Tyvek, foam, and tar paper

humdinger

I am installing foam baord and vinyl siding on a house that already has tar paper in good shape. Would it be ill advised to install tyvek house wrap over the tar paper then the foam insulation then my vinyl siding.

Or. Keep the tar paper as is, foam board Insulate, and install the vinyl siding?

thank you for any suggestions.

mrgins

Since when is Tyvek housewrap a moisture barrier and not an air barrier? I'd be more inclined to tape the osb joints and/or the foam joints and not even install housewrap.

ThatDaveGuy

I know this is a continuation of an earlier conversation, but the whole exterior wall construction issue is one I follow avidly here.

So is the consensus sheathing- housewrap- foamboard- siding? So that any water intruding behind siding is repelled/ shunted away by the drainage plane of the foamboard and not trapped against the Tyvek layer, allowing it to intrude and recondense behind it? Or am I reading this backwards?

mrgins

I've seen pictures of Tyvek that has deteriorated around doors and windows (yes I know, they didn't use window/door seal) which shows it should not be used as a vapor barrier. In heating zones, it's supposed to keeps cold air being pulled in while allowing warm moist air to escape the wall cavity

Gary in WA

Welcome to the forum, humdinger! I started your own thread on your question rather than piggy-back on a 2 year old one. Less confusing to the readers (and me, LOL). Hope you don't mind...

1. How thick is the foam board.

2. What type of sheathing?

3. Where are you located?

Gary

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jklingel

Tyvek has a perm rating of about 40 or 50; very vapor open, and a good water deterrent. Over or under the foam is debatable, but tape and goo it w/ goo that is compatible w/ Tyvek. Read on greenbuildingadvisor.com and buildingscience.com. If your OSB is already in, keep it dry. If not, use plywood instead; far more durable if it ever gets wet.

Tom Struble

i don't know about that durability statement,it may stay wet longer but ive seen ply delaminate pretty quickly when exposed to moisture

jklingel

My experience w/ OSB is that it is very susceptible to water; it swells and gets mushy. The pros on greenbuildingadvisor.com say it "turns to oatmeal" too often. I've had plywood delam BEFORE it got wet, but that is a rarity in my DIY experience, and from what I read on various forums. I've had plywood exposed in my boat for years, doing fine. The OSB, even oiled, did not last but a few seasons. So, I'm not an OSB fan. Maybe wrong, but... I also root for the Cleveland Browns, if that tells you anything.

mrgins

I know builders who prime the edges of the osb before they remove it from the skid. The edge of it is most susceptible to water. As an aside, I built my daughter a play house that sat 4" above the dirt. It was made of osb that was painted. Lasted ten years before I gave it to my neighbor. He's had it 8 yrs and it's still in fine shape

Tom Struble

no argument from me J