of the window and thereby prevents the formation of mould. A warm edge spacer significantly reduces the circulation of air near the window that gives you better life quality inside your home.

Key Features

Increased thermal performance
Supreme bonding properties, guarantees gas tightness
Reduction in external condensation
Promotes mould reduction

Paint Finishing

All our windows come with four workshop applied coats of Teknos Aqua Top,Micro-Porous paint, two undercoats, two finishing coats with a standard colour ofRAL 9016, Traffic White. Our dedicated painters take every precaution to make sure every coat of paint is perfectly applied. We have an extensive colour range to match your requirements with over 200 RAL colours to choose from.

Combined Hardiness & Elasticity

Teknos coatings dry to a hard but elastic finish. They penetrate deeply into pores to form a protective, flexible shield, which resists cracking due to the natural movement of the wood and maintains surface integrity.

Hard yet flexible surface resists cracking (to the left: standard coating, to the right Teknos coating)


Quality Starts Well Below the Surface

Using state-of-the art technology, particle sizes of pigments and binders have been progressively reduced. The resulting improvements in flow, penetration and saturation have raised quality to new levels.

Teknos exterior and interior wood coatings stand for quality and environmental responsibility on every parameter.

Superior Adhesion

Teknos coating systems provide outstanding adhesion. Primers, intermediates and topcoats are all formulated on a selection of compatible, premium quality binders, creating a high degree of synergy in the final coating system.

The optimal protection and adhesion achieved thorough formulation technology that enables nano particles to penetrate deeply into the wood.

Impregnation and wood preservative fluid contains actives that penetrate the woodFluid evaporates but actives remain to protect the wood against fungus and decay.

Quality Starts Well Below the SurfaceSuperior Adhesion

Excellent Stain Locking

Specially developed products ensure excellent result on all timber species typically used in exterior joinery; resisting extractive staining on hardwoods and minimising discolouration from softwood knots. These water based anti-bleeding and knot sealer products lock in extractives, significantly reducing opaque topcoat discolouration.

High Water-Vapour Permeability

Teknos coatings also allow wood to breathe; essential for keeping windows and doors in top condition. Teknos micro porous coating systems allow moisture vapour to pass through, allowing the timber moisture content to maintain equilibrium though the seasons and reduce the risk of moisture accumulating in the wood, eventually causing blue stain or decay. Water is repelled while moisture is allowed to escape.

Effective protection of wood and colour against UV radiation

Thanks to light-fast pigments Teknos protective coatings colours do not turn yellow or fade for many years. Wood does not turn grey or become rough.

Key Features

Combined hardness and elasticity
Superior adhesion
Excellent stain locking

High water-vapour permeability
Effective protection of wood and
colour against UV radiation

Excellent Stain Locking

Draught Proofing

Common casement draught proofing may have exposed brushes or stuck on surface mounted rubber tape, along with being unsightly these can have poor function. At North London Box Sash all our windows come fully installed withSchlegel gaskets, a hardwearing durable draught proofing gasket with supreme capabilities including soundproofing and insulation

Key Features

Leading technology gaskets
Durable materials
Compliments effortless operation.



Choice of Finishes

Satin Chrome
Polished Brass
Polished Chrome
Antique Brass.

Operating Handles

Traditional Style
Modern Style

Multi-Point Locking System

Exceptional Security
• Easy-Clean, Frictionless Hinges
• Compliments Effortless Operation.
• Choice of Traditional or Modern operating master handle.

Installation Process

• Our fitters will arrive on site for 8:00am.
• Teams will start on the top floors and work down, but can start alternative rooms at clients request.
• Standing objects will be covered in each room with light-weight plastic non dust penetrating sheeting. Floors covered with heavy-duty dust proof and water proof sheeting, an additional hard surface membrane laid down on direct working areas.Foot traffic cover throughout your home, covered by either stick down carpet protector or dust sheeting.
• Removal of existing casement frames and openers, all stored externally in a safe area, if there are no safe areas all refuse will be taken of site immediately.Installations that are book for one day, refuse will be removed same day regardless.
• Your new casement windows to be supplied & fitted.
• If required, new internal 70mm OG architraves will be fitted with bullnose.
• All surrounding interior plasterwork will be made good where required, and plastered ready for finishing and painting.
• New windows will be externally re-pointed using the traditional sand & cement method or, low modulus mastic applied to the external perimeter of the window.
• All work areas will be fully cleaned and vacuumed each evening.
• All glass and work areas will be fully cleaned internal and external on completion, gutters cleaned and debris removed externally on ground floors.
• All rubbish will be removed from site on completion.
• Our fitters will check with the client to see if they are 100% satisfied with the installation and cleanliness.
• Your final invoice will be issued of the remaining 50%
• FENSA will be informed of your installation and a certificate with the details of your project will be sent via post.

Guaranteed Excellence

Our Guarantee

Our standard double glazed casement windows come with a 7-year guarantee.

What’s Covered?

• Timber fermenting
• Paint, internal and external
• Glass, internal unit misting, cracks

• Draught proofing seals
• Ironmongery
• Workmanship

Over 30 Years of
Knowledge & Experience
Fully Accredited
Individually Hand-Crafted Windows & Doors
Every Detail of Existing Windows Can Be Replicated
Free Home
Surveys & Quotation
Full 7-Year
Comprehensive Guarantee 
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