Stone Carriage House Gym: Part 5, Adding A Window to a Stone Wall
Welcome back to the series on our Stone Carriage House Gym expansion. Today, I’m going to show you how we added a window to a stone wall.
My speciality is very niche topics that less than 1% of you will ever need to know.
Below is the stone wall in question. As you can see, aside from the window headers, the entire window opening is fieldstone and brick. The bricks will be removed partly for aesthetic reasons and partly because we need to remove that window grate.
We don’t know why there is an iron grate instead of a glass-paned window in this wall, but it made the building drafty. It’s also might as well have had a neon sign over it that said, “All critters who can squeeze through are welcome here.”
Let’s shake off that thought and get down to specifics.
How do you secure a window to a stone wall? There’s no wood framing.
We are using the general technique that a craftsman hundreds of years ago would have used. We are familiar with this technique because we had the privilege of being able to see how the existing windows in this stone Carriage House were installed when we restored and repointed the walls on the other half of this building.
Here’s one of the windows that we learned from.
The key to installing a window in a stone wall is a diagonal piece of wood.
The vertical sections of your window frame or side jambs need to have at least two diagonal pieces of wood coming off each side. These diagonal pieces of wood need to be mortared into the stone.
That’s what will hold the window frame in place.
We pocket-holed the diagonal pieces to the side jambs. We used pine for the frame and scrap ash and cedar for the diagonal pieces. The pine won’t be exposed to the elements when we are done.
P.S. Please ignore the rotten window header for now. It will be coming out and replaced just as soon as we secure the sides.
How do those diagonal pieces of wood stay in place?
We mortar them in! They will not move after being secured into the wall with lime mortar and fieldstones.
This does mean that you have to either be very strategic about where you place your diagonal pieces, or like us, you have to rebuild the window wall around the side jamb.
How do you install a window frame or side jamb in a stone wall so that it is plumb and level?
That’s the tricky bit. It’s helpful to have two people for this part.
For this window, we couldn’t install a completed frame all in one piece. That would have been nice though. The reason for this was we had to remove the supporting stones/bricks under the window headers to make room for the new window and we had to replace a rotten beam.
This meant we had to install the window frame section by section, starting with the sides.
We have a jack supporting the window headers while we work.
With a little trial and error, we discovered that sandwiching the top of the side piece in between two scrap pieces of wood temporarily screwed to the window header was helpful for holding the side piece in place.
Then one person held the board in place while constantly checking for plumb and level while the other person mortared the first diagonal pieces coming off the side into place. We used a big rock to hold the side jamb in place while the mortar set up.
Since we were essentially rebuilding this portion of the wall around the window, we had to work from both the inside and outside of the building to rebuild the wall and secure the window frame side pieces.
However, the window will be installed from the outside.
It’s not perfect and we’ll probably need to use some shims later, but we have enough wiggle room to get the window installed.
Once the side pieces were secured, we could replace the rotten window header.
Hopefully, you don’t have to do this step! We used a pressure-treated 4×6 to replace the rotten header.
You can see how it’s sitting on the side jambs AND rocks now. We appreciate fully supported beams.
How does the window header get secured in place?
Not with nails or screws. It is mortared into place like the rest of the beams.
Once the gap between the new beam and the existing wall is filled with new stones and lime mortar, it will be secure. Gravity is your friend here. Plus, once the rest of the trim is nailed into place, that beam really won’t move.
Here’s how it looks with the rocks all mortared in.
All the exposed wood and stones you see here will get covered by trim and/or a skim coat of mortar to make it look like the rest of the building.
Please note that this window header is going to act as the top jamb of the window going forward.
But what about the rest of the window headers?
Every window (and door frame for that matter) that we’ve seen in our stone buildings have a wood window header. This is the top, horizontal piece(s) that goes over the window opening.
Our window headers are usually 2 or 3 wood beams (4x6s or 6x6s, hand hewn if original) that span the window opening and are also, you guessed it, mortared into the stone wall.
The window headers are supported by the rocks underneath them. In turn, the window headers help support the wall of rocks above it.
These beams are sometimes covered over with wide planks nailed to the beams to finish them off. These planks prevent mortar and dust from falling through the gaps between the beams.
The original planks covering the window headers in our building are not tongue and grooved together, but we used the technique on our window. It should be helpful when the wood expands and contracts.
We did a rough scribe on the boards touching the stone sides of the window. This will be finished off with oakum and lime mortar to seal the gap. We’ll also add a small trim piece to cover the exposed tongue and groove seams where these boards meet the window header.
How does the exterior sill (bottom) of the window frame work?
It can be nailed or screwed to the side supports, but it will also get mortared into the wall. Can you see there’s a theme here?
Keep in mind that the exterior sill needs to be angled so that water will run off of it and away from the window. Ours sits at a 22 degree angle and slopes away from the building.
We also added bottom supports to our exterior sill. This helped raise the sill to the correct height for our window. The supports are screwed into the sill and into the side jamb, which secures the exterior sill in place.
Keep in mind that our exterior sill is set away from the building because we still have to add trim and skim coat the exterior of the building to cover up the rock faces.
One other item to note is that we installed a couple of pieces of vertical casing on the inside of the window at the same time we installed the exterior sill.
What happens after the frame is in place?
Then the window installation is more straightforward or similar to how you’d install a window in a stick-framed home. It’s not super helpful to get into particulars here because there are so many different types of windows.
If you’re using an old single-paned window, the glazed side goes on the outside.
Our interior window sill will be stone, not wood. That’s personal preference for this project.
Come back soon and I’ll show you, in another blog post, how we build those! We might even have this window trimmed out and totally finished by then. Crazier things have happened.
What questions do you have for installing windows in a stone wall? We will try to answer them to the best of our ability! You can always comment on this blog post, email me here, or reach out via Instagram or Facebook. I respond to all of your comments.
Happy DIYing!
P.S. We use NHL5 lime mortar for repointing our stone foundations.
P.P.S. Please check building codes in your area before you install any windows. This technique may not conform to current codes. Build responsibly.
Thanks for hanging out with me today for this very specific topic. If you like stone buildings, you might like one of these blog posts too.
What We Didn’t Anticipate When Repointing Our Stone Walls
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