Expert: Bruce E. Johnson - 6/10/2009

Question
QUESTION: My house is located in Southern California. It was built ca. 1925 with exterior clapboard siding directly over the wall studs. I would like to replace an existing window on a gable-end wall with a French door. As I will be removing all of the clapboards from the exterior of the wall in question to facilitate the framing of the new opening, I was wondering if it would be worth the effort and expense to go ahead and apply plywood sheathing to the entire wall prior to re-applying the clapboards. If so, would 1/2" plywood suffice? Should I install an air infiltration barrier such as Tyvek over the plywood, or just building paper? Should I apply battens to nail the siding to in order provide an airspace behind the clapboards for moisture control? Presently, the exterior walls of the house are not insulated. What about installing insulation at this time? I'm concerned that if I install fiberglass bats without adding an interior vapor barrier I might get condensation problems inside the wall. Not sure if this would be a problem in Southern California though. Any insight you might offer is greatly appreciated. Thanks!

ANSWER: Hi Mark, first of all you will need a permit to do anything to the wall including replacing the window unless it is just a remove and replace and the cost is under $500 dollars and there is no structural work involved.  Secondly, if you are removing the siding then by all means you should a. insulate with batt insulation, faced with foil or paper toward the inside of the house.  b. use 1/2" plywood cdx or better c. cover with a tyvek or typar house wrap or felt paper d. then reinstall your siding.  That is the proper way to construct a wood framed wall.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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QUESTION: Hi Bruce,
Thanks for your reply. When applying the wood clapboards over the plywood sheathing is it ok to nail them directly to the plywood, or should I attach 1 x 2 wood battens vertically 16" o.c to provide an air space behind the siding? Thanks again.
Mark

Answer
Hi again Mark, it is not necessary to install furring strips over the plywood. Generally the only time furring strips are used is when the wall is masonry.   I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com