Replies

1. 
   davidmeiland | Jun 22, 2010 10:00am | #1

   If I understand you correctly

   you now have celotex over the studs, with furring and shingles over that. No felt or housewrap?

   Whatever you do you will be making significant changes to how the wall performs, possibly both good and bad. Right now you have a wall that breathes extremely well, and any excess interior moisture or water infiltration into those walls has very good potential to dry out, because there's very little in the way of an air barrier.

   I think your idea of installing sheathing, foam insulation, and then shingles directly over that will work, if the foam is only 3/4", because you can use fasteners long enough to hit the sheathing (2" stainless staples would work). That much foam won't get you much in the way of additional R value, but your air barrier will be so much more effective that it will seem like a major improvement, provided that you detail the foam correctly.

   And... what about felt or housewrap? If you tighten your walls up like you are proposing you need to be sure that you are flashing all of your openings well and keeping all of the rain out of your walls. I would certainly install felt or housewrap, unless you can determine that your method of installing (and taping?) foam makes it into an effective drainage plane. 

   One upgrade from installing shingles directly to the foam would be to install them over Obdyke Home Slicker, which will let the backs breathe and allow for better drainage of any water that blows behind.

   Next step would be to research the "outsulation" methods that are proven effective in your area, and possibly to have a blower door test and air leakage study done. That way you have a measure of air leakage and an indication of whether expensive improvements to the walls are going to be effective. An energy auditor can run the blower door test and find the large air leaks fairly quickly, and help you tighten your house up safely (don't forget that your gas appliances, if any, may be using fresh air that leaks in thru the building shell, and you don't want to starve them).

1. 
   Matty_D | Jun 28, 2010 09:17pm | #3

   "One upgrade from installing

   "One upgrade from installing shingles directly to the foam would be to install them over Obdyke Home Slicker, which will let the backs breathe and allow for better drainage of any water that blows behind."

   Thanks for pointing me to Obdyke Home Slicker. It looks like a good solution for my project. It comes in two thicknesses, 1/4"  and 7/16". Canadian codes seem to require the thicker stuff. Do they know something that we don't?  I'm not in Canada; just thinkin'.    I'm leaning towards 3/4"OSB sheathing ( good nail backing for the shingles), a 1/2" of iso-board insulation and 7/16" of this obdyke home slicker.

   The WRA cedar information was all about installing cedar clapboards, not shingles. Good general info,  though my main questions about sidewall shingling were not covered. The Obdyke stuff solves that though. -- Matt

1. 
   Piffin | Jun 29, 2010 06:38pm | #5

   There is no good reason for sheatrhing thicker than 5/8". 1/2 is plenty. If you want better, go to Huber's Advantec. It doesn't do the floppy Tuna so much.

1. 
   Matty_D | Jun 30, 2010 06:12pm | #6

   With shingles, of course, it's not possible to nail to the studs. So I thought of the thicker sheathing as the nailing base. Maybe 5/8" is enough.

   If I go with 1/4" furring strips instead of one of the slicker products (at a good cost savings), what material should I use for the furring? I'm thinking 1/4" exterior grade plywood.

   I was also thinking I might go with XPS insulation board instead of tuff-r iso board so I don't end up creating a vapor barrier outside of the sheathing, due to the iso's low permeability.

   Can the XPS act as a drainage plain (substitute for house wrap) if it's fitted well and taped?

1. 
   Piffin | Jun 30, 2010 06:39pm | #7

   Either one creates a VB.

    esp if taped at seams

   I don't know your climate so..

   The 1/4" furring is not  anial baser, only a shim, so th enails or staples need enough length to penetrat the sheathing.

   If you use 3/4" instead of 1/2", you ne3ed longer staples possibly. 1/2" is plenty fo rthe sheathing.

2. 
   Hokuto | Jun 22, 2010 11:13am | #2

   The WRC Lumber Association has a PFD file about installing cedar siding that may be of help. Look here:

   http://www.wrcla.org/pdf/WRCLA_Installing_Siding.pdf

   And for finishing it,

   http://www.wrcla.org/pdf/WRCLA_Guide_to_Finishing.pdf

3. 
   Piffin | Jun 29, 2010 06:36pm | #4

   You do need a drainage plane behind those shingles or they can rot out pretty quick, unless you live in dry desert country.

   I do it with furring as thin as 3/16". So you can go with 1/2" foam and then 1/4" strips in the same space.

   Or look at the Cedar breather or home slicker line of products

   http://www.benjaminobdyke.com/visitor/subcategory/subc/rainscreenProducts