House Wrap (Plastic sheeting)

[Jerry.Tan]

This is about that plastic wrapping they use to cover the exterior of a house under the siding. (Not a house that plays Rap Music) :)

Anyhow, it seems that every new house built, and every house that gets new siding, is covered with this plastic wrap. Then, they use a wide tape, and apply the tape around doors and windows. The end result is a home that is similar to living inside a huge plastic bag.

First, I have wondered if the people living in these houses are getting enough oxygen to breathe, particularly if they are retired older people who dont go out much.

Second, doesn't all the moisture inside the house get trapped in the walls, which will cause the wood to rot? (And most new homes are built with chip board, which does not hold up well in moist conditions).

Somehow, I dont agree with the use of this material, and would not use it on my own home, if I was going to build a new house or reside (which I am not planning to do either).

Years ago, they applied tar paper, which was a paper coated with tar. That would shed any water that got beneath the siding, but still allowed for ventilation. To me, that made more sense, and it worked pretty well. It was not taped around doors and windows, but was often left so the door or window frame would overlap it, and form a tight seal.

[trader_4]

What you're saying would largely be true, if it were just a plastic wrap that was totally impermeable. It's Tyvek or similar, which keeps rain and wind out, but at the same time, allows water vapor to pass.

Houses today are built with a lot less air infiltration than they had

100 years ago, or even decades ago. But I think there is still plenty of air exchange due to leakage. And if you want more air exchange, a heat recovery ventilator can be added. That's a much better way of getting fresh air than having leakage, because most of the heat is saved as opposed to going out the window, so to speak.

[clare]

First of all, house-wrap is NOT plasic. It is generally Ty-Par which is waterproof but vapour permeable. The vapour barier goes on the inside. Any moisture that gets into the wall cavity can "breathe" out through the house-wrap, but humidity inside the house cannot get out into the insulation to condense on the cold outside sheathing and wet the insulation. The plastic from the vapour barier is wrapped to the outside and taped to stop ANY leaks from the interior into the insulation space.

The new house-wrap is MUCH better than tar paper - and todays houses are very well sealed - which is why many now have heat recovery ventilators installed as standard equipment. Warm moint air goes out through the recovery unit, warming the dry incoming cold air - recovering most of the heat.

There is usually an air space between the house-wrap and the final siding or brick which allows air circulation to let any moisture that migrates through the housewrap out, and to let any water that gets through the siding drain away.

Building any other way today would be foolishness on your part

[gregz]

Tyvec. Woven polyethylene.

Greg

[Mayayana]

As others have said, it's vapor-permeable wind-barrier wrap -- the same basic material as those envelopes that you can't tear; also used often for bank card covers.

I wonder about it in the very long term. What if it breaks down over years? (I wonder the same about flakeboard sheathing.) But in general it's a good solution. With the outer wall breathing and plastic vapor barrier under the drywall on the inside, moisture stays inside, providing for better air quality on warm winter days. I have a brother who built his own house that way in the 80s, using 6" studs for better insulation. He heats it (in NH) with only a wood stove. There are no drafts. The down side is also that there are no drafts. :) One needs to open the windows a bit to get fresh air because the house is super-sealed, essentially a plastic bubble.

Tar paper is fine, but doesn't breathe as well. House wrap solves the problem created by interior use of plastic vapor barrier. In older houses, vapor freely moves through the walls, but if you seal the interior with plastic sheet you need a way to let moisture in the wall get out.

[Frank]

Right but Tyvek is not woven but spun bonded, that is the polyethylene fibers stick together during the spinning process.

[dadiOH]

When my wife inherited a log house a few years ago, we had to do some repairs because the "builder" (her idiot ex-step FIL) had not had the windows installed properly in the upper story (which has stud walls). Everytime it rained, water ran into the walls. The Tyvek was shot; the OSB was sawdust.

[clare]

The Tyvek/Typar degrades slowly in ultraviolet light which is why it has a finite lifespan when un-covered and MUST be covered with some sort of siding in, I believe, a maximum of 6 months.

As far as the flake board is concerned, I have virtually no use for it. As a subloor it is terrible, and as a sheathing not much better. As a roof???? Fergettit!!!!

[nestork]

Jerry:

The point you're missing is that water VAPOUR can escape through Tyvek, but liquid water cannot pass through Tyvek.

The reason for this is that the size of a water molecule is smaller than the average distance between water molecules in liquid water. In order for liquid water to pass through a film the holes in that film must be large enough for several molecules to pass through the hole simultaneously. Otherwise, NONE will pass through the hole because surface tension causes water molecules to attract each other. Consequently, liquid water cannot pass through a hole only large enough to allow one H2O molecule at a time because the attraction between water molecules prevents them from leaving their group, except in the case of evaporation.

The plastic that Tyvek is made of has molecules closely packed together that will allow individual H2O molecules to pass through it, but not liquid water. In that way, it allows any humidity that gets into the wall to pass to the outside through the Tyvek, but it won't allow rain or snow melt into the wall. This keeps the walls dry and prevents mold from growing in the wall.

[rbowman]

Material like Tyvek (DuPont's trademarked name) is used for FroggTogg's line of lightweight and inexpensive raingear since it passes water vapor readily but repels liquid. It works very well.

So, short answer, it passes water vapor by design.

[rbowman]

Long term? As I watched them throw up apartment building next to where I work I came to the conclusion long term wasn't one of the criteria. Bulldoze it in 30 or 40 years and throw up whatever is stylish that decade.

[trader_4]

I recently had to pull off some cedar siding that's above a roof on my house. The Tyvek was 30 years old, still in good shape and looked capable of still doing what it needs to do.

[Mayayana]

To: [e-mail] As others have said, it's vapor-permeable wind-barrier wrap -- the same basic material as those envelopes that you can't tear; also used often for bank card covers.

I wonder about it in the very long term. What if it breaks down over years? (I wonder the same about flakeboard sheathing.) But in general it's a good solution. With the outer wall breathing and plastic vapor barrier under the drywall on the inside, moisture stays inside, providing for better air quality on warm winter days. I have a brother who built his own house that way in the 80s, using 6" studs for better insulation. He heats it (in NH) with only a wood stove. There are no drafts. The down side is also that there are no drafts. :) One needs to open the windows a bit to get fresh air because the house is super-sealed, essentially a plastic bubble.

Tar paper is fine, but doesn't breathe as well. House wrap solves the problem created by interior use of plastic vapor barrier. In older houses, vapor freely moves through the walls, but if you seal the interior with plastic sheet you need a way to let moisture in the wall get out.

--- SoupGate-Win32 v1.05 * Origin: (1:249/999)

--- Synchronet 3.15b-Win32 NewsLink 1.92 SpaceSST BBS Usenet Fidonet Gateway

[Frank]

Right but Tyvek is not woven but spun bonded, that is the polyethylene fibers stick together during the spinning process.

--- SoupGate-Win32 v1.05 * Origin: (1:249/999)

--- Synchronet 3.15b-Win32 NewsLink 1.92 SpaceSST BBS Usenet Fidonet Gateway

[Col. Edmund Burke]

Sheeeet!

--- SoupGate-Win32 v1.05 * Origin: (1:249/999)

--- Synchronet 3.15b-Win32 NewsLink 1.92 SpaceSST BBS Usenet Fidonet Gateway

[dadiOH]

When my wife inherited a log house a few years ago, we had to do some repairs because the "builder" (her idiot ex-step FIL) had not had the windows installed properly in the upper story (which has stud walls). Everytime it rained, water ran into the walls. The Tyvek was shot; the OSB was sawdust.

[Oren]

Jerry,

Search for 'weep screed', dampness drains at the bottom edge of the wall. I have this on my three coat stucco exterior walls.

Sample view:

[clare]

The Tyvek/Typar degrades slowly in ultraviolet light which is why it has a finite lifespan when un-covered and MUST be covered with some sort of siding in, I believe, a maximum of 6 months.

As far as the flake board is concerned, I have virtually no use for it. As a subloor it is terrible, and as a sheathing not much better. As a roof???? Fergettit!!!!

--- SoupGate-Win32 v1.05 * Origin: (1:249/999)

--- Synchronet 3.15b-Win32 NewsLink 1.92 SpaceSST BBS Usenet Fidonet Gateway