Ventilation for flat roofs insulation kingspan great. For that reason, cold flat roof construction needs to keep in mind the need for unblocked airflow. It is usually the most acceptable type of construction for domestic possessions and belongings as it avoids the need for aeration of the roof construction. Systems may be used at a greater pitch where they meet the requirements of this chapter, and materials are adequately held in place. Roofs can be designed and constructed to be either vented or unvented in any hygrothermal zone.
Flat roofs known for being stylish, modern, and efficienthit a lot of items on your home bucket list. Nov 11, 2016 the recognised flat roof build ups for best design practices are. The recognised flat roof build ups for best design practices are. The insulation is below the deck, but above the plasterboard. Unvented flat roofs 475 high performance building supply.
The vapour control layer is above the decking but below the insulation. There is nothing wrong with cold roof construction as long as it is correctly constructed and insulated and adequate ventilation is provided. A great and strong roof ensures no trouble during rain and strong winds for the residents. In most flat roofed homes, heated spaces are situated directly under the roof, without any buffer from an unheated attic.
Depending on your roofs climate, picking the right roof type is important. A warm roof is much more straightforward to install and provides a superior thermal performance and is therefore more costly. But they also come with a reputation for leaks, cracks, and collapse. Generally, roofers discourage this method for cold climates because it can promote condensation and requires ventilating the roof, which may be difficult to do in small or tight spaces. A vapour control layer must be used below the insulation. Interactions on a flat roof construction blue colour moisture. Warm flat roof vs cold flat roof designs jtc roofing. This is to minimise any risk of harmful condensation. When constructing a cold flat roof, the thermal insulation layer is positioned underneath the structural decking.
In case of warm roofs they have an insulation above the roof deck, in this way it keeps the deck warm. The requirement for roof void ventilation in cold roofing designs means it is generally not recommended as a design for new build flat roofs. The major difference between the warm flat roof and the cold flat roof has to do with the air flow between the roofing timbers known as joists that help to hold up the roof. A cold roof places the insulation between the rafters, underneath the ply roof covering.
A guide to constructing a flat roofing system roof stores. Warm roof construction is the easiest method and is often cheaper. A cold roof design usually leaves a 50mm gap between the top of the insulation, and the roof deck above. In flat roof construction there are two main differences warm roof and cold roof. Flat roof construction how to build a flat roof flat roof. In flat roof construction thermal insulation can be placed above and below the structural roof deck or waterproofing layer. Flat roof constructions are generally classed as either cold or warm roofs depending on the position of the thermal insulation.
Flat roof design considerations flat roof construction. In a warm roof construction the principal thermal insulation layer is located above the structural decking, resulting in the structural deck and support structure being at a temperature close to that of the interior of the building. However, cold roof insulation on an existing flat roof system is anything but simple. Cold roof construction is probably the most commonly known type of flat roof, however most new builds are opting now for warm roof construction, primarily because the insulation value is greater. In the warm flat roof construction, there is insulation packed into every possible space where air can flow. The term cold roof refers to traditional roofs in which insulation is placed in the ceiling of the home, so it is underneath the attic space, which is not conditioned. A warm flat roof may require anywhere from 120 to 200mm of insulation on top of the roof.
The choice of construction theoretically rests on two different methods of handling moist air. Guidance flat roof condensation building regulations 4. Flat roofs there are two common forms of construction for flat roofs. Unvented flat roofs a technical discussion flat roofs have often been built with the insulation all on top of the vapor closed drainage plane as this avoids dew point condensation issues inboard of the roofing. This video shows the key features of a flat roof cold deck construction and how to draw the details to a scale of 1. Condensation within a flat roof mainly occurs during cold weather when moisture vapour in the air which has been generated within the heated building rises from the room below into the cold roof void above the ceiling. I link to two other videos one on warm flat roof construction and one thats a in depth comparison between cold and warm flat roofs also showing. In this case ventilation is required and the roof can still become wet with condensation which may cause materials to decay. The incidence of direct or diffused sunlight short wave irradiation on a flat roof surface is very important in helping to dry out the construction to the inside. In cold and very cold climate zones where there is likely snow accumulation on roof surfaces, there is also the likelihood of icedamming. In order to control icedamming, heat flow form the interior to the roof cladding must be minimized. Cold roofs are typically characterized by the ability for outside air to freely flow under your roof s sheathing. Cold roof construction is a more expensive and timeconsuming method of building a flat roof for an extension project. Jul 11, 2014 part 2 of this four part guide to roof construction covers pitched roof tiles, basic pitched roof designs, cold and warm pitched roofs and pitched roof construction.
Flat roof constructions insulation kingspan great britain. Types of flat roof construction warm and cold flat roofs. Domestic roof construction is the framing and roof covering which is found on most detached houses in cold and temperate climates. A waterproof exterior layer is essential and there are a number of options including bitumen based felt or asphalt, epdm rubber and pvc based systems, as well as cold, applied liquid systems bitumen coverings. From there, the flat roof system you choose will determine the materials you apply. The insulation material is placed immediately above the ceiling between the rafters. Apr 01, 2019 make sure your comply with flat roof building regulations. Other flat roof construction details often refer to the types of flat roof coverings. In the case of cold roofs, the residential flat roofs have the waterproof placed directly on the deck, and any insulation would be placed above the ceiling. This cold deck construction is considered problematic in the humid, temperate climate of the uk where the effective. The insulation is immediately below the waterproofing layer. Although simple and utilitarian, the main goal of a roof system is to maintain the watertight integrity of a building and keep its contents dry. So it makes the job entirely more complex and increases the timescale of the project extensively. In traditional flat roof construction, it is prevented from penetrating the roof fabric from the building below through the use of a vapour.
Flat roof construction how to build a flat roof flat. However in many situations the insulation may need to be primarily or entirely below the flat roof membrane and between the roof joists if so, what are the best options. There are three recognised designs of flat roof construction. Part 2 of this four part guide to roof construction covers pitched roof tiles, basic pitched roof designs, cold and warm pitched roofs and pitched roof construction. Then there must be ventilation between the deck and the insulation traditionally a generic mineral wool to prevent moisture vapour. The 3 most common materials used for flat roof construction.
In general, the installation of a cold roof is not recommended for the construction of new properties. A cold flat roof is one where the insulation is between or between and below the. In a cold roof installation, the insulation is placed below the roof rafters. Hopefully this video will help explain the difference between cold flat roof construction and warm flat roof construction, this videos show detailed drawings how a cold flat roof is constructed. Part of the successful design of a flat roof is in preventing such a condition from occurring. We investigate the different types of flat roof construction. How to design a flat roof that wont leak architizer journal. There are three different types of flat roof construction. Builtup roofs have solved the low pitch roof problem for ages, a challenge that asphalt shingles could never handle builtup roofs are installed using several layers of a special type of roofing felt that has been asphalt impregnated and embedded in bitumen applied with a hot mop. As such, they allow for outdoor living gardens or a living space on top. In a cold roof construction, the sikatrocal membrane is installed directly to the structural decking usually timber. The cold roof is very similar to traditional ventilated roofs in the sense that air is allowed to enter the eaves of the roof through a vent. Whats the difference between a warm roof and a cold roof. The insulation sits between the joists of the roof structure, on top of the interior ceiling and a vapour or moisture barrier with gap of 50mm minimum created between the insulation and the underside of the roof deck.
There should be no insulation below the deck and no ventilation is required. In a cold weather, such roofs are inherently prone to condensation, which can cause material decay and deterioration. Cold roof construction requires that a suitable ventilated air space exists above the insulation layer, within which the air is constantly mobile, being replenished by fresh incoming air, whilst the air resident within the void space is being expelled via a natural vent action at another point. Roof stores stock a range of klober flat roof ventilation solutions designed specifically to meet the criteria above. A warm roof is one in which the insulation layer is laid on top of roof structure or above the loft or attic space in the case of pitched roofs so that. In these days of energy preservation, a roof can also contribute to preventing warmth being lost from a building. How to ventilate your flat roofing system roof stores. In the case of a flat roof, insulation is usually either a rigid board above the deck, or a mineral glasswool quilt immediately above the underdrawn ceiling, depending on the type of roof design and construction.
Warm roof in a warm roof construction the principal thermal insulation layer is located above the structural decking, resulting in the structural deck and support structure being at a temperature close to that of the interior of the building. Warm flat roof insulation solutions flat roof build ups. The incidence of direct or diffused sunlight short wave irradiation on a flat roof surface is very important in helping to dry out the construction. It requires the existing roof surface to be ripped up so that the insulation can be laid in between, before a new roof surface is then placed over the top. Cold roof designing buildings wiki share your construction industry knowledge. A flat roof cannot be used for long spans without using columns and beams. Hot roofs tend to have insulation very close to the roof sheathing and are typically closed off to a fresh airflow. The air travels up the roof pitch and exits at the roof peak. Well, a cold roof is created by laying insulation between the rafters. Flat roof construction can come in the form of a warm roof or cold roof depending on the requirement of the owner and architect as they relate to the building regulations regarding heat loss and insulation. Todays variety of flat or low slope commercial roofing options roof pitches ranging from 12 to 3. Consider geography, budget and use for the roof to determine the best option. Cold deck flat roof construction, repair and replacement. A cold flat roof is one where the insulation is between or between and below the roof joists.
Sometimes the excitement of starting a new construction project or building venture can lead you to forget about the finer details such as planning permission and local building regulations. Everything you need to know about flat roofs, from. In a cold roof construction, the sarnafil membrane is installed directly to the structural decking usually timber. Dec 16, 2015 cold roof construction is a more expensive and timeconsuming method of building a flat roof for an extension project. In a cold roof the thermal insulation is laid between the joists below the structural deck. In cold climate zones the minimum total rvalue for the entire unvented roof assembly should be r40. The cold flat roof method, however, creates space for ventilation in the form of massive air gaps above the insulation and in between the structural joists and the structural deck. This method is often problematic because it leaves room for the heat of the sun to damage the structural elements because theyre not protected by insulation. This option avoids the requirement to ventilate the roof. This is where the insulation is typically packed between the rafters. Cold roofs, by the way, are not recommended for high humidity areas see the blog on how to insulate roofs of swimming pools, saunas and high humidity areas. Cold deck flat roof construction, repair and replacement with an epdm rubber roofing membrane. Today we will look at what is involved in warm roof construction and later in the month we will examine the cold roof technique.
Pitched roof need much more area of roofing material than flat roof. Although not recommended today, and actually banned in scotland, until recently cold flat roofs were fairly common. With a cold flat roof construction, it is critical that a minimum of 50mm of cross ventilation is provided underneath the roof deck. May 21, 2018 the construction work of upper floor can be readily taken up in case of flat roof, whereas in case of pitched roof, the entire roof has to be dismantled before the construction. These things will affect the timing, cost and overall running of your project.
In order to avoid that situation we use a ventilated cold roof. Guidance flat roof types building regulations 4 plans. A warm flat roof or a builtup roof bur is one where all the insulation is above the joistsdeck, making them part of the warm fabric of the building. On a warm flat roof, the layer is installed underneath the insulation to stop moisture interacting with it through rising thermal pressure lower down in the building. These are created when heat transfer from a homes interior melts the snow on a roof which then refreezes as it makes its way to the outer edges of the roofs surface. A 50mm air gap must be left above the insulation and allowance for venting must be made at roof perimeters.
Building design expert warm roof or cold roof which. The 18mm roof grade deck is then fixed on top of the rafters leaving. In a warm roof construction the principal thermal insulation layer. Flat roof advantages and disadvantages flat roof types. Mar 30, 2017 evan a flat roof should have excellent isolation and keep the interior safe from all the outdoor turbulence. In cold climates, the primary purpose of attic ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow, and to vent moisture that moves from the conditioned space to the attic.
For cold flat roofs, the vapour layer needs to be positioned underneath the insulation layer, on top of the room below to create an effective barrier. The driving factor in terms of outside temperature is the sun. Such roofs are built with mostly timber, take a number of different shapes, and are covered with a variety of materials. This means that anything above the ceiling of the uppermost area of the building, is cooler than the living space. In these cases, a cold roof is a preferable alternative to warm roof insulation. It should also be noted that a warm roof adds height to a flat roof and. This approach uses insulation with no air gap either immediately above or below the roof deck. A cold roof is roof in which the thermal insulation layer is located between the ceiling joists meaning that everything above the insulation, such as the rafters, and any roof space, will be colder than the living space below it. As a result of the height difference, warm roofs cannot be used on balconies and flat roofs extensions with doors leading onto the roof.
Consequently, it is important that the void is well ventilated. A cold roof is an easy option when creating a flat roof, simply placing insulating between the rafters. What you need to know about flat roof houses and snow. Cold roof vs hot roof what you need to know when picking a. A cold roof design is not generally recommended for new build flat roof applications due to the added requirement for roof void ventilation and the difficulties in preventing cold bridging through the system. A warm roof is defined as being when the all or the majority of the insulation is above the joists or deck. Warm deck roof with this type of roof the insulation is placed above the roof deck but below the weatherproofing.
Cold roofs have the waterproof layer placed directly onto the roof deck and the insulation inside the roof, just above the ceiling. Cold roofing designs can be extremely tricky for existing flat roofs. Which makes sense, as this space is otherwise empty, and so its a simple, lowimpact way to insulate a roof. Ventilated roofs remove moisture from roof cavities, structural members, sheathing and insulation.
Going back about 120 years, the grandfather of flat roofs is the builtup roof or bur. A warm deck roof is much easier to install, offers great thermal performance but adds height to the flat roof. It allows insulation to be added without having to replace the waterproofing on. Less thermally efficient than a warm roof construction, cold roof construction remains the most common form of construction for existing flat roofs. Flat roof construction types thermal design 1 manchester university warm roof in a warm roof construction the principal thermal insulation layer is located above the structural decking, resulting. A few key points to consider are how the roof interfaces with other elements. Each of these constructions have draw backs to the building designer. It is the standard method employed on flat roofed extensions but it is rarely used for new builds today. A cold roof is best when youre initially creating a flat roof and is cheaper than a warm roof, but does provide an inferior thermal performance. A roof is mainly considered to keep out rain and snow from a building. Then there must be ventilation between the deck and the insulation traditionally a generic mineral wool to prevent moisture vapour being transmitted from the building outwards where it could condensate in the roof construction interstitial condensation. There are several methods and materials for the design of the exterior surface of a warm or cold flat roof. Dec 30, 20 cold roof construction, is what is found on most older flat roof buildings and almost all houses both old and new. This was the traditional way of flat roof construction and as insulation has increased.586 650 89 8 406 1017 809 1246 1207 259 1005 130 10 343 1221 435 716 276 1388 1285 1472 1258 332 699 1094 504 1440 573 439 846 1252 463 261 391