Adding a 12 ft by 30 ft addition to our home...wondering what is the typical spacing for concrete pier would be and how many rows?
Welcome to the forum rangerbeeg. Any answers you'll get will be heavily dosed with "that depends." What it mostly depends on is whether you live in a place where a building inspector has a say in how home construction is done. The next "it depends" is how the existing home is built. To ensure consistent movement, or lack thereof, your addition will ideally have the same foundation as the original house. That ensures that the addition responds to frost or settling in the same manner as the house.
Foundations and footings are designed to distribute the weight of a building evenly into the ground, with the added functions of anchoring the structure against uplift forces and bracing the structure against shear forces. Piers are about the least effective way of accomplishing any of those objectives, which is why they are not included in the residential code. If ground conditions necessitate building with piers, you should consult with an engineer to determine what the design loads for the addition will be. Piers are sized according to the compressive strength of the soils and the weight of the structure they support. A heavier building requires larger or more piers. Actual spacing would entirely depend on the design for the floor, walls and roof as to where the support needs to be focused.
I hope this doesn't come across as too much of a downer. But adding on to a house is a huge investment and you want to make sure it's a good investment by doing it right. If you update your profile to show the region in which you'll be building then other folks will be able to offer more relevant advice that takes into account the conditions you can expect.
Thanks for the reply. I live in texas and my house is built on pier and beam.
Also the area I am adding on to is mostly already covered by a roof that was a carport. It is already being supported by metal poles.