# Felt & Wrap under Hardiplank?



## Ohming (Jul 21, 2009)

I am installing Hariplank lap siding. The manufacturer recomends felt under the siding. Is it good practice to use wrap first, then felt, or just felt. Is using both overkill or detrimental in any way? Thanks


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## ropers (Jul 30, 2009)

this is my opinion but i have always thouht that felt paper was alot better house wrap but much more difficult to install...especially on new construction....however i do believe that one or the other is more than adiquate.....


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## Scuba_Dave (Jan 16, 2009)

Actually they require:


> water-resistive barrier


And flashing between joints
I use felt for the flashng between the joints


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## framer52 (Jul 17, 2009)

Ohming said:


> I am installing Hariplank lap siding. The manufacturer recomends felt under the siding. Is it good practice to use wrap first, then felt, or just felt. Is using both overkill or detrimental in any way? Thanks


Either, not both!:thumbsup:


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## Gary in WA (Mar 11, 2009)

Framer nailed it! My first choice would be felt, here is why: http://www.umass.edu/bmatwt/publica...s_feltpaper_weather_penetration_barriers.html

And Typar over Tyvek: http://www.typar.com/pdfs/Typar_vs_Tyvek.pdf
Be safe, G


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## Scuba_Dave (Jan 16, 2009)

Why felt when from that 1st article:



> Our test results showed that after a series of 2-hour test runs, clean water never leaked through Tyvek or R-Wrap





> *15-pound felt lost 30% of its water on average*; and all other products drained completely. It was especially noteworthy that the perforated wraps (Amowrap, Pinkwrap and Barricade) lost more than 80% of the water in the first 15 minutes.* The performance of Felt and Typar was highly variable.*





> Typar and *Felt often held water for 30 minutes or more* before leaking.


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## Gary in WA (Mar 11, 2009)

Granted, Dave, if a 70 mph wind hits a house the felt will let some water through after it is saturated when Tyvek will not. That was the test quoted. But a far more common senario was not quoted: "That’s because I believe that under certain circumstances, felt outperforms housewrap. For example, an ice dam or roof leak may allow liquid water to get behind the felt or housewrap. It’s also possible for the sun’s heat to drive water vapor through the housewrap from the outside, where it can condense on the sheathing. In either of these cases, you now have liquid water on the wrong side of the wrap. Under these conditions, the liquid water would be trapped by the housewrap, which is permeable only to water vapor. Felt, on the other hand, will absorb the water, and more quickly dry to the outside."

And another quote:
"Wood is an absorbent material. It stores water. Since rain is sucked through butt-joints, seams and even upward past overlapping edges, it has access to the back surface. We usually paint the face of siding to reduce water absorption. But many builders leave the backside raw. You don’t want to store water in a place that has direct contact with vapor permeable housewraps. The sun’s heat can turn the stored liquid water into vapor. The vapor moves inward when the temperature of the siding face is warmer than the air behind the siding. And since housewraps are vapor permeable, they can allow vapor to pass into the building envelope from the outside. As the sun sets or moves to another side of the house, the temperature of the wall may drop below the dewpoint temperature, changing the vapor back to liquid. And guess what? The reconstituted liquid is on the wrong side of a water-resistant barrier! This set of conditions is suspected to have caused wet sheathing in several unusual cases. I have seen this twice. Just the personal reasoning I believe is true from my 36 years in home building. Be safe, G


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## Scuba_Dave (Jan 16, 2009)

OK, thanks ! - missed those points


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## campos202 (Oct 21, 2008)

Scuba_Dave said:


> Actually they require:
> 
> 
> And flashing between joints
> I use felt for the flashng between the joints


Do you just put the felt over the tyvek?


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## Scuba_Dave (Jan 16, 2009)

Yes - over the Tyvek & over the lower boards - but not visible
That way any water that gets in between the butt joints runs down & out


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## campos202 (Oct 21, 2008)

Scuba_Dave said:


> Yes - over the Tyvek & over the lower boards - but not visible
> That way any water that gets in between the butt joints runs down & out


Thanks!


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## Scuba_Dave (Jan 16, 2009)

Some people do use house wrap
My siding is blue so white house wrap would stick out
Other people use metal flashing


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## MJW (Feb 7, 2006)

Roof felt is not the same as felt for walls. Make sure you use the right stuff. 15 lb is not worth using on a roof or walls, IMO.

Always use what the manufacturer suggests. They are the ones giving you the warranty.

The key with any siding to me is......make it water proof (not just moisture proof) before the siding is applied.

Gbar is dead on with what he said.


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## Ohming (Jul 21, 2009)

Great points guys, appreciate all of the input and links. I have decided on felt. If 15 lb roofing felt is not the preffered, what is, 30 lb? Or is there a special type for walls?


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## MJW (Feb 7, 2006)

Personally I would use hardiewrap or 30 lb felt. If you try to use 15lb. you will find out very quickly how easily it breaks, cracks, and tears.


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## Ohming (Jul 21, 2009)

Thanks MJW, much appreciated. I'll go 30 lb.


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## Scuba_Dave (Jan 16, 2009)

Yes, I'm using the 30# too


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