Here in rainy B.C. we are now using rain screen systems in all homes that have less than a 2 foot overhang or are taller than one story. These changes have just come in and there are a lot of different technics being discussed. I was in at our window supplier yesterday and they have a rain screen window that has it’s nailing flange back 2″ so it can be nailed directly to the sheathing but extends out further to accommodate the extra strapping involved in the rain screening. It also comes with a sloped sill piece that goes in first. This is another requirement(the 6 deg. sloped sill). I was wondering if any one out there has had any experience with this or a similar product. Or are people finding good ways to do rain screen with traditional flanged windows. one of the advantages cited to me with the rain screen window as opposed to just strapping under the window, is that it keeps the window glass in line with the studs and doesn’t push the glass out towards the cold zone causing potential moisture problems. Any thoughts would be appreciated. Thanks.
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Replies
Have you got a link to the product?
Dave
Post the link. I am really interested in this and I'm just south of you in WA state.
http://www.starlinewindows.com/newweb/starline-web/vinyl/new-construction.php?7000-rainshield-casement-awning
I just looked up the window on the net and here is one of the ones I was looking at.
The price is about 25%more for the "rainsheild" window over the regular. with the new reqirements it might be worth it.
I just ordered windows from Starline. Jay Clark never said a word about these new ones. Some salesman!
...it keeps the window glass in line with the studs and doesn't push the glass out towards the cold zone...
I'm not exactly sure what this means... why would keeping the face of the glass back an inch or two thermally shelter the window from the elements? Maybe I'm just missing something.
Also, what does "strapping" mean in the context of this discussion?
I'd like to hear more about this "rain screen" concept. Please post more.
With rainscreen construction the wall is sheathed, papered and then vertical strapping is applied to create an airspace between the paper and siding, to keep any water that penetrates away from of the wall. Much as is done with brick veneer.
The window is installed on top of the strapping, and the concern is that it might be more susceptible to condensation than if it were further back on the studs where the wall is warmer.
Thanks for the info about the rainscreen concept.
So what's used for the vertical strapping? 1x2s or something like that? Is horizontal siding just nailed directly onto the strapping then, without an additional layer of sheathing? I guess if you applied horizontal skip sheathing, you could then apply shingles, too.
We just did a cedar shingle job that had a 5" reveal. the assembly was 1/2" ply - tar paper - vertical strips of 3/8 pt plywood spaced at 16"o/c nailed to the studs - horizontal 1x2 pt spaced 5" o/c to nail the shingle on to. looked a lot like lattice.
That sounds real old school! Funny how the oldtimers really had things figured out.
Speaking of "old school", old windows had a 2x8 bevel sill set at a 10-degree angle. Sounds similar to what's being specified in the new rain screen construction.
Sometimes I'll make traditional frames, nail them in place, and then install a modern unit WITHOUT fins inside the finished opening. The modern unit is just trapped between the blind stop and the interior stops. It's some extra work, but it yields a continuous sill, and makes nailing off casings and traditional stools, etc., much easier in the end.
I agree with your description in all ways but one... why would the window me installed on top of the furring? That would create a lot of difficulty in integrating it into the WRB (felt paper in your example). Seems a lot easier to me to simply sheathe, paper, install windows as normal, and then add the furring strips and siding. In most of the discussion I've heard and read the furring is only ~3/8", so we're not talking about much.
Didn't check out the window link but I assume they're just adding slightly deeper jambs.
Much of the water damage that the rainscreen is designed to prevent occurs at penetrations like windows, vents, etc. If you move them back to the wall plain, you defeat the purpose of the rainscreen. Also, depending on the wall finish, the depth of the strapping can vary. you can find yourself well past the sill.
The CMHC (Canadian Mortgage and Housing Corp.) publishes "Best Practices Guides" for various climatic zones. They include rainscreen details and are worth a look, but are a bit pricey.
Edited 2/22/2007 12:48 am ET by fingersandtoes
I'm not a building scientist but I still differ with you here. The window trim has to be furred out just like the siding, so that water getting past it runs down behind and does not enter the wall by capillary action. Rain screening is all about creating a capillary break and reducing or eliminating pressure differentials. It just seems to me that it would be SO much easier to waterproof a window at the wall plane rather than trying to install those flanges on top of a rainscreen and then waterproof back to the wall and WRB. That makes the window flashing a three-dimensional affair rather than two.
Haven't seen the Canadian details but I know that it's close to becoming code over in BC, which is about ten miles away.
Its not close to becoming code, its done. No rainscreen, no permit.
I still don't see how you intend to seal the flange on a metal or vinyl window if it doesn't extend out as far as your strapping. You should take a look at the Starline window link to see why they altered the profile.
OK, I looked at the Starline link. What I see on the first screen is a window with flanges that are against the sheathing per usual, and a frame that is deeper to the outside so that it doesn't get "recessed" behind the siding. It's a visual thing. This window would install like any other flanged window, rainscreen or no. Am I missing something?
No there is nothing more to it. But it isn't just a visual thing if your window is not deep enough to cover the ends of the siding. Its as though you sided a house in hardiplank and used 3/8" corner trim.
I see what you're saying. It is very rare that I run siding right up to a window unit--there is almost always casing around the window and usually a sill at the bottom. Most of the windows I install could accommodate a 3/8" rainscreen space without a problem. The 1x furring that has been mentioned here might start to cause the windows to be too deeply set.
3/8 is the minimum allowable. most are using 1x2 ie 3/4" in the case of my shingle wall or board and batten the double straping came out to 1" ( the 1x was actually 5/8")
In Nova Scotia, most people who can afford shingles are putting them on privacy lattice for a rainscreen. Doing things the old fashioned way, shingling directly on board sheathing with dry sheathing paper would only last a century or so, after all.
I still haven't got a good handle on how to properly flash and seal windows and doors into this new kind of assembly. It's a work in progress.
Ron
It sounds like no one has used this or any thing similar. So now I am wondering what others are doing as far as details to rainscreen around windows. In our last job I papered with right up to the r/o, trimmed the ro with 3" wide strip of 3/8 ply and then with an 1.5" strip of the 1x2. (the head trim was both 3" wide to accommodate the 1.5" window drip cap) Then I installed the flanged window and a drip cap flashing. then with 6" peel and stick I peel and stuck up the sides from the edge of the window over the strapping and out on to the paper. the extra wide 3/8 strip gave a backing for the horizontals to land on. over the top I peel and stuck over the drip cap and the 3" straps and up onto the paper. Then after all the rain screen straps were installed I put up the 2x6 trim as per usual and flashed over all with a 3" drip cap going back up and under the original paper.
long winded but I hope you get the picture. What are you doing. I wonder if there is a way to do this with out all the peel and stick.