Replace sill plates in a garage

[Jennifer Appelman]

Hi All,

  I am looking at a property where the garage sill plates are 3/4 % rotted and in need of replacement. Does anyone have experience with this problem. Is it a costly repair or should the garage be demolished? Thanks for the feedback.

[James C.]

Jennifer,

A lot of this depends on the size of the garage, and the how the rest of the garage is. If the sill plates are shot, how are the stud ends? If they are gone too, then you need to sister or replace them as well. You will want to investigate why the sill plates are rotten. If the garage was built slab on grade, and no concrete block was used to get the sill plates off the ground, then that makes some sense (they probably didn't use pressure treated (PT) wood either). If there are a couple of courses of concrete block, then investigate further. Also, look at the garage floor, if it's gone too, then you are probably in for a replacement. Also depends on if there were footings poured. In northern climates, that is sometimes done. This all needs some investigation.

I see a few options, in two main veins:

Piecemeal replacement:

1) Jack a section from the inside by attaching a support beam to the studs and take enough pressure off the structure to knock out all the rotten wood, cut and sister the bad studs and put in pressure treated lumber. Once that is done, lower it back down and move to the next section.

2) If it's slab on grade, and no concrete block, and you want to eliminate the slab on grade then you can piecemeal it by jacking a section, cutting the studs to the correct height, putting the sill plate on (still use PT), then putting concrete block underneath that section and lowering it down. You probably won't have to sister studs here, since you will be cutting them back enough to remove any rot.

Jack the whole structure up.

3) Jack the whole structure to replace sills all at once (block/no block). Reinforce the inside of the garage to keep the walls from shifting out, and jack it from the rafters, or with beams through the windows and jack from the outside. From there, replace all the sills, sister/replace the studs, or put block down etc. then lower the whole structure back down.

Or, as a last resort, demolish the garage, put in the block (if necessary) floors etc. and rebuild. 

Hope that helps.

Good Luck,

Jim