How to install stool on NC window?

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Old 11-17-07, 03:18 PM
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Question How to install stool on NC window?

Hi All –

I recently installed a bunch of Andersen 400 double-hung new construction windows. My house is a 1912 Victorian and the other windows [newer replacement ones] still have the stool & apron for the bottom trim. I’m wondering the easiest way to replicate this with these new construction windows, which have no sill.

Further complicating things is that I need jamb extensions. The base of the window merely has a dado for a jamb extension, just like the head and sides. Andersen sells (for big $$) a kit with a special “sill jamb extension”, which then accepts a standard stool I think. Any other options come to mind? Thanks much. -steve
 
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Old 11-18-07, 06:14 AM
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You're going to need to make up a bunch of extension jamb stock. Shaping a tongue on the extension jamb that will fit into the groove on the window isn't a big job if you have a table saw or router. Around here, S4S poplar, oak or #1 douglas fir or pine would be the material of choice. I suppose MDF would also work if you're wanting painted trim.

As for the stool, it can either be one piece, like your extension jambs, but wider, then you notch out the ears on each side... or you can just make an extension jamb on all 4 sides and add a small piece of trim onto the face of the extension jamb to make it look like a stool.

Andersen's extension jambs attach to the window by using pocket screws. This works very well, provided you have enough room in the rough opening to get your driver bit back there to drive the screws. (If you don't, you should have installed the extension jambs on the window before you installed it into the opening!) If you'd like to look into pocket screws, I'd suggest the Kreg pocket jig. A single hole jig and stepped drill bit costs maybe $30. You clamp the jig to the back side of the extension jamb (the side that will face the rough opening) set the stop collar on the drill bit to the right depth, then drill a pilot hole. This hole will then accept a pocket screw, which will allow you to screw the extension jamb to the window by inserting a long driver bit into the rough opening at a slight angle to the jamb. Not sure if you can picture that, but it's pretty simple to do, and its the same method Andersen uses for their factory jambs. You're just saving money by DIY.

If you want to forget the tongue and groove, and forget the pocket screws, you can also just shoot all the trim together like a frame (by taking careful measurements and building it in the shop), then bring it into the room, shim it into the rough opening, and attach it to the rough opening with finish nails.
 
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Old 11-19-07, 02:32 PM
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Fastening the jambs

Thx, XS. One problem is the jamb extensions will only be perhaps 3/4” in depth so it’s tough to shim & nail them to the window framing, though I have 2 casement windows where I will do that. Sheetrock and plaster are already done, so I really just need to make teh jambs flush with that. Do you reckon I can pilot/screw though the depth of the extension into the actual jamb? Could countersink, and the screws would be behind the casing anyhow. (Yes, it seems I should have put on the extensions before installing the window, but then how do you know the exact depth you will need after board & plaster? Do you end up planing them to the proper depth?)

Unfortunately, screwing through the “face” won’t work with the stool, given it will be probably 2” deep. For that, maybe I’ll screw though the ears to the framing, then face nail it downward onto the top of the apron, which should be solidly fastened to the stud across the bottom of the window. I could – as you suggest – add a roughly ¾” deep jamb extension to the sill dado, then and a 2nd piece say 1” deep to make it look like a stool … but how to fasten? I reckon the stool piece must be solidly fastened, since you have to assume people will lean on it. Or, again, does nailing to the apron provide enough support?

Anyhow, as you have probably figured, I’m a real novice as a finish carpenter so your advice is much appreciated. (I’m also going to pick up the Kreg jig…maybe won’t be using it for this but seems like a very handy tool. Thanks for that.)
 
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Old 11-19-07, 04:44 PM
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Hi Steve,

If the extension jambs are only 3/4" wide, then you can probably just shoot them to the window with a finish nailer. I wouldn't use screws, but if you are sure they will be covered by the casing then go ahead. I wouldn't use screws because when you put the casing on the chances would be pretty good that you'd hit a couple of the screw heads with your finish nails. That's a good way to nail your fingers if you're using an air nailer. And believe me, you don't want to do that!

Putting the extensions on beforehand is just a matter of measuring the wall thickness and comparing it to the window thickness. If your wall thickness is 4 3/4" before drywall goes on, it will be 5 1/4" after drywall is on... that's your total wall thickness. If your window is 4 9/16", you'd just do the math to figure out how big of an extension will be needed (11/16"). It's always better if the extension jamb is flush or slightly recessed below the surface of the drywall. You really don't want it to stick past the drywall at ALL- if it does, yes it can be planed down, or belt sanded, but you're far better off if it's flush in most places... and 1/8" below in a few spots. In most cases, you aren't going to have a perfect wall where your extension jamb is perfectly flush all the way around.

In extreme cases, you might need to taper your extension jambs to match a very crooked wall. Or, if they are proud, instead of planing or sanding them down you can float drywall mud around the window so that the casing will lay flat instead of being tipped. But those would be unusual "fixes".

If you want to do the stool in one piece, I'd say you would still want to pocket screw it to the window from underneath. Your apron should cover up your pocket holes. Then the side extension jambs will sit on top of that.

If you end up putting the jamb on all 4 sides, you would make a little "step" or 1/8" shadow reveal where the stool meets the extension jamb. (just like your casing should have an 1/8" shadow reveal where it meets the extension jamb.) You'd glue the back side and then nail through the face in 3 or 4 places, depending on how wide the window is, to hold it solidly back into the wood glue. If it's only 1" wide, you'd use a 2" nail.

Like you said, once your apron is installed you could pop a couple nails through the stool and down into the top of the apron, just to make sure the stool is secured well. With such a narrow stool, you really don't have to worry about any downward pressure on it.

Finish work can be kind of nerve wracking, but I think it's the best. If you have an eye for detail, don't get in a hurry and enjoy being careful and precise as you work, you'll make a great finish carpenter.
 
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Old 11-20-07, 09:43 AM
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window stools, etc

i think i got it! thx much
 
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