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I have a roof terrace on a flat roof, which I'm planning to take apart to clean the boards themselves and the roof underneath, which is currently full of moss and other junk preventing rainwater from running off. In a builders report it was recommended that the roof be insulated on the outside to prevent the wood from rotting due to condensation coming off the cold roof.

Since the terrace is coming off anyway I figured I'd place some XPS insulation on the roof before putting the terrace back on. As far as I can tell, you are supposed to put the terrace right on top of the XPS tiles, but are those things really strong enough to carry the load of a terrace + furniture + several people? I'm kind of hesitant of putting all that stuff on a block of foam.

The terrace, by the way, consists of boards screwed to three perpendicular beams which rest on some rubber tiles, on the bitumen. So technically the entire load would be upon the areas directly beneath those rubber tiles.

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Yes, the tiles will hold. If you look up the specs, they are even used under concrete in factory floors. Just make sure the surface is flat. If you lay them on uneven surface, they will bend and break. Also it would help if you showed a picture..

  • Can't tell a lot from a picture as is... everything of interest is hidden under the boards. – Bas Jan 16 '17 at 16:56
  • Also, a concrete floor would distribute the load evenly across the entire surface, where for me the load would only be where the terrace's beams are lying... would it still hold up? – Bas Jan 16 '17 at 16:57
  • Ok, so generally, the tiles will hold a LOT of weight if it is evenly spread and are not bent. – Miro Krsjak Jan 16 '17 at 16:57
  • You can also get (probably not at HD/Lowes) XPS in different load ratings (pounds per square inch or equivalent) so you could get a certain number that are high-load rated for the loaded areas, and use "standard" XPS for the rest. Also never a better time to think about adding a new membrane, since you'll be doing 90% of the work needed for one... – Ecnerwal Jan 17 '17 at 1:39

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