Front Porch Foundations

Essential to a Strong, Long Lasting Porch

We normally don't think much about front porch foundations because usually they are not visible. But when it comes to foundations, what you can't see can hurt you.

I'm sure you've passed a house or two where the porch was literally falling off or sorely in need of porch repairs. There could be several reasons for this but a poorly built foundation may be the major culprit.

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Build a porch foundation the right wayFooting, pier, and post foundation for front porch

Foundations for porches aren't that much different than foundations for homes. A foundation has to safely bear not only the weight of the porch substructure but also the roof, railings, columns, and more as well.

Download our free "How to Square Your Porch or Deck" ebook.
Details below

Consider These Before Building Your Front Porch

Consider the following:

  • Geography: Where do you live? Unstable water or soil conditions may require deeper porch footings, thicker walls, or reinforced concrete. (Silty-clay soils, as an example, have an extremely poor load bearing capacity). In addition, if you live in areas with prominent frost heaves (which have tremendous force) footings must be placed below the frost line.
  • Weight: How much does your porch structure weigh? The foundation must be strong enough to support its weight and the weight of your furniture and guests. We've all heard of accidents where a deck gave out because there were too many people on it.
  • Slopes: Foundation construction is also determined by the slope of the area. Flat areas or very slightly sloped areas, still need a good foundation. Even if you have a patio porch, the slab still needs to be stable. Any shifting of the roof can cause consider damage to the home.

In addition, regardless of the slope, always build to ensure water runs away from the structure. Soil structure is also important and will dictate how deep your footings need to be.

For steep slopes, you will need either piers (columns of reinforced concrete) that sit on concrete slabs deep into the ground or perhaps even an engineered foundation.


Did You Know There Are Different Types of  Foundations for Porches?

Learn the Lingo of Footings and Pier Foundations

These usually consist of short columns of either concrete block or poured concrete (piers) that rest on concrete pads called footings. Often these are poured as one unit. Typically, wood posts are then anchored to the piers which in turn support beams that are attached to the posts.

IMPORTANT: Although the process and structure of building your porch's foundation is similar to that of a backyard deck, the foundation will be carrying significantly more weight and must comply with your local building codes. Therefore, it is extremely important to understand what is involved to ensure your porch will be safe and maintain its structural integrity for years to come.


Footings

Footings carry the weight of the porch directly onto the soil. Depending on your specific geographical location, footings must be a minimum distance below grade to extend beyond the frost line and be sufficient in size to spread the load. The load includes the weight of your structure (known as the dead load) and people, furniture, and snow (known as the live load).

Don't let this intimidate you. In most cases, your local building codes department will be able to tell you the minimum requirements for footings which incorporate the load factors for your area.

When building footings consider the total weight they will carry. If you are planning to install heavy objects like hot tubs, stone fireplaces, etc., be sure to address this with your codes department or a construction engineer before you pour your footings.

Dimensions of piers, footing depth along with footing size, are determined based on geographical areas. I've found that 16 inch square footings (or up to 18 inch diameter footings) that are 8 inches thick to be fairly common. Check with your local building codes department.

Footing Details: Two typical footing and pier construction techniques:


pier diagramsPier diagrams
NOTE: Although this may be permissible by local building codes in some areas of the country; we do not recommend placing posts directly into concrete as this significantly increases post degradation due to moisture. You can avoid this problem and increase the longevity of your posts by using post bases as shown below.

Concrete Footing Forms

Concrete footing forms like the Quikcrete® concrete form featured below are ideal for pouring concrete footings for porch foundations. They usually come in 4 foot lengths are come in 8, 10, or 12 inches in diameter.


Pouring concrete into concrete formsPouring concrete into concrete forms

Piers

Like decks, piers are an essential part of porch foundations. Piers are short concrete columns on top of footings that support posts. Piers, which are normally below grade, are meant to transfer porch loads to the footings.

In the photo below, footings and piers are poured simultaneously. Note a piece of sonotube is used to form the pier.

Using a precast concrete pier (example at right) as part of your porch foundation is sometimes acceptable in geographical locations where there is little to no frost line.


diagram of pier on footingDiagram of pier on footing
Have You Heard of Diamond Pier Foundation Systems?

Here's a novel way to install almost "instant" piers for your front porch or deck. No muss, no fuss, and you can start building the same day.

Learn about diamond pier foundation systems.


Posts - Why Not to Place Them in Concrete

Typically, posts are usually treated 4x4s, 4x6s, or 6x6s. As a general rule, concrete and wood don't mix so I almost always try to avoid mixing the two: I avoid placing my posts directly into or onto concrete.

Rather, I use adjustable mounting hardware to keep the two apart while simultaneously ensuring a solid connection.


Installing beam on posts and piers with post basesInstalling beam on posts and piers with post bases

Front Porch Slab Foundations

Concrete front porch foundations usually consist of concrete poured at grade over a base material like stone or gravel.

Porch foundations from slabs don't have to be just at ground level. Concrete slabs can be poured at any height and offer many different finishing options.

If building a porch a few feet off the ground, concrete blocks are typically used to create the form. It is then filled with stone to within four inches of the top. Concrete is then poured on top.


Filling concrete block foundation with stoneFilling concrete block foundation with stone
Pouring concrete over stone on front porchPouring concrete over stone on front porch
Putting the final touches on the front porch concrete floorPutting the final touches on the front porch concrete floor

If the porch is considerably higher, steel channels and steel sheathing panels are installed to height. Concrete is then poured over the steel sheathing.


Steel channels and sheathing being installed to receive concreteSteel channels and sheathing being installed to receive concrete

See our concrete flooring section to see exactly how its done.


Perimeter Foundations

These usually consist of a continuous poured concrete footing supporting foundation walls that support the structure. They are often used where water is an issue or on steep slopes.


Know This: Why Ledger Boards Are Integral in Porch Foundations

Unless your porch is free-standing, you will need to attach the ledger board to your home. Like piers, ledger boards transfer the load from the structure directly onto the home's wall to which it is attached.

Just as important, they help displace the lateral load making for a substantially more stable porch.


Ledger board installed under door thresholdLedger board installed under door threshold

As with deck ledger boards, there are a few planning basics that are important to note about front porch foundation ledger boards:

porch foundation diagram
  • The surface of your front porch should be lower than the interior floor leading on to it.
  • To avoid a tripping hazard, the porch floor can be located just below the door threshold which will also make it easier to navigate with a wheelchair.
  • For those who must contend with snow and ice, you should plan on your porch floor being at least four inches below the interior floor. Local building codes will probably dictate the distance.
  • To position the ledger board, consider both the distance from the interior floor and the thickness of your porch flooring material
  • You ledger board should be the same size as your joist material.
  • Determine the length by subtracting 3 inches from the total width of your porch framing. This allows the end joists to overlap the ledger board. You may need to make the ledger even shorter if your porch flooring is going to overhang the porch framing.
  • Unlike decks, ledger board flashing for front porches may or may not be required. I; however, highly recommend flashing your ledger board even though it will be protected with your porch roof. It is inexpensive and easy to do. Check your local building codes to see if it is required in your area.

We would be remiss if we didn't address a few porch foundation ledger board installation basics too:

  • Most importantly, whether its a deck ledger board or front porch ledger, it must be attached through your home's sheathing and the rim joist with bolts or in some cases, lag screws. Your home's siding, brick veneer, or sheathing is not sufficiently substantial to hold your ledger board.
  • Building codes normally dictate bolt spacing. If they do not, a rule of thumb is to space 1/2 inch bolts at least every 14 inches with spans up to 10 feet; 10 inches for spans of up to 14 feet; and 8 inches for spans longer than 14 feet.

Ledger board installation optionsLedger board installation options
  • Allow for drainage behind the ledger board by attaching washers to the bolt after it penetrates the ledger and before it is inserted through the sheathing.
  • If your home is constructed with I-joists or other kind of manufactured wood system, consult with your building department or a construction engineer.
  • If you have siding, you will have to mark and cut the siding in order to install the ledger board. Install flashing as indicated in the drawings above and caulk to create a weather tight seal.

Do You Know Your Local Building Codes?

Local building codes normally dictate your ledger board requirements. Many porch and deck failures are the result of poor ledger board installations. Therefore, in many locations, ledger boards must not only be attached to your home as indicated above but also supported by posts and footings as shown below.

Or, in some cases, porches or decks must be built as stand-alone structures as indicated below.

So be sure to check with your local building codes department before you start construction.


Ledger board supported by post and pierLedger board supported by post and pier
Stand-alone porch foundationStand-alone porch foundation

Video: See How a Porch Floor is Constructed

Free Tutorial: Squaring Your Porch Foundation

free pdf tutorial on how to square your foundation

Dave wrote a 14 page tutorial with tips for building a square porch or deck foundation. 

When building a quality foundation, squaring it is important and this will make the rest of your project go more smoothly.

You can download our free tutorial right here.

Look at Some Sample Pages...

Square your porch foundation - sample pages

Porch Flooring Beams - Not Exactly Like a Deck

Traditional front porch floors are constructed a bit differently than decks. Whereas decking materials usually run horizontal to the home, porch flooring traditionally runs perpendicular. Therefore, it is important to note that one or more additional beams are required.

As a general rule joists that are spaced 16 inches on center can extend 1 1/2 times in feet their width in inches. Thus:

a 2x8 can span to 12 feet (8 plus 4" (half of the width) = 12 feet)

a 2x10 can span 15 feet

a 2x12 can expand out to 18 feet.

However, this can vary by geographical area and sometimes by the type (or species) of wood you are using. Be sure to check with your local codes department.

I've included graphics below to illustrate how a porch foundation is typically constructed. Depending on the length of your porch, you may need to add an additional beam to carry the joists.


Front porch beam layoutFront porch beam layout
front porch joist layoutFront porch joist layout
Front porch decking materials laid perpendicular to houseFront porch decking materials laid perpendicular to house

You must see our porch flooring section for additional details regarding hanging joists and adding your porch decking materials.

If you are considering building or replacing your existing front porch you owe it to yourself to check out this video courtesy of Vintage Woodworks - great must-know information!

Or watch it right here:

See Our Porch and Deck Foundation Pictorial

Installing lag screwsInstalling lag screws

Putting up a porch foundation? Take a look at our porch and deck foundation pictorial to see how builders constructed a back porch foundation in six hours.

Know Your Porch's #1 Enemy

Your porch's #1 enemy isn't birds nesting, though that may be a nuisance to some. The best thing you can do to protect your porch is to prevent water from reaching it.

  •  Ensure you have adequate slope away from your home and porch to direct water away from it. If you have water issues, consider installing French drains, ensure your down spouts empty at least 10 feet from your porch, and add channels for water using crushed stone.
  •  If you have a crawl space underneath your porch consider covering it with plastic to form a moisture barrier
  •  Ensure your porch floor slopes slightly away from the house to direct water away
  •  See our waterproofing tips for your porch floor - especially if you have a two story porch
  •  Bevel hand railings
  •  Use good primer paints and paint; keep up with porch repairs and maintenance
  •  Ensure you have air access underneath your porch (use vents)

Porches need a solid foundationPorches need a solid foundation

Before You Go...

beautiful patio area outside of home

Before you go, take a look at these tips to help you protect your wood porch foundation.

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