Technical Details: An Architect’s Guide to Hidden Gutters and Building Corners
Emma Walshaw is the founder of First In Architecture and The Detail Library, and has written a number of books aiming to facilitate a better understanding of construction and detailing. Contributions by Aida Rodriguez-Vega, architect and researcher at the Detail Library.
It is becoming increasingly popular to create a solid building volume by using cladding materials for both the roof and the façades. When doing so, a key junction to consider is the eaves — that is, where the wall meets the roof. Traditionally this would have an overhang and gutters. To avoid the common look of visible gutters (as an addition to a building rather than a thought through design element), hidden gutters are becoming an integral part of architectural design. Hidden gutters, if detailed correctly, can be extremely functional.
When using cladding materials across the entire building, another important junction are the corners of the building. Depending on the material chosen, location, use of the building, a detail should be chosen which is robust, weather tight and frames the entire building. This article offers key insights into detailing hidden gutters and buildings corners in a variety of materials, including timber, zinc and tile.
Four Key Design Considerations When Detailing Hidden Gutters:
1. Roof Pitch
The angle at which the roof pitch is designed is key in deciding if a hidden gutter is suitable. Too steep and the rain can struggle to run off into gutters, too shallow and some materials may not help drain water into gutters.
2. Roof Drainage Calculation
The size and number of rainwater downpipes required will depend on a number of factors. It is key to undertake a rainwater calculation on your roof before designing hidden gutters. Most manufacturers provide this service. The calculation is based on the area of the roof, slope, materiality, location, safety factor and BS EN12056:2000 requirements amongst possible others.
With this information the flow rate of roof, diameter and frequency required for the outlets can be calculated.
3. What to Do With the Downpipe?
Once a hidden gutter has been detailed, there are three main was of detailing any downpipes required.
I. Adding a visible hopper and downpipe to the façade.
II. Integrating a downpipe into the cladding zone so that it is outside but not visible externally.
III. Integrating the downpipe internally.
4. Access to Downpipes
It is very important, especially in option 2 and 3 that the downpipe has suitable access for maintenance, including leaf clearing and possible leaks. For internal pipework, it is especially necessary to consider thermal bridging, sounds transfer and that more internal space will be used up with the boxing out of pipework.
Detailing Timber Corners
The most important design considerations when detailing timber corners is that there are enough support battens for the cladding, as well as leaving movement joints throughout the cladding and corners to allow for movement. Timber cladding should always have continuous ventilation gap behind to prevent moisture buildup.
There are a huge range of timber corner details that can either be bought pre-formed or cut to size on site. Additionally, other timber sections can be used such as solid timber corners, which create a more framed and robust edge.
Detailing Hidden Gutters in Timber Cladding
Due to the versatility of timber and ease of adaptability on site, timber cladding can be one of the easiest façades to use when integrating hidden gutters. Within timber cladding, downpipes can be designed externally and internally. It is also relatively easy to design downpipes into the cladding zone, just as making an area of timber cladding removable is an easy way to allow for maintenance of the down pipe.
Depending on how much flashing you want visible and how robust you require the detail to be, there are a number of options when detailing timber cladding and hidden gutters. For a more robust option, a bespoke gutter can be installed with the suitable dimensions according to the drainage needed. This should have continuous flashing with a drip detail which drapes over the façade timber cladding. Breather membranes should always be draped into the gutter to allow for any water infiltration into the cavity to drain away from the building.
A less robust option is to clad timber over the gutter. The junction between the gutter and timber can be weak and it is therefore key to seal the junction in accordance with the roofing / cladding manufacturers’ recommendations.
Detailing Zinc Corners
When detailing vertical and horizontal standing seam zinc panels, there are a huge range of corner options to choose from. An important consideration when picking the corner design is the proximity to people passing.
If the corner is in an area of high foot traffic, it is desirable to have a folded option so that it is not affected by any knocks from people walking past. If the corner is away from where people have access, a more decorative option can be selected to enhance the edge of the building. It is also important to consider how this corner detail will work with the window surrounds and general standing seam details.
Detailing Hidden Gutters in Zinc Cladding
Most zinc manufacturers can provide generic details for hidden gutters and even calculate the roof drainage requirements. The width, depth and slope of gutters will vary from project to project depending on circumstance such as location and roof pitch.
A key considerations when detailing zinc hidden gutters is maintaining the ventilation throughout — from the base of the cladding to the highest most point. Zinc cladding is normally built over a plywood base and requires ventilation behind. As the gutter and cladding are made from the same material, zinc creates excellent continuity between façade and roof.
Detailing Clay Tile Corners
If detailed correctly, corners to clay tiled buildings can be very elegant. There are a number of options for corners, including using a solid timber corner. Options such as bespoke corner tiles, or painted galvanized steel 45° and 90° angles are more popular options.
Galvanized steel can be factory painted to match the clay tiles and window surrounds and provide a robust corner to set out the tiles from and avoid the edges becoming damaged.
Detailing Hidden Gutters in Clay Tiled Cladding
It is harder to adapt clay tiles to hidden gutters due to the difficulty in cutting clay and need for flashing. There are a number of options when detailing clay tile cladding and hidden gutters depending on how much flashing you want visible and how robust you require the detail to be.
It is not recommended to take rainwater pipes internally due to the need for suitable thermal and sound insulation whilst creating access for regular maintenance. If this option is chosen, care must be taken so that pipes do not clash with structure whilst maintaining an adequate slope to allow water to drain properly.
If you want more inspiration on hidden gutters, styles and applications, be sure to follow Detail Library on Pinterest where we have hundreds of modern hidden gutters and rainwater, and roof ideas!
There are plenty of resources to help in choosing and how to detail hidden and visible gutters for each specific project. Below is a small selection of links.
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