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I have heard many people say that it's important for a building's exterior materials to be able to "breathe." In particular, materials like brick are desirable because of their breathe-ability, whereas vinyl siding would be undesirable.

What is the impact of this characteristic on the durability of a home? What problems would be caused by using materials that don't allow air to penetrate?

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Walls don't need to breathe--people do! What these people mean is that it is important for walls to be able to dry out when they get wet; that they should not trap moisture. This is true, but is only orthogonally related to "breathability." In practical terms, what this means is that in reasonably moist climates, you want a wood-framed house's wooden sheathing to be able to dry to either the interior or the exterior if it gets wet. The sheathing would dry to the exterior if it's placed closer to the siding than the interior drywall, and to facilitate this, you would want there to be a ventilated rainscreen gap between the siding and the tar paper or housewrap covering the sheathing. If, on the other hand, the sheathing is covered up with a bunch of rigid foam insulation, it needs to be able to dry to the interior, which is accomplished by not putting any totally impermeable materials between the drywall and the sheathing like plastic sheeting or closed-cell spray foam.

As to how this relates to the siding material: it's irrelevant. Vinyl siding in no way impedes a wall's drying power, and in fact often improves it because it automatically includes a weak form of rainscreen gap in the form of the open channels behind the planks.

On a wood-framed home, you should choose brick as an exterior cladding because you like its look, durability, low maintenance, or acoustic advantages, not because of its moisture-related characteristics. In fact, brick is more dangerous in a cold and rainy climate because the brick will soak up water, which can freeze if the temperature drops far enough before the water has all drained out of the brick. And the brick siding absolutely needs a ventilated rainscreen gap separating it from the tar paper or housewrap covering the sheathing. Otherwise a phenomenon called "inward solar vapor drive" can force any water in the brick into whatever's touching behind it--such as the wooden sheathing!

  • One thing I've heard is that with wood siding, moisture problems will become evident as the wood will show rotting. Whereas if covered with vinyl or aluminum, there could be moisture problems underneath. I should have mentioned the question is for what to look for while home shopping. I assume there's no way to determine whether siding was installed correctly without removing it? – glenviewjeff Mar 28 '15 at 15:27
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    Correct. When home shopping, I generally assume that everything was done incorrectly and budget accordingly. The advantage with vinyl siding at least is that if there is bad moisture management beneath it, the siding is easy and cheap to remove so that the problem can be corrected. – iLikeDirt Mar 28 '15 at 15:58
  • I would assume the same as far as concealed things being done incorrectly. My problem is that I'm largely ignorant to the possible consequences and costs of them. I was under the (incorrect?) impression that masked exterior problems could make their way to moisture then mold on the interior walls eventually. And that air permeability would minimize this possibility. – glenviewjeff Mar 28 '15 at 21:03
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    Well, the thing is that you don't want air movement through the wall, from one side to the other; you want it to do go up-and-down between the sheathing and the cladding: a ventilated gap. Vinyl siding sort of provides this by virtue of its very nature. – iLikeDirt Mar 28 '15 at 21:38
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I am a builder in northern maine and your house has to breath for sure.I am in buisness with my dad who has seen alot in 40 years of new construction and ripping apart old consruction. We startwhen framing and sheathing we only use Typar house wrap because its breathable.Then when insulating we use craft face fiberglass insulation that also breathes well.We use continous vent strip on the eaves which pulls the moisture out of the roof and attic and comes out thru the peak continous ridge vent.With the roof vent you will need to use rafter vent from soffit to peak also to keep the air flowing.So there you have it a breathing house you can use whatever you want for siding,or roofing.Our houses dont have any ice building on the eaves or any ice dams in the vallies it works very well,and no rotting houses either.

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