Conservatory base construction. We have been asked many times how a conservatory base should be constructed. We have compiled a basic conservatory base construction guide which should cover the majority of cases and answer your questions.

The construction of a typical conservatory base is very similar to that of an extension to your house.

It is a general belief that; because a conservatory is lighter than an extension the foundation does not have to be very deep. This is not necessarily correct.

Firstly it is not possible to know precisely how deep the foundation will be until the ground is excavated and inspected for any 'made up areas' - this is where earth has been placed on existing ground.

Therefore it will be necessary to excavate a trench through this layer into load bearing ground. By doing this you will ensure that the conservatory has a good foundation base, as we expect that you do not want to wake up one morning to find your conservatory at the bottom of your garden!

Normally foundation trenches are between 650 - 1000mm deep.

The other factors which determine the foundation depth will be tree roots, drains and services.

Conservatory Base Works

Reduction of Ground Levels

The areas where your conservatory is to be built should have any hard materials removed, i.e. patio, concrete slab, etc. and any vegetation soil removed to an approximate depth of 150mm.

Excavation of Foundation Trench

Normally the foundation trenches are excavated to the following dimensions. (Ready to receive a mass concrete foundation) 450mm wide by 650/1000mm deep dependent upon ground conditions.

Existing Underground Drains

Where an existing drain punctures a foundation the foundation must be below the drain invert (bottom of drain) and a precast lintel placed above the drain so ensuring that no weight is put onto the drain.

Casting of Foundations

The foundation trench can now be concreted. A mass fill is normally used as this tends to be quicker and therefore cheaper. The concrete is normally finished 150mm below ground level.

It is always a good idea to knock 350mm x 10mm steel pins into the side of the trench at 600mm centers leveled with a spirit level so you will know when the concrete in the trench is at the correct height.

Substructure

From the foundation level build up the D.P.C. level in matching brickwork to the external face and common bricks or concrete blocks to the inside skin.

Oversite and Foundation Construction

100mm Concrete slab reinforced with a 142 steel mesh on 50mm sand blinding, on 250 micron damp proof membrane on 150mm (min) well consolidated clean hardcore.

Oversite Construction with a Suspended Floor

Should the ground where the conservatory is to be built drop away more than 600mm (2ft) a timer or concrete suspended floor may be more desirable and be more cost effective.

With a suspended floor air bricks must be built into the substructure to ensure subfloor ventilation is achieved.

Should the conservatory design be glass to floor the base would normally be left at this stage with a D.P.C. (damp proof course) bedded onto the external brickwork. Ready for the conservatory to be erected we would add that the brickwork and concrete are normally left to cure for approximately 5-10 days dependent upon weather conditions.

Dwarf Wall Option

From the D.P.C. level the brickwork can then be raised to the required height in cavity brickwork. Normally the cavity would be insulated with either expanded polystyrene of fiberglass to ensure a high degree of insulation to the conservatory. The 2 walls are held together with wall ties.

Specialist Foundations

In some conditions specialist foundations may be required e.g. brown filled sited (these are areas where old buildings have been demolished and a new development built, or areas where there are trees or very poor ground). All of these areas can be built upon but specialist foundations may be required such as a raft or piled foundations.