In one house cool, in the other warm and humid.

Hi,

we bought 2 houses.

One is a solid construction from 1989, about 200 sqm, the other from 2005, about 125 sqm, probably also solid.

In the first one, it is cool and pleasant in the hot weather. In the other, it is muggy and humid in such weather.

Does anyone have an idea what it could be due to? Or do you need more info to speculate!? ;)

We really suffocate in the newer house in this weather, especially the hallways are different; in the older one it is always cool, in the new one it is even the most muggy area...

Both houses in the same location?

How thick are the walls? What was used for insulation? Where are the houses located, how much window area, etc.

Especially modern houses often have more window area, and these, if not shaded, simply heat up the house. The humidity should actually be identical if no ventilation system is in operation.
How are the two houses used? One a weekend house, the other during the week? How many people live in them, how often is cooking, washing, drying laundry done...

You see, many questions, and probably no one can give you a suitable answer.

My guess: it is due to the different volume, or it is a subjective perception. You only get more meaningful results if you take measurements with the same hygrometer in both houses under similar conditions.
So same time, same number of people, both houses equally shaded, and so on.