Roof Edge Aluminium Drip Trim – Internal Joiner

A flat roof is only as good as its weakest point, and on a drip trim run, that weak point is wherever two lengths of trim meet. If the joint is not properly connected, water finds its way behind the fascia, the timber softens, and before long you have got a repair bill that dwarfs the cost of doing it right in the first place.

Our aluminium drip trim internal joiner gives you a clean, tight splice between adjoining trim lengths. It slides inside the trim profile, keeps both lengths perfectly aligned and creates a weathertight connection that looks as good as a continuous run. Whether you are finishing a flat roof on a kitchen extension in Chelmsford, a garage conversion in Brentwood, or a commercial unit in East London, this joiner is the small detail that makes the whole drip trim system work.

Product Overview

This internal joiner is a short aluminium splice piece shaped to match the profile of our aluminium roof edge drip trim. It slides into the end of one trim length, the next length butts up against it, and the joiner bridges the gap internally, keeping both pieces aligned and providing a weathertight connection behind the visible face of the trim.

We stock the joiner in 14 sizes, from 75mm right up to 400mm, so you can match it exactly to the drip trim size you are using on the job. Each joiner can be ordered in mill finish or powder coated to any RAL colour to match the trim itself. At just a few pounds per piece, it is one of the cheapest components on the project, but one of the most important for getting a clean, lasting result.

Online Metal Store Ltd manufactures these joiners at our factory in Chelmsford, Essex, alongside the full drip trim system. Ordering the joiner and the trim together from the same supplier means the profiles match precisely, which is not always the case when you mix components from different manufacturers.

Key Benefits

Precise profile match

This joiner is manufactured to match the exact internal profile of our aluminium drip trim. It fits snugly inside the trim without any gap, wobble or misalignment. That precision matters because even a slight misalignment at the joint shows up as a visible step in the trim line, which looks poor and can trap water.

Watertight connection

The joiner bridges the inside of the joint, preventing water from tracking behind the trim face at the splice point. For an extra level of protection, run a bead of sealant along the joiner before sliding the second trim length into place. On exposed elevations or in areas with heavy rain, that sealant step is worth doing.

Maintains a clean, continuous line

From the ground, a well-installed drip trim should look like one continuous strip running the full length of the roof edge. The internal joiner makes that possible. It keeps the two trim lengths flush and level, so the joint virtually disappears. On domestic extensions and commercial buildings alike, that clean line is what separates a professional finish from a bodged one.

14 sizes from 75mm to 400mm

We stock the joiner in every size that matches our drip trim range: 75mm, 100mm, 125mm, 150mm, 175mm, 200mm, 225mm, 250mm, 275mm, 300mm, 325mm, 350mm, 375mm and 400mm. Whatever drip trim size is specified on your project, the matching joiner is available.

Powder coating in any RAL colour

If your drip trim is powder coated to a specific RAL colour, the joiner should be too. Even though the joiner sits inside the trim and is largely hidden, the visible edge of the splice can sometimes be seen at close range, particularly on lower roof lines. A colour-matched joiner eliminates any chance of a mismatched edge showing through.

Made in Chelmsford, shipped across the UK

We manufacture these joiners at our facility on Southend Road in Chelmsford, Essex, using the same production line as the drip trim itself. That means the profiles are a guaranteed match. Orders go out quickly across the country.

Technical Specifications

Material: High-grade aluminium

Type: Internal splice joiner for aluminium drip trim

Available Sizes: 75mm, 100mm, 125mm, 150mm, 175mm, 200mm, 225mm, 250mm, 275mm, 300mm, 325mm, 350mm, 375mm, 400mm

Finish Options: Mill finish as standard, or polyester powder coated (PPC) to any RAL colour

Compatible With: Online Metal Store Ltd aluminium roof edge drip trim system

Manufactured In: Chelmsford, Essex, United Kingdom

Custom Fabrication: Yes. Powder coated to order. Non-returnable unless faulty.

How to Install a Drip Trim Internal Joiner

Fitting the joiner is simple, but doing it neatly matters. Here is the process:

Fix the first length of drip trim to the roof edge in the normal way, using screws or appropriate fasteners into the timber substrate. Leave the end of the trim unfixed for the last 50mm or so, to give you room to slide the joiner in. Push the joiner into the open end of the first trim length until it sits roughly halfway in, so that an equal amount of the joiner extends beyond the end of the first trim.

For extra waterproofing, apply a bead of sealant along the top face of the joiner before fitting the second trim length. Our colour coded sealant is ideal for this, especially on powder coated joiners where a colour-matched seal gives the cleanest result. Slide the second trim length onto the exposed end of the joiner, butt it tightly against the first length (leaving a 2mm expansion gap if recommended for the run length) and fix it down. The joint should now be flush, level and weathertight.

On longer runs with multiple joints, repeat the process at each splice point. Keep the expansion gaps consistent and ensure the joiner is always centred across the joint so that both trim lengths get an equal amount of internal support.

Where Drip Trim Internal Joiners Are Used

Domestic flat roof extensions

The most common application by far. A kitchen extension, a side return, a garage roof. The flat roof edge needs a drip trim to direct water into the gutter, and unless the edge is shorter than 3 metres, you are going to need at least one joiner to connect the trim lengths. On a typical domestic extension with three exposed edges, that is usually three to six joiners depending on the roof dimensions.

Commercial flat roofs

On larger commercial buildings, flat roof perimeters can run to 50 metres or more. That means a lot of drip trim joints, and every one of them needs a proper internal joiner to keep the line straight and the connection weathertight. On these projects, ordering the full system together, including the drip trim, internal joiners, external corners and internal corners, ensures all the profiles match and the whole system goes together without any issues on site.

Garden rooms, offices and outbuildings

The garden room and home office market has grown enormously across the UK in the last few years. Most of these structures have flat roofs with aluminium drip trims at the perimeter. The internal joiner is an essential accessory for any run longer than a single trim length, which is most of them.

Refurbishment and re-roofing

When a flat roof is being re-covered with EPDM, single ply or felt, the old perimeter trims are usually replaced at the same time. The internal joiner ensures the new trim system goes in neatly and stays watertight. On these jobs, you may also need an aluminium termination bar at the upstand details and aluminium roof flashing where the roof meets the wall.

Frequently Asked Questions

What is a drip trim internal joiner used for?

A drip trim internal joiner is a short aluminium splice piece that connects two lengths of drip trim together. It slides inside the trim profile at the joint, keeping both lengths aligned and creating a weathertight connection. Without it, the joint between two trim lengths would be an open gap that allows water behind the fascia and creates a visible break in the trim line.

How do you join two drip trims together?

Slide the internal joiner halfway into the end of the first trim length. Apply a bead of sealant along the top face of the joiner for extra waterproofing. Then slide the second trim length onto the exposed end of the joiner and butt it against the first length, leaving a 2mm expansion gap if required. Fix both trim lengths to the timber substrate. The joiner bridges the gap internally and keeps the two pieces flush and level.

What size drip trim joiner do I need?

The joiner size must match the drip trim size. If you are using a 150mm drip trim, order the 150mm joiner. We stock joiners in 14 sizes from 75mm to 400mm, covering the full range of our drip trim system. If you are unsure which drip trim size is installed or specified, measure the visible front face of the trim and order the corresponding joiner.

Do drip trim joiners need sealant?

It is good practice to apply a bead of external-grade sealant along the top face of the joiner before fitting the second trim length. This adds an extra layer of waterproofing at the splice point. On sheltered elevations with light rain exposure, the joiner alone may be adequate, but on exposed sides of the building or in areas of heavy rainfall, sealant is strongly recommended.

Can drip trim joiners be powder coated?

Yes. We offer powder coating in any RAL colour. While the joiner is mostly hidden inside the trim, the visible edge of the splice can sometimes be seen at close range, especially on lower rooflines. A colour-matched joiner ensures no bare aluminium edge is visible at the joint.

Part of a Complete Drip Trim System

This internal joiner is one component in a complete aluminium drip trim system manufactured by Online Metal Store Ltd. The full system includes the drip trim in 3 metre lengths, internal joiners (this product), 90-degree external corners and 90-degree internal corners. Ordering all the components together from the same manufacturer guarantees that every profile matches precisely, which makes installation faster and the finished result cleaner.

The system is available in 14 sizes from 75mm to 400mm and can be powder coated to any RAL colour across all components. Whether you are specifying for a small domestic extension or a large commercial flat roof, the complete system is available from stock with fast UK-wide delivery.

Standards and Compliance

Our aluminium drip trim system, including this internal joiner, is manufactured from high-grade aluminium and powder coated with external-grade polyester paint for long-lasting durability. The system is suitable for use on flat roofs in accordance with BS 6229:2018 (flat roofs with continuously supported flexible waterproof coverings) and is compatible with EPDM, single ply, felt and liquid-applied membrane systems. For new-build projects, always check the relevant NHBC Standards chapter for guidance on acceptable perimeter trim details.