This isn't a generic folded box gutter. It's a complete external rainwater system made up of matching gutters, brackets, outlets, angles, stop ends and 100mm downpipes.
The gutter itself measures approximately 120mm wide × 75mm deep and comes in 3m lengths. That gives the system a noticeably squarer appearance than conventional half-round guttering and makes it particularly well suited to contemporary homes, extensions, garden buildings and commercial projects.
The system is manufactured by Zambelli, a German rainwater specialist, and the range includes natural galvanised steel alongside black and anthracite-coated finishes.
If you prefer a more traditional curved profile, have a look at our wider galvanised steel guttering range instead.
Galvanised, Black Or Anthracite?
The profile stays the same, but the finish changes the look quite a lot.
Natural galvanised steel box guttering has the familiar metallic appearance of exposed galvanised steel and works particularly well on industrial-style buildings, timber structures and projects where the metal itself is part of the design.
Black gives the gutter a stronger traditional contrast against brick, render and lighter fascias.
RAL 7016 Anthracite Grey is normally the one we'd look at for contemporary projects, especially where the property already has anthracite windows, doors or cladding.
If you're trying to colour-match other exterior products, check the actual finish before ordering rather than relying entirely on how it appears on a screen.
How Much Water Can The System Handle?
One of the reasons people choose a 120mm steel box gutter is capacity.
With one 100mm downpipe, the system has a published flow capacity of approximately 3.2 litres per second. When correctly configured with two 100mm downpipes, that increases to approximately 6.4 litres per second.
That doesn't mean every roof automatically needs two outlets.
The correct arrangement depends on the roof area, pitch, outlet position and how the gutter run is laid out. A large gutter still needs enough downpipe capacity to actually move the water away.
For a straightforward house or extension, one outlet may be perfectly suitable. For a large or complicated roof, don't guess. Send the roof dimensions or drawings to Trade Warehouse and we can help you work through the basic layout before you order.
Why The 100mm Downpipe Matters
The box gutter is designed around a 100mm steel downpipe.
That's a useful point to know before you buy because this isn't one of those systems where a large gutter narrows immediately into a tiny pipe below.
The matching downpipe range includes bends, offsets, clips and shoes, allowing you to continue the steel system down the building rather than mixing materials halfway through the installation.
How Does The Dry-Joint System Work?
This is where the Zambelli system is really handy.
Standard gutter lengths are joined using a purpose-made union with a rubber sealing element. The two gutter ends are brought together with the required movement gap, then the connector locks around the joint.
So, unlike some metal guttering systems, you don't need to run silicone along every standard gutter connection.
It's cleaner, quicker and considerably less messy. Don't interpret “dry jointed” as meaning the joint doesn't need a seal. The rubber sealing component is an important part of the connector and needs to be installed correctly.
Can The Gutter Be Cut On Site?
Yes. The 3m lengths can be cut where required, which is useful when the final section of a run doesn't work out to an exact full length.
Use suitable metal-cutting equipment and deal with the cut edge in line with the system requirements, particularly on coated black or anthracite products.
Always measure the complete run first. It's much easier to work out where your outlets, corners and final cuts will land before you start cutting expensive gutter lengths.
Wrap-Around Or Prefabricated Outlet?
There are two useful ways of getting from the gutter into the 100mm downpipe.
Wrap-Around Outlet
A wrap-around outlet gives you more flexibility over where the downpipe sits.
You position the outlet on the gutter run, create the opening in the gutter and fit the outlet around it. That's particularly handy when the downpipe position is dictated by windows, doors or drainage below.
Prefabricated Outlet
A prefabricated outlet section removes some of that work on site because the outlet detail is already formed as part of the section.
If you're building a straightforward new system and know exactly where the downpipe needs to sit, this can make the installation quicker.
Neither is automatically the “better” option. It really comes down to how much flexibility you need when positioning the downpipe.
Which Stop End Do I Need?
You've got a similar choice at the end of a gutter run. Loose stop ends are useful when you're working with standard gutter lengths and want to finish the run yourself. There are also prefabricated stop-end sections where the end detail is already incorporated into a shorter gutter section. These can be particularly handy when you want a tidy factory-prepared finish without fitting the stop end separately on site.
Just remember that stop ends are handed, so check whether you need the left-hand or right-hand version when looking at the gutter from the front.
Build The Complete Steel Rainwater System
A proper steel box guttering installation normally needs more than a few straight gutter lengths.
Depending on the roof layout, the system can include:
- 3m gutter lengths and fascia brackets
- union connectors and rubber seals
- left and right stop ends
- prefabricated stop-end sections
- internal and external corners
- wrap-around or prefabricated 100mm outlets
- 100mm steel downpipes, bends, clips and shoes
Keeping everything within the same compatible system means the profiles, joints and fittings are designed to work together.
It also avoids one of the most common problems with metal rainwater goods: buying a component from another manufacturer because it is described as “120mm” and then discovering that the actual profile or joint detail doesn't match.
Is This An External Or Concealed Box Gutter?
This is worth clearing up because “box gutter” can mean two quite different things.
The products on this page form an external fascia-mounted 120 × 75mm steel gutter system. The gutter remains visible along the roof edge, just like conventional half-round guttering.
It is not a concealed internal gutter built into a roof valley, behind a parapet or between two roof slopes.
If an architect's drawing shows a hidden fabricated gutter inside the roof construction, this isn't automatically the correct product.
For that sort of detail, send the drawing across before ordering.
Steel Box Guttering Or Aluminium Box Guttering?
Both give you the same kind of straight-lined architectural look, but they're different systems.
Steel offers a robust metal rainwater system at a very competitive price, with the Zambelli dry-joint connectors making installation refreshingly straightforward.
Aluminium gives you a different material choice and can be particularly useful where a powder-coated architectural rainwater system has already been specified.
If you're still deciding between the two, browse our aluminium box guttering alongside the steel range before committing.
Why Buy Steel Box Guttering From Trade Warehouse?
The big advantage here is that you can buy the whole system together rather than trying to piece it together one fitting at a time.
We supply the gutter lengths, unions, brackets, stop ends, corners, outlets and matching 100mm pipework, with next working day delivery available across stocked products when ordered before the 11:30am cut-off.
Working from drawings? Send them over. Trade Warehouse can help identify the main components and quantities before you place the order.
Steel Box Guttering FAQs
Can Zambelli Box Gutter Components Be Mixed With Another Manufacturer's System?
We wouldn't assume so.
Two manufacturers can both describe a gutter as 120mm while using slightly different profiles, bead shapes, unions or fitting dimensions. Where possible, keep the gutters and fittings within the same compatible system.
Does Steel Box Guttering Need A Fall?
Yes. The gutter needs to direct water towards the outlet rather than sitting completely flat.
Plan the outlet position and fall before fitting the brackets, and follow the installation guidance for the system rather than setting the brackets by eye.
Can I Replace Just One Damaged Section?
Usually, yes, provided the existing gutter is the same compatible Zambelli profile.
Check the profile, size, finish and joint arrangement before ordering a replacement length. If you're not sure what is already installed, send us a clear photograph of the gutter end and union.
Can Steel Box Guttering Be Used On Sheds And Garden Buildings?
Yes. The clean box profile works particularly well on modern garden rooms, workshops, sheds and timber buildings as well as houses and commercial properties.
The important thing is making sure the fascia or supporting structure is suitable for the brackets and the roof drainage is sized correctly.
Can The 100mm Downpipe Connect Into Underground Drainage?
Yes, although you may need the correct adaptor or drainage fitting at ground level depending on the underground system being used.
Don't force the metal pipe directly into an incompatible plastic fitting. Plan the transition properly so the connection remains secure and water can discharge freely.
What Happens If The Coating Gets Scratched During Installation?
Small areas of damage should be dealt with rather than left exposed.
On coated black or anthracite products, use the appropriate compatible repair coating for the system. Taking a little care when cutting and handling the gutter lengths will also help avoid unnecessary damage in the first place.
Is Steel Box Guttering Suitable For Replacement Projects?
Yes, but measure the existing system carefully before ordering.
Check the gutter width and depth, downpipe diameter, bracket arrangement and any corners or outlets already in place. Older box gutter systems are not necessarily interchangeable just because they look similar from ground level.
