· by Michael Blair, editor
A sunroom is a hard room for a floor. It gets direct sun through a wall of glass for hours, so the floor heats and fades; in a three-season room it also freezes in January, so it moves. It is the room people walk into from the yard, the pool or the deck, so it gets wet, gritty and muddy. And it usually sits on a slab or a shallow frame that runs cooler and damper than the house. The floors that work in the living room fail here in specific ways, and the ones that work here are chosen for those conditions.
What the sun does
Ultraviolet light fades color and breaks down finishes. A hardwood floor in a sunroom develops a lighter rectangle wherever a rug sat, and the finish chalks over a few years. Vinyl fades and can soften. Carpet fades and holds the heat. Anything dark absorbs enough sun to be uncomfortable underfoot in summer and to stress the material.
Low-E glass in the sunroom cuts UV substantially, and a floor in a room with it lasts much longer than the same floor behind clear glass. If the room is older, the glass is the first thing to check, because it decides how much abuse the floor is about to take.
What temperature swing does
A floor in a room that goes from below freezing to over ninety in a year expands and contracts more than the product was tested for. Laminate and rigid vinyl plank have stated temperature ranges, and a three-season room usually falls outside them; the planks gap in winter and buckle in summer. Solid hardwood does the same. Adhesives soften in heat and let go in cold.
A four-season room that is heated and cooled with the house is a normal room for this purpose, and most floors are fine. A three-season room, or one on a mini split that is turned off when unoccupied, needs a floor that does not care about temperature.
- Four-season, conditioned: most floors, with UV protection from the glass
- Three-season, unconditioned: tile, stone, sealed concrete or outdoor-rated products
- Any sunroom: nothing dark, nothing that fades, nothing that dislikes water
The floors that hold up
Porcelain tile is the standard answer. It does not fade, it does not care about temperature, water sits on it harmlessly, and it is cool underfoot in summer, which in a sunroom is a feature. Choose a textured or matte finish so wet feet do not slip, and a light or mid tone so the floor does not become a radiator. Natural stone works the same way and costs more; slate and travertine both suit the room if sealed.
Sealed or stained concrete, if the room is on a slab, is the least expensive durable option and looks right in a modern sunroom. Outdoor-rated porcelain pavers and some outdoor-rated vinyl products are made for exactly these conditions. If the room is conditioned and the glass is low-E, luxury vinyl plank in a lighter color and engineered hardwood are reasonable, with the plank’s temperature range checked against the room.
What goes under it
A sunroom slab is often uninsulated and poured at grade, so it is cold and it can wick moisture. Test it for moisture before any floor goes down; a plastic sheet taped to the slab for a day tells you whether water is coming through. A moisture barrier under anything that is not tile, and a crack isolation membrane under tile on a slab that has cracked, are cheap compared to redoing the floor.
On a framed sunroom floor over a crawl space or piers, insulation and a vapor barrier under the floor keep it from being the coldest surface in the house and keep the humidity below from reaching the flooring. Radiant heating under tile is worth considering in a room that is used in winter; tile is cold, and the room is already the coldest one.