How to Replace Individual Tongue and Groove Siding Boards

Not sure how to replace your tongue and groove cedar siding? Think of it as a challenging puzzle. When the pieces don’t fit right, just get out your circular saw.

Before having our house painted last year, Eric and I had to replace much of our cedar siding. Some of the boards were still in great shape, but some (approximately a zillion) were beyond hope.

Cracked and damaged tongue and groove siding

But how do you squeeze interlocking siding into boards that are already in place?

It sounds impossible, but it can be done. If you’re faced with this predicament, here’s what you need to do to swap out some of your tongue and groove boards.

Just remember before you get started that old house paint and stain may have lead in it. You might want to test the paint for lead before you start prying or cutting your cedar siding boards.

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Materials to Replace Tongue and Groove Siding

1. Figure out How Much Lumber You Need

Start by taking a sharp eye to the entirety of your home’s perimeter, looking for peeling, soft or rotted boards. Use chalk to mark all of the boards that need to be replaced. Cry as the numbers start adding up…$100 in lumber here, $150 there.

Tally up approximately how many linear feet you’ll need to replace. Add about 20% to that, because lumber suppliers often sell cedar in random batches. For instance, you can’t just order 50 12-foot boards. You order a batch, and each board you get may be a different size. Trees are weird like that.

2. Gather Your New Lumber

Finding your replacement boards can be tricky, especially with an older house with siding from 50+ years ago. You’ll need to figure out exactly what kind of siding you have.

  • Does the wood have knots, or is it clear without knots?
  • How wide is each board?
  • How thick is each board?
  • What’s the tallest board you’ll need? Ours reach up to 16 feet in some spots.
  • Is the wood surface smooth or rough?
  • What does the tongue and groove look like? There are different shapes of tongue and groove so you need to make sure your new boards will fit with your old boards.

At this point it might be a good idea to cut out a piece of one of your damaged boards so you can take it to lumber suppliers in search of a match. And keep in mind that the boards on one side of your house could be different from the boards on another side of your house.

Picking replacement siding boards
Found the match!

When Eric and I started shopping, we discovered that our cedar siding is thicker on the south and west sides of our house to protect from the harsh southern and afternoon sun. All of the boards we needed to replace were on the south and west sides, but at first we were shopping with a thinner spare board sample that matched the north and east sides. SO GLAD we figured this out before ordering a big batch of the thinner boards.

We cut out a sample of the thicker board and took it to our local lumber suppliers, looking for clear cedar in the correct shape. After the first few suppliers didn’t have matching cedar available, we started to worry that we wouldn’t be able to find a replacement. Then we found the clear cedar we needed at Lakeside Lumber. Yay!

3. Pry Out the Old Boards

Now the dirty work begins. You need to remove your damaged old boards while keeping your good old boards intact on your house. (Easier said than done, and you will probably lose a few good boards. That’s OK, you ordered extra lumber.)

Prying out old tongue and groove boards

You can use a ladder to reach the higher parts of the board. Or if your house is taller you might want to use a multipurpose scaffolding, so you can easily stand and use both hands to get the work done. And I recommend wearing a mask and covering your edible plants for protection from wood chips and dust.

Set your circular saw to the depth of your cedar siding. When you cut into your siding, your saw should ideally just cut through the board but not into your vapor barrier or the rest of your house.

Run the circular saw up the middle-ish of your bad board. Then use your pry bar, with your hammer if needed, to pry out the board. Make sure you get all of the scraps of wood and remove any nails.

Do this with all of the bad boards around your house. Now your home looks super unattractive. This should help motivate you to finish the project.

Restoring your fixer upper? See my home improvement guide >>

4. Replace Vapor Barrier as Needed

Behind all of your siding should be some kind of vapor barrier to keep water from leaking through the cedar boards into your house. If this barrier got torn up when you removed your bad boards, you will need to replace it.

Cut and place the vapor barrier with a little bit of overlap, sliding it under the nearby boards if possible. Staple it on and you’re all set.

Damaged vapor barrier on house siding
Here are some spots that need new vapor barrier, where the black paper is missing.

5. Cut Your Boards to Size

Unless your roof is flat, your cedar siding boards will probably need to be cut different lengths. This works out since you have different sizes of cedar boards sitting in your driveway. Now you just need to figure out how to use the lumber wisely.

Start by measuring the areas that need the longest replacement boards, and match those areas to the longest new boards you have available. Then work your way down to the smaller boards.

In each section, measure the total length and the angle at the top (could be flat, or could be angled if you’re under the pointy side of the roof). Then cut your corresponding replacement board to match, but leave it an inch or so longer so you have some wiggle room. You can cut along the bottom when you’re done to make all the boards line up.

6. Insert New Boards

Once your boards are cut, it’s time to fit the puzzle pieces together. Just remember the tongue sticks out. The groove is the side of the board that is indented, where the next board’s tongue fits into.

Replacing damaged tongue and groove siding boards
So many X’s still need to be replaced here…

To squeeze a board in between two interlocking boards that are already in place, you will need to remove part of your new board’s groove.

Carefully slice the back part of the groove of your replacement board, but leave the front part of the groove attached. You can use your circular saw set to the depth of just the back part of the groove.

Insert your new board’s tongue into your old board’s groove, and lay the new board’s front groove over the other old board’s tongue. Make sense?

If you’re replacing several boards in a row, you will only have to cut the back groove from the board on one end to place all of the boards. So the first boards will remain whole. Insert and nail them one at a time until you get to the last board, which will have the back groove cut out in order to fit.

As you’re putting your new boards up, try to nail through the tongue so the nails will be hidden. Just make sure the nail is flush with the tongue so the next groove can fit. Then on the last board you will need to nail through the board, but you can paint the nails when you’re done.

Nails can be spaced up the board about two feet apart, and they do need to be stainless steel. Other types of nails will leave stains on your siding.

7. Cut Any Uneven Edges

You’re probably a hot mess right about now. Good thing we’re almost done.

House siding replacement in progress

Your boards are up, but they need to be cut a bit if you left them a little long when you measured. Follow along the bottom edge of your boards with your circular saw to carefully cut your new boards even with the old boards. You can use a 2×4 as a guide. Then you’re all done!

So Will Old and New Cedar Boards Match When Stained?

When my home’s siding was done, I wondered if the old and new siding would blend together under my soon-to-be-applied opaque stain. I had brand new boards next to 50-year-old boards. Would the stain smooth everything out or would it look weird for the next several years until the new boards weathered?

New siding boards ready for stain
Before staining.
After staining new siding
After staining.

After a few weeks of anxiously waiting to see how the stain would look, I discovered that opaque stain is awesome. Every board on the house has its own character, but you really can’t tell the new from the old. Even older cedar looks good under a fresh coat of stain.

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