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A Handyman Helping Hand

Re: Hardi-Plank

Posted By: Joe
Wednesday, 23 August 2000, at 1:13 p.m.

In Response To: Hardi-Plank (Susan)

You should not confuse housewrap (Tyvek, PinkWrap, etc...) with a vapor barrier. Nor should you confuse Visqueen (which gets installed under drywall and on top of studs) with vapor barriers. NEITHER are vapor barriers. Both are AIR BARRIERS.

This gets a bit complicated technically but suffice it to say that warmer air inside the home is also moister. This means that moisture tends to pass thru exterior walls toward the outside in the form of gaseous water.

The problem is what does the gaseous water tend to do when it exits the home?: it CONDENSES.

How you deal with that condesation is the REAL problem here and how you deal with it affects the other building materials.

In most cases. exterior sheathing is covered with at LEAST a Builder paper. This resembles roof paper but is not tar impregnated.

It allows moisture to pass thru the sheathing and paper and protects the plywood or OSB if it does condense on siding materials. Tar paper has the same result but is not as effective at letting moisture thru in the first place.

Lets talk a moment about siding materials:

Siding materials need to have methods to handle condensed moisture. Vinyl siding has 'weep holes' built in which allow condensed water to drain out the bottom of each panel.

Other types of siding do not and steps must be taken to allow water to naturally drain when it condenses.

The method most commonly used is for siding such as brick, cedar, t1-11, Hardi-Plank, or any other type of clapboard, to be installed on furring strips or not in contact with the sheathing (as with brick).

This allows whatever moisture that enters the cavity behind the sidin to condense (generally) upon the back of that siding and drain downward without touching the sheathing.

All that said, IF your builder is placing the HardiPlank on furring strips THEN it is not imperative to have a paper of any sort on top of the sheathing because the moisture will condense on the back of the siding and drain downward. It is still advisable to HAVE a sheathing paper but not NECESSARY.

If, however, your builder is NOT installing the HardiPlank on furring strips, but instead is placing the siding directly on the sheathing, THEN a sheathing paper is ABSOLUTELY NECESSARY otherwise the siding will hold the moisture against the sheathing and cause rot.

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