I understand that with a plastic house wrap like Tyvek, the seams
should be sealed with a wide sheathing tape. Does it make sense to do
when using 30 lb felt paper as a house wrap?
OK, just to be clear, I understand plastic house wrap is an air
barrier, and that is taped at the seams to provide better infiltration
protection. Is 30 lb felt also a good air barrier, and so would
sealing the seams (if possible) also be beneficial? Some plastic
house wraps suggest caulking the seams as an alternative to taping to
them, would this be an option with felt?
Not really. You would have a hard time doing this, also. The
caulking procedure would be hit and miss due to the felt being
pliable. If you tried it, you would see what I mean.
When we want to get a more secure application of felt, be
simply overlap more. If you double lap the felt, which means
that you lay the felt halfway down the previous run, you get a
double layer of felt. This provides a better alternative than
trying to tape or caulk. Sometimes we double layer the felt
for additional protection, although this is most often done on
roofs (as in a low slope situation).
If you are really worried about this, you should just use
housewrap. It will act more as a air barrier than the felt,
although both will perform for moisture protection. I have
torn off siding that has been in place for over fifty years
and found the felt behind it brittle, but still in good condition.
Keep in mind that I am not a proponent of housewrap. I use
both for differing purposes and kind of use them
interchangeably on walls, depending upon the application.
I think you are asking the pros and cons of house
wrap and felt. Felt has been used for years and
can do a good job, since it is a barrier to
liquids and gas. Heck if you put on felt but
don't cover it with siding, you have a tar paper
shack (might be a very big shack though). Since
felt is always overlaped, it sheds water and
depending on how the siding is applied it may also
allow moisture to move through the overlaps and
still be a very good barrier to air flow.
In contrast, Tyvek shed water but allows moisture
to pass through, but stops gross air flow if
applied correctly (taping joints and all holes).
Tyvek essentially prevents all air inflow, but it
allows moisture in the form of gas to pass
through. That supposedly helps keep the insulation
drier by allowing the moisture to move to the outside.
From looking at a large number of housed under
construction, I would suggest that the
construction is far more important that the
material used. I've seen Tyvek with holes, rips
etc. that would allow all kinds of air inflow.
The same is true of felt applications.
Yes. It can cause condensation and rot if used outside insulation on a house
in a cold climate. I've read new houses in Minnesota have fallen down after
5 years because the studs rotted inside the vapor barriers.
On 2005-12-03, email@example.com wrote:
Yes, I understand plastic house wrap will trap liquid moisture, so
vapor that condenses inside it will not be able to escape. That is
why I'm going to use 30 lb felt. Felt will slowly absorb liquid water
and then allow it to evaporate as it it dries. Drying will be aided
by the Home Slicker drainage plane I plan to use between the felt and
the cedar sidewall shingles.
But, the question I have is whether it would be useful and feasible to
seal the seams between courses of felt. So far I have heard it is not
feasible with tape, as tape will not stick to felt very well. Still,
would it be useful to seal the seams? That is, are the seams a
comparitively large source of air infiltration, relative to the felt
itself? If so, is there some other way of sealing the seams?
There is some debate as to whether plastic house wraps outperform
felt. See, e.g., the first google hit on "house wrap comparison":
In the absence of compelling evidence that plastic house wrap is
superior, I'll stick with the tried and true. I will be using Home
Slicker under cedar sidewall shingles to provide a positive drainage
plane, that is an invention that makes alot of sense to me.
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