Friday, January 28, 2011

Siding Mockup

I've built a small mockup of a wall section so I can make sure my siding installation fits together as planned.  I started with a scrap piece of plywood, covered it with housewrap, and then added two plywood strips, the same as I used outside.

The first step is to install the bottom bug screen. The bug screen prevents bugs from getting up inside the airspace between the housewrap and the siding, but will still allow moisture to drain out.  There will also be a bug screen at the top of the wall.
I'm using a strip of fiberglass window screen about 10" - 12" wide.  I pull the bottom edge of the furring strips away from the wall just enough to slip about 4" of the screen up between the plywood strip and the housewrap. Then I fold the screen around to the front of the strip, and then fold it down on top of itself. Finally, I staple through the front folds into the plywood strip to hold it in place. The bulky folds of the screen will hold it tight enough to the back surface of the siding to stop bugs from getting through.  

The next step is to cut a slit in the housewrap just below the plywood furring strips.  The top edge of the flashing goes up through that slit and behind the housewrap.  The flashing will be screwed every 16" into the plastic webbing embedded in the ICF wall.  Any moisture that comes down the face of the housewrap will travel over the flashing and drip onto the ground. 

Once the flashing is in place, then I attach the starter strip to the wall. The starter strip is the component that the bottom row of siding clips on to. It will be screwed through the plywood strips and into the plastic webbing inside the wall.

 You can see the "S" shaped bottom edge of the starter strip here.  The bottom edge of the first row of siding will clip around that "S" shape, holding the siding to the wall.

The next step is to install the bottom row of siding. Vinyl siding isn't really difficult to install, but there is one thing that's extremely important to remember: Vinyl siding must not be attached tightly to the wall.  In fact, vinyl siding isn't so much "attached to" a wall, as it is "hung on" a wall. The screws cannot be driven in tightly, in fact they need to be driven in so that there is approximately a 1/32" gap between the screw head and the siding. (That's about the thickness of a dime.)

The reason for this is that vinyl siding expands and contracts with heat and cold. If it is attached tightly to the wall, it will buckle when it expands in the heat of the summer. When this happens, it's very noticeable and looks terrible. So, it's extremely important to leave that gap between the head of the screw and the siding. Also, the screws should be placed in the center of the slots so that the siding can move freely in either direction.

To install the first row of siding, the bottom edge of the siding is first clipped under the bottom edge of the starter strip, and then the top edge of the siding is screwed to the plywood strips. The next row of siding follows the same principal; the bottom edge of the siding is clipped under the top edge of the siding below, and the top edge is screwed to the wall.

 Here you can see how the bottom edge of the siding clips around the top edge of the row of siding below.

When the siding is finished, I'll install a trim board (called a water table) underneath the flashing on the bottom.  In this case, the water table is strictly cosmetic, it's only purpose is to give some definition to the bottom edge of the siding, separating it from the bare area on the bottom portion of the wall. 


  1. Hey there, I'm a long time reader and have been enjoying the detail provided as we recently built an ICF house. I was wondering if you considered cement fiber siding? We used that, mostly because after deciding on ICF walls I tended to want as much concrete as possible.


  2. Hi Andy. Nice to hear from you. I did consider that as an option, but after doing some research and talking to guys who have used it, I decided to go with the vinyl as it's feasible to do it by myself. The fiber cement stuff is nice, but the length and weight of it requires two guys to install it.

    Hey... I'd like to see some pictures of your project if you've got any to share. You could email them to me at marlon4141 at gmail dot com.


  3. Thank you for the very clear instructions. I've followed your blog from day 1 and have learned from your experiences.
    Joy from BC

  4. Hello Joy. Thanks for the kind words! I'm glad to hear that someone else besides me is learning from this project.