Rain screen

qbryantJune 23, 2014

Is the use of a rain screen needed in Oklahoma,we will be using hardie board and batten and lap siding?
What's the biggest difference in building styles between vermont and Oklahoma (insulation-framing)?

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Brian_Knight

Its a great question and should be considered by all those building a new home. The only places that are currently required to install rainscreens are Oregon and coastal BC although I expect other places will start requiring them soon. Does VT have something now?

This makes it seem like only rainy climates need them but all climates can benefit from a rainscreen. Its one of the best ways to add durability and resiliency to the exterior siding and structural sheathing or framing that the siding is meant to protect. I think they are most appropriate for real wood or other vulnerable systems and exposed locations not protected by wide overhangs which tend to be the gable ends of a home.

I will enclose a link to the best rainscreen article resource I know of but there is another decent one out there if you search for; Rainscreens simple strategies for protecting one's biggest investment.

Here is a link that might be useful: GBA; All about rainscreens

    Bookmark   June 23, 2014 at 5:28PM
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Brian_Knight

As for insulation I strongly recommend folks build to the current 2012 IECC International Energy code. The 2015 update is quickly approaching and while I doubt they will up the insulation minimums I think they will increase the airtightness levels. OK is in building climate zone 3 and the panhandle is in 4 which is a fair bit more mild than VT's zone 6.

One important take away (zones 3 and 4) is that a wall in OK should have a cavity Rvalue of 20 or a cavity R value of 13 + R5 of continuous insulative sheathing. This typically means framing with 2x6 only (cavity R20) or 2x4 with 1" of foam sheathing (+5). I suspect the 13+5 would give better performance than a typically framed cavity R20.

VT is REQUIRED to use insulative sheathing R20+5 or R13+10.

There is a big difference between attic/roof minimums required for zone 3 (R38) and zone 4 (R49). If you are doing a vented attic with fluffy insulation than I think the R49 is a fairly cost effective level just remember to over compensate for settling.

These insulation levels are cost-effective for most situations in my opinion but there is an important caveat: they assume a certain level of airtightness as proven by the blower door test. As mentioned, I feel the current level of blower door minimums in the 2012 IECC leave lower hanging fruit on the table. Air-sealing is cheaper than insulation and far more effective and important for most current projects.

The blower door test minimum for zone 3 is ACH50 of 5. Thats a very leaky and inefficient home in my opinion. Zone 4 is ACH50 of 3. This is better but I think 1.5 is a better target for staying balanced with the insulation minimums in the 2012 IECC. These are code minimums we are talking about or.. the poorest performance allowed by international law.

    Bookmark   June 23, 2014 at 6:00PM
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qbryant

Thanks a bunch,I'm in ne oklahoma but we are thinking about using a architect in vermont,I'm just looking into these important issues so I will have a better understanding.
This will be built on a slab/stem wall because of a sloped site and will have a large patio door in the living room that will face the south or east,most likely us aluminum windows.What other recommendations could you provide!
Thanks

    Bookmark   June 23, 2014 at 10:43PM
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millworkman

I agree completely with Brian, a well designed and installed rainscreen system will definitely be a plus. What brand aluminum windows are you speaking about? I do hope you mean "aluminum clad wood"? Windows are part of the bones of a house and pain in the ass to change in a few years making them a very important choice in my opinion. Stay away from box store brands whatever you do in my honest opinion.

    Bookmark   June 24, 2014 at 7:15AM
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shiltsy

This is great information as we prepare for our build in MN. Our last home was new construction with wood siding and we had a TON of leaking. This one is 16 years old with vinyl and has had some issues. Leaking is expensive! An ounce of prevention........

    Bookmark   June 24, 2014 at 7:24AM
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renovator8

I can't think of a reason to use a rain screen wall system in Vermont but you should check to see if the municipality has adopted (or plans to adopt) the new "stretch code" that increases the thermal insulation requirement by 15 to 20%.

Unless you design a Frost Protected Shallow Foundation (not recommended for a seasonal house) even a slab on grade will require up to a 5 ft deep footing so you're going to build most of a basement anyway.

A Vermont architect will be your best guide regarding these issues.

    Bookmark   June 24, 2014 at 8:03AM
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qbryant

I'm building in north east Oklahoma and using a architect in vermont,I'm not sure on windows,I'm sure he will have some ideas,going for a modern looking window so I'm guessing they will be aluminum clad?

    Bookmark   June 24, 2014 at 9:04AM
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Brian_Knight

Yeah, most modern windows are AL clad these days. I would look into Fiberglass FG clad though. It depends on the particular brand and product but I think FG has the potential to be more durable as the seal between frame and glass should theoretically last longer. More importantly, choose the appropriate SHGC and U values for your building climate zone. Its also important to implement the correct flashing details.

Poorest performance values allowed by international law:
Zones 3&4 Uvalue = .35 or less
Zone 3 SHGC = .25 or less
Zone 4 SHGC = .4 or less

Those SHGC values assume you are not doing passive solar design but I would strongly suggest you consider it. I think its one of the smartest and most cost effective decisions you can make in the design stage.

Here is a link that might be useful: GBA: Passive Solar Design

    Bookmark   June 24, 2014 at 9:45AM
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Brian_Knight

I would also look into exceeding code minimum values for slab insulation. Zone 4 requires R10 underneath the slab (and edge) for 2' horizontal depth but it might be smart to insulate under the whole thing.

    Bookmark   June 24, 2014 at 9:52AM
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qbryant

I am very interested in passive solar design.
We are also going to keep the finish floor concrete.

    Bookmark   June 24, 2014 at 9:52AM
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renovator8

"we are thinking about using a architect in vermont"

I guess you meant an architect from Vermont. That's a big difference.

    Bookmark   June 24, 2014 at 7:05PM
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rollie

Good building techniques dont care what state they get implemented in

Here is a picture from tonight of a cedar lap siding house that I built in 1989 with a vented rain screen application.(Iowa)

Even more impressive, is that in talking with the owners, they have only painted the siding twice in 25 years..

My first rain screen application was 1983, and I hope to go there tomorrow and see how this 31 year structure is fairing..

    Bookmark   June 30, 2014 at 11:58PM
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Brian_Knight

I think the excellent condition of that siding and the fact its only been re-painted 2x in 25 years has a lot to do with Rollie's forward thinking. Its safe to say that the structural sheathing is probably in better shape too with less problems from bulk water leaks. I think all real wood siding should be including some type of rain screen system.

Whats the word on the 1983 install? These older examples for rainscreen performance are somewhat rare..

    Bookmark   July 1, 2014 at 10:43AM
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rollie

Theres no doubt that theres added value to a rainscreen application. Its getting our customers on board to pay for the initial install. Ive probably done about 5 different styles of rainscreens over the years, with the 1983 model being 3/4" strapping. The flashing details were nightmarish with that thick of a rainscreen, and un needed.

Lstiburek has done extensive research on the minimum amount of space needed for water not to suspend in the space, but from my perspective, any gap is better than no gap. Im using 5 mm coroplast now for a space.

Im headed to the 1983 job today and will take pictures there. This is verticle cedar V groove cladding.

    Bookmark   July 1, 2014 at 11:07AM
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rollie

31 year old home..

I couldnt get real close to this house, as no one was home, but the cladding looked incredibly good for its age. This is the south facing gable end of the garage..

    Bookmark   July 1, 2014 at 1:17PM
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rollie

5 mm VRS installation behind Cement board siding: 2005.

Pictures 137-161.

Here is a link that might be useful: Delores House

    Bookmark   July 1, 2014 at 1:26PM
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