Minimum Screed Thickness Over Insulation?

I’m Andy Parkin, Managing Director of the Multi Award-Winning Spreed Screed.  Today we are here to talk about minimum screed thickness over insulation.

Minimum Screed Thickness Over Insulation

When we talk about a minimum thickness, we would need to look at the type of floor construction the screed is going onto. When it is over insulation, it is normally termed as “floating”.   If the screed is on top of insulation there is going to be move “give or “movement” than being laid directly on to a structural substrate.

Insulation will have a strength rating. a KPA value. Generally, a domestic property will have a minimum KPA of 70, and a commercial operation generally starts at 100.  The higher the KPA, the stronger the insulation is.

During the design stage the loading of the insulation needs to be taken into account, and a suitable KPA value specified.

In broad terms exactly what are the minimum depths for screed on top of insulation? If we look at the different groups of screed.

Flowing Screeds

Liquid screeds/flow screed or calcium sulphate screeds as they are sometimes called.

  • 35 mm on domestic, 40 mm if it is a commercial project, 45mm with underfloor heating pipes in
  • 35mm with underfloor heating pipes using a specialist calcium sulphate product
  • 15mm using a specialist calcium sulphate product

Modified Sand And Cement Screed

A traditional screed with additives in.

  • 35mm minimum a rapid strength gain product.

If you are looking to move the project forward quickly with regards to trafficking and loading of the screed, then a modified screed is ideal.

Fast Drying Modified Screed

  • 40 mm minimum
  • 55 mm minimum with underfloor heating pipes

The cement is blended with hydraulic binders within, and if you are looking to get your floor coverings on very, very quickly and don’t want to wait months then a fast drying product is the solution.

Traditional Sand And Cement

A traditional sand and cement screed with a typical mix ratio of 1:4 or 1:3

  • 65 mm for domestic and 75 mm for commercial are the recommended minimums.

For any further questions about the minimum screed thickness over insulation please contact us.

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