How to Build a Hearth for Your Wood-Stove
If you're heating your home with a wood stove or a fireplace, a hearth pad is a must.
It keeps the flooring under your woodstove from catching on fire, holds the embers away from you and your floor, lets you comply with building codes and insurance requirements, and helps your fireplace become the stunning focal point it was born to claim.
Store-bought hearth pads can be very expensive, ranging from 250 to 900 dollars online or at your local big box store. Mass-produced hearth pads are also not very likely to match your decor or personality.
Fortunately, with a bit of know-how, basic carpentry skills, and a little bit of patience, you can have a custom-made hearth pad sitting under your stove in no time.
In this article, we'll help you design a hearth that works with the requirements of your stove, looks great, and does not break the bank.
What Is a Hearth Pad?
All other considerations aside, a hearth pad is a way to keep your highly flammable flooring, yourself, and equally highly flammable most everything else in your home from being set on fire by the wood stove that burns at up to 900 degrees Fahrenheit ( coal stoves burn even hotter).
Hearths also serve as a convenient place to store firewood, keep the embers and soot away from the floor and add a nice decorative touch to your room.
They range from a simple piece of flagstone seating under a stove in a mountain man cabin to an extravagant contraption with multiple levels, areas for wood storage, and more decorative touches than the rest of your home.
The design we're building falls somewhere in between the two-modern enough to avoid dragging a 300 lb boulder into your living room and simple enough to skip hiring out an 18th-century masonry stove builder.
Minimum Fire Prevention Requirements
Let's start with determining the minimum requirements your hearth will need to meet to keep your home from going up in flames and your insurance agent from having a heart attack.
Start by looking for a certification sticker on the back of the stove. Most newer wood and coal stoves will have one, and on it, you'll see manufacturers' requirements for a hearth size, insulation value, and minimum distance to flammable surfaces. It will also list the type of chimney pipe you should use and the distance it needs to be kept from the wall.
If you're not seeing a sticker, there is a very good chance a code inspector will apply the general requirements used for an uncertified stove, and they're likely to be much more stringent. Plus, frankly, it's a good idea to err on the side of caution when a mistake can result in your home going up in flames.
Your hearth will need to meet the following requirements on size, insulative value, and fire resistance.
Minimum Dimensions
The minimum dimensions of the pad are mostly to protect the surrounding surfaces from getting too hot and going up in flames as well as to stop an errant ember from burning your floor.
National Fire Institute (NFI), the American gold standard, recommends extending the hearth at a minimum of 8 inches to the sides and back and 18 inches in front of the dimensions of the stove.
Keep in mind that this is just the size of the hearth. You will also need to account for the minimum distance from the woodstove to the nearest combustible surface-which is 36 inches to all sides.
Insulation Value
Insulative value is there to prevent the combustible materials under the hearth from heating up, drying out, and starting a fire. The thickness of the hearth will be dependent on how far the bottom of the burning chamber of the stove is located above the floor.
2 to 4-inch distance to the floor will require a layer of hollow masonry of at least 4 inches thick covered by a 24 gauge sheet of steel. 4 to 6 inches of space will cut the masonry layer to 2 inches.
Fortunately, masonry is not the only way to insulate the stove from the floor. There are a number of other materials that do just as good a job weighing much less.
Fire Resistance
Fire resistance is simply the ability of the hearth to keep itself from going up in flames-no point protecting the floor and joists underneath if the hearth is going to start the fire.
The common recommendation is a continuous layer of metal or stone, with grouted tile as one of the most commonly seen options. Keep in mind that stone and metal can add up in weight very fast, and your floor joists are only rated to 40 lbs per square foot of weight.
Frame Styles
An airtight stove can weigh more than 400 lbs, so the structure that supports it must be able to handle that weight. Most frame designs for hearth pads can be split into the following three categories:
Flat
Flat hearth-which is, just as it sounds, a hearth that barely rises above the level of the floor. Flat hearths are used when the floor itself is already fireproof or the stove does not radiate much heat toward the floor.
With a flat hearth, there is no need for the frame, and you can skip this portion of the article and move straight to the center layer.
Medium
A medium hearth is the most common design, usually ranging between 3 and 8 inches in height. It's easy to build, gives you enough room to separate the floor from the hot parts of the stove, and looks great.
Tall
Tall hearth designs are not very common and are used if there is a need for additional storage space, or the stove needs to be raised for aesthetic reasons. This design is more complicated and will usually require a professional involved.
The shape of the hearth pad is determined by the size of the stove and the distance to flammable walls.
Building the Frame
1.
Start by determining the floor space you need to protect against the heat coming from the stove and ambers. The abovementioned 18 inches from the front and 8 inches to the side of the stove's outside dimensions are a good start if your stove is not certified.
2.
Adjust the shape of the pad to make sure the stove is positioned far enough from the walls. For a certified older stove, assume that you need at least 36 inches to each side. A stove with a certification sticker will give you more exact numbers. If you're planning( and you definitely should) to add non-combustible wall protection, that distance will decrease.
3.
Decide on the height of the platform and assemble it using either 2-by-4s,6s, or 8s, keeping the distances between the joists at approximately 16 inches, similar to the way your house's floor is built since the hearth platform is designed to withstand the same amount of weight.
4.
Double up the joists in the area the legs of the stove will be positioned.
5.
Cut a sheet of 1/2 or 5/8 inch plywood or OSB to shape and attach it on top of the frame using 1 1/2 inch screws, spreading them about 8 inches apart.
Now that the frame is done, the following steps will apply equally well to any of the three types of hearth pads.
Center Layer
The center layer of the hearth pad provides the majority of the insulation and reflects some of the heat radiation back, keeping the frame and the floor beneath it from overheating and catching on fire. It also serves as a point of attachment for the ever-popular tile or flagstone but can be the decorative layer on its own if properly finished.
To build it, you'll need a cement board (Durarock or Hardibacker board are commonly used brands), screws or nails, anti-alkaline tape, thin-set mortar, and a 24 gauge steel sheet. All common-use items found in any big box store.
1.
Spread construction adhesive on top of the plywood to help keep the cement board in place.
2.
For stoves with legs 6 inches or longer, use one thickness of cement board, cut to shape, and attach with either corrosion-resistant 1 1/4-inch screw or roofing nails. For stoves seated closer to the floor, add additional layers of cement board to improve insulation.
3.
To cut cement board, score it with a work knife and snap along the line. Use a jigsaw for more intricate shaping.
4.
Just as when attaching plywood or OSB, position screws 8 inches apart but keep them an inch away from the edges to avoid breaking off a piece of the board. Tape the seams between cement board pieces with anti-alkaline tape and spread a thin layer of thin-set mortar over them.
5.
If the legs on your stove are shorter than 6 inches, it's a good idea to build up additional thickness by using two more layers of the cement board.
6.
Place a sheet of 24 gauge steel under the layers of cement board- steel will help reflect heat radiation back towards the stove, keeping the floor under it cooler.
If you've opted for a low hearth pad, you can simply lay two layers of cement board on top of 24 gauge steel straight on the subflooring, creating a more modern look. Make sure your stove has legs over 6 inches and does not require additional insulation in the pad if that's the design you've chosen.
Decorative Layer
The decorative layer will make your hearth pad look presentable and add an additional layer of fireproof material to your design. For this part of the project, you'll need tile, thinset, a notched trowel to apply it, grout, a grout sponge, tile spacers, and a tile saw.
1.
Start by making sure the tops of your cement board surface are completely flat. The time spent on ensuring you're laying tile on a flat, smooth surface will be repaid tenfold in the end.
2.
The next step is to dry fit your tiles, cut them to shape, and make sure both you and everyone else likely to chime in with their unasked-for opinion is happy with the appearance. Thinset sets relatively fast, and it's best to have everything ready before you start counting the minutes.
Lay out your tile design dry, starting from the center front of the pad, marking the tiles that need to be cut. Cut the tiles using a tile saw or a circular saw tile-cutting blade. Try to keep the cuts to a minimum, and don't leave pieces of tile less than 1 inch wide.
3.
Once done dry-fitting and cutting to size, transfer the tiles to a nearby flat surface, laying out a copy of your finalized design. This will help in keeping track of which piece of tile goes where without marking them.
4.
Mix a batch of thinset, following the proportions on the bag and using a drill (preferably with a 1/2-inch chuck) with a cement mixer bit attachment until the mixture sticks to the trowel when held upside down. Keep in mind, the less water added into cement, the stronger the final product.
5.
Spread a thin layer on half the pad ( or a quarter if you've chosen to go with an extra large design) and notch it with a notched side of the trowel by scraping the trowel through the thinset. Notching will help the thinset distribute itself more evenly under the tile, avoiding air bubbles that will become weak points in future use.
6.
Carefully place the tiles on the thinset, following your dry-fitted designs. Set down and twist each tile as you set it on the thinset. Remember to position spacers between the tiles as you're going through them.
Thinset has a working time of 20 to 40 minutes, depending on the mix and humidity levels. Make sure to only mix the amount you need to finish the area you're working on.
7.
Give your project a minimum of 24 hours for the cement to set to let it get to the point when it is set enough for you to walk on the surface. Remove the spacers.
8.
Mix a batch of grout until it is a consistency of cream cheese and apply it to the tops of the tiles, keeping the trowel diagonally to the edges of the tiles until all the spaces between them have been filled.
Once done, scrape off the excess grout and let it set for an hour or two. With grout firm to the touch, grab a sponge, generously soak it in water and wash off the excess grout left by the trowel.
9.
Give your new hearth pad a day or two to set and come back to remove the haze the wet sponge left as it was removing the grout. In most cases, a simple buff with a dump close will do the trick, but if you're having issues mix 1 part vinegar to 4 parts water and apply this solution to clear the haze off your tiles.
Conculsion
While complicated at first glance, building a hearth pad is a simple project if taken step by step, and the fruits of your labors will be the joy and pride of your house for years to come.
