Detailing Rain-screen Siding
I am siding a house (with Teak) and the owner wants me to use Tyvek. Like other contractors I am worried about installation of siding directly against the wrap and have read several articles by authors such as Lstiburek, Fisette & Katz and have concluded that an airspace is the way to go. However, Katz reccomends pressure treated strips with building paper stapled to them which adds a considerable amount of time to the job (but I will do it if needed). Would it be as effective if instead of pressure treated strips I were to staple asphalt strips (used for furring walls) instead (doubling them up if need) or should I stick to the lumber/building paper method?
I’m not sure what finish will be used but whatever it is should I coat the backside & edges of the siding before hand with the same stuff?
I just saw a rainscreen presentation by Bill Robinson, who worked on the JLC article with Gary Katz. They used plywood for their rainscreen strips, and I think it was PT ply but he said that someone he talked to at the APA told him non-treated would be OK. Sounds nuts to me but he said it plainly. I do not remember him talking about using felt over the furring strips.
My personal choice would be to use cedar lattice. They sell the stuff built into 4x8 panels and you can also just buy the lattice as loose pieces. If you use PT plywood you have to be concerned about the siding nails that go thru it. You might be using SS with teak anyway, but the PT just adds another issue.
The asphalt strips sound questionable. Teak is heavy. I would be looking to have wood to nail thru.
This topic has been discussed quite a bit on the JLC Online "Exterior Details" forum. You should probably check it out over there.
All very good points, the only concern with the cedar (or Redwood) lattice strips may be the one regarding the 'surfectants' on the Tyvek. If that's not a problem then the strips would save a bit of time. Thanks
That's right, you said Tyvek. Good catch. Can you get him to go with Typar instead?
I'm sure I could but why wouldn't Typar have the same problem?
timc, what about cedar breather? can't see why that wouldn't be a lot faster and less headache.
Unfamiliar with cedar breather!
tim, cedar breather is the older brother of Home Slicker, both are from Benjamin Obdyke, check the previous link and you'll see a header for it, it was originally designed for wood roofing shingles but is usable for sidewall apps. as well.
The manufacturer says Typar is not susceptible to tannins from cedar.
Felt is good...
"Work is the curse of the drinking classes."
Would felt strips be compatible with Tyvek or Typar?
Would the air gap be sufficient?
>> However, Katz reccomends pressure treated strips with building paper stapled to them which adds a considerable amount of time to the job <<
Are you saying the idea is to cover house walls with housewrap, apply wood firing strips, apply strips of hand cut tar paper over the firring and then the siding?
>> Would it be as effective if instead of pressure treated strips I were to staple asphalt strips (used for furring walls) instead (doubling them up if need) or should I stick to the lumber/building paper method? <<
asphalt strips? What are those? anyone have a link? Or are you talking about something you make on site? If so, exactly what type of material would you use?
BTW - what type of windows are you using and what type of molding treatment will be around the windows and doors? 1x4s? Brick mold? Something else? I'm interested in how you plan to detail around these openings with the added thickness of the firring strips. Do the windows have nailing flanges?
And - does anyone know the actual cost difference between Typar and Tyvek?
Sorry - no answers, just questions. I'm pretty interested though in these rainscreen exterior cladding techniques...
Yep, cover the house with Housewrap, then add p.t. strips and cover them with building paper to prevent moisture from the p.t. wicking into the back of the siding.
Asphalt furring strips are just strips of asphalt paper cut from a roll that comes in widths of about 1 1/2" wide.
Wood windows with flange, I haven't seen them yet and I'm not installing them but I'll want to discuss the installation with the installer after I've seen them and before he installs them so that we can allow for the thickness of the air gap. I'm thinking that the furring strips should be added around the windows (wider strips) and integrated into the housewrap (i.e. on top of the housewrap at the bottom & sides and below it at the top. Once the window flanges are caulked and the flashing applied over the flanges the trim will be installed with metal flashing at the head and the housewrap lapped over that and taped. The siding will butt up to the trim. How does that sound? I'd be interested in other peoples methods.
There is also this.
How much is that Teak siding? Sounds awful expensive. And yes I would coat the back and edges with the coating of choice.
Not sure of the price but I'm not supplying it.
I've checked http://www.benjaminobdyke.com/html/products/slicker.html already and although it seems promising my local supplier stocks it but hasn't sold any. I don't want to be a guinea pig. Also, Katz and others mentioned these but they all conclude that without doubt the best method is to use strips. I'd rather listen to these independent guys (with experience in the field) than web sites or magazines that are pushing their own product.
The Canadians have a lot of info. I was reading an article about it the other day. They actually drill small holes in their sheathing because their framing lumber is green so it needs to vent out as it dries.
We hare seriously thinking about trying a rainscreen, but we'd do what Dave said about cedar strips. Housewrap goes on the sheathing, cedar goes on to fir out the siding and trim 1/4", then siding. Vent at the bottom of the wall and top and screen to keep bugs out at the bottom. It is pretty straight forward and with a good production mentality can go very quickly, especially if you apply houswrap and strips while the wall is flat on the deck during framing.
I'm curious why you would go with the cedar strips Tim. Seems to me that 1x3 strapping would be less expensive and just as adequate for the job. This area isn't meant to see heavy, constant, or even occasional wetting. It's my understanding that a rainscreen is there as a "just in case" type of situation, so that if water does get behind the siding (which we can probably agree, will happen) that it has a place to drain. Seems like 1x3 strapping wouldn't see enough water to be a real concern for rot, if that's what you were worried about.
I've never done rainscreen installation myself, I'm just curious. I could be missing something obvious, and that's why I ask. Thanks in advance.Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
There was a Canadian study done somewhere on the rates of drying behind the sheathing as a function of how big a space there was in the rain screen; I saw it while Googling the subject. In parts of Canada where code calls for (or at least recommends) a rain screen, the thickness is supposed to be at least 10 mm (3/8 inch). Benjamin Obdyke's Homeslicker-10 meets this requirement. The regular Homeslicker is only 7 mm (1/4 inch). Obviously, pushing the siding out only a quarter inch vs. 3/4 inch for 1x3 strapping creates fewer problems on trim around windows, etc. The Homeslicker is a bit expensive, but it is said to go on easily, and the savings in labor can't be ignored. I'd like to see others who have actually used the stuff comment on things they learned with it, as I am planning to use it myself.
When I was doing research for the Housewrap article a few issues back, I talked to Mike Guertin about the 'slicker products. His experience was that using it behind shakes or shingles was a pain, because the material has some give to it, and when you press the nose of the nail gun against the siding it wants to crack under the pressure. Of course, if you were fastening with nails and hammer, I would imagine this problem might be far worse.
That's the only hands-on I've got to offer, and they weren't my hands :)Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
Tim is right on. The air space doesn't have to be 3/4 in. 3mm is enough to break the surface tension of water and allow it to drain, but 10mm is required by coastal Canadian codes to break capilarity caused by pressure differentials--thus that wider space. I think rips of felt paper wouldn't be firm enough at that thickness, and also more of a pain. And cedar stripping would be fine rather than PT plyood, and you wouldn't have to cover the stripping. The thought is that surfactants and tanins from cedar might reduce the ability of a housewrap to hold out liquid water because most housewraps depend on surface tension to keep water out. Typar is superior in this regard because it has a higher perm rating. But the issue is probably null with a rain screen wall where water vapor and liquid water aren't 'driven' so dramatically by pressure differentials AND air circulation provides diffusion and evaporation between the siding and the housewrap.
HomeSlicker doesn't give that much, but I woudn't use it behind say a joint in horizontal siding, or around windows and doors or corner boards. I'd use solid 1/4 in. strapping or stripping. So if you're going to use that much stripping, maybe you strip the whole house? I would sure use HomeSlicker inside columns, pilasters, etc. where blocking or stripping would prevent what little circulation you're able to encourage. Columns fail so easily today. They need all the help they can get. Same with trim on dormers or reduced overhangs on gable ends, etc.
Bill Robinson and I have been talking about and researching improvements from a two-layer housewrap system (he's MUCH more up on this stuff than I am!) and in a lot of areas that's probably fine. But I'm more concerned about--and the whole reason I started reading about this stuff--some of the exterior trim products we use today--about getting water and moisture away from them quickly, allowing them to dry quickly. I think that's one of the real problems with fresh-growth wood today, and one of the reasons that paint doesn't last so long anymore. What got me started on this was the article in FHB by Mark Synder (feb/march 2001), and his update that FHB published a year or so ago. WHAT AN EYE OPENER!
Thanks for taking the time to reply Gary, that's some great information. I'm especially impressed with the idea of using homeslicker for columns, what a fantastic idea!Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
> Seems like 1x3 strapping wouldn't see enough water to be a real concern for rot, if that's what you were worried about.
It may be a regional thing. Here in drywood termite country, I'd think treated would be better. As I understand rain screens, there's plenty of room for them to get in, and it's nice and dark in there -- bug heaven.
I haven't thought out all the details yet. If I did, I hope I would have come up with your idea. One thing I didn't want was the trim to stick out past the window and didn't want to have to mess with the window opening.
Thanks for posting, you gave me some ideas to think about.
I do not think the asphalt-impregnated felt will serve you well as furring strips in this application. You will need a minimum clear 3/16" to break capillarity. To achieve that it is necessary to use 3/8" furring
According to the APA PT is not required.
However, if you do use PT it is necessary to provide a slip sheet between the PT and the siding.
Consider using Coroplast.
Edited 11/20/2006 9:57 pm ET by BRobinson
I live here in The lower mainland of BC Canada. We have probable rebuilt 3/4's of all multifamily housing built from the mid 80's to the late 90's when rainscreen came into play. Look up leaky condos. And here every project I have seen or worked on are done almost the same. Walls are strapped with pt ply rips covered with a breather board if stucco finish or covered with hardi, vinyl etc. Wholes are drilled in the sheathing to allow moisture to escape. Our lumber used in framing is kilm dried not green as suggested. Before vapour barrier goes on and seals framing in a building envelope specialist checks for framing moisture content and check the exterior finish.