Sheet goods for deep extension jambs?
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I’m replacing all the windows on an old brick building, total wall thickness ranges from 12 to 16 inches (The interior wall is straight, exterior.. not so much!)
I built out extension jambs out of primed pine 1×8 for the first one, then I realized this is going to cost >$1000 in lumber just for extension jambs, and I could save 75% by switching to sheet goods.
Bit of detail: I’m leaving a 1/16 gap between the extension jamb and the window to isolate any moisture or movement of the brick wall + vinyl window from the wood framed wall, I’ll caulk that gap with big stretch. The window is almost 5″ thick, well sealed around the perimeter, I’m not sure if there’s a huge condensation risk on the inside of the frame, but I want to think it’ll be fine.
Now I’m having analysis paralysis on what to use.
I’ve used MDO for an unrelated project in the past and I loved its mix of stability, moisture resilience, and hard paintable surface. I think I might be able to track down some 3/4″ MDO at a cabinet supply place nearby, but it’s not available at the orange or blue. I think the veneer is about 1/16 so if I do a 3/16 reveal there’s a small chance of running into voids and having the paint a plywood edge.
If I did MDF, I could do the sill in pine, for the moisture resilience. People are certain to put mugs and plants down on these 8″ deep sills. I’d do a 1/8 roundover on the inside to reduce the chance of the edge falling apart. Then prime and paint the whole thing.
If I did regular ‘ol plywood, I’m a little worried about voids in the ply showing up, I’ve seen people say to fill the edges with spackle or caulk, but I’m not totally keen on that technique. Or maybe I could just do no reveal on the casing, make the casing 1/32 too small and sand off the lip of the casing to make it sit flush against the plywood veneer. Or I could leave voids showing and do a bead of big stretch between the casing and extension jambs, then hope that makes the edge easily paintable.
What would you do?
Replies
I'll tell you what I just did on a similar project. I used Versatex/Azek sheet goods ripped to size and then glued and screwed to the jambs.
If you use the cortex screws which come with plugs it leaves a good finished surface that doesnt require any paint. The finished product is more impact resistant than wood. It's water proof and if you do end up painting it it takes a coat very well.
Baltic birch has no voids.
For deep jambs, I did baltic birch with a 1/4 solid wood strip glued and nailed to the edge. Then I could do a normal reveal. I cut the strip a little bit wider than the plywood and sanded it flat with 80 grit on an orbital. When painted the seam was invisible.