Tyvek needed under Crane Solid Core vinyl siding?

I recently discovered that my house's previous owner did not install Tyvek home wrap over the exterior sheathing before installing new Crane Solid Core vinyl siding. I am worried that the siding will allow moisture behind it (like vinyl siding is designed to do) and, with no home wrap, cause the sheathing to rot. The sheathing material is fiberboard, which apparently was acceptable to use for exteriors when the house was built in 1977.

I had three different contractors look at the condition, each with a different recommendation. One said that the Crane siding is a premium product and the foam backing should prevent moisture from causing a problem, plus the fiberboard is rot resistant. Another contractor said while Tyvek may not be required with the product, if it were his house, he would install Tyvek. The final contractor said the condition is completely unacceptable and Tyvek needs to be installed immediately to prevent any further damage to what may have already occured.

The siding is only 6-7 years old and in great condition. If the siding is removed to install Tyvek, it is cost prohibitive to try and salvage and re-install it due to increased labor costs, so I'd be looking at re-siding the whole house. What do you experts think? Do I need to be concerned about sheathing rot with this condition?

 

I am not familar with the Crane product specifically but I would not agree with the third contractor. Nothing that you described indicates a neccessity to do something immediately. There are many different types of wood fiber board and many different types of facings for the board. Which type you have could greatly impact the decision as to how you should proceed.

I would agree partially with the second contractor that some type of wrap should have been used. I am not as sold on Tyvek (or similar mylar wraps) as most of the industry is. Applying 15 or 30 lb. felts with lapped joints will also work (though Dupont will tell you otherwise). Still depending on the type of fiber board you have this may not be required at this point.

Tyvek was developed as an air infiltration barrier. It does also help resist water infiltration but I am not convinced you must have it in your situation and I believe the third contractor is working to get himself a project by overstating the problem. The product name, quality and type of the wood fiber board is the key in my opinion.

 

Thanks for the insight, spiper.

 

According to the 2006 IRC Table R703.4 a WRB is required underneath vinyl siding. This is a change from the 2003 IRC.

That being said, in my experience, the fiberboard sheathing that you have can resist some occasional wetting without compromising its integrity. I'd suggest you unzip the siding below a window and inspect the bottom left and right corners around the window to see if the sheathing has experience any damage in the past 6-7 yrs. If not, don't worry about it. The siding was installed to code back then... it's just not code now. Its not usually feasible to go back and fix everything in a house that is not up to current codes, since codes are always changing.

You could also see this similar older thread. In their case, the house (2 yrs old) was clearly not being built to 2006 IRC code. However some places are a little behind the times.

PS: the contractor who said the foam backing would prevent any moisture problems was incorrect. The foam backing does nothing to prevent water from getting behind the siding at penetrations. However he was partially correct in saying the sheathing is "resistant" to moisture problems... but that depends on how wet it gets and how often. It will most certainly rot if its constantly wetted.