Cold roofs? Warm roofs?
Cold roof construction is the traditional method of building roofs both flat and sloped. It has been used by builders for years. It is easy to construct and far less expensive than construction of a warm roof. What does it involve? Cold roof construction, is what is found on most older flat roof buildings and almost all houses both old and new. A cold flat roof insulation requires more work, taking off old boards and replacing them and the roof surface. The thermal efficiency isn't as good as with warm roof insulation. A warm deck roof is much easier to install, offers great thermal performance but adds height to the flat roof.
How to file 2010 taxes online for free also makes it a more cost effective choice.
One issue to consider is if you have limited ceiling height as the insulation will reduce not only the height of the room, but may impede doors and windows opening too. Warm roofs tend to be more common with pitched roofs which feature a higher profile where this is less of an issue. An example of a Warm Roof set up. Cold roof insulation is placed between the floor joists meaning that there is little to no loss in height - although space for ventilation is required.
On a cold day the rafters would conduct some of the cold into rooms below known as thermal bridging meaning a lower overall house temperature.
This can be reduced at the floor level with a layer of insulation across the ceiling, this can lower the ceiling by 50mm but will stop thermal bridging.
A cold roof is easier to install at the build phase, trying to insulate between floor decking retrospectively can be both messy and time consuming.
An example of a Cold Roof set up. A warm roof is the easiest and most cost effective type of insulation and is an ideal choice for pitched roofs. For roofing insulationcheck out our range which includes insulation board and thermafleece.
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Government Support Guide. Health and Wellbeing. Branch Opening. Free delivery what does the page of swords mean selected areas. Warm Roof vs Cold Roof. Warm Roof A warm roof is where the insulation is attached to the floor decking and rafters, this makes it a quick and easy method, offering the most thermal protection.
An example of a Warm Roof set up Cold Roof Cold roof insulation is placed between the floor joists meaning that there is little to no loss in height - although space for ventilation is required. An example of a Cold Roof set up Warm Roof Vs Cold Roof A warm roof is the easiest and most cost effective type of insulation and is an ideal choice for pitched roofs.
Warm Roof Construction – requires that the entire roof construction is encapsulated within the insulation envelope of the building to be kept ‘warm’. The object being to design out the possibility of warm moisture laden air coming into contact with a cold surface and condensing. It is obvious that this cold roof space should be decoupled from the internal, conditioned building space. An airtight ceiling will prevent a flow of potentially moist air into this space, and insulation will minimise heat losses. Unvented roofs. Warm roofs, on the other hand, should be . Warm Deck/Roof – A warm deck/roof is where the insulation is placed on top of the rafters/joists and the roof covering is then placed over the insulation. No ventilation is required for these types.
They are often caused by:. Moist air from the living quarters can easily move upwards into the attic space through openings such as old-style downlights and become trapped there. If surface temperatures then drop below the dew point temperature, condensation will occur. Construction moisture can also be an issue. Wet timber that is closed in too early combined with an airtight roof space is a major concern. This problem often remains undetected, since visits to the roof space are rare.
The industry is aware of this phenomenon, and there are a number of strategies to reduce the risk. BRANZ has also covered this topic in science seminars on ventilation in , the Build article mentioned above and in the Design, science, build feature in Build Properly designed and well constructed, these roofs avoid condensation issues as the insulation layer is positioned outside the structure.
There is no cavity below the roof cladding that is exposed to the outside climate. However, fibreglass insulation pushed hard against the cladding does not constitute a warm roof. This practice is still found in some buildings but must be avoided at all costs. Clarifying the physics behind this should explain why. The assembly of metal cladding, roof underlay and wire mesh, mounted on top of the purlins creates a space above the insulation.
This space can be very large for normal truss roof spaces or a few millimetres deep in a skillion roof design see Figure 1. The space created in between the roof cladding and the insulation is more or less ventilated and exposed to the outside climate.
Consequently, this space will get cold when the outside temperature drops, only moderated by the heat loss through the ceiling insulation layer. If the surfaces get cold enough, condensation will form. In techspeak, we say that the condensing surface — the underside of the roof cladding — is not controlled.
Any condensation that may occur will need to be removed by ventilation. It is obvious that this cold roof space should be decoupled from the internal, conditioned building space. An airtight ceiling will prevent a flow of potentially moist air into this space, and insulation will minimise heat losses.
Warm roofs, on the other hand, should be regarded as unvented roofs. The design is such that condensation will not form on the underside of the roof cladding.
We say that the condensing surface is controlled, and this can be achieved in two ways:. The second method is uncommon in New Zealand, but it is important to understand that any air-permeable insulation product is not a suitable replacement. Moist air can easily flow through the insulation layer to reach the cold roof deck to form condensation in direct contact with the insulation, spelling trouble.
Skip to main content. Search the site Search. They are often caused by: not enough indoor ventilation in increasingly airtight new buildings see Build Airflow through ceilings pages 82—83 a ceiling that is permeable to this moist air a relatively airtight roof cavity.
This constitutes a dire threesome. A triple whammy Moist air from the living quarters can easily move upwards into the attic space through openings such as old-style downlights and become trapped there.
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