Deckman, how do you know if your concrete patio is frost heave protected or not ? i live in the SEATTLE, WA area, lots of rain but no bone chilling temps. usually. I am planning to build this deck over a nice aggregate style concrete patio which is in good shape and level. I have never noticed any difference in its height from season to season, does this mean that it doesn't rise or fall at all ? my designed height from the door down to the current patio is 13", so you can see my dilemma, i want to make sure it doesn't RISE to 14" or 15" which would cause the threshold of the deck to be above the door frame, not good dude. Lemme know what you think.

A frost protected patio is rare, 95% of patios are NOT, but if your concrete is more than 4 inches thick it could be. You would have to dig down to see if there is a footing aound the outside perimeter of it. If it is not frost protected, the patio will move with the floating foundation deck system.

We are located in Minnesota. During the winter months, about 1/2 inch of rise will occur during extreme conditions. Frost heave can still occur in warmer climates, so you will want to check if you have a frost line.

If the deck is placed next to a door, the deck should be between 1/2" and 1" below the door's threshold. Or if you want a step up to the door, the deck should be between 6-7 inches below the door. You don't want anything between 1-6 inches; this will create a trip hazard.

Deckman