Rooftop pool
user-1147510793
| Posted in General Questions on
We’re working on a hotel with a rooftop pool that sits over conditioned space. The depression of the pool (concrete) is formed with 9″ thick gunite and fnished out with tile. The current drawings call for 4″-6″ of rigid insulation to be run into the pool sitting on top of the concrete. We have a pool consultant on the team who says he has never installed rigid between the concrete and gunite. Thoughts?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Heather,
The terms gunite, shotcrete, and "low-velocity sprayed concrete" are used interchangeably by some writers, although other writers make distinctions between these terms.
To answer your question, sprayed concrete (or shotcrete) can be applied to rebar and wire mesh adjacent to rigid foam. This technique has many applications, and the resulting concrete assembly can be quite strong, as long as an engineer is involved to determine the necessary steel reinforcement and the concrete thickness, and as long as the installers are experienced and skilled. For an overview of the technique, see "Building Walls with Low Velocity Sprayed Concrete."
In the case of a rooftop swimming pool, the engineer has to consider both structural issues (involving the weight of the water in the pool as well as the weight of the concrete, of course) and water-entry issues (which require assurances that the pool itself is waterproof, and that the rigid foam insulation stays dry).
Heather,
is between the Gunite and the concrete the best place for the insulation? would it perhaps be better on the inside and underside of the concrete slabs?
Seeing now common roof top pools now are, what is the standard detail other architects are using?
In my area, mostly what I see for pools on roofs with CIP concrete is as follows:
structural concrete box is poured and cures out.
Box is is stress-tested by filling with water.
Box is waterproofed and all cracks and corners are detailed -- often with hot rubberized asphalt;
Box is water tested again.
XPS insulation is placed on the deck and rebar is placed.
shotcrete is installed.
i can't ever recall seeing insulation on the pool walls, but i guess it could be done -- would just be reinventing the wheel when it gets to the pool coping. I have not seen a good way to avoid a thermal bridge through the concrete stemwalls, though in climate zone 4A, the energy penalty is a little lower than in more harsh climates.
pinch points are the ladders, lights, disabled access lift, filtration trough, pool coping areas and tie-in to the WP at the deck. lightning grounds are generally a nightmare.