Environmental performance

Conservatories by their nature perform differently than conventional extensions using con- ventional house construction. They will benefit from solar heat gain and will provide a thermal buffer to the house during colder periods but will also suffer from heat loss through the glaz- ing and roof at these times.

Good design can maximise the usability of the conservatory and the potential to effectively benefit from the solar heat gain it can provide during cooler periods. Heat gain during warmer periods can be effectively managed with good ventilation.

5.4.1 Thermal separation – England and Wales

Exempt conservatories must be thermally separated from the dwelling by a wall, window or door or a combination of them. Where the thermal separation is to be modified, new door

Section 5 - Superstructure Design

Where there is no thermal separation between the conservatory and the dwelling, the con- servatory will be treated as an integral part of the dwelling and the relevant building regula- tions will apply.

5.4.2 Conservatory heating – England and Wales

If a conservatory is heated and the heating is an extension to the dwellings heating system, even if fitted with isolation valves and separate thermal controls, the conservatory is not exempt from building regulations and will need to be built in accordance to the relevant regulations.

If the conservatory heating is totally separate from the dwelling heating system, the conser- vatory, provided all other criteria are met, will be exempt from

building regulations.

5.4.3 Thermal performance

The U-value is a measure of the rate of heat transfer, the lower the value the greater the resistance to heat loss.

The superstructure glazing should meet the following elemental U value:

· In England and Wales, the advised maximum U- value of the glazing, vertical or sloping and other thermal elements, should be as shown in section 2.6.4.

· Most conservatories in Scotland will be subject to building regulations and the relevant U-values contained in those will be used.

5.4.4 Solar control

Where a conservatory may be exposed to significant solar heat gain, the correct choice of glazing is essential to provide an energy efficient method of controlling overheating and increasing the us- able time in the conservatory.

The solar heat gain coefficient of the glazing (g value) is a measure of the solar radiation that passes through it, expressed as a number between 0 and 1. The lower this figure, the less solar heat it trans- mits.

The aspect of the conservatory and shading needs to be consid- ered when assessing what degree of, if any, solar control needs to be incorporated into the glazing specification. Shading from trees and surrounding property will affect the exposure of the site to the

It is Good Practice for exempt conservatories to be built using the U- values contained in relevant building regulations.

Tip

The site may have 3 different aspects (i.e. 2 sides and 1 front elevation), to consider when de- ciding on what So- lar Control is re-

Section 5 - Superstructure Design

Sun and the resultant solar gain.

Thermal insulation without solar control may result in overheating in summer due to the solar heat gain being trapped inside the conservatory during summer

months.

However, there may be conflict between the need to control over- heating in the warmer months and reduce the heat loss in colder months.

5.4.5 Light transmission

The amount of visible light entering the conservatory can be controlled by the glazing specification or the installation of blinds. The performance value of the glazing will be between zero (0), for no light transmitted and one (1) for full transmission.

Consider the amount of glare that may occur in the conservatory and whether the adjoining rooms will require or supply extra visible light. Internal surface finishes (walls, units, worktops and floors) must be considered as the colour and gloss levels of these will affect the amount of glare experienced by the occupants.

Privacy glass or obscure glazing can be used where the conservatory is near to a boundary or may be overlooked.

5.4.6 Ventilation

Conservatories maximise the benefits from solar heat gain dur- ing winter but, may require increased ventilation and shading in summer. Achieving a thermal balance is the goal and this will in- volve careful selection of glazing specification and provision of suit- able and adequate ventilation.

Purge ventilation

Ventilation to conservatory and adjacent room is provided by opening lights.

The adjacent habitable room and conservatory should have a rapid ventilation area at least equal to 1/20th of the com- bined floor area of the habitable room adjacent to the conser- vatory and conservatory.

Some of the purge ventilation should open at high level, 1.5m or above floor level to provide cross-flow ventilation which can

Adequate ventilation is essential to provide a properly functioning conser- vatory, helping to avoid condensation and excessive heat build-up in sunny

weather.

Tip

Roof vents are an effective means of

ventilation and may be thermo- statically con-

Section 5 - Superstructure Design

use of opening roof vents to aid ventilation and prevent overheating during sunny peri- ods.

Background ventilation

Background or trickle ventilation areas in existing dwelling windows covered by the conser- vatory shall be replicated in the conservatory. It is recommended to use trickle ventilators within conservatories.

Mechanical Ventilation

Extract fans can aid natural ventilation and should be installed at high level. Consider the means of introducing air into the conservatory at low level to balance air inflow and outflow.

Roof ventilation

Roof vents provide good ventilation particularly for south-facing locations to reduce heat build up during summer.

Existing under-floor ventilation

Where the dwelling has a suspended floor and there are ex- isting provisions for under-floor ventilation that would be ob- structed by the conservatory base, provisions should be made in the conservatory substructure for the continuity of the under-floor ventilation. Alternatively, new provisions for under-floor ventilation should be made outside the conserva- tory base.

5.4.7 Specification guidance

There are many design factors which therefore have to be taken into account when optimising the environmental, comfort and energy-efficiency aspects of a con-

servatory. It is also necessary to take into account the orientation of and the level of exposure to the Sun of each side of the conservatory when deciding on the type of glazing and means of ventilation to be installed. It is important to note and ensue the customer is made aware that the glazing may not be the same specification on all sides of the conservatory.

· North facing

The objective here will be to maximise the benefits of the solar radia- tion from the Sun and to minimise heat losses through the wall glazing.

Glazing with a high solar heat gain coefficient and low U value will be desirable. Roof glazing however may require solar control if there is no external shading and the roof is exposed to di- rect sunlight in summer.

· East and West facing

Where there is little external shading, solar heat gain through wall glazing can be significant in the morning (east facing) and evening (west facing). In general it is beneficial to maximise this

Section 5 - Superstructure Design

· South facing

Minimising summer overheating is a major design objective, which means combining the benefits of glazing solar control, ventilation and dissipation of heat through high U-value glaz- ing must all be considered. Advanced glazing products aim to

keep the conservatory warm in winter and cool in summer by combining a low U value with high solar control and high light transmission. In roofs there should be ample ventilation (e.g. two roof vents), using roofing products with a high degree of solar control, lower light transmission products and/or blinds may be required, to reduce glare.

5.4.8 Air conditioning

Air conditioning systems use additional energy and therefore careful consideration should be given to maximising the efficiency and effectiveness of the other control methods to reduce the cost of cooling. The installation of a combination of solar controlled opening vents, suitably designed shading, blinds and solar control glass can perform almost as effectively as air condi- tioning without the associated additional running costs.

5.4.9 Condensation

Condensation occurs when moisture suspended in air comes into contact with a cooler sur- face. It can appear on any surface, including glass, walls, tiled floors, vinyl covered solid floors and metal bars. Condensation can and does occur within conservatories, this is more likely to occur in winter when the temperature difference between the interior of the conservatory and outside are likely to be greatest.

The following factors will assist when dealing with condensation:

· Do take steps to ensure the newly built conservatory “dries out” thoroughly. In summer keeping doors and windows open (when safe to leave open).

· Do allow air to circulate freely within the conservatory, using opening windows to provide rapid ventilation and the use of ventilators within the structure will as- sist.

· Condensation can be reduced by incorporating trickle ventilation into the walls, eaves and ridge zones.

· When drying out a new conservatory, forced ventilation (electric powered ex- tractor fans) may assist by increasing the natural airflow.

Tip

The energy used for cooling (air conditioning) can

be 3 times that