How to frame an arched wall?

bigkid

Good morning,

I will preface this by saying I have had two carpenters look at this for quotes, and both of them were quite unsure as to how best to do this, not leaving me with a lot of confidence in their ability to get it done well.

So I am turning to the experts here to see if anyone has done anything like this before, in the hopes of being able to give them some guidance, or possibly do this myself. I used to work as a landscaper and am a hobbyist wood worker so think I could possibly pull this off with the right advice.

Basically looking to frame up an arched shower wall like the one shown in this AI mock up. The frame will then be impregnated with marine epoxy (bote-cote), then sheeted with fibre cement sheeting (likely villaboard), and then painted up with a waterproofing membrane. The shower side will be tiled, the rest will be rendered and painted. Ignore the weird trim moulding, the AI put that in. The arch also won’t be that severe, it will likely only come down 3-400mm at the walls, and maybe 100mm at the centre.

My question is what is the best way to frame this up to limit movement and maximise strength? And what is the best method to create the arched ‘lintel’ or header? As I see it there is a few options:

1. 90x45 LVL top plate fixed to roof rafters and 90x45 LVL studs fixed to brick walls. Then cutting 90x45 LVL into short (maybe 300mm?) sections with angled cuts to match the curved shape, glued+screwed+nail stripped together to make the arched header. Then brace the arched header with angled and vertical LVL studs fixed to the top plate and wall studs. Villaboard can then be cut into the arched shape, and screwed into all timbers, so that includes the top plate, arched header and all studs.
2. Tracing an arched header ‘beam’ 45mm in height onto 12mm marine ply. Cutting out 8 of these and laminating them together using marine epoxy and screws to make the arched header. Then bracing this header using the same vertical and angled studs fixed to the top plate and wall studs like in option 1. Then sheeting in the same manner as option 1.

I was thinking LVL would be better than solid pine framing due to its much better dimensional stability, resistance to warping and bowing. I think this would give less chance of movement affecting the tiles on the shower side. I’m not sure if waterproofing the timber will be an issue. I figured with the marine epoxy impregnating and coating the timber, plus the waterproof membrane over the villaboard, plus the fact that it will not be getting directly wet from the shower it will mostly be steam/humidity, that it would be ok?

I know this seems over the top, but I personally think it is quite simple when you break it down into its component steps. I just need advice on how to make it all structurally sound. I know arches are not for everyone but both my partner and I love them and think it adds a really nice feature to the bathroom to make it stand out from modern bathrooms.

Cheers for any advice.

JacobZ

Hi @bigkid,

I can see what you are trying to achieve, and you have clearly put a lot of thought into it, but I will be upfront with you on this one.

Because of the shape and how an arch distributes load, this moves beyond a simple framing question and into structural design. Even though it is technically a non-structural feature, once you start creating an arch, the way loads are transferred becomes a lot less straightforward than a standard straight opening. There are also a few layers here that add complexity, with the main one being the tiles on the inside of the wall. This adds considerable weight to the frame, which needs to be considered in the design.

Due to the complexity, it is outside what I would be comfortable advising on. This is really something that should be designed or at least signed off by a licensed builder who is experienced and confident with this type of work, or even a designer or engineer if needed. That way you know the load paths, fixing methods, and materials are all appropriate for your specific situation.

What I would suggest is finding someone who has actually built similar curved or arched features before, rather than trying to guide a contractor who is unsure. This is one of those projects where experience with the detail makes a big difference to the end result.

Allow me to tag @Nailbag who is an experienced renovator, to see if he has any thoughts on how to proceed.

Jacob