Rigid Insulation Under Concrete Slab

One of the best ways to save money on rigid foam insulation installed under concrete slabs is to ensure the material is not over engineered.

Rigid insulation under concrete slab.

For installation on concrete foundations and under floor slabs the rigid foam insulation you choose can make a difference of tens of thousands of dollars on a project. A common design assumption leads to specification of rigid foam strengths that are many orders of magnitude higher than necessary which can double the insulation material cost. For under slab applications the rigid foam insulation typically should be installed over a gravel base with a poly vapor diffusion retarder between the gravel and insulation. Concrete 4 existing drywall 2 plywood 5 wood 3 sheathing type.

I will always place the poly on top of the rigid insulation as spoke of in the superinsulated slab article. Eps 3 xps 2 faced or unfaced. 4 10 2012 3 climate zones e301 1 6 5 8 4 slab r value table 402 1 1 insulation and fenestration requirements by component e402 1 1 climatezone slab r valued 4 10 2 ft 5 10 2 ft 6 10 4 ft 9. Placing poly under the rigid foam runs the risk of the concrete while being placed will find its way below the rigid foam thru cracks and joints.

Walls foundations roof and roof decks air distribution ceilings interior. R 7 7 rigid foam insulation model 310891 18 35 18 35. Water resistant rigid board for under concrete slab insulation and slab support in traffic bearing applications. Depending on your location you may need rigid foam insulation under and around the edges of the slab by martin holladay issue 245 aug sept 2014 while walls and roofs have long been a point of focus foundations seem to be the final frontier when it comes to insulation.

For me this is a no brainer. With a minimum of 70 recycled content the installed thermafiber products contributed to valuable leed credits helping the building earn a leed platinum certification. Horizontal insulation placed less than 12 inches below the ground surface or that portion of horizontal insulation extending outward more than 24 inches from the foundation edge should be protected against damage by use of a concrete slab or asphalt paving on the ground surface directly above the insulation or by cementitious board plywood. Additional insulation is applied along the edges of the slab because that is a primary surface for heat loss.

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