There are a number of items to address with your foundation contractor. Here are some key elements and why they are important.
Foundation Height
You would think it is the same as the existing foundation, right? Not so fast. What if the original house is older and uses solid wood whereas the new addition will have engineered trusses? There is likely a height difference. What about the type of flooring to be used? Also, is the man cave you always wasted going into the basement below your new master bedroom? Soundproofing plans should be decided now. Two layers of ¾” plywood flooring may be a good investment to not wake up your better half during your Friday night card game. Each of these items affect the height of the floor and therefore affects the height of the foundation for a level transition into the existing home.
Stake out the Area
Foundation contractors usually have someone else stake out the foundation and they dig to these markings. In this DIY case, you’d want them to mark it and to make sure it is square.
Location of Utilities
When the excavation happens, it needs to be deep especially if there is a basement room. Any utilities in the path will of the new foundation will be cut unless you know where they are and the depth. If they need relocated, do this in parallel with your foundation contractor. Have this lined up.
What to do with Excavated Dirt
Hauling the dirt away is an expense. You know how you always hated that slope in the backyard? Now might be the time to correct it. It will cost some grass seed or relocation of plants but may be worth it in savings. This can be a win-win situation.
Securing the New Foundation into the Existing Home.
Especially important if there is to be a basement with this build. The tie-ins should be structurally connected into the existing home. Ask the distance and quantities of these anchors for ensuring the pressure of the outside ground does not move your new foundation. Again, building inspectors can aid you in ensuring this is done properly.
Backfill
Enough ground will be left to backfill into the cavity once the molds are removed (for a poured concrete foundation). Make sure if there are any penetrations such as piping that the ground under this piping is completely packed in. the weight of the ground above can dislodge fittings causing more expense and rework to fix plumbing.
Cutting into the Existing Home
If you have a basement how will you enter this from the new area? When will this cut be made? You may wish to mark and drill this now and leave the cutting for later once you are ready to break into the new addition. This depends largely on your build.
Beam Pockets are not Like Hot Pockets
If the addition above needs a structural beam make sure to address a beam “pocket” where applicable to house the new beam in the new foundation and the existing home. This can mean cutting into the existing foundation for placement of the beam. Negotiate this as part of the scope.
It is highly recommended that you use the book in the links section of this blog has a list of detailed questions to ask your contractor that will be building the foundation to ensure the scope of the effort is clearly laid out and some of the core items to address. It is 180 pages and meant to educate the reader farther than these blog posts and provide the questions and items to look out for as you negotiate with each of the contractors. This step by step guide to aid you in the DIY build process. There are risks with any effort but the rewards provide a ton of value. Make sure that you understand these risks and address them according to your specific build.
