How concerned do I need to be about my OSB SIPS getting rained on during construction?

I broke ground on my house in early August.  Practically no rain all summer!  The SIPs arrived on September 10th.  We've averaged 1 rain day each week since they started setting the panels.  Fortunately each day of rain was isolated & followed by days in the 70s with 10-15 mph breezes.  I think the panels dried out fairly well.

Currently all the panels are set except a 3 season porch  (the entire shell is SIPS including the roof).  The crew has taped most of the interior seams.  Yesterday we got another heavy rain with more rain expect over the next 2 days.  I inspected the jobsite last night and noticed water dripping from the taped seams of the roof panels & standing water on the subfloor.  After the rain, once things dry out, do I need to have the contractor retape the seams?  If water is leaking through the seams then they are obviously not air tight & the adhesive has failed with the rain.  On the flip-side, I don't think I want the seam tape holding water in between my panels!

Thanks for your input!

Joel

Posted By joeldunn21 on 03 Oct 2013 08:15 AM
How concerned do I need to be about my OSB SIPS getting rained on during construction?

 I inspected the jobsite last night and noticed water dripping from the taped seams of the roof panels & standing water on the subfloor.  After the rain, once things dry out, do I need to have the contractor retape the seams?  If water is leaking through the seams then they are obviously not air tight & the adhesive has failed with the rain.  On the flip-side, I don't think I want the seam tape holding water in between my panels!

Thanks for your input!

Joel

As long as it is allowed to dry off, it shouldn't be a problem during construction. With that being said, I would not be taking too long in getting the home sealed up. OSB can only take so much before it will start to cause problems, swell, lift, and eventual rot.

I would retape it since the adhesive failed. When wood gets wet it swells and begins to move around. I suspect the tape adhesive failed and allowed the air/water to come in.

Are you going to put in furring channels on the SIP walls and roof?

I'm planning to do furring strips on the roof with a ridge vent.  For the walls the plan is standard housewrap (Tyvek, etc) and steel siding.

Tape over OSB is an infiltration barrier it, but it will not prevent water intrusion from rain
there would be no reason to replace it, just get the felt or roof underlayment over the OSB as soon as you can

Posted By joeldunn21 on 03 Oct 2013 08:42 PM
I'm planning to do furring strips on the roof with a ridge vent.  For the walls the plan is standard housewrap (Tyvek, etc) and steel siding.

You should also provide a rain channel and use furring strips on the walls. Many Building Science experts recommend this for OSB SIPs to keep the SIPs from rotting. You need to get airflow behind them when using siding on the walls.

I definitely would not recommend placing siding directly onto the OSB SIP wall (even with Tyvek) without having a furred out channel for airflow to allow drying.

Where are you located at?

I'm in west central MN.  Even through my SIP supplies, several installers & 2 homeowner's I've talked with told me it wasn't necessary, I decided to put furring strips & a second deck on the roof after reading several discussions on roof failures with OSB SIPS.  I've also read the articles recommending furring out the walls to add a rain screen, but I haven't read about many real would cases of wall failures due to not back venting the siding.  Would you recommend something like Drain Plane?  I've also read that some siding as considered "self venting".  Would steel siding be considered self venting?

I would consider steel or vinyl sidings as self venting,
it has very little contact with the wall surface, fateners should be loose for expansion,
felt or tyvek would be your drainage plane

Don't forget your air barrier (many drainage gap moisture issues are actually air movement issues). And two air barriers are better than one - for example, you might tape all of the SIP joints (both sides) and tape the Tyvek.

I would check the end of all the drainage paths and get any standing water drained off. Also If you are still expecting rain, get a tarp over that roof. Pay attention and get it off as soon as you can so you can give that osb as much drying time as possible.

Your biggest problem is the improperly trained installers that applied joint tape to the inside of your SIP assembly prior to ensuring a water-tight roof was in-pace.Your second biggest problem is getting advice from "experts" who haven't even confirmed where your building and how the building science should be considered when offering building advice. Remove the tape entirely!! let the assembly dry with the aid of a finished roof and after your roof has had ample time to dry, you should re-tape the joints if you're in a climate zone that requires interior joint tape and if your joint type is one that should be taped. The OSB that is commonly used in the North American market is an exposure 1 rated product and can handle a great deal of wetting and subsequent drying without causing long term harm. What will cause long term harm is locking moisture inside your wall or roof assembly.Remember that giving moisture a path out of your assembly is more important than the futile act of trying to keep it from entering in the first place. Know your building science when building any type of super-insulated structure. It will improve performance, comfort, and durability.

"Tape both sides of the SIP" This may be the worst advice I've ever read on how to handle a SIP concern! Locking moisture into your assembly with no path to dry? I can't believe this is being recommended.

Posted By acobb on 11 Oct 2013 11:20 PM
"Tape both sides of the SIP" This may be the worst advice I've ever read on how to handle a SIP concern! Locking moisture into your assembly with no path to dry? I can't believe this is being recommended.

Once a finished roofing material is applied, a roof SIP shouldn't be leaking in the first place. If you don't tape the wood SIP attachment areas/joints, you will get moisture problems and the wood SIP will rot anyways.

Make the roof OSB watertight, install a cold roof/furring above the wood SIP roof, vent it. I would still tape the joints to prevent air leakage and moisture mitigation during winter.

Otherwise just go with a Steel SIP roof and you don't have to worry about rotting wood.

Lbear, you appear to not understand the reason that industry professionals and building scientists recommend taping joints on an assembly. The addition of tape to an already completed SIP roof is to act as a vapor barrier and as part of the air-barrier. Bulk water infiltration on a clad roof is seldom a problem (assuming the roofer is competent) However, vapor drive via air-leakage and material permeability are factors that can't be ignored. The use of joint tape is a proven strategy in a climate zone such as the reference house. And, because the vapor barrier is always specified on the inside in these northern climates, it should be applied to the inside only.
I agree that a vented roof should be used in this climate and the reason is to promote drying! When any high-performance envelope assembly is being used, the inherent air-tightness of the assembly limits the capacity to dry. It is this reduced capacity to dry that designers should worry about in all types of materials including metal clad SIPs. A vented roof or self venting cladding is a method of increasing your roof assemblies capacity to dry. However, the moisture that is sure to get into the assembly will have a decidedly difficult time drying outward if you tape the exterior joint. In fact, if you (Joel) do tape the exterior joint, you should know that the permeability of the OSB will still allow some drying unlike the zero permeability of a metal clad SIP.
In almost all cases, it's not the product that should be berated, but the poor detailing and improper installation that is so prevalent in building failures. In the SIP industry, its a combination of bad advise, lack of building science education, and believing the notion that SIPs are a DIY product that have lead to most of the industry's project failures.