Materials for Bottom Window Sill
Ryan_SLC
| Posted in General Questions on
Hey all,
I can’t find thin beveled cedar lap siding/clap board that I keep reading about to use for window sills for my 2×6 rough.
Anyone have a good idea for another material that might work to give that slope?
It will be covered in liquid flashing.
Thank you!
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> I can’t find thin beveled cedar lap siding/clap board that I keep reading about to use for window sills for my 2×6 rough.
Where are you looking? :-)
Homedepot and Lowes.
Hardie and LP Smartside are about the only thing those sell. I can't find anything thin and beveled online.
Reach out to some "real" lumberyards. They're more likely to stock it.
Ryan_SLC,
You don't need to slope the whole sill, just the portion under the window. If the sills are already framed, use a circular saw with the blade set at 6 degrees and slope it from outside.
Do you have real lumberyards nearby? I shop at those when possible and hope they don't disappear entirely. Here in New England, every lumberyard has wood clapboards.
Is the wall already framed? When framing new, I just bevel the top of the cripple studs at 5°.
In my opinion and experience, a sloped sill is not as important as having a back dam, so if you have to chose one, go with a back dam.
You can always saw your own using a tablesaw. Or make a jig for a thickness planer that will create a consistent bevel directly on the rough sill, before installation. Or use a hand-held thickness planer.
I agree. If you have a sill-pan and a back dam, the slope is nice but not necessary. More important is some path for water that does accumulate to drain to the exterior under the bottom flange.
Okay...rookie question.
I cannot find online a single person who goes so basic as to say what a back dam should be made of or how thick and location. I know. It's a combo of not searching right and being that new to it :)
Thanks!
1x2 furring strips:
https://www.homedepot.com/p/1-in-x-2-in-x-8-ft-Furring-Strip-Board-160954/100009348
Holy cow! 1 inch? I kinda assumed it would be like 1/8" or something tiny.
Thanks
It depends on the overall details but I often use a 3/4" x 3/4" strip of wood. Sometimes only 1/2" tall.
I just looked at my local Home Depot, they have seven different kinds of clapboard in stock.
But the cheapest is around $7.50 a linear foot. Ripping pieces on the table saw isn't looking bad.
I know. Table saw for a garage warrior is like the gold standard of "I have all the tools."
I am almost there, but not ever going to reach table saw level. So I am hosed.
Mind sharing a link? I might be searching HD wrong?
Thank you!
https://www.homedepot.com/p/1-2-in-x-6-in-x-96-in-New-England-Pine-Bevel-Siding-144/202691720
I kinda have this impression cedar siding might be a coastal kinda thing. Dang it.
Nothing. But thanks for the link!
Is it code acceptable to put the slope on the cripple/sheathing?
It's going to be problem if the inspector doesn't like it :D
Some people will do that -- cut the cripples at a slight angle. You need to bevel the sides of the sill to avoid a corner sticking out that makes it hard to nail sheathing and drywall to.
Realized since sheathing is up, that's not going to work with a circular saw. I'm going to either end the cut too earlier or have to cut too much past to get the cut complete.
I've seen a belt sander used, throw a nice rough belt on it and it shouldn't take more than a minute per window. If its already sheathed you can do the sill and sheathing in one go from the interior side to prevent tearout of the plywood/OSB.
You can finish the cut with an oscillating multitool, a hand saw, a chisel, a well trained beaver, whatever you have on site. This isn't finish carpentry so don't get too hung up on how pretty it is or isn't.
Thank you. As basic as that sounded, that helps me understand it much better.
A 5° bevel on a 2x6 projects just over 3/32". You can split the difference between the interior and exterior. That's often within framing tolerances, though I prefer to be a little more precise than that.
You might see what PVC trim board profiles your supplier carries. There are usually some that will be molded with a slope for this kind of application. You can otherwise build things in the usual way (and I agree about back dam), but with PVC, water ocassionally pooling doesn't carry any risk of the material deteriorating over time.
Bill
I bought SureSill top cap and bottom sill covers. I am trying to see if I can do it cheaper while doing it right. I will be doing liquid flashing under it all to be double protected. No one responded to my question if these were good or not...
For the amateur and actual homeowner, it does seem like a nice level of protection with preformed PVC, but truly, I don't know what I don't know.
https://www.homedepot.com/p/SureSill-6-9-16-in-x-80-in-White-PVC-Sloped-Sill-Pan-for-Door-and-Window-Installation-and-Flashing-Complete-Pack-HDO-6-63S-080/202074146
$68/window?!?!?! Wow. Unless that's a multipack that's going to really add up. Beveling the sill is not that complicated even if the walls are up and sheathed. Just cut the first couple inches to a slight bevel with a circular saw. Use a belt sander. Use a flap disc on a grinder.
It doesn't have to be perfect as the window itself will be leveled and squared sitting on shims and nobody will ever see this detail once the window is in.
There's a dozen decent ways to do it, and if all that fails just back dam it and liquid flash the whole sill.
I know. 4 new windows on our addition.
One thing, for regular old home depot only shoppers, there aren't these massively great options for a drip edge. So I kinda thought just do these, why not the bottom too.
I don't know. I'm feeling like Benjamin Obdyke liquid flash that I have will be sufficient for the bottom, but the exact total rookie back dam and sloping doesn't exist. There is a level of knowledge in everything I'm reading that seems to skip the most basic placement and such...
Ryan_SLC,
A bit late for you, but this is how I install flanged windows, and it is very rookie friendly:
- I slope half the top of the 2"x6" rough-sill 6 degrees on a table saw (but you could use a circular saw too) before installing it.
- Once the sheathing is on I set my circular saw depth at 3/8" and hog out several 3/4" wide grooves in the plywood at the sill.
- The membrane sill-pan gets installed and run 6" up the jambs. It also gets pushed into the grooves to form a drainage path into the rain-screen gap.
This description leaves aside how you treat the jamb and head, which can be done a number of ways.
Yeah, I forget that so much of what we do is just taken for granted as easy or obvious after we've done it a few times (or seen someone do it). If you've never even seen it done, it can be a bit daunting or require a bit of head scratching to figure it out. The first time I put in a window by myself it took me the better part of an afternoon. Now I do a house worth of windows in that time.
Andy,
I think Ryan makes a good point in post #32 about some of the sections that get published too. They are overly complex, and often I'd say fanciful, making what are fairly straightforward tasks needlessly difficult.
The biggest "risk" with PVC trim board is that painting it dark colors can cause problems if it gets a lot of sunlight.
Bill
If you are installing the windows in the thermal center of the wall (where the thermal bridging is minimized) and you have thick walls, your windows may be recessed by 6" from the face of the wall. Treat the sill like a roof, so a 4/12 slope on the sill flashing and sill membrane / back dam below. So a 2" drop over the 6" recess. I often see EPS foam cut down to make the slope. You don't want rain or snow hanging out at this location for any length of time.
Okay. Every detail I see even on GBA shows a spray foam or back backer rod between the window/sill (otherwise, how would the air not just come in from there).
What I don't understand is the back dam is behind it all. How is water ever getting that far to begin with. And if it does get behind that foam, how is it then returning back through to leave?
Ryan_SLC,
Foam or backer rod at the jambs and head, but the window frame at the sill sits directly on the rough-sill. The space under the sloped portion is left as a drainage plane and is not insulated.
I forgot that you place the window on shims to create that gap. That was my bad for sure.
I want to blame it entirely on myself, but if you search on GBA, almost all window details cross section drawings miss this point or the drawings really suggest full foam/back rod at the bottom. It's almost dangerous for us rookies who get so caught up in these cross sectional drawings. I totally forgot myself in these to remember the window is hanging in space for a reason at the bottom. Extremely easy to then see a rookie like me spraying the gap thanks to the cross section drawings.
So think like a rain drop,. Water could in theory get past any amount of material you put between the sill and window, so there needs to be a gap all the way between both the sill and the jam. Got it.
Thanks.
On your "hog out strips", you basically described creating the "SureSill" profile in the cripple and the sheathing. I like that. Since it's all getting liquid flashed, I'll not sweat the appearance. Thanks!
> Foam or backer rod at the jambs and head, but the window frame at the sill sits directly on the rough-sill.
I think this can be slightly dependent on field conditions. For instance, if you have an addition and you're trying to hit a consistent head height on interior trim, it might be necessary to frame with a tolerance and then shim the window to the right spot.
Even in purely new construction, depending on your trim tolerances, shimming the sill might be warranted.
Patrick,
Sure, most large windows need some shimming at the sill, but with or without shims, it's best to just seal at the interior face of the frame and not fill the void with foam.
> Sure, most large windows need some shimming at the sill, but with or without shims, it's best to just seal at the interior face of the frame and not fill the void with foam.
I think I'm in agreement! What I would say is that "sealing" often requires backer rod for the sealant to perform optimally, and sometimes a light spray of foam is a good kind of backer rod. (It's at least my preference.)
> Okay. Every detail I see even on GBA shows a spray foam or back backer rod between the window/sill (otherwise, how would the air not just come in from there).
Some folks use tape. Other use sealant if the gap is tight enough.
I personally use carefully applied spray foam (so that it doesn't fill the whole sill cavity) trimmed flush with the jamb, and then robust sealant over that (Zip Liquid Flash or similar, Contega HF, etc.). I don't feel the need for a back dam in such a scenario, but opinions differ.
I have zero options to buy from homedepot/lowes a beveled material except for cedar shingles which I happen to have a few boxes for my siding.
https://www.homedepot.com/p/SBC-16-in-Long-Natural-Kiln-Dried-Eastern-White-Cedar-Shingle-Siding-EHD0810399/204994648
If we accept it's too expensive...it's 3/8 max. So it's pretty thin, bevels down....
I'm just not trusting I'm not going to mess up my cripples by going at them with a saw
Wild idea from the original poster?
What if I take cedar or composite shims, like the two below, attach them to the cripple to the sheathing edge, individually in a line, and then liquid flash over?
https://www.homedepot.com/p/15-in-Cedar-Wood-Shims-42-Pieces-Per-Bundle-0801415/327550852
or
https://www.homedepot.com/p/8-in-Composite-Shim-12-Bundle-10011700/301757699
Bad idea?
Ryan_SLC,
Just to keep things clear: We are talking about how to deal with the sill. Cripples are the studs on each side of the opening that support a header.
Yes you can use multiple pieces, and cover then with either liquid flashing, or a membrane.
Yes. Sorry. "base plate" that is now the window sill.
Thank you!
Alright, after a lot of patiance and learning from you all...I have plan finalized unless someone says stop.
I'm going to return all of the SureSill pre made pans and head flashing. Not only for expense, but an HD review with pictures was very harsh on the product for not having a visual appeal. Fair enough.
I'm going to pick up this 5/16 thick pvc trim board and attack it with a sander to create a slope for the sill. I'll afix this beat up trim board to the sill. I'll attach the pre made Benjamin Obdyke plastic "HydroCorners," I'll add a back dam to sill and then Obdyke liquid flash over the whole thing. Wet mil gauge just arrived.
https://www.homedepot.com/p/7827-5-8-in-D-x-3-1-2-in-W-x-96-in-L-PVC-Composite-White-Flat-Casing-0782708007/204342947
This was an adventure for you all in tolerance, but I tell you what, these finer beginning details made all the difference for me on a rather basic project. Thank you a million for the guidance.
Now I'll patiently wait for guidance on what is the gold standard for house wrap at this point; wrapped into the window walls with liquid flashing then applied on the house wrap or cut before with liquid flashing applied on house wrap, sheathing, and into windows.
> I'm going to pick up this 5/16 thick pvc trim board and attack it with a sander to create a slope for the sill.
I hate to be difficult, but power sanding PVC to bevel it is going to make you very unhappy. The dust will be incredible and it will stick to everything.
As a professional, I can see your point. But factor in how unhappy I have been trying to figure this detail out that everyone just inherently knew.
At this point, if that is truly the worst thing, I'll consider the mess confetti for my personal parade of saying goodbye to the endless hours spent trying to find these finer points :D
Ryan, none of us came out of the womb knowing how to do a sloped sill--we either learned from trial and error, or others' trial and error. I agree with Patrick about the PVC--I haven't used that product and maybe it sands easier than the Azek and similar cellular PVC I have installed miles of, and sanding it will not be fun. Do you have a belt sander? That might work, but your average orbital sander will very likely clog up.
With only four windows, if you want to sand, I think you'll have better luck sanding the rough sill itself in place. Or take a little more time, pull the nails holding the rough sill in place, rip a bevel with a circular saw and reinstall it. I truly think that will be faster and less aggravating than sanding a slope into the PVC. But maybe that particular PVC product is lightweight enough and/or has fillers that will make your plan reasonable.
Okay, reading the room here.
I will plunk down for one board and have the best update of a "you told me so" story.
Trying to find a wood option that is thin and wide is a challenge.
Is there a reason you don't want to just pull a few nails and cut the rough sill that is already there? All things considered, that would likely be the fastest and least expensive option.
Replying to a reply doesn't appear linear...let's see if this works.
It's a thought for sure. I need to go look. The inspector said they nearly over nailed the whole thing, so I am kinda remembering that in my case it would be a metric ton of nails.
Just looked and just moving the house wrap by an inch I saw 2 nails in the sheathing into the 2x6. Across four 3' spans, it's just going to be an epic journey to get those puppies out without destroying the sheathing.
The inspector said they came very close to having put in too many nails that she almost failed their sheathing. She found a few that were too close, but overall it was just over done but not damaging.
So that's what I would be dealing with on removing the 2x6s. Eek.
I would recommend checking the fit of your window in the RO before adding something to the bottom. I recently went through this and had carefully ripped and cleaned up a scrap piece of beveled cedar siding and attached it before realizing that the window didn't fit anymore. I thought I had accounted for the extra space when framing my RO, but apparently not. I ended up cutting an angle into the front of the sill with a reciprocating saw (AKA sawzall). It's not pretty, but it seemed to work out alright. I actually had an unrelated roof leak right above the window later that week (old sewer vent boot got bumped around and lost its seal) and was pleased to see the water drained out nicely.
Disclaimers: total amateur, in case that wasn't clear. Also, this was 2x4 framing.
Oh, total cart before the horse for sure. I ordered 2 1/2 months ago. Home Depot says they are hopefully delivering by Friday.
I admit to not having read all previous comments so excuse me if this is repetitive.
An alternative to a tapered piece added to the sill is to cut the top of the cripple studs with a 5 degree angle in them, instead of cutting them square. Then the sill lumber itself is automatically sloped the correct amount. Matt Risinger shows this approach being used by many contractors in his videos.
jgsg,
See posts #8 to #17.
What I don't like about any of the methods that slope the whole width of the sill is that you then have that slope on the interior where you are going to case the opening.
So I understand what I don't know...The back dam is at the end of the 2x6 (interior) at 1/2-1" height...why does the slope continuously up 100% to the dam cause issue? Wouldn't that best?
Go gentle. I am just not picturing the problem taking my sloped material all the way to the back dam.
Thank you!
Ryan, I'm not completely clear on what you're asking but I usually spec EITHER a slope or a back dam. Including both is a belt-and-suspenders approach but either one will work as long as the slope is steep enough, can drain to the exterior and the window doesn't take on too much water. If it's taking on enough water to overwhelm a 5° slope or a 1/2" back dam, you have bigger problems than the sill detail.
Malcolm, your framing tolerances must be tighter than mine:
Michael,
I meant the top of the sloped sill. When you come to case the opening, the stool is not supported where it meets the interior of the window frame - and there is a good chance someone is going to stand or sit on it at some point.
Ryan_SLC,
No the back dam should be at the inside face of your window frame at the sill. That's also where your interior air-sealing occurs.
If the slope continues on past that it a) serves no purpose, and b) means the interior sill, whether made of wood, or a drywall return, needs shimming flat first. So first you spend time sloping it, then you spend time leveling it. Unlike the jambs and head, interior window sills (or stools) get things put on them, or on occasion people stand on them when fixing window coverings, etc. so it's best if they are well supported.
GBA cross sectionals have struck again with me as a noobie.
To you pros, you'll probably think what am I smoking. But if you look at the back dam cross sectionals, there is not detailing colors or arrows or call outs saying where the window unit ends in these things. Even in the often repeated sill won't rot video people reference on this subject. Totally missing this critical part of where it goes in relation to the window yet the construction part is so basic. ugh.
Okay. Edge of window (internal side) straight down from there goes the back dam. Now it makes total sense why the whole 2x6 sloped would be a pain.
Thank you. Very helpful.
Can you share an example of what you mean for GBA details?
If I google "GBA back dam window" or "sloped window sill with back dam," I'm not seeing aligning the window with back dam ever mentioned or detailed.
I see what you mean. Like I wrote above, it's a detail that has evolved a lot in recent years. Here's one of my details from a few years ago: https://www.finehomebuilding.com/project-guides/insulation/prohome-wall-thermal-moisture-control-layers that includes spray foam at the sill and the back dam placed away from the window. The best-practice only fully clicked for me 3-4 years ago in an Instagram post by Christine Williamson--aka Building Science Fight Club. I'll suggest it to the editors as an idea for an article.
I'd like to read the room a bit from my neophyte position. It seems like I am hearing a few saying "if" you do one, do the dam. K. Got that.
Is there any reason I'm missing to not do both the slope and the dam? Just want to confirm. Money clearly isn't a concern since I have 300 bucks of plastic SureSill pre-formed plastic head and pans in my garage for my four windows. Not because I want to waste money or time, I want to do it right while this isn't my profession.
Thanks!
K. Going to be building the sills out today.
Just to final answer, the back dam vertical face does in fact touch or is a millimeter away from actually touching the window frame on the interior side?
Thank you!
Ryan_SLC,
You need to be able to conceal it when you trim out the interior of the opening.
Thank you!
In an unfortunate turn of events for the top sill flashing work, I've discovered the 26ga building code requirement of flashing.
Home Depot and Lowes sells drip cap edge that is 30ga. The difference is so significant, I don't even want to cheat it as a home owner.
I just don't have time for searching out or figuring out who can make the right stuff for me. Just infuriating the garbage that is sold when I would pay the money for the right stuff--so sell the right stuff.
The Tamlyn flashing looks like a fantastic product, but 700 dollars freight shipping.
I ended up rebuying the SureSill top pvc made head flashing unit off amazon and it's shipped, again.
You should contact a local hvac shop and have them bend all your flashing. Usually they only take a day or two and are very reasonably priced. You just need to find someone with a 10’ brake.
I didn't know that was something that they could do.
Honestly, all my local HVAC companies are super booked for normal work. In Salt Lake City, there really isn't down time for these companies.
I think the SureSill may work. I don't like their end dam look, but I I'll have to look to see if I could just razor blade it to look nicer.
We'll see. Thank you for your time!
The ones that have a brake and shop generally have a shop guy who’s availability has little relation to the field guys schedule. This is how you should do all your flashing as it allows for properly sized and angled flashing with proper drip edges rather than the box store generic stuff. I have also found that the metallic rustoleum spray paint holds up for about 15-20 years before needing a repaint, in case you need to paint it.
Thank you!
On the top flashing, what do you all think about this Marvin flashing install video?
I'm not clear on what the first part is about cutting the z bar, but if we forget that...
https://www.youtube.com/watch?v=FWH1qqyTiNk&t=54s
Ryan_SLC,
The head-flashing should include end dams.
https://hammerandhand.com/best-practices/manual/1-flashing/1-2-head-flashing/
Yep, you're right.
I mean to say on the SureSill head flashing pvc thing, it comes with end dams extended below too which I assume is probably on purpose to shed water that hits the outside of the dam to flick it out. However, I don't see that in anyone's mock up of end dams, so I'll see if I can cut that extra area off for appearance.
oops! I think I understand you as critiquing the Marvin video. Agreed.
Here's a good video to review: https://www.youtube.com/watch?v=pDa2yVaLXQE
Andy - thanks, great vid. One of the better ones that I have seen from TOH...particularly the commentary regarding the air gap and reasoning NOT to fill the space between the window and the RO with spray foam. Good stuff. (no Great Stuff ;)
Ryan,
I'm curious what code you are referring to with this: "...for the top sill flashing work, I've discovered the 26ga building code requirement of flashing."
IBC specifies 26ga or thicker. 2015, 2018, 2021 is where I am seeing the reference.
But I could be reading it wrong. I'm not a professional in this field.
Got it - I'm not a pro either, so I get the challenges to decipher code stuff.
Hopefully an expert will chime in. My understanding is that IRC would apply to 1 or 2 family residential construction. Ref. https://buildingcodetrainer.com/what-is-the-difference-between-ibc-and-irc/
In either case, there should be a specific year/code requirement for your locale. In my smallish Maine town we are still on 2015 IRC (among other codes, modified and wrapped into MUBEC).
I'm not suggesting that a rigid head flashing / drip-cap is not required or preferred, but if you wanted to go with the existing integral head flashing/drip cap it may be acceptable if you wanted to explore it further.
Good luck!
Thank you very much!
So update. Don't lose your gosh darn sausage gun ring! haha.
I liquid flashed two windows today. Both with sloped sills and back dams. One I did by cutting composite shims and the other by sanding 1/4" pvc trim.
The composite shims I cut and then brad nailed. That was a stupid idea on my part. Half blew apart and in the end, the liquid flashing is the only think that saved it.
The pvc trim saved down to a slope I shaved with a hand pocket plane. While tedious, the pocket plane collected a lot of the debris. This actually turned out to be great.
I made the back dams out of 1/2 X 2 furring strips, which I didn't know existed but I noticed were randomly in Home Depots pile of 2x2 that I was sorting through to get. The 1/2 worked great.
I liquid flashed with Benjamin Obdyke's flash. My misplaced my sausage gun tightening ring for the tips. So I cut and smeared on. Needless to say, I overnight shipped a replacement ring for the other two windows tomorrow. That was extremely messy.
Overall, I think I have two good sloped and back dam sills. Thank you!