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Building in MA, rainscreen or just wrap under siding?
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Posted by drtechno (My Page) on Wed, Nov 4, 09 at 12:38
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Hi all.
I've been looking for more info on whether we should use a rainscreen system or just a Tyvek wrap underneath the siding in our new construction. It will be Icynene insulated so the only issue is wind-blown water drainage. Is it worth the extra cost of going with a rainscreen construction instead of just a wrap underneath horizontal tongue and groove (ctr match) red cedar siding? |
Follow-Up Postings:
RE: Building in MA, rainscreen or just wrap under siding?
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| The rainscreen not only provides a superior moisture run off behind the siding,(moisture/condensation concerns, not just physical water run off from leaking, etc), but also provides an air space behind the siding allowing the siding to breath on the back side as well. This is good for longevity of the siding. It is also a good bump up insulation wise with the air space. You can also vent the air spaces into your soffit venting with the rain screen method to keep your walls cooler in the warmer months. The hot air is trapped between the siding and the sheathing of the house wall and is carried out through the soffit venting. This is enhanced when you cover the sheathing with radiant barrier which blocks the heat gain form entering the walls. Contrary to popular belief, it also has an effect,(radiant barrier), on holding the heat in the winter, but typically when the ceilings/attics are addressed as well Which ever route you take, when installing the siding, it should be seled on all four sides including cut ends when installing. |
RE: Building in MA, rainscreen or just wrap under siding?
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| Provided there is sufficient distance between the lap siding and the Tyvek, the Tyvek is the drainage plane. Building Science Corp. says a minimum of 1/4" should be enough. Many builders prefer a much greater space provided by 1x2 furring. |
Here is a link that might be useful: Rain Control in Buildings
RE: Building in MA, rainscreen or just wrap under siding?
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| Have you considered a waterproof sheathing, like Huber Zip wall? Then you wouldn't need either. |
Here is a link that might be useful: Huber
RE: Building in MA, rainscreen or just wrap under siding?
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| There are also spray on coatings such as StoGuard. |
RE: Building in MA, followup
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| There are also spray on coatings such as StoGuard. I have no experience with either system. But I know that Lstiburek is sceptical of the long-term effectivenss of building tapes used on house wrap. Since both these alternative systems depend on tapes and variants, I would have the same concern. |
RE: Building in MA, rainscreen or just wrap under siding?
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| There's also good ol' fashioned 30# saturated felt with 1x2 furring strips 12-16"o.c. and sealed all sides siding. At the base of the starter course, screen/mesh wire is used to keep out critters/bugs. What's in your wallet? |
RE: Building in MA, rainscreen or just wrap under siding?
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| Unless you are in an unprotected oceanfront location strapping is not technically necessary for the amount of rainfall found in MA, however this spring was unusually wet. IMHO the best reason to use strapping in MA is to avoid all of the staple and nail penetrations in the weather/air barrier. Spray/roll-on vapor-permeable liquid membranes avoid this issue too. Benjamin Obdyke offers a good PDF on this subject but of course they think their products should be used everywhere. |
Here is a link that might be useful: Managing Moisture in Residential Building Envelopes
radiant barrier
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| IMHO foil-faced wall sheathing would provide little energy conservation benefit in MA and would create a vapor barrier on the cold side of the wall forcing the addition of rigid insulation over the sheathing (on strapping I guess) in order to move the dew point out of the wall cavity. If you are willing to do that you might try covering the wall with Vycor and eliminating all air and water penetration issues at once. |
also
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| If you are interested in drain wraps, DuPont makes a commercial grade version of Tyvek DrainWrap/StuccoWrap called Tyvek CommercialWrap D. If you put it up with capped nails it is pretty tough stuff. You have to ask yourself, "why would a cheap chain hotel deserve a better air/weather barrier than my house?" Of course, you have to be related to someone in the business to actually get a roll of it. |
Here is a link that might be useful: Tyvek CommercialWrap D
StoGuard
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| The best thing about the StoGuard system is that reinforcing mesh tape is placed over the sheathing joints and into the window jambs and sills, then coated with StoFill, then coated with GoldCoat either by spray or roller. It's the ultimate DIY air/weather barrier and flashing system but trying to get a contractor to use it on a house is not easy. OSB requires 2 coats and plywood only needs one. |
RE: Building in MA, rainscreen or just wrap under siding?
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| Well I suppose in my particular case, the issue is that I already have an effective vapor barrier in place, Icynene. So the issue becomes rainwater runoff and the presence of an air gap offerring additional (but limited) insulation. Is it worth the labor of felt paper/furring strips or cost of a Tyvek DrainWrap simply to give wind driven rain a place to drain from? |
RE: Building in MA, rainscreen or just wrap under siding?
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| Icynene is an open-celled foam and is not a vapor barrier like closed-cell foam although it is not as vapor permeable as house wraps and may not need a separate interior vapor retarder in your situation. According to the manufacturer:
"Icynene is water vapor permeable and allows structural moisture to diffuse and dissipate. It will not entrap moisture in materials to which it is applied.
Water vapor transmission properties: (ASTM E96 data)
6 perms @ 3" thick
4 perms @ 5" thick" You may be thinking of the low air permeance of Icynene. According to the manufacturer:
"Because of its low air permeance, Icynene is not infiltrated by moisture laden air. When applied to a vapor permeable surface condensation will not occur within it. It does not require a vapor barrier unless applied to a non-vapor permeable surface in extreme vapor drive conditions. A vapor retardant paint is adequate in such situations." Since wood siding is not a water reservoir cladding like brick or stucco and the summers are not unusually hot, you should be OK without an interior vapor retarder. |
RE: Building in MA, rainscreen or just wrap under siding?
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| If you put it up with capped nails it is pretty tough stuff. While Tyvek and others recommend the use of capped nails and similar products, the most common fasteners I've seen used are ordinary staples. Even Bob Vila uses them. |
RE: Building in MA, rainscreen or just wrap under siding?
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| So much for learning by observing common practice. If DuPont pays Vila, he'll use their cap nails, cap screws and cap staples all on the same job. |
RE: Building in MA, rainscreen or just wrap under siding?
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| ROFL macv. PS- Thx for the Icynene info. So then, felt paper + furring strips or Tyvek Drainwrap probably still recommended in my situation to prolong the life of the siding? |
RE: Building in MA, rainscreen or just wrap under siding?
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| The infamous Bob "might as well" Vila! |
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