I am installing an exterior garage door and would like to create a low (1-1.5″) concrete sill that the finished aluminum door sill rests on. My concern is providing a barrier to water entry. The door opens out onto a small landing that is located 12″ below grade. The garage slab is an additional 24″ below grade. The landing has a drain to prevent water entry to the garage, but is essentially flush with the top surface of the concrete steps down in to the garage. Hence if the drain slows due to leaves and debris the rain water would easily rise over the low aluminum door sill and flow down into the garage (This has already happened). Would it be better to use pressure treated lumber with polyurethane caulk or concrete? I don’t want to increase the sill height more than 1.5″ since it would create an additional trip hazard.
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The door opens out onto a small landing that is located 12" below grade. The garage slab is an additional 24" below grade.
This sounds like a building blunder to me.
Will your new sill be placed overtop of existing concrete? If so you may want to go the PT and gasket route. It will be virtually impossible to create a seal when pouring an 1 1/2 inch sill onto an existing slab.
I would agree that this is a problem with the original building construction. Essentially, the house is a 50 year old custom design located in a hilly region. The builder obviously, made a mistake at this door entry. However, I need to repair it as well as possible. My concern with the concrete is just what you mention. That a water tight seal won't be achievable. Although waterproof paints like Drylock seem to work well. What type of gaskets would you recommend for the PT lumber?
Rob,
Treated wood will be ugly and unstable, though it may do the job. I suggest you use a piece of Trex (or similar solid plastic lumber) bedded in polyurethane caulk and held with a few screws to the concrete. It can look good for a lot less effort than PT, and no paint needed.
Bill