Load-Bearing Windows & Unsupported Sill Plates

I’m starting to look forward to the next home improvement project, which will probably be replacing three small windows in the basement.  The current windows are basically inoperable.  The two that are currently closed won’t open, and the one thats currently open won’t shut.  It may be a tricky project, though, because the reason two of the windows won’t open is because they’re currently helping to hold up my saggy old home!  So I could really use some advice from the great wise interwebs about how to approach this project.  If you’ve got any tips, I’d appreciate if you let me know in the comments.

But first, since I know not all of my readers (including myself) are up to snuff on their construction terms, let’s do a little review of the part of the home known as the sill plate.  As shown in the graphic below (which I stole from Fore Front Home Inspections), the sill plate sits on top of the foundation.  The floor joists & band joists, and subsequently the rest of the entire house, rests on top of the sill plate.  So it’s important, y’all.  What I’m trying to get y’all to understand is that the sill plate is supposed to be supported by the foundation (as opposed to, say, a piece of glass…)

OK.  Now that we all know all about sill plates, let’s look at some photos of how my house was constructed. The sill plate on my home appears to be a 1×6 or 1×8 (instead of the more modern standard of 2×6 or 2×8).  The three windows in my basement are cut right at the top of the foundation, leaving nothing left to support the sill plate.  Take a look:

You can see the white foundation, and the sill plate resting on top of the foundation.  Above the window, however, there is no header to support the sill plate.  Thus, two of the floor joists are resting on the unsupported portion of the sill plate.  As you can guess, the sill plate has sagged under the weight, and now the window is helping to support the sill plate.  In fact, part of the reason the window won’t open (other than that fact that somebody nailed it shut) is because it’s supporting the weight of the house.  Take a look at this close-up of the top left corner of the window:

The sagging sill plate creates a gap between the window frame and the sill plate towards the edges.  And yes, if you’re wondering, cold air gushes through that gap at the corner of the window.  The same sag is visible in the following two photos from my basement as well:

Now, before we go hating on the peeps that constructed my house back in 1905, we should remember that nearly every home in South MPLS was constructed the same way.  If you live in South MPLS, head down to your basement and see if you can recognize the something similar.  Also, total sag after 100 years is only about a 1/4″ – not exactly critical… the rest of the house is WAY more wonky than these joists….

So all this leaves me with a few key questions that I would love to have some help answering from the all-wise interwebs:

1. Anybody got any great ideas about how I should try to construct some sort of header in this small space so that the new window isn’t supporting any weight?  This is probably one of the main reasons why these windows are commonly replaced with square glass blocks (I’m hesitant to call those blocks “structural”, but they’ve gotta be stronger than some new vinyl window…).  Obviously, I’ll want to temporarily support those floor joists while I’m replacing the windows…

2.  When I replace the windows, do y’all think I should try to jack the sagging sill plate back up into it’s original location, or should I just embrace the sag and try to support it where it currently is?  My biggest worry about lifting it back up into place is that doing so would probably cause lots of problems elsewhere (cracking walls, doors that won’t shut, windows that won’t slide very well, etc.)  I’m not sure it’s worth it, especially since Mel and I aren’t planning on living here forever – at some point we’ll be moving on to bigger and better homes.

3.  I’m not entirely clear on exactly how the old window framing is constructed.  If you’ve got any experience with how these things were constructed, I’d appreciate you sharing your knowledge with me.  For example, the piece of the window frame immediately beneath the sill plate – how far back on each side of the window does that thing extend?  Do y’all think that’s something that should be removed with the window?  Or is it embedded far enough back into the foundation on each side of the window that I’m better off just leaving it in place?  Or should I cut it off on each side?

4.  You may notice in a couple of the photos (especially the last one) that there are concrete wedges on top of the sill plate between the floor joists.  Any idea what this is?  It’s actually a mound of dirt piled on top of the sill plate covered in a sheet of concrete.  What the heck is this all about?  Was this just an early version of spray foam trying to insulate that space?

5.  Finally, when I install the new windows, do you guys think I should stick with the combo storm window / interior window setup I’ve currently got?  Or is  a single, newer window going to be good enough?  I really like the idea of being able to open these windows.

Finally, as I hang my head in shame, take a look at this last window from my basement:

Now if that dryer duct through the window isn’t classy, I don’t know what is.  The duct tape falling off just adds a special something.  Observant readers will notice that sagging is not a problem with the sill plate above  this window since the window is parallel to the floor joists, and is thus not supporting any weight.  Also, a related project will be re-routing that dryer duct so that it’s not venting through the window.  And yes, freezing cold air is gushing through this window as well….

18 comments to Load-Bearing Windows & Unsupported Sill Plates

  • To many questions to answer at once but I would love to come over Sunday and give some advise to point you in the right direction

  • When you are done, make sure you caulk the sill plates, which should take care of your air infiltration problem. Don't you love that you're friends with an insulator?

  • Live, have you tackled a project like this before?

    Rachel, yes sealing gaps around the sill plate is a great idea. I'm sure there will be a lot of caulk and spray foam involved in this project…

  • yes i have it is pretty easy

  • I wish I had some good advice to give you about this, but I don't. You're right about every old house in Minneapolis being constructed this way – same with Saint Paul.

    One thing that might make you feel better is that your rim joist will actually be supporting a good portion of this load.

  • btw, in your illustration, the rim joist is referred to as the "band joist." Regional difference.

  • One more thought – don't jack anything up. You're exactly right about making cracks in your walls.

  • InspectorReuben – thanks for the advice about not jacking anything back up into place.

    have you ever seen dirt piled on top of the sill plate and sealed in place with about 1" of concrete before?

  • Yes, I've seen the dirt and concrete, and I have no idea why it was done. I have it at my own house, but I never tried breaking it apart to find out what was inside. Dirt, huh? I always just assumed it was always concrete.

    I'll ask around a little and I'll let you know what that's all about.

  • By way of information, the rim joist is also sometimes called a bellyband.

  • bellyband? I think I saw an infomercial for that once.

  • That concrete at the rim joist (bellyband?) was used to keep the floor joists from twisting. At some point, someone figured out that the rim joist would do that.

  • InspectorReuben, thanks for the info. A few of mine have been crumbling away, so I've just been removing them and filling the space with insulation.

  • To be honest, I got a little tired reading up there, but I have a question which may seem kinda stupid, but would help. Maybe I have a series of questions. Anyways, so if there is no header, and the sill plate is sagging, what is the sill plate resting on besides the window at other locations? foundation walls on footings? Are there gaps? Why is the foundation wall not supporting the sill plate? Humor me here. Is the crushed, compacted rock, gravel, sand whatever below foundation not cutting it, or is it natural settling? Then, are there any other members carrying the load of the sill plate? Does the window have jambs? Do you want a header with jambs that run down? You jack up the house temporarily while replacing the window. Too much would cause cracking. There isn't a whole lot you can do if the fundamental problem is with the foundation what continues to settle. Is it a gradual thing you think? If so, it will probably keep happening and it is kinda a lost war unless you do major fixes to the foundation. You may have to tear out some of the wall to see what is going on if you don't know. It's kinda hard since you only know what has been happening to that house for the last few years. Then again, I just looked at a couple of pictures. Have to be there for a better look. Either way, insulation is probably the least of your worries, though would be the most direct gain as a fix if you aren't staying there for long.

  • To be honest, I got a little tired reading up there, but I have a question which may seem kinda stupid, but would help. Maybe I have a series of questions. Anyways, so if there is no header, and the sill plate is sagging, what is the sill plate resting on besides the window at other locations? foundation walls on footings? Are there gaps? Why is the foundation wall not supporting the sill plate? Humor me here. Is the crushed, compacted rock, gravel, sand whatever below foundation not cutting it, or is it natural settling? Then, are there any other members carrying the load of the sill plate? Does the window have jambs? Do you want a header with jambs that run down? You jack up the house temporarily while replacing the window. Too much would cause cracking. There isn't a whole lot you can do if the fundamental problem is with the foundation what continues to settle. Is it a gradual thing you think? If so, it will probably keep happening and it is kinda a lost war unless you do major fixes to the foundation. You may have to tear out some of the wall to see what is going on if you don't know. It's kinda hard since you only know what has been happening to that house for the last few years. Then again, I just looked at a couple of pictures. Have to be there for a better look. Either way, insulation is probably the least of your worries, though would be the most direct gain as a fix if you aren't staying there for long.

  • To be honest, I got a little tired reading up there, but I have a question which may seem kinda stupid, but would help. Maybe I have a series of questions. Anyways, so if there is no header, and the sill plate is sagging, what is the sill plate resting on besides the window at other locations? foundation walls on footings? Are there gaps? Why is the foundation wall not supporting the sill plate? Humor me here. Is the crushed, compacted rock, gravel, sand whatever below foundation not cutting it, or is it natural settling? Then, are there any other members carrying the load of the sill plate? Does the window have jambs? Do you want a header with jambs that run down? You jack up the house temporarily while replacing the window. Too much would cause cracking. There isn't a whole lot you can do if the fundamental problem is with the foundation what continues to settle. Is it a gradual thing you think? If so, it will probably keep happening and it is kinda a lost war unless you do major fixes to the foundation. You may have to tear out some of the wall to see what is going on if you don't know. It's kinda hard since you only know what has been happening to that house for the last few years. Then again, I just looked at a couple of pictures. Have to be there for a better look. Either way, insulation is probably the least of your worries, though would be the most direct gain as a fix if you aren't staying there for long.

  • @Joel & Jen Christopher – It's ok, I got a little tired reading your comment, too. There is no problem with the foundation. It's as solid as it's ever been. The foundation is supporting the sill plate and the rest of the house beautifully everywhere except directly above the three windows. The foundation doesn't support the sill plate in these locations because it doesn't exist in these locations. The foundation was originally designed with three cut-outs for the windows to fit in. Most of the weight of the floor joists above this cutout is being supported by the band joist, I expect, but as it's sagged, the window frame has received some of that pressure as well.

  • Cornel

    Did you end up doing this project? If so how did you solve the problem with your window supporting the house?
    I have a similar problem with a metal window supporting a sill that was joined right above the window.