Hi Mark,

We looked into the drainage wraps and ultimately passed as the most common brand we found in our area is Homeslicker, made by Benajamin Obadyke (sp?), and it has a small compression value, and we didn't want to have any concerns over wavy fiber cement. We chose, instead, to use vertical furring strips to achieve the same drainage plane result. We also used a product called coravent located at key openings (windows, skirt board, etc) which is designed to allow air flow, while also preventing insect entry.

I would suggest doing a search here for Rollie's Delores house which provides an excellent reference for this sort of exterior design. Keep in mind that it is especially important to ensure your flashing details are sound when using this method..... it can get a tad tricky.

We're using Nichiha siding and I know their reps are perfectly comfortable with this installation (ie no warranty issues).

Good luck!

House Wraps like Vortec that don't want to tell you how it is made, are probably micro-perforated polyethylene which, in my opinion, is not sufficiently water resistant to be used in a wall assembly as a weather barrier. I would recommend spunbonded wraps like Tyvek and Typar. You might consider using Tyvek Drain Wrap or Stucco Wrap (same thing) if you think the amount of rain in your area justifies it.

Vortec is high-density polyethylene. (See technical specifications at the website below.) Under wood siding, I've used Tyvek followed by wood furring and appropriate flashing.

Here is a link that might be useful: Vortec

Thanks for the feedback--appreciate clarification. If Vortec is HD Poly (as opposed to regular poly), is that satisfactory for water resistance? I like that the pattern is non-directional, compared to Tyvec, which has to be installed only one direction. --Mark

According to the manufacturer, the product is laminated and micro-perforated, as opposed to spunbonded polyethylene and polypropylene.

It has a lower permeability than either Tyvek or Typar.

But you also might want to look at comparisons for tearability, surfectant resistance and a host of other things. The fact that it is said to drain in all directions is not that important to me.

In our mixed-humid climate, we've used Typar with Homeslicker rain screen, and Nichiha shakes/siding. Nichiha is slightly thicker than Hardie, but I can't comment on the warping issue.

Here's the website that Niff suggested...

Here is a link that might be useful: Delores House

Most house wraps are made of polyethylene or polypropylene. Some are cross-woven with a micro-perforated coating, some are porous film laminated to scrim, some are non-woven spun-bonded, and there are other variations. The micro-perforated ones are the least water-resistant. I recommend using the non-woven ones like Tyvek, Typar and WeatherSmart (Fortifiber) and would only use one of the others after testing it for water-resistance.

The benefit is when using a drainable house wrap over a flat conventional is the drainage capabilities. My pick would be Obdyke or TamlynWrap because they are non-woven and the spacers that form the drainage gap (mini rain screen) do not compress as would be the case with a wrinkled house wrap such as Tyvek's. Install siding over it and with the nail pressure will cut off any drainage capabilities. As per furring strips, lay treated wood over the house wrap and see what would happens over time. The chemicals in the treated wood with breakup the membrane and will allow moisture into the wood and the rotting begins...

When recommending Benjamin Obdyke materials it is important to specify which one you mean. Their "Slicker" rainscreens are used over the house wrap of your choice or they can be bought with non-woven spunbounded Typar wrap attached to the mesh. The company also makes HydroGap, a drainable house wrap about which little is revealed by the company.

I was talking about HydroGap and TamlynWrap are the only house wraps that I know of in the market that have a true drainage capabilities. With all other wraps something else has to be added to create a drainage gap, such as furring strips or meshes. These two have the rain screen bonded to the membrane. They install like regular house wraps and no modifications have to be made to the structure as you would need to do at windows and doors when furring strips are installed.

HydroGap looks great but with a drainage gap of about 1/32" its not a rain screen.