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Old 10-16-2011, 05:26 PM   #1
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New Siding- Add Foam, Tyvek


Next year, we'll probably get new siding, windows, and deck for our house. It is a small two-story built in 1977 with a full basement. It has aluminum siding backed by a paper product and the deck and most of the windows are original.

When renovating the kitchen and bathrooms, we had many walls open and I was shocked at how leaky the construction was. Big gaps between the sheathing (which was silver on the inside) and the studs let in lots of outside air, as evidenced by dark spots on the insulation. There were many nails coming through the sheathing that missed the studs. I sealed it all with caulk and spray foam, but I'm sure the leakiness is equally bad all around the house.

We'll probably go with a good quality vinyl to minimize cost and maintenance. Can we add a layer of foam boards and Tyvek to seal up this house?

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Old 10-17-2011, 12:12 AM   #2
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New Siding- Add Foam, Tyvek


Sure. Done all the time. You want to make sure that the foam is thick enough to keep your sheathing above the dew point (1" to 6", depending on where you live). Seal the joints of the foam w/ appropriate caulk and tape, too. I think you'll find that you use a lot less fuel when you are done, between the air sealing (the big variable) and the extra insulation. Read about this stuff on buildingscience.com and greenbuildingadvisor.com.

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Old 10-17-2011, 09:58 AM   #3
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New Siding- Add Foam, Tyvek


I agree with jkringel's comment about the dew point. From your description it sounds like the sheathing has an interior foil facing which may act as a second vapour barrier in the wrong location by today's standard. Adding "outsulation" will help.
I suggest that you consider Typar rather than Tyvek.
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Old 10-17-2011, 04:04 PM   #4
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New Siding- Add Foam, Tyvek


"I suggest that you consider Typar rather than Tyvek."----- Marvel, may I ask why?

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Old 10-17-2011, 05:23 PM   #5
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New Siding- Add Foam, Tyvek


i install foam on just about every house i reside and for new construction. it creates a more energy efficient building. the key thing is to use foam that is 1" thick or greater, 1/2" foam does virtually nothing for the performance of the thermal break as your only gaining an additional r-2 or r-3 depending on the type of foam, where as 1" foam is atleast r-5.

in regards to tyvek or typar.. both do the same thing but typar is much more tear resistant if left exposed when there is high winds.

on the note of the missed nails.. if you do pound them out just be sure to do this before the new foam and tyvek goes on the wall otherwise youll be patching all kinds of tears and blowouts on your new rainscreen.. the other thing is some of these nails might just have been for the siding. i wouldnt worry about it to much unless the sheathing is loose
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Old 10-18-2011, 08:19 AM   #6
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There is a subtle but not well known difference between Typar and Tyvek. Tyvek allows both exfiltration and infiltration of water vapour. Typar allows exfiltration but not infiltration.
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Old 10-18-2011, 10:58 PM   #7
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A one-way housewrap…. years ago that was the belief when it first came out....... could you direct me to that link?

I've read Typar (11.7 perms) and Tyvek (58 perms) are both good in different applications- stucco tyvek wrap behind T1-11, etc.: http://www.finehomebuilding.com/PDF/Free/021177066.pdf

Some work better than others with cedar lap siding, etc., yet I found more info. with further research. How do they compete against mold by stopping the moisture movement (diffusion) wetting the OSB- which should never get wet.
Check out the multitude of housewraps on the market- pp.17 here: http://www.energy.ca.gov/2007publica...esidential.pdf
Notice on page 24: “A laboratory and modeling research program on wall drying in hot and humid climates identified air leakage and point source water intrusion as prime contributors to moisture accumulation in wall systems. The research cites two studies, one that reports air leakage accounting for 6 to 100 times as much moisture transfer as vapor diffusion, and another that concludes that point source water intrusion accounting for 20 times the moisture associated with air infiltration, while air infiltration accounts for 25 times the moisture movement associated with diffused moisture (Boone, 2004). This study also compared drying rates of OSB samples inside WRBs with various perm ratings in a controlled laboratory environment. In addition, it included hygrothermal modeling of wall assemblies with vinyl siding and different WRB options.
The study concluded that at laboratory conditions of 75ºF and 55% RH, the breakpoint for promoting drying a wet OSB specimen was between 18 and 24 perms. It also recommended further work in computer modeling, laboratory testing, and field studies designed to study the impact of the drying capability of a wall system and vapor permeable membranes.
Laboratory testing and hygrothermal modeling coupled with field data from a construction site in North Carolina identified a situation during the construction period under which higher perm housewrap can be more effective than lower perm housewrap at transferring condensed moisture from the OSB sheathing to outdoors before it causes moisture distress on the OSB (Weston, 2004).

And page 25: Ideally, water vapor from the conditioned side of the WRB would be able to easily pass through the WRB and out of the wall cavity, while water vapor from the exterior would be blocked from entering the wall cavity. However, due to a lack of ‘one-way’ vapor permeable membranes on the market, the primary direction of water vapor flow must be determined prior to selecting an appropriate design permeance.

In that test you would need 40 days of additional drying with a low perm (Typar) HW, vs. a high perm (Tyvek) HW to grow mold, page 17: http://repository.tamu.edu/bitstream...pdf?sequence=4

Just don’t foam on one or both sides of OSB, use recommended two layers of HW, and incorporate a rainscreen if location warrants it.

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Old 10-19-2011, 10:19 AM   #8
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If you want a tough house wrap, check out http://www.siga.ch/Majcoat-detail.133.0.html?&L=1. An individual who builds super-insulated houses here is now using it. It feels like it is rhino proof.
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Old 10-20-2011, 10:58 AM   #9
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tyvek cannot be used with stucco directly. the chemicals in the stucco will destroy the water proofing ability of the tyvek. there must be a contact break between them


the same goes for wood siding, the oils in cedar also break down the water proofing ability of tyvek. however wood siding requires a rain screen system to allow for drainage when water gets behind... this creates a 3/4" space between the siding and the tyvek. or you can use a more expensive product called cedar breather
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Old 10-20-2011, 01:03 PM   #10
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Great links GBR

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