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Concrete Ground Floor Slabs

 

Work Included in this Section

 

The work in this section is covered in the Technical Guidance Documents (TGD) Part C.

 

The work includes hardcore filling and blinding, radon sumps and associated piping and fittings, damp-proof membrane/radon barrier, under floor insulation, under floor drainage and waste installation, under floor plumbing services installation and concrete floor.

 

Hardcore filling used under ground floor slabs should be a minimum of 150mm thick and conform with ISEN 13242:2002 and meet the specification as outlined in Annex E of the TGD Part C to this standard, SR21:2004 + A1:2007. The hardcore should be well compacted, clean and free from material liable to cause damage to the concrete.

 

The blinding layer used should be a minimum thickness sufficient only to fill surface voids and conform with Annex E of SR 21:2004 +A1:2007 for fines material.

 

The radon sump and associated piping and fittings should be installed in the hardcore filling. The sump should be within 15m of all of the external walls. In some cases one sump may not be sufficient and additional sumps may be required. (See Section on Radon Barriers)

 

The damp-proof membrane should be at least 1200 gauge material and should be laid with joints sealed.

 

The radon membrane must carry an independent certification from an approved body such as the National Standards Authority of Ireland (NSAI) or the Irish Agrement Board (IAB) and should be laid with joints sealed. (See Section on Radon Barriers)

 

The under floor insulation should be of a type and thickness to meet the requirements of the current Building Regulations. (See Section on Ground Floor Insulation)

 

Concrete used in floor slabs for housing, if un-reinforced, should be a minimum strength classification of C16/20 and not be less than 150mm thick.

 

Some floor slabs depending on ground conditions may require stronger concrete mixes than those mentioned above and may also require steel reinforcement. It is essential that the Engineer details the concrete strengths and where and how he wants the steel placed for such floor slabs.

 

What You Will Need to Do

 

Appoint your Radon Installation Subcontractor (if using a radon barrier)

 

Appoint your Plumbing and Heating Subcontractor (Plumbing Services under floor slab)

 

Ensure all under floor services are installed.

 

Ensure the blinded hardcore filling has been fully compacted and is free of sharp projections which may puncture the radon barrier or the damp-proof membrane.

 

Ensure the radon sump and associated piping and fittings are installed in the hardcore filling. All pipe joints and where it passes through the wall should be sealed to prevent drawing-in air from the outside.

 

Ensure, if using a damp-proof membrane, that there are no punctures, the joints are sealed with an appropriate tape, and that the edges have been turned up and laid over the block rising walls.

 

Ensure, if using a Radon barrier, that there are no punctures, the joints are sealed with an appropriate tape, that the edges have been turned up and laid across the internal and external rising walls and proprietary top hat seals are used around service pipe penetrations.

 

Ensure the under floor insulation is laid over the total floor area and that there are no gaps, and also, that the edge insulation is in place before the concrete floor is poured. To prevent the concrete from going under the insulation at the edges and joints the insulation can be covered with a light weight polythene prior to the concrete pour.

 

Ensure your Engineer will be available to examine and certify the floor concrete being poured.

 

Ensure any Instructions issued by your Engineer are followed exactly.

 

Ensure the top of the concrete floor slab is level and floated when it is poured.

 

What to Look Out For

 

Weather conditions: Concrete work should never be carried out in freezing conditions as the concrete will not set properly.

 

Damage to external rising walls, when laying and compacting the hardcore filling – ensure the foundations are backfilled around the rising walls as this work proceeds so as not to dislodge the blockwork.

 

Ensure the hardcore filling is placed and compacted in layers not greater than 225 mm thick and that it is compacted with a vibro roller or a whacker plate.

 

What You Will Need to Provide

 

Hardcore filling that complies with the current Building Regulations.

 

Blinding materials that comply with the current Building Regulations.

 

Underground drainage piping, fittings and concrete surround.

 

Radon sump(s) and associated piping and fittings

 

Damp-proof membrane, minimum 1200 gauge, complete with sealing and jointing tape – all to comply with current Building Regulations if radon barrier is not required.

 

Radon barrier, complete with all ‘top hat’ fittings and sealing and jointing tapes to comply with current Building Regulations.

 

Under floor insulation of a type and thickness to comply with current Building Regulations.

 

Light gauge polythene (500g) to lay over the Insulation prior to the concrete pour (optional).

 

Under floor plumbing services

 

Concrete for floor.

 

Mesh or bar reinforcement complete with tying wire and spacers, if required.

 

Timber for formwork to edges at door openings etc.

 

Vibro roller or whacker plate and power float etc.

 

Watching the Pennies

 

To avoid the additional costs of hiring items of plant and tools yourself, try to ensure that the ground works subcontractor and the concrete subcontractor you employ have included for providing all their own plant, tools and access equipment necessary to carry out their section of the work.

 

Detailed Costs

 

Get detailed costs for this section of your project at http://selfbuildrates.ie/index.php/managemybuild/login

 

Rough Guides

 

1.00m3 of concrete in a 150 mm thick concrete floor slab will cover an area of 6.66m2 (No allowance for waste or over pour allowed)