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What is a cold roof and how does it work?

12th July 2021

What is a cold roof?

A cold roof is one of a couple of different roof construction options for houses in order to insulate them effectively. Also sometimes referred to as a cold deck roof, it’s a roof where the insulation sits directly on top of the ceiling plasterboard, usually nestled between the floor rafters. The rest of the roof is then constructed above it, including the decking and roof membrane. Sometimes a thin layer of insulation is also added below the rafters on top of the plasterboard, but generally it sits snugly in between. A 50mm (minimum) gap is required above the insulation before the rest of the roof goes on in order to ensure that there’s enough ventilation so that condensation doesn’t build up. Cold roof systems are more popular in colder areas, as they help to prevent unwanted leaks or damage, especially when snow or ice are regular occurrences.

How does a cold roof work?

A cold roof offers a house good insulation, meaning that the rooms below it stay warmer than the space above. Warm or damp air is able to rise up through the ceiling and above into the ventilation space within the roof and circulate out as opposed to causing condensation. This ventilation space is incredibly important for a cold deck roof as otherwise when the warm air passes through and changes temperature, if it can’t escape it produces water droplets which can then cause damage to your ceiling. This is why a minimum 50mm gap is recommended above the insulation to allow for this air circulation.

What are the main benefits of a cold roof?

Although a cold deck roof can require more work to install than a warm roof (if applying to an existing house), there are lots of benefits to considering this type of roof, including:
• You’re utilising otherwise wasted space between the rafters.
• It doesn’t impact the height of the building, so can be convenient when considering door thresholds etc.
• It’s really easy to install in new builds and is widely popular.
• It’s cheaper than a warm roof.

Cold roof systems and cold weather

Another considerable benefit of cold roof construction is that it’s a great choice if you live in a colder climate where there may be frequent snow or ice during the winter. As the air above the insulation is cooler than the rooms below, it means that snow doesn’t settle on the roof and immediately begin to melt like it would on a warm roof system. By taking longer to melt, it means that there’s less of a chance of ice dams occurring along the edge of the roof. Ice dams cause additional pressure on the roof’s core structure and can mean leaks or damage equalling expensive repairs. Cold roof construction can also reduce humidity and moisture-related issues, meaning fewer potential problems with damp inside your home.
If you’re looking for the materials in order to build a cold roof, here at Frost Drainage we supply everything you’ll need to ensure that the drainage is in tip-top condition and lasts over time. If you have any questions about our roof or floor drains, please get in contact.

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