IntroductionFitting a warm-roof without a doubt the best way to keep your heat in, your bills down and your property nice and warm. Insulation has always been a confusing subject to explain to people, it's one of those unseen functions in a building that can easily be misunderstood and is very difficult to measure.
A warm roof is basically a roof that does not have a concealed cold space above the insulation line such as a typical loft in a house does.
A warm roof is a solid slab of insulation (Very similar to a polystyrene type material) which sits on top of the rafters of a pitched or flat roof and is positioned directly underneath the waterproofing layer. No cold area in any cavity or loft space will be present.
Warm roofs were introduced because they do not need ventilation to carry away any condensation or moisture build up that always escapes up into the roof spaces.
Instead of packing insulation between the roof timbers and hoping you managed to reach everywhere, the warm roof is built to create one continuous slab of insulation over the entire roof surface ensuring no gaps and no heat escapes anywhere.
Reducing Your Carbon FootprintAs well as keeping in the heat and saving yourself some money, it's nice to know that we are also doing our part to keep down the carbon footprint we create when burning fossil fuels to heat our homes.
This table from the Which? Website shows the savings in both money and CO2 that can be made by insulating a typical loft. (Note the payback time in orange at the end of each house type).
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VentilationA warm roof is designed for use without the need of ventilation to remove unwanted moisture and condensation in tight spaces.
Imagine a typical loft with a triangular roof construction. These spaces would normally have wool type insulation laid on top of the ceiling which prevents heat from escaping the warm rooms beneath.
The air above that wool layer is called a cold-roof space because the air above and the back of the roof is cold.
With any type of roof configured this way, some heat will always pass through the materials of the ceiling and the insulation, and meet cold air dropping in from above and become trapped in the cold space above the wool blanket.
Without adequate ventilation, this moisture can build up and in some cases where it can't escape through gaps or drafts, a microsystem will develop and condensation can form in huge amounts causing stains and damp in the roofspace.
In the most extreme cases, rot can develop and if the conditions are warm with moisture, more serious wet and dry rot can set in.
Dry rot is a disease that will then spread and the spores travel through the air and consume any other healthy timber in the vicinity. It's a very serious and costly problem to repair.
That's the worst case scenario, but illustrates the need for either adequate ventilation or a warm roof which doesn't need ventilating.
What is the difference between a warm and cold roof?
Why doesn't a warm roof need ventilation?
The exact point where the hot air rising meets the cold air falling and forms moisture is called the dewpoint. Its a bit like a single glazed window that is covered in moisture when its cold outside and you have the fire on. (The glass is the dewpoint)
The moisture will normally form on the back of a surface and when that surface is hidden in the depths of your roof structure, you're unaware of the problem until it's often too late.
With a warm roof, the dewpoint is directly in the centre of a slab of insulation which prevents the cold and warm air from meeting at all, therefore no moisture or condensation is formed and no ventilation is required.
A warm roof is also more effective in keeping in the heat as its one continuos slab of insulation whereas a cold roof is bits of insulation tucked in between joists and rafters - gaps are inevitable.
The waterproofing layer of the roof is then laid directly on top of the insulation slab either with a new deck, or in some cases it can be glued directly to the insulation boards.