Construction emissions are amortized over 50 years.
This question gets to the center of really important methodology questions. How to account for emissions from building a home or constructing a car? In the first year? Or spread out over time? The approach we use is to spread them out over time.
Here is a deep dive into how the UC Berkeley business calculator works (see PDF).
You can see the section on building construction says they assume 930 gCO2 per square foot. They go into much more detail on this in the household methodology paper (see PDF).
See page 19 specifically: "Amortizing these emissions over a 50 year expected life time for the average single-unit home built in 1997 of 2,150 square feet results in an annualized emission factor of 930 gCO 2 e per square foot."