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How Do Verge Trims, Sills, And Reveal Beads Work?

Verge trims, sills, and reveal beads are crucial parts of the external wall insulation system, creating a watertight envelope. Certain areas of your property are highly susceptible to water ingress and damp. Window reveals, corners, and window sills are the major stress points, and our products can help prevent them being issues. In this blog, we will discuss what verge trims, sills, and reveals are, and how they function as part of our EWI systems.

What is a verge trim?

A verge trim is a thin strip of metal or plastic that sits at the top of the wall where the insulation meets the roofline. The purpose is always the same; create a watertight seal on the roof profile. This prevents any moisture penetrating the external wall insulation system.

The inclusion of a verge trim is dependent on the width of the soffit. Soffit boards are the horizontal boards which fit under the roofline. Together with fascia boards or capping boards finish off the roofline in a weatherproof seal. When the soffit is wide enough, beading can be sufficient. The soffit requires a verge trim when it is not wide enough.

Verge trim install
15 degree slope on EWI Store trims

Due to the angle of the verge trim, as seen above, the water seamlessly wicks away from the roof profile. The trim is tucked behind the fascia board, with silicone sealant applied. The problem that arises with silicone sealant is the lifespan. It is not fully weatherproof, therefore it can disintegrate over time, compromising the watertight seal around the roof profile.

We also offer an Upstand trim.  Designed to be used in applications where you are fixing from above, such as the connection to a flat roof or where the upstand can slide up behind the fascia board. It is available in various different widths to house different thicknesses of insulation. The Upstand Verge Trim creates a completely waterproof seal without the need for silicone sealant or expanding foam tape, thus ensuring water falls away from the EWI system. Whilst more expensive, lead has the added benefit of being malleable, fitting around more roof profiles.

The perfect solution

The combination of trims and sealant is certainly effective, but the ideal solution is extending the roofline. We recommend this as a solution for gable walls where the tiles stop abruptly. The extended roofline is the completely waterproof solution for EWI systems, as the insulation boards can fit underneath; however, the cost of the procedure often dissuades people from installation. It can cost between £1,000-£1,500.

What sills do we offer?

The installation of an EWI system will usually add upwards of 100mm of thickness to the walls. This can present issues around windows, as it may extend beyond the existing window sills. The replacement of windows during the EWI system install is recommended for several reasons. Firstly, replacing the windows down the line will cause issues with the insulation. Secondly, the window sills can be pre-extended to accommodate the insulation boards.

The more cost effective solution is the installation of window sills. The simplest way to extend window sills is to install longer UPVC sills; the increased width will allow water to run off more effectively and not seep into the insulation below. The angle of the window sills is the same as our verge trims to facilitate the run off. Plastic UPVC is simple to match to existing plastic windows and sills. However, many pre 1930s properties have stone or tile sills. To match the existing façade, a combination of XPS and a mesh and concrete wrap is installed. This presents an incredibly strong, stable, and waterproof sill which can withstand the elements and is also load bearing.

Window sill extension
15 degree slope on EWI Store sills

Window beading in EWI

Beading is crucial to reinforcing stress points throughout the EWI system. Any corners or reveals are inherently weaker parts of construction. They also function as thermal bridges, affecting the thermal envelope. At EWI Store, we offer a diverse range of beading, as detailed below:

Window Reveal beadsThe bead makes contact with the frame of the window, resulting in a professional finish. The mesh attached to the bead runs along the window reveal, which prevents cracks forming. In addition, the rubber flap on the window reveal bead creates a weather-proof seal along the window frame and verge trim; moreover, the PVC composition has a longer lifespan than silicone sealant.

Window Head beadsWindow Head Drip Bead is used to the angle at the top of the window and door reveals. The bead helps the system to resist impacts and also prevents water ingress tracking back along the underside of the window reveal and back towards the window itself. This bead has 2 wings of mesh – both 100mm long, which integrates the bead into the EWI system.

Other beading

Corner beadsUsed for reinforcing 90-degree angles in the building structure. Corner beading is crucial for strength and clean lines around windows, corners and door frames. The corner bead is specifically designed to reduce and minimise the formation of cracks around openings. Mesh promotes durability in the corners of the construction.

Stop beadsDual purpose function in EWI systems; stop beads reinforce weak points, whilst also creating straight lines in the construction. This results in a professional finish.

Bellcast beadsOur Bellcast Bead has two purposes. The first is the bead helps create a clean, reinforced line where the render finishes. The second purpose is to help direct water away from where the render finishes at the bottom of the wall. The lip on the Bellcast Bead directs water away from the wall. Consequently, this ensures that water penetration is not an issue.

Arch beadsThe arch bead strengthens curved edges, also flexing to fit the profile of the curve. This provides a smooth and strong finish, and is the ideal bead for creating curves and arch forms for decorative plaster applications.

Movement beadsIntended for dividing up large expanses of render to ensure that the system remains stable and crack-resistant.

Window head bead
Corner bead

Final thoughts

Our range of verge trims, sills, and beading all contribute to waterproof your system at crucial stress points. They are an integral part of the whole system. If you need any advice regarding any of the components listed, call our sales team!

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