Rain Screen Siding Systems

[hausdok]

Hi All,

Did an attached town home the other day that had a rain screen siding system on it. Unlike most of the homes with these systems that I've seen, this one looked more or less "normal" until I got up close and could see that the trim around the windows was spaced out from the sheathing and there were gaps at the top and bottom of the cladding. I've attached a couple of diagrams of the system that this builder is using. You'll see two setups - one for vinyl siding and the other for hard claddings.

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Something else happened that I'd never expected. The builder actually thanked me for being critical for a change. I climbed up onto the roof and was suitably impressed with the fact that the roofer had used drip edge flashings - which almost no roofer uses around here. Then I noticed that where two adjacent gable roof planes come together they'd configured a sort of flat bottomed valley that empties into a tiny little gutter and downspout at the center of the front of the building.

Normally, when I see setups like that, they've used modbit to line the valley and they overlap the asphalt shingles onto the modbit. This wasn't the case. Here, the architectural grade shingles went from about a 6:12 down to a less than 1/2:12 before they reached the edge of that valley above that gutter. They were all tightly adhered to one another and went down the valley on one side, across the bottom and up the other side but the coursing didn't deviate at all. It was one of those WTF moments we all get way too often.

I climbed down, concerned about that valley and I was explaining it to the client, whose first language isn't English, when the Project Manager walked up to see how the inspection was going. I asked him about the valley and whether IWS had been used under the cover in those valleys. He told me that they'd used a doubled-up layer of roofing underlayment under that valley per their "Building Envelope Consultant's" site specifications.

I pointed out that a double layer of underlayment is the requirement for roof pitches between 2:12 and 4:12 but that at a pitch like they were using I suspected that most roofing manufacturers and experts would agree that at a minimum IWS should have been used. He seemed unimpressed; said that they'd spent a lot of money to have their consultant design a system that works, they'd never had an issue and he was confident it wouldn't leak.

I finished up. They had indeed spent a lot of time detailing the cladding but I was still bothered by the roof and told the client I'd be writing it up in the report. The PM called me the next morning at about 6:45 a.m. to tell me that he'd double-checked their specs and that their specs did in fact require a doubled-up layer of ordinary roof underlayment. He said that he'd then called the roofer to ask about the valley and the roofer had told him that IWS had been used under that valley and it was the roofer's policy that IWS be used under all valleys.

The PM thanked me for pointing it out to him and said that after talking to the roofer he was going to make a change to their spec book to ensure that IWS was always used in that kind of a situation from that point on.

Sometimes this thing we do works.

Any thoughts on this rain screen system?

ONE TEAM - ONE FIGHT!!!

Mike