Building a hard pelmet for a bay window

Bay windows give the perception of adding quite a bit of space to a room. In a bedroom, they allow furniture to sit a bit further back than it otherwise could, leaving more space for the occupants to stumble about in.

We've got a small unit sat in the bay, with the bed placed against the opposite wall: this layout allows for easy access to both sides of the bed, making the best possible use of the space that's available.

The one problem with this arrangement, though, has always been the curtains. Although they're heavy, lined blackout curtains, they do let a lot of light creep in around the top.

Photo of our bay window curtains

The windows have a thick frame, which the curtain pole mounts have to reach out beyond, resulting in there being more than enough space for reflected light to work its way upwards and into the room.

The effect in summer, is that at about 4am, any possibility of sleep is ended as a result of the room being flooded with sunlight.

AI generated cartoon showing a calm sun outside the window at 03:59. At 04:00 it's a burning fireball trying to climb through the window. Being AI generated, the feed look wrong and the sun's hand has somehow gone through the wall

Things are a little better in Winter: the sun's assault starts later (if it even bothers to show up that day), but the room ultimately gets similarly illuminated.

In order to help address the issue, I decided that we should install a pelmet (for the Americans, that's either a "Box Valance" or a cornice) over the curtains to block the path of those uninvited rays of sunlight.

There was one problem with that idea though: bay windows tend not to be uniform in size. In fact, even finding and fitting curtain poles tends to involve entertaining some kind of bespoke arrangement.

Clearly, buying and quickly fitting something pre-made was out and I've had to make my own.

In this post, I describe how I went about constructing and upholstering a simple hard pelmet for our bay window.


There's really not much to a pelmet: they're basically part of a box, consisting of at least one solid outer face and fixed in place in some way. They can run down from the ceiling, or be more box-like:

Photo of a box pelmet found on Etsy, the pelmet is a rectangular box with wallspace clearly visible above it

Our window frames finish near the top of the room: there isn't a lot of space above the curtain pole, so I decided that our pelmet would come down from the ceiling (with the additional benefit that there's no top surface of the pelmet to become a dust trap).

This made the design quite simple

  • Wood battens screwed to the ceiling
  • Upholstered plywood for the pelmet face

The shape of the bay is essentially half of an octagon, meaning we needed to create a fairly simple shape, with a small end covering on either side:

drawing of half an octogon

The simplicty of the design also meant that install should be quite simple, but did mean, however, that the ceiling needed to support the full weight of the pelmet.

Given that the ceiling was potentially lathe and plaster, I needed to keep things as light as possible.

The plan was that the pelmet would be upholstered to match the curtains: they are quite new and we had a second set (which had proven to be a little too short, but I hadn't yet got around to returning).

Installing Batten

I started by measuring and cutting a length of batten to run across the bay horizontally.

I thought this would be the easiest bit:

  • measure the bay
  • cut some 18x28 to length
  • mitre a 45° angle into the ends
  • Push up against the walls to install

I was wrong.

As I noted earlier, bays built in the early 1900s tend to have something of an irregular shape. That, of course, is only made worse when you consider that someone has also applied plaster to the inside: although the angles of the bay might total 180°, there's no guarantee that any given point on each of the planes is at 45°.

Getting the first batten installed involved quite a bit more swearing, "does that look straight?" and trips back to the saw than I had anticipated.

Once I had the batten positioned correctly, I held it in place and drilled through with a small bit to mark screw positions in both the wood and the plaster (which turned out to be plasterboard).

With all the screw positions marked, I removed the wood, used a bigger drill bit on the plaster, pushed wall plugs in and then screwed the batten in place.

At this point, I decided to change plans a little bit. Rather than creating half of an octagon, I decided to instead create half a hexagon, with the side planes tracking out until they met the wall:

drawing of half an octagon with half a hexagon inside it

This removed the need for a small face at the end, something that I assumed would probably prove to be quite fiddly and annoying to get right.

Installing the sides of the hexagon proved quite easy: I mitred 45° into the ends of two battens so that they could press against both the rear batten and the wall:

Photo of the installed battens. The first strip runs across the width of the bay, sited a little way forward of the curtain pole. There are then two pieces of batten installed at 45 angles of the original, roughly tracking the sides of the curtain pole

To help ensure that the weight was spread across all of the wallplugs, I put a woodscrew through each mitre, effectively attaching the edge planes to the batten at the back.

The two edges were affixed to the ceiling by 3 screws each, whilst the back had 5 in it.

Cutting The Front Face

For the face of the pelment, I used several sheets of 3.5mm plywood.

I ummed and ahhed a little on this choice: I could also have used 5mm, which would have been more rigid but heavier. In the end, I opted for the lighter option but, in hindsight, if I were doing this again I think I'd probably go for the 5mm.

I measured the exposed faces of each batten and then, to leave room for upholstery, subtracted 5mm (a number that I pretty much pulled out of the air):

Diagram showing the measured size of the bay and the plywood I cut

I used a circular saw to cut the plywood to size and then offered it up to the battons to check sizing.

I actually started with a depth of 30.5cm (the plywood sheets are 61cm wide, so it was convenient to just cut them in half), but they were quite visibly too deep, so I had to go back and trim them down.


This was a new one on me - I knew the theory but hadn't actually done it before.

Rather than applying the material directly to the wood, you first need to affix some form of batting to help give the piece shape and volume.

Batting material is not exactly something we keep in the house, but, I have a fish tank and so had some filter floss to hand. This stuff is so similar to batting that some aquarists use polyester batting as a cost effective alternative, so I figured it'd do the job.

I cut a rough rectangle of filter floss out and laid the first plywood sheet on top of it

Picture of a sheet of plywood lying on top of some roughly cut out filter floss

(Note: I adjusted placement a bit after taking the picture, the batting should overlap on all sides)

I folded the floss down at the top and staple gunned it in place.

Then, pulling it slightly tight, I stapled along each of the remaining edges until it was fully secured.

After attaching batting to the first sheet, I decided that I'd push on and upholster it before batting the others: the idea being that if I'd screwed something up, I'd find out before I had repeated my mistake(s) on all 3 sheets.

I laid the batted wood on the spare curtain (ensuring that the material was facing the correct way: the nicer texture facing down)

Picture wood wrapped in batten lying on a green curtain

Then, just as I had with the batten, I cut the curtain, ensuring a decent amount of overlap. Unlike the batten, though, I left enough overlap for the curtain to wrap all the way up the back: the idea being that anyone looking in through the window shouldn't see the plywood backing.

I flipped the board over so that the batting was facing down and then folded the top of the curtain down over the back of the board, running a line of staples along the top to secure it in place.

With the top secured, I carefully picked the board up and gave it a little shake to try and have the material settle naturally.

After placing it flat again I worked down the left side, pulling the material taught as I stapled.

The corners were a little bit like wrapping a present: you end up with more than you want, so have have to fold it in and (if needed) trim the excess away.

With the left side secured, I worked along the bottom, again, pulling the material tight as I stapled.

Before working on the final side, I picked the board up again and gave it a good shake, then stapled along it, securing the material in place.

Picture wood wrapped in batten lying on a green curtain

With a due sense of apprehension, I turned the board over and checked the front.... it looked OK (unlike the blurry-arse picture that I then took of it).

Happy with the results, I upholstered the other two panels in exactly the same way, having just enough filter floss to do the lot.

If I were doing this again, there are a couple of things I'd change:

  • Shorter staples: I only had 8mm staples. They're not quite long enough to poke through the material, but you can feel them if you press against it. Shorter staples would help reduce the risk of issues (of course, using thicker ply would help here too)
  • Iron the material: I didn't think this was going to be needed - the curtains looked reasonably wrinkle free, but when stretched across a flat face, any existing wrinkles show up much more.

Attaching the Pelmet Face

When designing the pelmet, I had considered there were probably two ways that I could attach the faces to the ceiling battens:

  • Screw/glue some more batten to the back and then screw through that into the ceiling batten
  • Nail through the front with small headed nails

Using additional batten would add extra weight (plus, I'd only really considered it before I decided to upholster all the way up the back of the panel), so I instead opted to nail through the front.

I put some 15mm brads into my nail-gun and offered up the rear panel (cue more "does that look straight?"). Once I was happy with the positioning, I shot a row of brads through, pinning it in place.

I had hoped that the head of the brads might disappear into the material - they didn't, but also aren't really visible from the floor.

I then climbed back up and offered the first side panel up, pushing it up against the rear panel before nail-gunning it into place.

The final panel went up in exactly the same way and the Pelmet was up and ready to block the encroach of unwanted sunlight

Emperor Palpatine Meme, reads: Now witness the power of this fully operational curtain pelment

Note: I did eventually notice that I'd knocked the curtain off the end of the rail and put that loop back up.

Picture of the installed pelmet, three green velvet panels running down from the ceiling to overlap the rail

I had intended, the next morning, to take an "after" picture to show the pelmet blocking light, but it's made it too dark in there to get a meaningful image (which is definitely a sign it's having the desired effect).


There are, undoubtedly, other ways to approach this need. As well as building a box pelmet, I could also have run some wood vertically to provide the panels with a rigid back support.

In this case, though, that would probably have been overkill, only really adding weight that the ceiling would have to support (going back to the wall is possible, but fiddly given the limited space).

Upholstering wasn't something that I'd done before, but I think the panels have turned out quite well even if there are a few things I've noted for "next time".

I do still need to do something about the light that leaks through the ends of the curtains (i.e. the sides of the window). Potentially, I could run a box from the end of the pelmet down to the floor (essentially enclosing the windows), but I'm not sure that we'd like the resulting look.

I think the most likely solution will be to add a hidden lip to the window frame in order to close the gap between curtain and frame (I actually used magnetic strips to stick the previous curtains to the side of the frames: it blocked light quite well but led to the curtains soaking up condensation).