General apartment question: What would turn an upstairs apartment into a sauna during regular weather? (house, live in)

[UniqueSoCal]

It has been nice and cool outside (about 60 degrees) yet when I walk into my apartment it's like walking into a 100-degree sauna! This has been going on pretty recently. If the weather were very hot outside it would make sense, but the weather has actually been hotter without this happening. I just purchased a dehumidifier and a new fan to try to make things bearable. (AC isn't allowed in this complex)

[EscapeCalifornia]

Downstairs neighbor running grow lights?

[mayorhaggar]

Sunlight hitting the windows and outside walls.

[recycled]

1. Maybe you live in a flat roof apartment with very little insulation in the cieling. Are the walls of the building a dark color? If so, they absorb heat from the sun.
2. I am guessing your apartment has single pane glass windows facing south or south west. The mid day sun during April and early May would hit your windows and turn the apartment into an oven. In the peak summer months the sun angle changes and goes higher in the sky, meaning it might not shine directly into the windows as much during peak summer.

[BRinSM]

i have the same problem with my house in the valley. the weather is warm all day, but the inside of the house stays nice. then in the evening as the weather cools off outside, the heat that has soaked up into the roof and walls all day starts seeping inside and it's warmer indoors than it is outside. i had the same problem at an apartment in santa monica. you have to keep the air moving in your unit to avoid things getting stuffy.

[bhcompy]

My upstairs bedroom in my apt is flat roof with no insulation and single pane windows. It gets really hot during the day if the sun is out, regardless of external temp.

Only other thing I've seen happen is a hot water leak. I've had electric waterheater go bad and a hot pipe in the wall burst, both turned the place very hot, but it was also moist air.

[greggd1]

I agree. Airflow Ventilation and some insulation.

[Adrianw2]

If it does turn out to be the window's position to the sunlight, I know tinfoil will reflect the heat very well.

[PureHapa]

The sun's position changes throughout the year remember, so it may have been hot earlier but the sunshine is just now hitting your windows and walls, like others mentioned. If you have a south-facing wall and windows, you'll need to get some good window coverings. Do you have a balcony?

[1200RT]

Originally Posted by BRinSM

i have the same problem with my house in the valley. the weather is warm all day, but the inside of the house stays nice. then in the evening as the weather cools off outside, the heat that has soaked up into the roof and walls all day starts seeping inside and it's warmer indoors than it is outside. i had the same problem at an apartment in santa monica. you have to keep the air moving in your unit to avoid things getting stuffy.

As always, BR is right - Airflow is key. Try to establish some kind of cross ventilation.