Every building needs a good foundation to stand up against the elements and a shed does too. A concrete slab helps to prevent the portal frame from flexing due to strong winds and provides extra rigidity to the overall structure. It also allows you to use the area to safely store your equipment without fear of damage.
The laying of a concrete base for a garage or large steel building should be performed by a professional and we do not recommend a DIY approach for any large projects. We have summaries some of the steps that are followed during this process to give you a better understanding of what is involved and why you should use a professional.
Positioning your building
Decide where the shed will be positioned and begin marking out the basic perimeter of the building. Start with the wall closest to the fence line or another building to ensure a straight finish to the surroundings. Diagonally check the measurements from one corner to another and confirm that the measurements are the same around the perimeter.
Using the measurements provided on the BOM & Plan documentation, position the footing pegs. It is important to get the base slab measurements accurate per the plans provided before proceeding to positioning of the footings.
Trenches are required for medium to larger shed due to the use of control joints in the design. Most traditional slabs have control joints to accommodate concrete shrinkage strains. Concrete shrinks as it matures and there is nothing that can be done to avoid it. Good construction practice, astute mixing and the use of certain additives will help minimise shrinkage, however they will not eliminate it.
One of the most common techniques is the use of slab joints to control and create cracks in the desired locations and to absorb any movements.
The standard slab joint used on most small to medium sized sheds is the sawn joint. It is the most popular concrete control joint because it is the quickest and cheapest to install. It comprises a saw cut made after the concrete is poured which penetrates the slab to about 25% of its thickness.
Importance of Concrete Joints
Concert cracks cannot be prevented entirely, but they can be controlled and minimized by properly designed joints. Concrete is weak in tension and if its natural tendency to shrink is restrained, tensile stressed develop and cracks are likely to occur. Joints provide relief for the tensile stresses and are less objectionable than random cracks.
Before the concrete dries out, most cracking is caused by temperature changes or by slight contractions that take place as the concrete sets and hardens. Later as the concrete dries it will shrink further and either additional cracks may form or pre-existing cracks may become wider. So people chose to use concrete cracking devices to assist in this process and control where the cracks will occur.
Dowelled Control Joints (used in medium/larger sheds)
Dowelled Control Joints comprise steel dowels that connect slabs on both sides of a straight joint. Control joints at regular centres are intended to minimise shrinkage strain at the joints.
The greatest problem with dowelled control joints is that the dowels must be installed in a single plane and in true alignment and parallel if they are to work as intended. Any failing in this respect will usually result in a ‘locked’ joint and the slab will often crack along one end of the dowels.
Make sure you always use a experienced concreting company, if you would like any assistance or recommendations feel free to contact our office and speak with one of our experienced project managers.