Foundations 101: Everything You Need to Know Before Your New Home Comes Out of the Ground

The foundation might not be the most exciting part of building a home.

There are no beautiful kitchens to choose. No flooring. No lighting. No paint colours.

But when it comes to the long-term performance of your home, the foundation is one of the most important stages of the entire build.

Everything above it depends on what happens below it.

A good foundation starts long before the concrete truck arrives. Excavation, soil conditions, drainage, elevations, reinforcing steel, formwork, underground services, waterproofing and backfill all have to work together.

And unlike many finishes in your home, foundation mistakes aren't particularly easy to change later.

Here's what homeowners should understand about foundations before construction begins.

It Starts With the Ground

Before you can build up, you need to understand what's underneath you.

Soil and site conditions can dramatically affect foundation design and construction.

Depending on your property, you could encounter:

• Rock

• Clay

• Sand

• Gravel

• Organic material

• Fill

• High groundwater

• Poor drainage

• Sloped terrain

• Unstable soils

This is why one home's foundation can be relatively straightforward while another property a few kilometres away requires considerably more engineering and excavation.

Your foundation should be designed for your house and your site.

Surveying Matters More Than You Think

Before excavation, make sure everyone is working from the correct information.

The house needs to be positioned properly on the property and constructed at the correct elevation.

A surveyor may be involved in establishing property boundaries, building location and elevations.

This isn't the stage where you want someone saying:

“It looks about right.”

Being slightly wrong at the beginning can become a very big problem later.

Excavation: The First Big Transformation

Excavation is when your drawings suddenly start becoming real.

The excavator removes material to reach the required depth and create space for the foundation.

This sounds straightforward, but several things can affect the process.

Rock is a big one.

If excavation reveals significant rock, removal can become expensive quickly.

Water is another.

If groundwater or heavy rain enters the excavation, additional pumping, drainage or site preparation may be required.

And unsuitable soil may need to be removed and replaced with appropriate material.

This is one reason having a contingency in your construction budget is so important.

You don't always know exactly what's underground until you start digging.

Don't Over-Excavate Without a Plan

Excavation needs to be coordinated with the foundation design.

Removing too much material can mean bringing material back in and properly compacting it.

Removing too little means additional excavation.

Your excavation contractor should understand the foundation drawings and required elevations before starting.

This is also a good time to think ahead.

Where will excavated material go?

Can some remain on site for future grading?

Does it need to be hauled away?

Where will trucks access the property?

Where will materials be stockpiled?

A little planning can prevent a lot of unnecessary material handling.

Footings: Where the House Meets the Ground

Footings are generally the widened concrete bases underneath foundation walls or structural elements.

Their job is to spread the building loads into the supporting soil.

Footing dimensions and reinforcement aren't something to guess.

They need to follow the approved plans and applicable engineering and building requirements.

Before concrete is placed, verify that the footing forms, reinforcing steel and dimensions are correct and that any required inspection has occurred.

Once concrete is poured, changing something becomes significantly more difficult.

Reinforcing Steel Isn't Decorative

You'll see reinforcing steel — commonly called rebar — throughout foundation construction.

Rebar strengthens concrete and helps it handle forces that concrete alone doesn't handle particularly well.

Its size, spacing, location, overlaps and connections can all matter.

If the drawings specify reinforcing, follow the drawings.

Don't move or remove reinforcing because it happens to be inconvenient for another component.

If there's a conflict, stop and get the appropriate professional involved.

Foundation Walls

Once the footings are ready, the foundation walls can be formed.

These walls may create a basement, crawlspace or simply support the structure above, depending on the design.

This is another stage where dimensions matter enormously.

Before the pour, check important measurements.

Are the walls in the correct locations?

Are openings the correct size?

Are door locations correct?

Are beam pockets or structural details accounted for?

Are required penetrations planned?

Is everything square?

Concrete is much easier to check before it's poured than to move afterward.

The Concrete Pour

Foundation-pour day can feel dramatic.

Concrete trucks arrive. Pumps may be running. Multiple people are working quickly. Everyone has a job.

This isn't an ideal time to suddenly reconsider the foundation design.

Decisions should already be made.

The crew should know the required concrete specifications, wall heights, openings and structural details.

Weather also matters.

Extreme heat, freezing temperatures and heavy rain can all affect concrete work and may require additional precautions.

Your concrete and foundation professionals should determine the appropriate procedures for the conditions.

Concrete Needs Time

One of the most important things to understand about concrete is that hard doesn't necessarily mean fully cured.

Concrete gains strength over time.

Just because you can touch it or walk near it doesn't mean it's ready for every load or the next stage of construction.

Follow the requirements and recommendations of the engineer, concrete supplier and contractor regarding curing and when subsequent work can proceed.

Trying to save a day or two isn't worth compromising something that will support the house for decades.

Plan Your Plumbing Before the Slab

If you're building a basement or slab-on-grade home, plumbing and other services may need to be installed below the concrete slab.

This is an important checkpoint.

Once the slab is poured, moving underground plumbing becomes considerably more complicated.

Before covering anything, confirm locations for things such as:

• Toilets

• Showers

• Tubs

• Floor drains

• Sinks

• Mechanical-room drains

• Kitchen plumbing where applicable

• Laundry

• Future bathrooms

• Utility penetrations

If you're considering a future basement suite or additional bathroom, this may be the time to rough in services even if you're not finishing the space immediately.

Planning now can be dramatically cheaper than cutting concrete later.

Take Photos Before Anything Gets Covered

This is one of the easiest things homeowners can do.

Take lots of photos.

Photograph:

• Underground plumbing

• Drain locations

• Foundation penetrations

• Reinforcing

• Drainage systems

• Waterproofing

• Utility locations

• Anything that will eventually disappear behind concrete or backfill

Take wide photos for context and closer photos showing measurements where useful.

Years from now, those photos can be incredibly valuable.

Foundation Drainage Is Critical

Concrete is strong.

It is not a magical barrier against every water problem.

Managing water around the foundation is extremely important.

Depending on the foundation design and local requirements, the system may include:

• Perimeter drainage

• Drain rock

• Waterproofing or dampproofing

• Drainage membranes

• Sump systems

• Proper exterior grading

• Roof-water management

The objective is simple:

Move water away from the house.

You don't want water sitting against your foundation looking for a way inside.

Waterproofing and Dampproofing Are Not Always the Same Thing

These terms are sometimes used interchangeably in casual conversation, but they can describe different systems.

Dampproofing generally helps resist soil moisture.

Waterproofing systems are intended to provide greater resistance to water penetration.

What your home needs depends on the design, site conditions and applicable building requirements.

A wet site or high groundwater condition may require a very different strategy than a dry, well-draining property.

This is worth understanding before the foundation gets covered.

Think About Exterior Insulation

Energy requirements have changed significantly over the years.

Depending on your climate zone, foundation type and building design, insulation may be installed on the interior, exterior or incorporated into the foundation system.

This should be determined during design — not improvised once the foundation is already built.

Western Canadian climates can put significant demands on foundations, particularly when it comes to moisture, freezing conditions and energy performance.

Follow the approved building design and local requirements.

Before Backfilling: Stop and Look

Backfilling is one of those construction milestones where a huge amount of work suddenly disappears.

Once soil is pushed back against the foundation, many components become difficult or impossible to inspect visually.

Before backfilling, confirm that everything that needs to happen first has happened.

Depending on the project, that may include:

• Required inspections

• Waterproofing or dampproofing

• Drainage membrane

• Perimeter drainage

• Drain rock

• Foundation insulation

• Utility penetrations

• Required protection board

• Drain connections

And take photos.

Backfill should never be used to hide unfinished work.

Backfilling Requires Care

Backfill isn't simply pushing dirt back into the hole.

The type of material, placement and compaction can matter.

Heavy equipment operating too close to newly constructed foundation walls can also create significant loads.

The contractor needs to consider concrete strength, wall bracing, foundation design and site conditions before backfilling.

This is another area where rushing can create expensive problems.

Think About Final Grade Early

Water management doesn't stop at the foundation wall.

Eventually, the property needs to be graded so surface water moves appropriately away from the house.

This affects:

• Driveways

• Walkways

• Patios

• Landscaping

• Retaining walls

• Stairs

• Decks

• Window wells

• Exterior doors

One common mistake is designing each of these elements separately.

They all interact with your finished elevations.

Think about the finished property while you're still working on the foundation.

Foundation Cracks: Should You Panic?

Concrete can crack.

Seeing a crack doesn't automatically mean your foundation is failing.

Some cracking can result from normal concrete shrinkage and curing.

Other cracks may indicate movement, water intrusion or structural concerns.

The important factors include the crack's location, width, direction, whether it changes over time and whether there are other signs of movement.

If you're concerned about a foundation crack, don't diagnose it from an internet photo.

Have the appropriate qualified professional evaluate it.

Radon Should Be Part of the Conversation

Depending on where you're building in Western Canada, radon protection may need to be incorporated into the construction.

Radon is a naturally occurring radioactive gas that can enter buildings from the ground.

Modern construction practices can include provisions below the slab to allow radon to be managed.

This is much easier to address while constructing the foundation than after the house is finished.

Check the requirements for your jurisdiction and building design.

Common Foundation Mistakes to Watch For

Many foundation problems aren't caused by one dramatic mistake.

They're caused by small details being missed.

Watch for:

• Incorrect building location

• Incorrect elevations

• Poor excavation planning

• Inadequate drainage

• Missing or misplaced reinforcing

• Incorrect openings

• Forgotten penetrations

• Plumbing in the wrong location

• Incomplete waterproofing

• Damage during backfill

• Poor grading

• Unplanned changes

• Work being covered before inspection

The best time to catch almost all of these problems is before the next stage begins.

Your Foundation Checklist

Before moving on to framing, make sure the appropriate people have confirmed the major foundation items for your project:

✓ Building location confirmed
✓ Elevations confirmed
✓ Excavation completed appropriately
✓ Soil/site issues addressed
✓ Footings completed according to plans
✓ Reinforcing installed as specified
✓ Required inspections completed
✓ Foundation dimensions checked
✓ Openings and structural details confirmed
✓ Underground plumbing confirmed
✓ Utility penetrations planned
✓ Photos taken before covering work
✓ Waterproofing/dampproofing completed
✓ Perimeter drainage installed
✓ Foundation insulation completed where required
✓ Radon provisions completed where required
✓ Backfill requirements confirmed
✓ Site grading considered
✓ Foundation ready for framing

Don't Be Afraid to Measure

One of the simplest pieces of advice we can give homeowners during foundation construction is:

Bring a tape measure.

You don't need to interfere with the trades or pretend to be the engineer.

But you should understand your plans.

If your garage is supposed to be 24 feet wide, measure it.

If there's supposed to be a door in a particular location, look for it.

If the basement layout is important to you, understand where the walls and plumbing are going.

Ask questions before the concrete is poured.

Most trades would much rather answer a five-minute question before a pour than spend two days trying to fix something afterward.

The Foundation Is Where Good Planning Pays Off

Foundations aren't glamorous.

Most of the work you're paying for will eventually be buried, covered or hidden underneath the house.

But this is exactly why it matters.

The kitchen can be renovated.

Paint can be changed.

Flooring can be replaced.

Your foundation is different.

It's something you want to get right the first time.

So pay attention during this stage.

Understand your plans. Coordinate your trades. Think about drainage. Confirm your plumbing. Take photos. Complete your inspections. Ask questions before concrete is placed.

And remember:

The best time to solve a foundation problem is before it becomes one.

A great home doesn't start with the finishes.

It starts with what you build underneath them.