Shutter BoysUpdated
The short version: choose inside mount when the opening is deep enough for the louvers to tilt, close to square, and clear of handles and locks. Choose outside mount when any of those is missing. If you can’t decide, measure both ways and tell us; we check every size before anything is made.
What the two words mean
With an inside mount, the shutter’s frame sits inside the window opening, screwed to the jamb. The window trim stays on show around it, and the shutter looks like part of the window. It’s what most people choose.
With an outside mount, the frame sits on the wall or the trim around the opening, so the shutter covers the opening from the front. The Shutter Store sums up the trade-off well: an outside mount “hides imperfections and gaps in the window opening”, but its “frame projects out into the room”[1].
Three checks that decide it
1. Depth
Louvers need room to tilt. Measure from the front edge of the opening back to the glass, or to the first thing that sticks out: a handle, a crank, a lock or an alarm sensor. That shorter number is the one that counts. Wider louvers need more room: on our louver table, 4½ in louvers give the widest view but need the most depth, and 2½ in louvers the least. Choosing a louver size
You can enter the depth to the glass for each window in the designer. It’s optional, but it lets us check the depth against the louver size you pick before we build.
2. Square
Measure the width at the top, middle and bottom, and the height at the left, centre and right. Then measure both diagonals. If they differ by more than about ¼ in (6 mm), the opening is out of square, and a shutter built to fit snugly inside it will show a tapering gap somewhere.
Installers say the same thing more bluntly. In one Garage Journal thread, a contributor who had fitted inset shutters wrote that “1/16” tolerances are the most you can get away with before things start to snowball”, and that with inset shutters, unlike doors and windows, “shims will be visible”[3]. That’s one person’s experience, not a standard, but it explains why crooked openings are the commonest reason to switch to outside mount.
3. What’s in the way
Crank handles, lever locks, alarm sensors, deep sills and sashes that tilt in for cleaning all affect where a frame can sit. The Shutter Store warns that an inside mount can “obstruct crank handles and lever locks on crank-out windows”, and calls outside mount “better suited to tilt-in and crank-out windows”[1]. List every obstruction in the notes for that window. Shutters on casement and crank windows
How out of square is too far?
Every seller draws the line in a slightly different place, because it depends on their frames and how much gap they think you’ll notice. These are each seller’s rules for its own products:
| Seller | Diagonals or out-of-square limit | What they suggest past it |
|---|---|---|
| Shutter Boys | About ¼ in (6 mm) between diagonals | Tell us; outside mount or a mounting frame |
| The Home Depot | More than ⅜ in out of square | “an outside mount application is recommended”[4] |
| Blinds.com | More than ¼ to ½ in | Outside mount[5] |
A worked example. You measure the diagonals of a bedroom window at 63⅜ in and 63 1/16 in. The difference is 5/16 in, a little over our ¼ in guide. That doesn’t rule out inside mount, but it’s the point where we want to know: tell us in the notes, and we’ll suggest a mounting frame, an outside mount, or a tight inside fit with a gap you’ve agreed to before anything is made.
How big an outside mount is
An outside mount is sized to what you want covered, not to the opening. The two retailer guides we checked set different minimums for their own frames:
- The Home Depot: “add at least 1 inch to both sides so that the shutters can hang properly”, and with a sill, measure “from the top of the sill to at least 1 inch above the window”[4].
- Blinds.com: on trim, “Most shutter frames require at least 1 ½” of flat surface to be installed properly”[5].
For ours, decide how far past the opening you want to go, check the surface is flat all that way, and enter the total size. Most people go to the outer edge of the trim, which also hides the joint between trim and wall.
What each choice costs on one window
Live prices from our price list for a 34 × 54 in opening in the basic build (flat moulding, paint stage 1, 3½ in louvers), before tax and shipping:
| Mount | Size ordered | United States | Canada |
|---|---|---|---|
| Inside mount | 34 × 54 in | $340 – $430 | $490 – $610 CAD |
| Inside, with a mounting frame | 34 × 54 in | $400 – $500 | $570 – $710 CAD |
| Outside, 1 in past each side | 36 × 56 in | $370 – $470 | $540 – $670 CAD |
| Outside, over 3 in trim each side | 40 × 60 in | $450 – $560 | $640 – $790 CAD |
So the mount itself is rarely the expensive part of the decision. Pick the one that suits the opening, then price your own sizes in the designer.
Side by side
| If the opening… | Inside mount | Outside mount |
|---|---|---|
| Is deep and square | The natural choice | Works, but hides the trim |
| Is shallow | Louvers may hit the glass | The frame sits in front, so depth matters less |
| Has diagonals more than ¼ in apart | Gaps show | The frame is square even when the hole isn’t |
| Has a crank or lever lock | Check the clearance | Usually clears it |
| Has a sash that tilts in | Can block it | Usually clears it |
| Has trim you love | Keeps it on show | Covers it |
| Has a sill you use | Keeps the sill clear | The frame may sit on or over it |
Where a frame comes in
Some sellers name their frames by shape. The Shutter Store, for example, describes an L-frame as “a subtle square frame” that can be pulled forward to gain depth, and a Z-frame as having “a decorative lip that overlaps the wall”[2]. It also makes the point that “most windows are not perfectly level or square”, and that a frame gives the shutter “a perfectly square, level structure”[2].
In our designer it’s one choice: mounting frame, for out-of-square or shallow openings, which are common in condos. Tick it per window or for the whole order, and the price updates as you go. If you’re not sure whether a window needs one, say so in the notes; we’ll ask for a photo if we need one and tell you before anything is made.
Measuring for each
- Inside mount: measure inside the opening, three widths and three heights, and write down the smallest of each. Enter the exact opening sizes; don’t subtract anything for clearance, because we make the fitting allowances.
- Outside mount: decide how far past the opening you want the frame on each side, then measure the total width and height you want covered at the widest and tallest points. Check the surface is flat enough for the frame to sit against all the way round.
The full measuring guide has both, step by step.
Common mistakes
- Taking one width. Openings are rarely the same at the top and bottom. Inside mount takes the smallest of three; The Home Depot’s guide says to “Record the narrowest width of the three”[4].
- Taking the smallest size for an outside mount. It’s the other way round: Blinds.com uses the widest width and longest height for outside mounts[5], because the frame has to cover the opening at its biggest.
- Measuring depth to the glass when a handle sticks out. The handle is the limit. Measure to it.
- Subtracting for clearance. For our inside mounts, enter the exact opening; we make the allowances.
- Forgetting the sill. An outside mount that comes down to a deep sill may need to stop on top of it. Say which you want.
Fitting it
Either way, the frame is levelled with shims where the opening dips and screwed through its pre-drilled holes; don’t overtighten, because it can pull the frame out of square. If anything doesn’t fit, stop and contact us before you cut, plane or force it. How to install
Common questions
Is inside mount or outside mount better for plantation shutters?
Inside mount looks built in and is what most people choose, but it needs an opening deep enough for the louvers to tilt and close to square. Outside mount sits on the trim or wall around the window, so it suits shallow, crooked or obstructed openings. Neither is better in general; the opening decides.
How square does an opening need to be for inside mount?
Measure both diagonals, corner to corner. If they differ by more than about ¼ in (6 mm), say so when you order: an out-of-square opening may suit an outside mount or a mounting frame better than a shutter fitted tight inside it.
Do outside mount shutters cover the window trim?
Usually, yes. You decide how far past the opening the frame reaches on each side, and most people cover the trim. Check the surface is flat all the way round so the frame sits tight against it.
Does an outside mount cost more?
A little, because the shutter is bigger than the opening. For a 34 × 54 in opening in the basic build, inside mount is $340 – $430; an outside mount reaching 1 in past each side (36 × 56 in) is $370 – $470, before tax and shipping, on our current price list.
How far past the opening should an outside mount reach?
You choose, but leave enough to screw into something flat and solid. The Home Depot’s guide asks for at least 1 in on each side; Blinds.com says most of its frames need at least 1½ in of flat surface on the trim. Check your trim is flat for the whole width you plan to cover.
Can I still open a tilt-in or crank-out window with inside mount shutters?
Sometimes not. A frame inside the opening can block a sash that tilts in for cleaning, or a crank handle or lever lock. Measure the depth to the first thing that sticks out, not just to the glass, and list it in the notes for that window.
Sources
- Inside or outside mount plantation shutters? (January 2020), The Shutter Store (retailer’s own claim)
- Internal shutter frames explained, The Shutter Store (retailer’s own claim)
- Plantation shutter help (forum thread, February 2020), The Garage Journal
- How to measure for plantation shutters (updated June 4, 2024), The Home Depot (retailer’s own claim)
- How to measure for plantation shutters, Blinds.com (retailer’s own claim)