houswrap...UNDER or OVER furring ?

[student2]

Frame>>> Ply Sheathing>>> 1.5" Cladmate>>> 1x3 furring>>> vinyl siding. Where should the housewrap go?

[David]

Under!

What do you get by using the housewrap in conjunction with XPS (Cladmate)?

[student2]

Thanks for the reply, David. My (limited) understanding is that foam panels --and the joints between them-- move with the frame as the wood expands or shrinks. Hosewrap, I'm told, lets the house "float inside" the enveloppe.

But you've got me thinking, here. Are you suggesting no wrap at all?

[David]

Personally, I don't buy that story. However, you won't be hurting yourself any by using housewrap.

As with most products, the devil is in the details. Be sure *YOU* know the flashing methods. Be sure *YOU* know the details of how the housewrap should be intalled. Then, if the installers do it right you can say well done, and if they do it wrong, you can tell them to try again.

[woodall83]

why furring at all?

[Sweep]

1.5" Cladmate has shiplapped edges is water-resistant, vapor permeable and a good air barrier.

Strapping might help wood and fiber-cement siding drain better but it's probably not necessary with vinyl siding.

[Rich]

I was pretty sure I read some articles on toolbase regarding how permeable vinyl siding is.. I believe it mentioned that vinyl should have the same drainage plane as any other material - and even more so. Of course, they also mentioned area - where large volumes of rain and high pressures will drive the rain behind the vinyl much like cement and wood. I think grumpy has mentioned several times - if vinyl is impermeable why does it have weep holes :) Don't take that to heart - it's been awhile since I read the article and was pretty sure it was toolbase.

[CThomp]

Do hardi-planks require a drainage plain?

It doesn't say you need one on their web page and I don't think i've ever seen that done down here.

[VALENT]

Do hardi-planks require a drainage plain?

It doesn't say you need one on their web page and I don't think i've ever seen that done down here.

I hope not.

[CThomp]

I'm guessing you've done hardi-planks without the drainage plain huh?

[VALENT]

on my own house, of all places!!!!!!!!

[CThomp]

Has your house rotted and fallen apart yet?

[Rich]

Drainage planes are mostly recommended for areas with wind driven rain - where the air pressure has large differences between inside and outside. Most siding product will not require a drainage plane. I believe there is a map of areas and what they recommend in the JLC's best practices manual. I'll check it and post again.

[David]

VALENT, oh please tell me you are joking. I can't predict the future, and thus can't say if you NEED one or not. But, I can say you should have one behind hardi.

Here's why. The intense heat in SE Texas combined with heavy raines and high humidity make us extremely succeptible to moisture driven by a thermal gradient. That is, the sun bakes/heats up the outside of our siding, driving the moisture inward to the house. Almost any siding here needs a drainage plane: vinyl, stone, brick, stucco, cedar, cement board (aka, Hardi)...

I would say almost anywhere in the country should have a drainage plane. Even in MT. They don't cost that much to add as a dp can be made of felt, housewrap, and rigid insulation (aka, EPS and XPS foamboard).

[David]

Do hardi-planks require a drainage plain?

It doesn't say you need one on their web page and I don't think i've ever seen that done down here.

Are you sure? Shiplapped rigid foam with taped joints counts as a good drainage plane.

In FL, just like in SE Texas, you SHOULD have a drainage plane behind Hardi...and virtually any other commonplace siding, too.

[CThomp]

Wouldn't just having a WRB (tyvek house wrap) count as a drainage plain?

[VALENT]

According to David it does. Well, I do have tyvek and OSB under the Hardi. I didnt know that counted as a drainage plane. Has your house rotted and fallen apart yet? Well, not yet, but its still early.

[David]

Wouldn't just having a WRB (tyvek house wrap) count as a drainage plain?

Of course it counts! Obviously they need to be installed correctly to be useful. An air gap is recommended down here in the south, but up north it's probably better to not have an air gap.

[Sweep]

Tyvek is a "weather resistant barrier" but not a "drainage plane" since siding is normally placed against it. A drainage plane must provide a space that will allow water to drain by gravity. Strapping works. DuPont's DrainWrap (same as StuccoWrap) also works. Green Guard's Raindrop and many other systems also work.

[Rich]

Sweep - have you used the Raindrop or Drainwrap on any projects?

[Sweep]

I've only used StuccoWrap which is identical to DrainWrap.

StuccoWrap was designed for use in an EIFS system but can be used behind stucco if it has another layer of underlayment over it to prevent the stucco from adhering to it.

I suppose the benefit of strapping and an air space is that the underlayment doesn't get penetrated by thousands of nails from the siding which to my mind is the great ignored flaw in DuPont's air/moisture barrier concept.

[concretemasonry]

How do you handle window guarantees without house wrap or equivalent? Can you install to manufacturers requirements?

Without the proper installation, the window guarantee might go as far as fogged IGUs if you are lucky.

[David]

Tyvek is a "weather resistant barrier" but not a "drainage plane" since siding is normally placed against it.

Normal for Mass, but not down here. ;)

[Sweep]

Window manufacturers provide limited warranties guaranteeing their products will remain free from defects in manufacturing, materials, and workmanship usually for 10 years and a usually 20 year warranty on the insulating glass air seal.

A warranty for installation would be from the installer.

[Sweep]

Housewrap might act as a drainage plane behind vinyl siding but it would not contribute much to drainage for most other kinds of siding as they found out with EIFS in the Southeast. Calling a membrane a drainage plane doesn't necessarily make it function as one.

[MCC]

I Beleive Your On The Right Track. The Houserap Should Go Over Furing As Not To Leave Any Wood Open To Elements. Don't Strech To Houserap Tight. By Doing This You Have A Tight House And The Proper Drainage You May Need. In Most Cases You Don't Need It With Properly Installed Siding But It Dosen't Hurt

[MCC]

Ps - I Agree With Sweep It's Good In Your Application And Definitely Not Under Rigid Sidings.

[CThomp]

So is a drainage plain necessary or not under hardi planks?

Or can I put the hardi-planks directly over the tyvek. I've never heard of or seen anyone using drainage plains down here.

[David]

Yes, for us, a dp is necessary and so is an air gap between it and hardi! In the hot-humid states you absolutely must have an air gap.

To be technically correct, you could use #30 felt over your OSB, then furring, then tyvek, then hardi. However, that would place your waterbarrier (felt) behind your air barrier (tyvek). If it were me, I'd use rigid insulation, but since you're not using it, then I suggest using tyvek over osb, then fur, then install hardi.

They do it here all the time, but that in and of itself doesn't make it proper, especially for FL. Yet the principal is still the same.
http://www.buildingscience.com/designsthatwork/hothumid/profiles/houston.pdf

[CThomp]

Interesting. I guess furring strips are cheap enough. This is gonna make my window trim a bit more interesting as well.

Why doesn't the hardi webstite have anything on this? Am I blind or what?

[David]

That would acknowledge water penetrates thru it! :)

[CThomp]

Good point.


So what would I put across the bottom? Screen? Don't want to give critters (Florida has TONS) a place to call home.

[David]

I was joking in my response. I think everyone knows Hardi absorbs water.

Sure. I know a builder who has done it. Not exactly sure how he does it. He uses the same type of screen used on screen doors.

[CThomp]

Yeah I know.

I'll check into the screen thing.

[CThomp]

So this screen.

My idea:

Cut the screen into 1' strips.

Staple 6" of screen to the bottom of the tyvek letting the rest of the screen hang while pulling tight.

Attach the furring strips 12" o.c.

Fold the screen over the furring strips and staple to the furring strips.

Nail the starter furring strip to the bottom of the furring strips.

Nail the hardi-planks to the furring strips.

No critters.

I'll use 1x6 for furring around my windows for the window trim.

[CThomp]

Just checked out that link David. Funny thing is I came up with my idea before I looked at his. I left out the starter strip for the hard-planks though which should be integrated. I'll do it his way.

[MCC]

We Have Been Using Hardiplank A Lot Up North On A Few Townhouse Projects And I Haven't Scene One Architect Spec A Drainage Plane. House Wrap Is Not A Drainage Plan. It Can Be Used As One If In Your Case You Put It Between The Furring And Hardiplank And Don't Stretch It Tight. But Why The Furring?

[David]

No, you won't see an airspace anywhere up North. You want to minimize air movement up there because of the freezing winters. That is not the case here. Moisture must be mitigated first. The movement of air around the envelope is actually GOOD down here.

The airspace is required in Hot Humid climates for 3 reasons
- allows cladding to dry to the inside. humidity keeps things from drying to the oustide. solar heat gradient keeps moisture from releasing outside and is actually pushed inwards.
- allows hot air, baked and released from cladding during normal hot days, to release up. Without it, the sheathing underneath heats up much quicker.
- keeps the chemicals in hardi from contaminating and destroying the wrap.

Note - the furring/airspace must between the wrap and hardi.

[CThomp]

Just wondering for my own reference...where'd you find this at David?

I'd like the literature on it for my own reading.

[David]

From the book "BUILDER'S GUIDE TO HOT/HUMID CLIMATES" and it can be ordered here: http://www.buildingsciencepress.com/books.asp?CatID=1

I think I told you to get this once already ;)

[CThomp]

I know you told me to get that once already. :)

I'm a slack a$$.

[David]

It's very good. It has a lot of illustrations, too. Very complete in it's approach.