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Conservatory Building Work
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A good surveyor can help you to ensure that your conservatory building work will conform with current Building Regulations and Planning Permission requirements.

However, many factors relating the construction of conservatory building work for your conservatory or orangery are outside the scope of these regulations, so they also aim to ensure that good building practice is followed.

Conservatory Building Work - Cross Section of a Typical Conservatory Base Plan
Cross Section of a Typical Conservatory Base Plan
Conservatory Building Work - Stainless Steel Wall Ties
Stainless Steel Wall Ties

Conservatory Building Work

Click on the image alongside to expand it

All parts of the conservatory base work cross section are labelled as follows:

A. External wall of the host property
B. Under floor insulation
C. Concrete floor, minimum 100 mm thick
D. Optional cement screed, 50 mm thick, recommended when floor tiles are to be laid
E. Damp proof membrane, 1200 gauge visqueen
F. Sand blinding over the hardcore to prevent the membrane above from puncturing on sharp stones
G. Type 1 MOT hardcore sub-base
H. Insulating glass sealed unit
I. Window frame
J. Internal window board
K. Internal brick base wall
L. External cill
M. Brick ties to attach the inner and outer skins of the base wall
N. Cavity insulation
O. Thermal blocks
P. Plasterboard, preferably foil backed
Q. Internal plaster skim
R. Ground level. Finished floor of the conservatory should be at least 150 mm above ground level
S. Concrete foundation

Stages in the Construction of your Conservatory Building Work

Firstly, and it may seem obvious, but you should accept in the process of completing your conservatory building work, the area where the conservatory is to be constructed is going to be a mini-building site for a while.

It’s not just the immediate vicinity that can be affected as the builder will require a working area around the new conservatory. That’s why it’s a good idea to incorporate some paving around the new structure into your design, to hide any damage to your lawn.

Your builder will need to excavate the ground and remove spoil possibly into a skip on your driveway but the surface of the driveway should be protected. Also, concrete for the foundations and floor will be moved, normally by wheelbarrow from the front to the rear.

A good builder will always tidy up after himself but as the saying goes, ‘you can’t make an omelette without breaking a few eggs’. The conservatory building work site should be left in a safe condition overnight and at weekends when your builder is not there, for good health and safety practice.

You should ensure that you have removed any prized shrubs or plants from the site of your new conservatory for safe keeping, as a builder may assume that they are unimportant and are to go into a skip. Completing your conservatory building work is not a clean job.

Any overhanging trees which weren’t a problem prior to construction may need to be trimmed back if they cause an obstruction for your new conservatory.

Your builders will set out the base area with string lines to mark the intended wall positions and it is important that you agree the size and shape of the conservatory with them at this stage.

The design and size of your conservatory building work can usually be obtained from a CAD drawing – why not ask for a copy?

The next step is to excavate the ground to remove spoil for a trench foundation.

A trench foundation for conservatory building work should be at least 450 mm deep and 450 mm wide.

Steel mesh or lintels should be installed where required to protect any underground pipework. It is important that your conservatory building work does not damage any underground pipes as this can be expensive to fix later.

The position of underground pipework can be checked by taking a line from any gullies, down spouts and soil & vent pipes adjacent to the house to the man holes.

In modern properties foul water from sinks, baths and toilets is dealt with through a separate pipework system from clean water; that from gutters and down spouts i.e. collected rainwater.

Concrete is then poured into the trench foundations or footings; for most professional builders concrete would normally be delivered ready mixed.

The concrete is floated to form a level surface and should be a minimum of 450 mm wide and 200 mm thick.

Concrete used for the foundations will normally be a different specification, or ‘mix’ to concrete used for the conservatory floor and would be delivered at different times.

The inner leaf of the cavity wall would then be built up to the conservatory floor level which in most cases is the same as the house floor level.

The conservatory floor level should be at least 150 mm above the surrounding ground level to reduce any splashing of rainwater onto brickwork above the damp proof membrane and to satisfy Building Regulations requirements (even if they don’t apply to your conservatory building work).

Where the ground level drops away from the house wall, this may be much higher at the front of the conservatory. Where the ground level rises away from the house, it will need further excavation beyond the front of the conservatory and possibly a retaining wall to hold the garden back.

Although this will involve greater cost, there is an opportunity to redesign the garden with steps up to it, incorporating landings and perhaps a patio area.

Hardcore, ideally Type 1 MOT, should be compacted and consolidated to a depth of at least 100 mm to form the base of the floor.

When installing the hardcore, it should be compacted at 50 mm intervals, especially when more than 100 mm is installed to ensure a solid base with no air cavities which could cause the concrete floor to sink at a later date.

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Sand, normally about 50 mm deep, is then levelled over the hardcore to stop any sharp stones from puncturing the damp proof membrane when it is installed

Visqueen damp proof membrane (1200 gauge) is then installed over the sand and should be lipped over the edge of the conservatory’s brickwork.

Where required, insulation at least 50 mm thick is then installed over the damp proof membrane.

A minimum of 100 mm thick fibrous concrete should then be installed, to bring the slab up to the proposed finished floor level (i.e. level with the house floor) this is also normally delivered ready mixed.

Fibrous concrete, as the name suggests, has small fibres which could be glass, steel, natural or synthetic materials. Fibres in concrete increase its structural integrity and control cracking due to shrinkage.

The concrete floor is then floated, or levelled to take tiles or another suitable finished surface. Sometimes a semi-liquid floor leveller is used or, more correctly, a builder will lay a screed surface over the concrete. This would normally be 50 mm thick and should to be allowed for in the excavation depth and hardcore installation.

.A vertical damp proof and wall tie starter kit should be used against the house wall, ready to take the inner leaf of brickwork.

This will help to protect the house wall from damp ingress and fix the base wall of the conservatory or orangery to the outside of the house wall.

The inner leaf of the base wall brickwork is completed to the required height and should have a minimum of five wall ties per square metre fixed between the courses, ready to fix to the external skin of brickwork.

The gap between the inner and outer walls should be at least 50 mm, and the cavity should be insulated.

Combination Conservatories - White PVCu P Shaped Conservatory with Blue Bonded Bricks

White PVCu P Shaped Conservatory with Blue Bonded Bricks

For conservatory and orangery walls with angled brickwork at anything other than 90º, bonded bricks can be used. These are bricks  (sometimes of a different colour to the rest of the external brickwork) which have been cut and bonded together so that the vertical line on the angled brickwork is much neater.

When Victorian style conservatories have equal angles and equal facet sizes, the angles for a three facet Victorian would be 135º and for a five facet Victorian would be 150º.

Certain products and conservatory specifications recommended by your chosen installer may seem unnecessary optional extras which appear to offer no real benefit, just cost.

Cavity Tray for a ConservatoryA competent builder, operating to best building practice may suggest certain products which others have avoided purely to keep their quotation relatively low – and so be in with a better chance of winning your business. This can be a short term view but if one particular product falls into this category it must be a cavity tray.

If the host wall for your conservatory is exposed to more than average rainfall then the outer skin of brickwork above the conservatory roof will (being porous) permit water to penetrate through to the cavity.

A cavity tray collects this moisture and returns it back to the outside – the shape and size of your conservatory roof will dictate the specification of the cavity tray. Failure to do this can eventually lead to a damp house wall inside the conservatory as water trickles down inside the cavity and penetrates back to the outside or the brickwork.

This can be a particular problem if that wall has been plastered; a cavity tray offers insurance against such problems.

Conservatory Finishing Touches

Most conservatory installation companies offer a range of additional extras and finishing touches for your conservatory or orangery to make it a comfortable all year round room.

• Electrical sockets so that you can watch TV, listen to music or surf the web, or perhaps an outside socket for your lawn mower and other garden machinery

• Installation of light fittings, such as down lighters, lamps and possibly outside lights

• TV point, telephone point or extension of your broadband or sky™ connection

• Plastering of the base wall and house wall, finished with architraves and skirting board

• Floor tiles or laminate flooring

• Under-floor heating with programmable thermostat for controllable heat

• Paving and landscaping around the conservatory