How to Build an Outdoor Fireplace

Outdoor Fireplace
 hikesterson / Getty Images

PROJECT OVERVIEW

  • WORKING TIME: 10 hrs
  • TOTAL TIME: 1 wk – 1 wk, 3 days
  • SKILL LEVEL: Advanced
  • ESTIMATED COST: $200 to $400

One of the best ways to turn your backyard from great to even greater is to build an outdoor fireplace. Creating an area where people love to gather transforms your backyard into a favored spot for family and visitors. Backyard features like barbeques, pools, hot tubs, pergolas, decks, and outdoor kitchens are important anchors for drawing people together—the same holds true for outdoor fireplaces. Outdoor fireplaces are worth it for a few reasons:

  • A fireplace offers more of a living space ambiance outdoors.
  • A fireplace can double as a privacy wall in your yard.
  • If your outdoor space is at a premium, a fireplace can take up less space than a firepit setting.
  • A fireplace is less smokey than a firepit and its flames are better protected from breezes, gusts, or changes in a wind’s direction.

Basics of Your Outdoor Fireplace

This fireplace may look like it’s made of stacked ledger stone, river rock, fieldstone, or any other decorative stone of your choice. But the real secret is that its superstructure is constructed of inexpensive 16-inch and 8-inch concrete cinder blocks. So the materials you need to build an outdoor brick fireplace include cinder blocks for the structure of the fireplace and veneer stone for the aesthetic envelope of it. Cinder blocks can withstand extreme heat and they are fire-resistant, but they are not completely fireproof. Since cinder blocks are porous, they can vent steam, which is important for relieving heat pressure in a fireplace. But, consider using refractory mortar for even more heat resistance.

A poured concrete slab provides a sturdy, level pad on which to build this simple outdoor fireplace. Atop this base is an open-front box made of cinder blocks for storing firewood. On top of this box are hearth blocks. This is where a second box—the firebox—is located. Besides providing room for the wood, this arrangement elevates the fire so that it is easier to maintain. Plus, it raises the fire to a more comfortable viewing height for those sitting around it.

Quarter-inch-thick cement board faces the concrete cinder blocks. Light-weight manufactured veneer store then faces the cement board.

Codes and Restrictions

It is important to check with your local permitting office for any codes and restrictions relating to outdoor fireplaces. Your community may require a building permit. Air quality measures may prohibit wood-burning fireplaces in your area when air quality conditions are poor.

WARNING

It’s required by law that you call 811 (or visit call811.com) before digging or excavating your property. Your local utilities will come out to your home to mark underground pipes and wires so you don’t disturb them when locating and building a fireplace.

What You’ll Need

Equipment / Tools

  • Protective gloves
  • Tamper
  • Tape measure
  • Masonry hammer
  • Hammer
  • Concrete trowel
  • Shovel
  • Bubble level
  • Circular saw
  • Square
  • Hacksaw
  • Hoe
  • Mortar mixing pan
  • Wood or metal stakes

Materials

  • 33 full concrete cinder blocks, 8-inch by 8-inch by 16-inch
  • 12 half concrete cinder blocks, 8-inch by 8-inch by 8-inch
  • Manufactured veneer stone
  • 6 cement backer boards
  • 2 metal flue caps, 24-inch by 24-inch
  • Mortar
  • 26 80-lb. bags quick-set concrete
  • 6 50-lb. bags gravel
  • Nails, 2 1/2-inch
  • 2 two-by-sixes
  • Rebar, 42 inches by 6 feet
  • 2 steel angles, 1 1/2-inch by 72-inch
  • 6 hearth blocks, each 42-inch by 32-inch
  • Masonry nails

Instructions

How To Build an Outdoor Fireplace

  1. Locate the Outdoor FireplaceOutdoor fireplaces should be close enough to the home for easy access, but not so close that it’s a safety hazard or a nuisance. Depending on local codes, an outdoor fireplace needs to be at least 20 feet away from the house. Nearby patio covers can trap smoke. The area underneath the fireplace should be strong. Water in the area should drain away from the fireplace. If water collects around or under the fireplace, the concrete pad will eventually crack.
  2. Clear and Level the Area for the PadClear and excavate a section in the ground 70 inches long by 56 inches. Flatten the ground and level it. Tamp the soil down with the tamper. Spread about 2 inches of gravel and flatten the gravel.
  3. Build the Fireplace Pad FormCut the two-by-sixes into two sections that each are 68 inches long and two sections each 40 inches long. Use the hammer and nails to construct the concrete form. Place the form on the gravel. Use the square to make sure that the form is squared off and perfectly rectangular. Cut the rebar to size.Place wood or metal stakes around the perimeter of the form to keep it square, level, and in place after the concrete has been poured.
  4. Pour the Fireplace Pad ConcreteMix the quick-set concrete with the hoe into the mixing pan. Pour half of the concrete in the form and place the rebar. Place the rebar around the perimeter of the form, about 6 inches from the edges.TipUse 3/8- to 1/2-inch-thick rebar.Pour the rest of the concrete.
  5. Allow the Concrete to CureThe concrete forms can be removed within one to two days. The concrete will be sufficiently cured to work on in four to five days, and a full cure will take about a month.
  6. Lay the Fireplace’s Wood BoxLay seven of the full-size blocks in a U-shape: three in the back and two on the sides. Lay the two half-size blocks at the ends of the U-shape. Mortar the blocks onto the concrete pad. This is the bottom course of blocks in a three-block level box.For the second course, alternate the blocks. The seams from the bottom course should straddle the middle of the blocks on the upper course.The third course is a duplicate of the first, bottom course.
  7. Create the LintelWith the hacksaw, cut the steel angle to 68 inches. Place it across the front of the wood box as a lintel for support.
  8. Lay the Hearth BlocksSecurely mortar down the two hearth blocks on top of the wood box. Mortar the seam between the two hearth blocks.
  9. Build the FireboxThe firebox will be built on top of the hearth blocks and is a smaller version of the wood box. Use two full-size blocks across the back, one full-size block on each side, and one half-size block on each side. Build three courses, duplicating the method used for the wood box.With the hacksaw, cut the steel angle to 48 inches. Place it across the front of the firebox as a lintel for support.
  10. Add the Chimney CapsAdd the two chimney caps side-by-side on top of the firebox.
  11. Lay the Veneer StoneCut and lay the cement board across all areas of the fireplace that will receive veneer stone. Mortar down the board and follow by nailing into place with masonry nails. Mortar and add the veneer stone to the cement board.TipCement board is optional: Veneer stone can be directly applied to the blocks using mortar, if desired.

FAQ

  • How far does an outdoor fireplace need to be from the house?Codes and regulations differ by state, so check with your town’s permitting office. General restrictions may mandate that an outdoor fireplace should be located at least 10 to 30 feet away from your home and at least 10 feet away from your property line.
  • Do you need a foundation for an outdoor fireplace?To build an outdoor brick fireplace, you will need a reinforced concrete slab as the foundation. The concrete slab should be about 4- to 6-inches thick for an outdoor fireplace with plenty of space around the structure. For example, you could make the foundation 3 to 4 feet deep and 4 to 5 feet wide, with more room in the front. But those dimensions depend on the size of your outdoor fireplace.
  • Does an outdoor fireplace add value to the home?If the fireplace is part of a well-designed outdoor living space or outdoor kitchen that can be used to extend the warm weather season, it can enhance the value of your home.
  • How much does it cost to build an outdoor fireplace?Building an outdoor fireplace can range from $1,500 to $20,000, depending on whether it’s a DIY project or if you hire a contractor. If you are going the DIY route to build an outdoor fireplace on a budget, consider a pre-engineered masonry kit or another type of prefab kit though kits still run well over $1,000. Of course, building a firepit for a few hundred dollars would be a way to build a type of outdoor fireplace cheaply.

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