Contraction Joints In Concrete Slab

[EViS]

We will be pouring our concrete slab over Celotex soon and wondering whether we need any contraction (or expansion) joints? The entire floor area is approximately 9m x 9m, with two load bearing walls marking of a corner (as pictured). Do we need any joints, or is a straight pour going to be fine for residential purposes.

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• EViS
• 26 Feb 2015
• 1

 

[Alastairreid]

The usual recommendation is for some form of movement joint to be created in a non-reinforced slab at a separation of approximately 30 times the slab thickness. So, for a 100mm thick slab, there should be some for of joint every 100m × 30 = 3000mm = every 3.0-3.6m and, in a 150mm slab, 150 × 30 = 4500mm = 4.5-5.4m. Naturally, there is some leeway with these calculations, and joints can be positioned to coincide with band courses or to be 'centred' within a slab for aesthetic reasons.

http://www.pavingexpert.com/concjnt1.htm

 

[tony1851]

If those walls are load-bearing, should they be built directly off an un-reinforced slab on insulation board?

 

[EViS]

If those walls are load-bearing, should they be built directly off an un-reinforced slab on insulation board?

They are already in place on footings. The slab is being poured around them.