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Cladding Gaps

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Howdy, new here. Have you all seen this document written by Joe Lstiburek that based on testing recommends the best air gaps behind various wall cladding? I'm interested in wood and 3/16 gap shown on page 70, table 2. How would I create the wall assemble shown? The furring strips has me confused. Thanks in advance. 

 

WUFI-Barking up the wrong tree_Lstiburek.pdf

 

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Right now you can just use an air space, 3/8", for horiz. furring until Chief adds this kind of feature, or you can create a double stud layer wall using a 3/8" stud on top of the main stud wall for vert. furring.

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Perry & David, thank you for the response, and David video very nice! Sorry about the late response. So, I created a 1/4 furring gap using stud material and everything is lining up on 24 OC to the studs, great! I don't however want the upper/lower plates on the furring layer only. Other than deleting them manually, is there a setting for this? Plan attached.

 

Also, is there a fast way to create 3D insulation in all my stud bays or do I have to use polyline solids one at a time?

 

ICTFlat.plan

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Anyone interested in this? The other thing going on here is if you read the BSC doc it begs the question about the need for controversial house wrap, and whether the small gap it produces is effective? The appropriate air gap as denoted in the doc should produce enough air flow friction to evaporate any vapor or liquid water and create capillary (drainage) action. Interesting part is according to test with these gaps, there is only a 1% change of either vapor or liquid water reaching any house wrap or substrate (insulation, drywall, etc), less with large overhangs. How is it so many homes did well for centuries before house wrap was ever created? :) WUFI is now ready to make sense of all the layers we use in America for one, thanks to BSC and the Germans. It's about time, now designers have to get it into homes...

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I'm not aware of any automatic method to model in 3D the insulation between the stud spaces.

 

"The other thing going on here is if you read the BSC doc it begs the question about the need for controversial house wrap, and whether the small gap it produces is effective?"

You may want to read Lstiburek's BSC-038 Mind the Gap, Eh!

 

"Interesting part is according to test with these gaps, there is only a 1% chance of either vapor or liquid water reaching any house wrap or substrate (insulation, drywall, etc)."

Lstiburek makes an assumption - and interpreting it as a 1% chance is misleading; he's making a prediction of volume, not probability - he assumes that 1.0E-5 (0.00001) percent of bulk water hitting any given area of a wall assembly will make it through the water control layer to the substrate. For 1 liter of bulk water, that's only 0.07 ml. That's not a lot of water, which is why modern housewraps can be effective with moisture control. Remember that a housewrap is - first and foremost - an air barrier and a water control layer. A grooved or crinkled product (like Tyvek Drainwrap) promotes hygric redistribution across the face of the wall. This enhances the ability of the sheathing (OSB, plywood, etc.) to cope with the infiltration of bulk water, and reduces the risk of moisture damage.

 

"How is it so many homes did well for centuries before house wrap was ever created?"

Perhaps this was a rhetorical question. But if it wasn't, the reason we didn't have problems before housewrap has nothing to do with housewrap. We've used housewraps for a long, long time: before synthetics we used asphalt-impregnated felt or paper. Plastic housewraps appeared around the same time as the other factors that led to under-performing walls: polyethylene sheeting, vinyl wall coverings, OSB, etc. Before we started installing vapor barriers (in cold climates) and packing the cavities with batt insulation, walls could dry to the inside or the outside. Water was getting in, but it could also easily get out. The wetting of the wall materials was temporary and produced few problems.

 

"It's about time, now designers have to get it into homes..."

We are. So are builders - at least in my neck of the woods. In some cases the builders have been ahead of the designers.

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On my latest project I used Henry BlueSkin for the house wrap. That is a peel and stick full air and water membrane that is self sealing . On top of that I used a layer of material to ensure a rain screen type gap. http://www.benjaminobdyke.com/products/slicker-classic-rainscreen-6mm

 

On a previous project I had used the product by Benjamin Obdyke that is a house wrap with small rubber bumps. I was much more confident that the gap would be maintained after the siding was installed with the rainscreen material.

 

It is not yet a requirement to have a rainscreen for walls in California but I suspect it will come soon. It is already a requirement in Washington and Oregon.

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