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When choosing a type of door for a green build there are many things to consider:
The choice of doors available allow a builder to often find a happy compromise and when coupled with properly insulated frame work / design can considerably reduce the amount of heat lost through these important building components.
The doors of a structure can prove a tricky problem for designers and builders interested in green building. Many people simply won't compromise on the security and aesthetics of a door in order to improve insulation efficiency.
This can be worked around using modern materials and building methods to create doors that are satisfying to the eye and to the environment whilst still being as secure as traditional door designs.
The traditional solid wood door while pleasing to the eye has a number of environmental pitfalls. First it is made from wood, which may not be forested correctly, and secondly it does not form a good insulator.
Doors have a large surface area and it is very important to make sure that they can be insulated as much as possible. It is to this end that companies have invested in creating composite doors.
These look just like a traditional wood door from the outside but are made from various materials.
Commonly a wooden frame is created into which wood fibres are added. These insulate better than a solid piece of wood.
This can come from renewable and sustainable materials such as cork.
The frame is then skinned with the wooden panels that can be seen from the outside.
The end result is a door that looks like a solid wooden door, insulates better than a normal solid wooden door, is lighter than standard (which in turn means it can be mounted onto lighter fittings) and is less prone to warping and weather damage than a normal solid door.
Extruded plastic exterior doors have been around for over 30 years and are a viable alternative when considering which material to use based on insulating properties alone.
Doors created from plastic are often filled with a polyurethane foam core (manufactured CFC free) which prevent the heat from escaping with a typical R-value range of 12-14. These doors can often contain windowpanes so consideration will need to be given to the type of glazing used. These doors are generally fire rated for 20 minutes.
Steel whilst strong and durable is not always the most pleasing to look at or the most insulating when used in door construction. However there are times when its use cannot be avoided for example as a fire door (a 20-gauge steel door has a fire rating of around 90 minutes) or in security door applications.
When steel is used there are a number of ways to decrease the heat lost through it. Using a small strip of wood as the door stiles (the vertical edges of the door) allows the door to be planed into as tight a fit as possible whilst providing a thermal break, stopping the door from losing heat into the framework.
In normal applications steel doors can be filled with a core of insulating foam to prevent heat loss. Steel can also be skinned with wood to improve aesthetics and add a further layer of insulation.
When dealing with external doors of any kind the framework and mountings of the door become very important to its insulating ability. It is imperative that doors be properly sealed so that when closed heat does not escape from cracks around the door and frame.
There are various materials available from DIY stores and builders merchants for this, including self adhesive foam and rubber strips (rubber is more durable and is better suited to external doors), brush strips (which are particularly suited for sliding doors/patio doors) and several different types of sealant which can be used to fill the gaps on uneven surfaces.
It is important not to insulate the door to a point where the purposely designed draught that passes under the house is blocked, as this provides the house with fresh air and prevents dry rot in timber.
Where possible a thermal break should be used on the stile of the door and care should be taken when placing heating sources so as not to lose an amount of heat to the door.
External doors also have a number of ancillary parts that can contribute to the loss of heat. Keyholes should have flaps on both the inside and out to prevent cold air from getting in. Letterboxes will also need to be insulated although a more efficient option may be to do away with it completely and use an external mailbox.
Door handles can also radiate heat if the handle on the outside is physically connected to the inner handle. To prevent this there a various types of lock and handle systems where the two handles remain separate yet use the same lock mechanism.
Door handles can also be recycled if care is taken during the demolition/de-construction of a building saving new materials from having to be used. These have the added benefit of adding to a building's character particularly, if older iron handles are used.
Internal doors do not need the weather protection or security of external doors allowing them to be made lighter and thinner.
Often internal doors are made from skinned wood fibre such as MDF, whilst this provides adequate insulation it is important to make sure all wooden doors are sourced from sustainable forests and are properly insulated to prevent against heat escaping from a warm room into a colder room.
Consideration must be given to frame insulation when thinking about internal doors.
The heating of individual rooms will also need to be considered.
This will stop heat transferring if a room is often used compared to a lesser heated room (i.e. a bathroom, which will not require constant heating in an energy efficient home).
In these circumstances rubber or foam strips will provide a more efficient seal then brush strips.