Flat roofs are commonly used on garages and extensions throughout the UK. They are trendy due to their open apex and affordable installation. However, these positives can quickly be reversed if proper ventilation requirements are not followed. This blog will discuss the importance of flat roof ventilation and how an insufficient ventilated roof can be a short trip to a roofing catastrophe.
Does a flat roof need ventilation?
Flat roofs are subject to extreme temperatures, which inevitably means they can incur damage over time. It is your job as a homeowner or roofer to maintain this temperature damage caused due to weather fluctuations within the country. This hot and cold weather will create expansion and contraction, leading to the progression of movement. Movement can very quickly rupture and expose weaknesses in your flat roof. Ventilation is the only way to stop the cascading issues arising from weather fluctuations.
A ventilated roof encourages a constant airflow to move around the roof, acting as a 'cooling' agent. This cooling effect stops the roof from rallying to such high temperatures and reduces the significant drop to the cooler winter months, thus reducing the chances of movement.
Another problem to consider with flat roof ventilation is condensation. The warm air rises and naturally collects beneath your home's roof, producing a thin layer of condensation. This can escalate to a significant issue like rot on your deck and roofing materials over time and even dripping down onto whatever is below it. Excellent ventilation helps protect the roof from your house-produced heat. You can vent the moisture and heat outside as they ensure a roof's temperature is like the air outdoors.
How much ventilation does your Flat Roof Need?
Ventilation is often optional on a warm roof because everything is compiled on top of the joists. On a cold roof, however, ventilation is very much needed. The amount of ventilation required for venting a cold roof is 25,000mm/ squared, which follows the British Standards BS5250. We will further explain on between cold and flat roofs below.
Warm flat roof vs Cold flat roof
In a cold flat roof, insulation is put between the rafters, and since the only thing between rafters is space, this is a relatively low-impact way to ventilate your roof. So why is it called a cold roof?
Although most of the ceiling below is well insulated, the roof structure (rafters) is uninsulated, meaning on a winter's day, the cold will pass through the rafters and into the gap beneath. Therefore, it is essential to ventilate every rafter gap. The reduction in height created by installing the insulation between the joists can often classify a cold roof as compared to a warm roof. Although the insulation between rafters consumes time during installation, the height reduction means that the cold roof is usually the predominant roof used in the area. Once the insulation is in position, you can install the decking on top of the joists and the waterproofing product of your choice.
The warm roof has insulation on the joists, forming a rise in the structure's height. The OSB will then be installed on top of the insulation. The warm deck roof is simple to install and offers higher thermal performance.
However, due to higher thermal performance, the underside of the insulation becomes warm. When household moisture gathers below and hits the insulation, it builds up condensation. A vapour barrier should be installed to tackle such issues. The vapour barrier will be installed on the underside of the insulation on top of the OSB board, wrapping all the sides of the insulation. It will act as a layer of protection between moisture and warmth. A warm roof is the preferred choice of roofers due to not having to cut the insulation to fit the rafter's gap, but rarely used due to height constraints.
Warm Roof vs Cold Roof - Key Points
Cold flat roof insulation requires more work, such as taking off old boards and replacing them and the roof surface. The thermal efficiency could be better with warm roof insulation.
A warm deck roof is much easier to install and offers excellent thermal performance but adds height to the flat roof. As a result of the height difference, warm roofs are not suitable for balconies and flat roof extensions with doors leading onto the roof. In these cases, a cold roof is preferable to warm roof insulation.
Which ventilation product is suitable for my flat roof?
As time moves on, more ventilation products make their way into the market, and it takes time to choose the right flat roof vent for your roof. General ventilation and extractor ventilation are the two ducts suitable for both types of roofs you have.
The ideal ventilation product is the Ubbink OFT 2 Flat Roof Breather Vent with an aluminium base and a hard-wearing plastic cap. This vent is short in structure, helping it to blend into its surroundings whilst packing a good level of breather capabilities.
For extractor ventilation, the Klober Flavent is perfect. The Klober flavent is made from hard-wearing black plastic with a connecting pipe reaching around 800mm below the roof structure. The long piping makes it easy for the roofer to attach the extractor fan ducting creating a seamless airflow.
JJ Roofing Supplies ensures our products are highly resilient and will not be damaged by adverse weather conditions or prolonged UV exposure. The vents and terminals are made from the highest quality source materials available in the industry, which guarantees that they will not crack, fade, or deform. As a result, you can rest assured that their joints can withstand extremes of hot and cold without any issues.
We offer a variety of high-quality roofing products across London and Hertfordshire. If you prefer looking at the material in person, click on the store locator and find the nearest store. Alternatively, you can message us at web.sales@jjroofing.co.uk or call 0333 700 1111.
