I installed a window in my basement 2 years ago and in the time since I've realized that I fastened the header incorrectly. Oops. I have to take it apart anyways to re-do the trim and match the other windows better, so I want to just fix it all.

The problem was the sill plate, which should lay flat on top of the header. It is tilted outwards about 10 degrees.

I have 4 options:

1) Wedge the header under it and leave the sill plate to only contact at the corner

2) Wedge the header and then try and screw it to suck it back straight

3) Use the table saw to match the angle on the sill plate and cut the header

5) Use shims to ensure full contact.

I assume the sill plate shouldn't be slanted anyways. What might cause this, is this a bigger issue than I know? Should I also add concrete anchors to suck it back down to the concrete? And do I need to put that foam membrane stuff around my PT framing?

Here's a diagram:

enter image description here

1 Answer 1


Ideally, you want the plate to fully bear on the header. The fact that a twist developed indicates there is not any appreciable load at this location, so it probably does not matter much what you do. It's tempting to try to take the twist out so everything is straight and true, but you may just end up causing the studs above to not bear on the plate. The installation may look better, but you have not gained better bearing. Further more, the suspended studs could eventually settle, causing cracks in the finish and creating stress risers nearby due to differential settlement.

This leaves the viable choices to either shim or cut the header top on an angle to match. While shimming has the appearance of shoddy work, it is actually the best way to ensure full bearing. Focus on getting good bearing under the studs above, the space between studs is not that important.

You should place sill sealer under the window's sill plate, some standing water could potentially sit here. You don't need it behind vertical members to protect the PT wood from moisture, but you will want to do something to limit infiltration. Sill sealer works well for this, but you can use other methods if you prefer, such as polyurethane foam, or simply setting the king studs in sealant.

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