Finishing pig growth in hoop and confinement buildings during summer and winter was evaluated using serial ultrasound measurements of backfat (BF) thickness, loin muscle area (LMA), and serial weighing. Pigs (16 to 124 kg) were housed in a hoop building (9.1 × 18.3 m) or mechanically ventilated, totally slotted confinement building. Forty-eight pigs from each building were scanned and weighed every 14 d during the last 56 d before market. In summer, BF accretion rates were greater for hoop pigs than confinement pigs 80 to 90 kg (P < 0.05), but did not differ 95 to 115 kg. In winter, BF accretion rates were similar 80 to 105 kg, but hoop pigs had less BF accretion 110 and 115 kg (P < 0.05). In summer, LMA accretion rates were similar 80, 85, and 100 to 115 kg, but were less for hoop pigs 90 and 95 kg (P < 0.001). In winter, the hoop pigs had greater LMA accretion rates 80 to 115 kg (P < 0.05). In summer, bodyweight gain was similar 80 to 95 kg, and was greater for hoop pigs 100 to 115 kg (P < 0.05). In winter, bodyweight gain was similar 100 to 115 kg, but was less for hoop pigs 80 to 95 kg (P < 0.05). Finishing pig growth is dependent on thermal environment. Hoop-reared pigs (particularly in winter) may compensate for an early lag with faster muscle growth and slower fat deposition later in finishing.