Building a basement foundation requires careful planning, preparation, and step-by-step execution to ensure structural integrity and prevent water damage. Here is a comprehensive guide to building a basement foundation from start to finish:
Page Contents
Assess the Site and Create a Plan
Before beginning construction, you need to assess the site conditions and create a detailed plan for the basement foundation. Consider the following:
Soil Conditions
– Test the soil to determine the load-bearing capacity and stability. Clay soils may require special engineering techniques.
– Check for groundwater level to see if waterproofing is needed.
– Excavate and inspect the soil at footing depth for composition and stability.
Foundation Design
– Choose a suitable foundation type based on soils, site topography, water table level, and local building codes. The common types are concrete block, poured concrete, and precast concrete.
– Determine the size and depth of footings based on load requirements, soil conditions, and frost line depth.
– Create a layout for the foundation including interior and exterior walls, column pads, and any openings.
Waterproofing Considerations
– Select waterproofing materials and techniques based on the water table level. Options include membranes, coatings, drainage panels, and sump pumps.
– Include a drainage system around the exterior of the foundation to direct water away.
– Design a perimeter drain inside the footing if the water table is high.
Material and Equipment Needed
– Order sufficient concrete, reinforcing steel, lumber, waterproofing materials, and hardware.
– Rent or procure equipment such as excavators, backhoes, concrete mixers, and pumps.
– Calculate requirements for concrete, gravel, sand, and rebar.
Excavate and Prepare the Site
With the plan completed, it’s time to start site work and excavation. Proper site prep sets the stage for constructing the foundation.
Clear and Layout
– Clear vegetation, topsoil, debris, and obstructions from the area.
– Stake out the outline of the foundation with batter boards and strings.
– Mark the locations for footings and piers as specified in plans.
Dig and Shape
– Excavate the area 2 feet wider and deeper than the planned footing size.
– Create a level, flat trench bottom and smooth, sloped side walls.
– Add ramps into the excavation to allow equipment access.
Install Dewatering System
– If groundwater is present, install dewatering pipes, sump pits, and pumps to keep the trench dry.
– Place drain rock and geotextile filter fabric around dewatering pipes.
– Activate the dewatering system well in advance of concrete work.
Build the Footings and Foundation Walls
With the excavation complete and dewatering in place, construction of the actual foundation can begin. This includes footings, foundation walls, column pads, and any embedded components.
Pour Concrete Footings
-Dig footing trenches 16”-24” wide and 6”-12” below final grade.
-Lay reinforcing steel rebar in the trench, supported on rebar chairs.
-Build wood forms on top of the trench to hold poured concrete.
-Fill the trench and forms with prepared concrete.
-Screed for level and smooth off the top surface.
Construct Foundation Walls
| For Poured Concrete | For Concrete Block |
|---|---|
| – Build removable wood forms. | – Lay a mortar bed on the footings. |
| – Install steel rebar, anchor bolts, and electrical conduits in forms. | – Place the first course of block and check for level. |
| – Pour concrete into the forms. | – Build up courses using mortar between blocks. |
| – Wait for concrete to cure. | – Stagger vertical block joints in each row. |
| – Remove wood forms. | – Install reinforcing steel and grout as specified. |
– Backfill against walls as they are completed to brace them.
Add Interior Concrete Column Pads
– Dig and shape column pad holes per plan locations and sizes.
– Compact gravel base layer and install reinforcing steel.
– Build wood forms and pour concrete into the pad holes.
– After concrete has cured, remove column forms.
Install Foundation Waterproofing and Drainage
Now that the concrete foundation structure is complete, it’s crucial to waterproof and install drainage systems to manage groundwater and moisture.
Apply Exterior Foundation Waterproofing
– Clean the foundation walls thoroughly with pressure washing.
– For membrane waterproofing, begin at the base and install course by course per manufacturer instructions. Seal seams and fasten top edge.
– For liquid applied coatings, apply product by sprayer or roller based on label directions. Protect adjacent areas from overspray.
– Install drainage panels or protection boards over the waterproofing.
Install Exterior Foundation Drainage
– Place graded gravel in a perimeter trench around the foundation walls.
– Lay 4” perforated drainage pipes in the gravel, sloped to drain away from the house.
– Cover pipes with more gravel, then filter fabric.
– Backfill the trench with excavated soil compacted in layers.
Add Interior Foundation Drainage
– Pour a gravel bed inside at the base of the footing.
– Place 4” perforated drainage pipes on the gravel running around the perimeter.
– Fit a sump pit and pump at the outlet to discharge water outside.
– Cover pipes with more gravel, then a concrete slab or vapor barrier.
Backfill and Final Grading
The last major step is to backfill around the foundation walls with structural fill and complete final grading to achieve proper drainage.
Backfill Foundation
– Backfill symmetrically on all sides with layers of fill soil compacted every 6”.
– Use only engineered structural fill, avoiding organic material.
– Compact to 95% with plate compactor or jumping jack.
– Stop backfill 2’-3’ below final grade to allow for topsoil.
Install Perimeter Drainage
– Place a drainage swale around the foundation perimeter.
– Line the swale with drain rock and perforated pipe per local code.
– Route downspouts and sump pump discharge to the swale or away from the house.
Final Grading and Landscaping
– Install topsoil around the exterior foundation up to grade.
– Grade to slope away from foundation at 5% slope minimum.
– Seed or sod grass, plants trees, and install hardscaping.
Inspect and Seal Foundation
Perform final inspections and apply sealants to complete the basement foundation:
– Make sure backfill is properly sloped and compacted.
– Inspect waterproofing for punctures or leaks and repair as needed.
– Apply foundation sealant around any cracks and cold joints.
– Seal perimeter edge and penetrations with polyurethane caulk.
– Install termite control measures and exterior insulation as applicable.
Conclusion
Constructing a properly drained and watertight basement foundation requires careful planning, preparation, and step-by-step execution. By following building codes and best practices for excavation, waterproofing, drainage, backfilling, and grading you can create a stable, durable foundation for your basement. Pay close attention to soil conditions, choose the right materials and equipment, and control water through every phase of the project.