Hey all...came across this site tonight as I am researching using SIPs. My wife & I are leaving Texas (too HOT!) and moving North to my home area of upstate NY (between Syracuse & Utica). We purchased 32 acres & I've been working with an architect for floor plans. As I talk with builders (I've also seen a few comments online), I keep having the question of long term integrity coming up. OSB, when wet, is not pretty. It would seem that if the OSB got wet, that would affect the structural integrity of the house and any load being placed on the OSB. Am I missing something?

Posted By Got2BTru on 10 Jan 2013 05:52 PM
Hey all...came across this site tonight as I am researching using SIPs. My wife & I are leaving Texas (too HOT!) and moving North to my home area of upstate NY (between Syracuse & Utica). We purchased 32 acres & I've been working with an architect for floor plans. As I talk with builders (I've also seen a few comments online), I keep having the question of long term integrity coming up. OSB, when wet, is not pretty. It would seem that if the OSB got wet, that would affect the structural integrity of the house and any load being placed on the OSB. Am I missing something?

That's the downside of OSB/wood SIPs. They must be kept dry or at the very least, allowed to dry out if they get wet. The latter is not always accomplished and what eventually happens is called SIP ROT. That is where the wood panel rots and delaminates from the EPS, therefore compromising on the strength and integrity of the entire panel.

With that being said, the one solution is Steel SIPs. Nothing to rot and delaminate, plus they are stronger, lighter and can span longer distances. Especially for roof applications, Steel SIPs is the way to go.

When it comes to walls, the same proper detailing must be done to make sure the exterior OSB is kept dry and if it does get wet, allowed to dry out properly.

What wood SIP companies are now doing for roof applications is installing furring strips onto the exterior side of wood roof SIPs. They would then run another layer of OSB over the furred channel area. For the roof area, this then creates a drainage/vent plane so when the OSB gets wet, the furred channel allows drying. Building Science now recommends this detail for OSB roof SIPs. Sadly, there are some SIP companies that are still not using this detail and I don't doubt problems will emerge 10-15 years from now. See below pic:




In extreme cases, especially humid and rainy climates, if you don't let the panels dry out  by using a detail like the above, this can happen:

Here is a great GBA article on the topic:

How to Make a SIP Roof Better

OSB is a very common building product that sheathes millions of homes. Its really not all that different of a situation when a typical osb sheathed stud framed wall rots; you replace the rotten areas and fix the problem of why it got so wet to rot. Roofs are admittedly harder to fix than walls. There are thousands of roofs out there with no furred vent doing just fine but its certainly better to include.

No product is perfect including steel SIPS. I think your biggest problem will be finding a builder who is comfortable using them which goes for all SIPS.

The one major disadvantage of OSB is its tendency to expand with moisture. SIPs are two to three times stronger than conventional construction material. Moreover, rain during construction do not affect materials in any way.

Posted By SpringtimeHomes on 15 Jan 2013 11:28 AM
OSB is a very common building product that sheathes millions of homes. Its really not all that different of a situation when a typical osb sheathed stud framed wall rots; you replace the rotten areas and fix the problem of why it got so wet to rot. Roofs are admittedly harder to fix than walls. There are thousands of roofs out there with no furred vent doing just fine but its certainly better to include.

No product is perfect including steel SIPS. I think your biggest problem will be finding a builder who is comfortable using them which goes for all SIPS.

The SIP is created at a factory and one cannot create a SIP at the field. It's not like stick frame construction where you can simply knock out the rotted members and frame in new wood on the spot. It's a lot more complicated and expensive with SIPs because the panels are factory created and structural. A rotted SIP would need to have the ENTIRE panel removed, front to back.

In a dry climate SIP roofs with no furred venting can do OK but the detailing must be perfect but if they didn't use a T&G design or foam insert where the panels met, you will get condensation there and the subsequent rot. The SIP rot issue went beyond just exterior moisture penetrating the OSB. Some of the problems were INTERIOR moisture and where the panels joined together. Since these issues became known, they have started to address this and change the design and approach.

I recommend reading the article as it goes into detail WHY the panels began to rot.

Posted By Roderick H on 16 Jan 2013 02:52 PM
The one major disadvantage of OSB is its tendency to expand with moisture. SIPs are two to three times stronger than conventional construction material. Moreover, rain during construction do not affect materials in any way.

What!! that has not been my experience, OSB starts to swell just as soon it gets wet

Yeah OSB swells when wet. So does wood. So what?

It would be a very rare situation for an entire wall panel needing to be replaced from one location of rot. Maybe less so with roof panels depending on extent. Field modifications are almost always necessary with a panel package and anyone familiar with how to work with SIPS can repair them without much more trouble than typical construction. They are very easy to work with and modify with traditional carpentry skills which is one of their greatest advantages.

As for why SIPS rot, its usually just like traditional construction; poor flashing details. In the quoted article;" Lstiburek concluded that air leaks at panel seams allowed moisture to escape and condense on the OSB, eventually leading to areas of rot." This is a well known, relatively isolated incident that most people in the industry are aware of; Seal the seams! There apparently was very poor workmanship at this incident compounded by an unforgiving climate, very cold and wet.

A few bad cases caused by poor workmanship shouldnt scare people away from one of the best building envelope systems available.

Posted By SpringtimeHomes on 16 Jan 2013 08:15 PM
Yeah OSB swells when wet. So does wood. So what?

It would be a very rare situation for an entire wall panel needing to be replaced from one location of rot. Maybe less so with roof panels depending on extent. Field modifications are almost always necessary with a panel package and anyone familiar with how to work with SIPS can repair them without much more trouble than typical construction. They are very easy to work with and modify with traditional carpentry skills which is one of their greatest advantages.

As for why SIPS rot, its usually just like traditional construction; poor flashing details. In the quoted article;" Lstiburek concluded that air leaks at panel seams allowed moisture to escape and condense on the OSB, eventually leading to areas of rot." This is a well known, relatively isolated incident that most people in the industry are aware of; Seal the seams! There apparently was very poor workmanship at this incident compounded by an unforgiving climate, very cold and wet.

A few bad cases caused by poor workmanship shouldnt scare people away from one of the best building envelope systems available.

No argument here, those are the unforgiving problems.