What should come between the panels and the clapboards?

We'll be using either traditional quartersawn clapboards from Ward Clapboards in New England or board and batten cypress for siding.

Should the siding be nailed directly to the OSB exterior of the panels? Do we need to protect the OSB from any moisture that sneaks in? Also, do we need to have a path for this moisture to escape, or can we figure it will leave the same way it got in?

Thanks, all.

Mark,

Hopefully someone from the panel world will also jump in here, but this has been our approach to this subject for several years, and so far so good.

There are two basic types of panels currently on the market. EPS (expanded polystyrene) panels are made from heat welded bead base foam bunks which allow moisture and air to move freely (permiate) through the core foam. Urethane (polyisosyanurate) panels are foamed during fabrication which creates a closed cell foam which is basically impervious (impermiable) to air and moisture migration.

It would seem that moisture (and it's effect on your siding) could be a problem for different reasons depending on the panel you choose. If the souce of moisture is from the inside (probably not very likely) it could become trapped behind the siding, if the siding is treated with a waterproof stain or sealer. If the moisture is from outside (rain, humidity, lawn sprinklers) theoretically it can't get behind the finish.

The problem has less to do with how the moisture gets there, than how it gets out. We base our siding recommendations on the concept that moisture will find it's way behind the siding no matter how hard we try to control it. We recommend firring (strapping) the panels before the siding is applied. We specify "roll-a-vent" or something equivalent between the firring at the bottom (to keep wasps etc. out) and at the top to allow the air to move. This is done by holding the freeze board away from the soffit.

Better safe than sorry, particularly if your house is built to last for centuries.

Mark, we side the majority of our houses with Cedar shakes or beveled cedar siding. I am a big believer in coating all 4 sides of any wood siding. As well as an excellent caulk, such as Tremco in all the cracks. The wood will eventually turn gray from the back is not coated. An exceptional but expensive product Sikkens is our preferred choice, 3 coat treatment though.
Recoating is necessary much less than any other product.
As an option to the furring strips there is a product called Cedar Breather thats sort of a fiber mesh (I know it's advertised in Fine Homebuilding).

Oh the price we have to pay for not joining the Vinyl establishment....when it's done though it's well worth it.

There is one and only one answer to this questions - AIR. You must have at least 1/4" air space to allow clapboard to dry after bulk and diffused moisture enter.

The rate of peeling of surface paint on wood siding is a function of the moisture absorption through the back side. OR water travels any place it can bridge the capillary gap.