WINDOWS & DOORS
Whilst it is obvious that a hut will need at least one door for access, it is important in the design of small buildings to consider a door’s other functions in emergency, ventilation, easy connection with associated outdoor spaces, solar gain and optimisation of views. In other words, a well-placed and specified door will provide much more than simply a point of access.
It is best practice to specify the main access door to account for as wide a range of people as possible, including wheelchair users and its clear opening width should therefore be not less than 800 mm with 300 mm of wall before any return on the opening side of the door. The threshold should not exceed 15 mm high.
The door handles should be lever type and around 1100 mm from floor level. An external platt at the same level as the finished internal floor should be provided of minimum 1200 x 1200 mm. This area should be extended clear of the door swing if the door opens out.
Doors can open inwards or out and, whilst the former is more common in Britain, a door that opens out gives more space internally. As the hut will be for recreational use, the potential for using some patio door arrangement either as the access or as a second opening would help to connect inside to outside. Hinged single or double doors, sliding doors, or folding doors are all acceptable as either main or subsidiary points of access.
Ventilation is necessary to provide fresh air, correct humidity levels, avoid condensation and to cool the hut. It can be provided by opening windows, “French doors” and permanent ventilators in any combination. Poorly built, single skinned huts may indeed be so “leaky” as to provide adequate ventilation but it is not good practice to rely on this! A minimum ventilation requirement will be met where the opening area of windows and doors is at least 1/30th of the floor area of the hut.
This is best achieved by windows capable of being opened and latched in combination with controllable slot ventilators in window frames or walls to provide background ventilation.
If huts are left unoccupied for more than a few days at a time then special attention should be paid to maintaining some fixed ventilation of the interior. A sufficient area of trickle ventilators in window frames or in walls becomes critical in this situation and it is important that they are left open.
In the same way that a well-placed and specified door will provide much more than simply a point of access, a well-placed window will provide a great deal more than a good view. Good daylighting plays an important part both in the visual quality of the internal environment as well as in functionality and energy conservation.
Careful design of the ‘fenestration’ as a whole will optimise the combination of ventilation, daylighting and solar gain for space heating (see Passive solar gain).
Good practice will ensure that the aggregate glazed area of all windows and glazed doors should not be less than 1/15th of the floor area.
PASSIVE SOLAR GAIN
A very important function of windows, especially in otherwise unheated huts, will be to warm the hut with energy from the sun. The heat generated can be calculated, but the basic principles are to maximise southerly orientation, minimise shading and improve glazing performance (see Energy considerations).
Concrete, natural stone or tiles in the areas where sunlight falls will store heat that can help to keep a building warm through the night. Consideration may need to be given to shading windows in the summer as overheating can also be an occasional problem in the sunniest locations.
Glazing can be a significant source of heat loss (as well as gain) and this becomes more critical with an insulated hut. This guide does not set a standard for performance of windows but encourages you to consider the benefits of higher performance windows (U value of 1.6 or better). The performance of glass has been dramatically improved by use of gas-filled, double or triple glazed units with various “low E” coatings.
Frames have also been greatly improved by the addition of insulation within the frame and timber frames remain the best choice for the environmentally conscious hut builder (as long as they choose certified timber only.)
But a window or door’s performance is only as good as the installation and the hut builder should take great care in sealing frames to the wall structure. Proprietary expanding foams and gunned sealants are popular for this task but the environmentally sound solution is sheep’s wool and air tightness tape.
SAFETY, ESCAPE AND SECURITY
In huts, the escape door will most often be the only or main door, which should therefore have a minimum dimension of 800 x 1981 mm.
Although not mandatory, provision of a secondary means of escape should be considered which can be another door or an unobstructed openable window with area of at least 0.33 m2 and a minimum of 450 mm high and 450 mm wide. The bottom of the openable area should not be more than 1100 mm above the floor. Escape windows may be appropriate to sleeping platforms in which case a safe route to the ground such as a stored rope or rope ladder may be sensible.
Glazing below 800 mm from the floor level and glazing immediately adjacent to, and within, doors must be toughened as a minimum safety requirement. Laminated glass is also suitable and is a requirement for skylights, whether opening or fixed. Both types of safety glazing must be marked with a BS kite mark, which confirms its authenticity.
It is preferable not to fit window locks as this can prevent easy opening for ventilation and escape but if they are desired, keys should be located next to the window.
To prevent heat loss at night, provide privacy and enhance security, consideration should be given to blinds, curtains and shutters. Raised platforms and galleries will provide the best privacy for sleeping and may be the warmest places in a hut.
For the safe cleaning of windows it should be possible to reach all points of the external glass whilst standing on a firm surface, safe deck or floor. This is achieved in modern windows by fully reversible or tilt and turn mechanisms and is essential in opening roof lights. For the external cleaning of fixed glass above 4.0 metres, where safe cleaning is not possible from within the hut, you should provide ladder hooks on walls and secure masonry pads at ground level outside for ladders.
MATERIALS AND MAINTENANCE
Window and door frames can be made of timber, plastic or metal (and combinations) and this guide recommends the first of these as the material with the most suitable aesthetic, the most versatile for alteration, the easiest for DIY construction and the most environmentally sound. All the above materials are subject to oxidation of their surfaces and ensuing decay and timber frames and sills require proper maintenance if they are to last well. All the same strategies for timber choice and treatments apply to timber window and door frames as apply to timber claddings (see Walls).
There are many opportunities for the hut builder on a restricted budget to procure second hand windows and doors, which will minimise both cost and embodied energy. It is also possible to make your own fixed windows for huts by simple framing and beading methods. If you decide to make your own window frames or external doors, you will want to choose the most durable timbers only and to treat with preservative and a high quality surface coating on the exterior to protect your investment. This guide recommends that if new windows are specified, glass is uninterrupted by astragals wherever possible to minimise leaks and heat loss.
Windows come in many shapes and sizes. Because huts will often be low cost constructions, the opportunity to use windows that are being thrown out in building alteration and demolition is very good. The hut design obviously will be steered by the windows available but the chance of free components makes the compromise worthwhile. Traditional windows are often portrait i.e. with a greater height than width.
Modern designs also use small square windows, long slot windows or even whole walls of glass. The possibilities are endless.