My gut tells me no...but their web site and a few on line training videos seem to indicate Tyvek's Rainscreen product called Drainwrap is a dual hybrid product?  This can't be correct?

I know Ben Obdyke offers a product called Home Slicker + Typar that is a dual product but it is .90 a sq', which is pricey.


Tyvek's drainwrap is appx .17 a foot.  Probably doesn't work as well as Home Slicker though.

Thoughts?

OSB wall sheathing, Hardi or Certainteed cement fiber board lap siding, 40-60 inches of rain a year, so I need some type of capillary action wrap between the sheathing and siding

your best bet is to forget about these new whiz bang fabrics and build a real rainscreen. OSB/15# felt (or Tyvek if you prefer)/vertical 1x3 strapping nailed onto each stud (SF wall x 1.1 = LF x $.15= under $200 for each 1000 SF of wall; cheaper at a sawmill)/siding. Cut 1/2 width pieces of roll vent (for roof ridges) to seal between the bottom of the strapping to keep critters out. That gives you a real live air space for the siding to climatize & dry out. Quick to install also.

What Bob said! There's nothing quite like 3/4" of air as a capillary break, and vented both top & bottom the convection-drying is IMMENSE, pushing far more air than you can get with any mesh underlayment approach.

With only 3/4" of wood you'll need to use ring-shank to get the necessary fastener retention for the siding, and pay attention to the material & finish compatibility of the nails with fiber-cement.

cement board is unnecessary IMO with this method since the main problem of wood claps is moisture drive which is eliminated, and since there are houses in my town with 100-200 year old pine claps I know they last. If you're using them anyway, pine is probably better than spruce for the strapping since there is less chance of splitting. rough pine (as I said, inexpensive at a sawmill) works just fine.

I too am an advocate for using wood, but the summertime forest fire hazards are sometimes significant in Humboldt County, if somewhat less right along the coastal bluffs than in the foothills:

http://frap.cdf.ca.gov/webdata/maps/humboldt/fhszs_map.12.pdf

Most of Trinidad is in the "Moderate" hazard zone, but on the point just north of town there's a section of coast that is in the "High" range right down to the water.

So a more fire resistant siding isn't necessarily a bad thing here.

Doug-fir and redwood are probably more common at the local mills than pine, given there are fewer than 3K acres of all pine species combined in Humboldt county, compared to 700K+ of douglas fir, 400K+ of redwood, and effectively zero spruce:

http://co.humboldt.ca.us/gpu/docs/meetings/natl_res/06chapte.pdf
Doug fir is GREAT stuff to work with, and while we on the right coast usually have to pay a premium for it, douglas fir is the most commonly used timber in the PNW.

Avoid any chance of rot and use 3/8" fan fold XPS foam to create the gap (as Building Science did).

That xps is 4' x 50' folded every 2'

What does bldg sci suggest? Cutting it into 2" strips and nailing it to the OSB where the studs are? sorry I did not check their web site (needle in haystack).

As I recall, yes. More info here.

JonR..thatnks for the link to the BSC article. Very interesting.

I would like to discuss the concept of using 3/8" XPS as a shim for an air gap between WRB wrap on wall sheathing and Hardi Plank.

Does anyone else think this is an interesting alternative to a rain screen or wood strips?

A single 2x50 fan fold of XPS would make an bunch of 2" strips and if you banged out some sort of jig you could saw through a folded stack with a band saw (probably a better more elegant way).

Once you had the 2" strips, it shouldn't take any more time (if any) to install over the WRB Tyvek than wood strips. Maybe a little more time than a rain screen but certainly more time than a combo WRB/Rainscreeen product.

Here is the BSC link http://www.buildingscience.com/documents/reports/rr-1306-vancouver-test-hut-hardieplank-walls

Anyone have any suggestions on the most time effective way to cut the fan fold into 2" strips?

Anyone have any thoughts on the proper way to "nail" the strips to the exterior of the house?

These would need to be attached at the points of the wall studs, no? And the Hardi-Plank nails should drive through the XPS strips, through the WRB wrap> OSB sheathing> wall studs. Ring shank nails a little longer than what would normally be used (if no air barrier were present)?

The fan fold we have at the local Lowes is 1/4" thick blue XPS. It is 4'x50' and folded every 2' forming a bundle 2' x 4'. If you take 5 flats and cut it in the fold from the rest, that would give you 10' strips if layed out flat. Set your table saw and fence to cut 2" strips. Keep the 5 flats folded together tightly and rip 2" x 10' folded strips off on the table saw.

Weep holes in this scenario.

The weep hole necessity has me concerned on several fronts.

1. When the water draining down behind the Hardi Plank hits a window, it would stop an pool up, no? You'd have to have a weep holes every 16 or 24" Depending on your XPS shim spacing. And the holes would have to be above the windows as well as at the bottom of the wall? This seems like a lot of weep holes. Am I missing something?

Normally all the area around a window are sealed with silicone caulk?

Of course the weep hole questions are there regardless of which shim material you chose, or for that matter, regardless of which rain screen product you choose?

And on a 2 story house, I would think you'd want to line up your XPS strips (as long as the wall studs line up) so there would be one long 2 story water channel?

On one side of my house the outside wall will be broken up by a2 nd story deck.  The ledger board normally would have a flashing on it (tucked underneath the nearest lap of the Hardi-Plank) - which might keep the water from channeling down to the bottom of the first floor. But now that I think of it, the flashing would be between the XPS shim ans the Hardi-Plank, so it probably would not impeded the water flow on down.

Posted By arkie6 on 19 May 2013 10:37 AM
The fan fold we have at the local Lowes is 1/4" thick blue XPS. It is 4'x50' and folded every 2' forming a bundle 2' x 4'. If you take 5 flats and cut it in the fold from the rest, that would give you 10' strips if layed out flat. Set your table saw and fence to cut 2" strips. Keep the 5 flats folded together tightly and rip 2" x 10' folded strips off on the table saw.

This was exactly what I was thinking and the size of your saw blade would determine how many you could cut at once.

Posted By JohnRLee on 19 May 2013 11:46 AM
Weep holes in this scenario.

The weep hole necessity has me concerned on several fronts.

1. When the water draining down behind the Hardi Plank hits a window, it would stop an pool up, no? You'd have to have a weep holes every 16 or 24" Depending on your XPS shim spacing. And the holes would have to be above the windows as well as at the bottom of the wall? This seems like a lot of weep holes. Am I missing something?

Normally all the area around a window are sealed with silicone caulk?

Of course the weep hole questions are there regardless of which shim material you chose, or for that matter, regardless of which rain screen product you choose?

And on a 2 story house, I would think you'd want to line up your XPS strips (as long as the wall studs line up) so there would be one long 2 story water channel?

On one side of my house the outside wall will be broken up by a2 nd story deck.  The ledger board normally would have a flashing on it (tucked underneath the nearest lap of the Hardi-Plank) - which might keep the water from channeling down to the bottom of the first floor. But now that I think of it, the flashing would be between the XPS shim ans the Hardi-Plank, so it probably would not impeded the water flow on down.

The flashing must be on the bare osb. The house wrap lands on the flashing. Then the XPS strips . Then the Hardie. Virtually or in real live, once the house wrap is on, pour water at the top right under the eaves and trace it down. If there is any place where it can get behind the flashings, you lost the game!!

Technically you don't have weeping holes. The whole space between the shims should be open at least as high off the flashing as the shims are thick. Put bug screen or mesh of some type in this gap. Reread what Bob I. and Dana have written!!

After reading several documents om the BSC web site (since my last post a few days ago), I see that the flashing at the bottom of the wall tucks underneath the wrap and if your first lap of Hardi is nailed down slightly above that flashing, that provides for your weep at the bottom of the wall. But so far, none of the docs I've read on BSC detail how this is accomplished above a window or door.

Reading between Dana and Bob's lines in their posts, it's possible the air gap itself provides enough space for what little water would collect or pool, to simply convect and evaporate up. If either one wants to correct me on this, I'd appreciate it.

I am leaning heavily towards XPS strips as air gap shims, instead of fir strips, but I'm not totally head strong on XPS. I like the idea of the XPS, as it won't rot or absorb water.

Posted By JohnRLee on 22 May 2013 07:40 AM
After reading several documents on the BSC web site (since my last post a few days ago), I see that the flashing at the bottom of the wall tucks underneath the wrap and if your first lap of Hardi is nailed down slightly above that flashing, that provides for your weep at the bottom of the wall. But so far, none of the docs I've read on BSC detail how this is accomplished above a window or door.

Reading between Dana and Bob's lines in their posts, it's possible the air gap itself provides enough space for what little water would collect or pool, to simply convect and evaporate up. If either one wants to correct me on this, I'd appreciate it.

I am leaning heavily towards XPS strips as air gap shims, instead of fir strips, but I'm not totally head strong on XPS. I like the idea of the XPS, as it won't rot or absorb water.

John - it is really the same above the windows. You must provide a header flashing (or drip cap, depending on what they call it in your part of the country) above each window and door. Than the h.w. goes over it and the siding is installed with a gap at the bottom.

There is only a few times that the flashings go on top of h.w. A few examples are if it is the undersill flashing (under a window), a flashing for a material change part way up the wall or if you are installing a water table trim on the house. In the last two examples, the flashing goes over the lower house wrap but the upper house wrap starts over the top of the flashing.

What Bob I was trying to say is that the XPS shim might give enough void for drainage but not likely enough for drying. If you have a bigger gap, it will air dry and there is no chance of rot so using wood is not a problem.

the other issue with using xps is that your siding may not lay flat. you will get some compression thru the foam when you're nailing; you can decide if it lays flat enough. I used Cedar Breather on one job under cedar shingles and will never use it again for that reason. XPS is less compressive than CB of course, but the polyiso SIPS, for example, always compresses at the nails.

Here is typical Phoenix, Arizona construction: 2x4, no OSB, Tyvek or tar paper strung across the 2x4's, 1" of sectional EPS, chicken wire, 1/4" - 1/2" of stucco.

This wall has more 2x4's due to the windows but usually it's 16" or 24" o.c. Of course the insulation is R-13 fiberglass batts. The thermal bridging is very high in this type of wall assembly and in the end you  end up with a R-8 wall assembly and $500 a month A/C bill in the summer. Not to mention the constant water leaks coming into the home and the scorpions living inside of your walls.

After they installed the exterior 1" EPS and chicken wire, I went inside of the home and counted over 100 rips and tears in the Tyvek from them installing the styrofoam and chicken wire.

No diagonal steel straps for racking? No stucco/drain wrap to get some drainage? Holes wouldn't concern me too much if they tape them up later. And use another taped air barrier layer on the inside. R8 isn't right if you count the foam.

With R13s you'd be at about R8 just for the framing + fiberglass layer. Add another R0.5 for the stucco + gypsum, and R4 for the inch of EPS, so you're at about R12-13 whole-wall.

With roof overhangs sufficient to limit direct rain-wetting you might be OK in that stackup from a moisture point of view in that climate. With no sheathing to soak up moisture being driven off the stucco in the noon-day suns you only have to worry about the stud edges, and with highly permeable unfaced batts the air conditioning would keep up with the moisture loads. It was pretty common in the desert SW 50-70 years ago to build uninsulated studwalls with stucco applied directly to exterior lath, and they don't seem to succumb to moisture in that climate.

But it's pretty a pretty crappy build- I too am surprised code allows it without bracing from wind-loading/structural point of view notes- it doesn't take much. Maybe they're counting on the structure of the chicken-wire reinforced stucco for racking resistance?

Posted By jonr on 23 May 2013 05:35 PM
No diagonal steel straps for racking? No stucco/drain wrap to get some drainage? Holes wouldn't concern me too much if they tape them up later. And use another air barrier layer on the inside. R8 isn't right if you count the foam.

What you see is what you get.

Taping them later? They give a guy making $7 an hour just one hour to try and seal up all the rips and tears. Trust me, I've personally seen the work myself and they do an atrocious job of it. Even after the fiberglass batts and sheet rock installed, when the winds go above 10MPH, you can literally see sand & dust pouring out the wall outlets. Scorpions come into the homes from the outside as they find all the cracks, gaps and rips in the walls. That is why the scorpions (and other bugs) come out of wall outlets, ceiling light fixtures, baseboards, and anywhere else they can.

I stand by the real life R-8 value because the wall air infiltration is so atrocious in these homes and when you calculate the thermal bridging, air infiltration, and the poor installation of the batts. Not to mention they use 1/2" EPS on portions of the outside when the framing sticks out, they will switch from 1" EPS to 1/2" EPS to keep things flat on the outside.

As far as racking goes. When the winds blow around 30MPH the homes will creak, pop, and nail pops in the drywall are galore. When we have 40MPH + winds during a T-storm, the house sounded like it was about to fall apart as it was racking so badly.

This is junk construction and the energy usage on these new homes are atrocious. They were getting a rash of home break-ins in Phoenix and the burglars were breaking in through the walls because they are easier to get into than breaking down a door or window.