The general strategy was to create exceptionally tight halves of the enclosure, and then manipulate the airflow so it was always house-to-pool and out, and never pool-to-house and out.
The pool enclosure was timber framed with a T&G ceiling. We installed a peel and stick air barrier over that and then used rigid insulation to achieve a continuous R42.
What the builder and his subcontractors thought was extraordinary attention to air sealing and thermal bridging we performed the hard way 15 years ago—today it’s routine in high performance construction!
Windows are the first condensing surfaces in a pool enclosure and the trick is to move air across them. I persuaded the architects to let me install a fabric-duct loop around the pool with long slots cut in it to bath the glass with air. We installed tiny electric “baseboard” heaters under some of the high glass so they would not fog in winter.
The architects left us what they thought was plenty of space for a “mechanical/storage” room in a 10x10 leftover corner. When we dug the pool, we included a full basement under the living area and it is filled with equipment, and of course deck chairs, tables and blow-up toys.
The pool is heated with an outdoor boiler which supplies hot water to a pumping and control board serving a large domestic water tank for multiple long hot showers; in-floor tubing warming some floors; and hydronic duct coils backing up the twinned heat pumps on the residential side and the dehumidifier for the pool side.
A remarkably small exhaust fan operates in the gable end of the pool room, while a variable speed make-up-air fan was coupled to the range hood to match the exhaust flow.
Thus, the warm wet side stays under slightly negative pressure while the cool dry side stays slightly positive. Air reliably flows from house to pool and never from pool to house—even with a commercial range fired up. Helps with the wood fired pizza oven, too.