We didn't "blow" the budget of the build. We were 3% over. Most of that was excavation, fill, and additional concrete and other adjustments required due to incorrect topographic survey. That came pretty quick into the process. The rest was plumbing which resulted from a miscommunication and that bill came much later.

We blew the original budget months before, during the design phase of the project!

What I've seen is: once framing is done, people start envisioning their spaces differently, and then make changes (bathroom upgrades, etc). The kitchen is one area where it goes bad, fast.

We've blown it in soil and site - but kitchen appliances and fixtures for bath already purchased - so at least that won't be a "surprise". Soil conditions requiring rock hammers and a low pressure septic were big drivers of our initial over run.

Out of four total draws we were getting close to our total to spend when we handed over the third draw, but after a short stress out session I realized all the material was already bought and the only money needed was the final draw for labor to the general after everything was done, so we had plenty.

we were actually under budget until dh decided to triple the driveway size and i agreed to it...... i think if you have a good builder who understands what your expectations are and has built homes recently you won't really go over budget

When they dug the hole, it filled up with water (hit a spring). It was an additional $20,000 right off the bat to do extensive additional drainage. What a way to start our build! But during recent flooding, most of our neighbors had wet basements, and we are always dry. So maybe a blessing in disguise.

wow joyce that's an expensive find

Dirt and no we didn't dig and strike gold but we didn't hit a natural spring either, yikes Joyce. Ouch. That is really the only surprise. Other areas we didn't WANT to spend more but it didn't mean we couldn't. We went over our 'it would be awesome if it was under this number' but we were still within our budget if that makes any sense at all.

Our renovation budget got swallowed up by unexpected flooding that buckled the newly laid wood floors. Backhoes had to be brought in to dig a drain along side the foundation -- and thousands were added to the proposal price of that because they ended up moving huge rocks that took an extra few hours. The wood floors were replaced with tile. Yes water is expensive...

Many things about our build were atypical, and one thing is that we never set a budget! That may not sound odd to rich people, but we were on a very tight budget, building out-of-pocket as the money came in. We had a general idea of what it would cost, although I'm sure we went over that. I kept good records, but still haven't sat down and added it up. It's fully paid for, so I just might stay in my little bubble of delusion a bit longer!

About the time I got home on the first day of digging and the excavator walked up and said, "well, we've got a problem here...". Turned out to be not as bad as finding ledge, but our site is pure sand that meant he had to dig a bigger hole due to the walls falling in and had to do a lot more moving material around to fit on the site. (We were on the beach about 40M years ago and apparently there is about 180 feet of beach sand under our house. We warned the guy about the sand, based on other holes we had dug, but he dismissed it as "not possible". Hah!)