Replies

1. 
   dthodal | Mar 27, 2002 07:01am | #1

   jed, Question your use of the term vapour barrier in regards to building paper under siding. You want to allow moisture to migrate thru the walls and be evaporated off on the outside. To wit, the outside of your wall needs to be more permiable than your inside to avoid condensation from building up inside the wall cavity.

   Both 15 and 30# felt have traditionally been used for building paper. I think 30# is overkill and no more effective than the 15#. neither are considered vapour barriers either and you are correct in that both will absorb water. As to which one absorbs more I do not know.

   Personally I like using red rosin paper for building paper as I believe it allows moisture to be evaporated off quicker than either felt or any of the modern housewraps. Your siding should be installed properly to begin with and not rely on your building paper to serve that purpose. One reason I do not reccommend using ####sealer that does not breathe on wood siding. Use a penetrating oil finish instead.

   With the advent of solid wall sheathing such as plywood , you have minimized breathability behind the siding and create the possibility of more water born problems in the between. A rain screen or furring strips is an excellent idea for this reason as well as allowing more equilibrium in moisture and temperature of your siding's inside and outside face. This is even more critical when using a rabbited bevel that has the inside face of the siding tight to the sheathing.

   david

   walk good