Let the surface area of the larger dog house be denoted as \( S \). According to the problem, the surface area of the smaller dog house is \( \frac{1}{2} S \).
To find the difference in surface area between the large and small houses, we calculate:
\[ \text{Difference in surface area} = S - \frac{1}{2} S \]
This simplifies to:
\[ = S - \frac{1}{2} S = \frac{2}{2} S - \frac{1}{2} S = \frac{1}{2} S \]
Now, to express how much smaller the surface area of the small house is compared to that of the big house as a fraction of the larger house's surface area, we set up the ratio:
\[ \text{Fraction smaller} = \frac{\text{Difference}}{S} = \frac{\frac{1}{2} S}{S} \]
This simplifies to:
\[ = \frac{1}{2} \]
Thus, the surface area of the small house is \(\frac{1}{2}\) the surface area of the large house. Therefore, the surface area of the small house is \(\frac{1}{2}\) smaller compared to the surface area of the large house.
In conclusion, the answer is:
\[ \frac{1}{2} \]