Vinyl Siding over Existing Lap Siding

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Old 06-20-06, 02:47 PM
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Vinyl Siding over Existing Lap Siding

Hello, I'd like to thank everybody in advance for listening.

Here's my problem:

I have a small ranch that I'd like to put vinyl siding on (DIY). It has engineered lap siding. The existing siding is solid and in good shape. Therefore, I'd like to put the vinyl over the old siding. From reading around the internet, I found out that putting on 1/4" foam backing is the best course of action. I went to Home Depot and purchased Owens Corning 1/4" Fanfold. I put that on one side of my home. However, I'm worried that the foam is not rigid enough. Obviously, as a result of having lap siding there are natural peaks and troughs because the panels overlap. Well, I installed the foam and it looks pretty good. Except, I can press the siding with my hand and it's got some movement right below where the next lap starts (ie, the hollow part).

I'm afraid this is going to be a problem for the vinyl. I measured out where the vinyl will meet the existing siding on the sides of the house that I have not foamed. Instead of meeting at the same point on the old siding, they will meet on different points. Meaning, the vinyl will be attached closer/farther from the house depending upon where it meets the old siding. Now, I've put a the section of vinyl against the foam and it does it pretty good job of holding the siding back from going into the hollows of the existing siding. But, I'm concerned that the foam is not providing a solid enough surface.

Since I've read that 1/4" Fanfold is pretty standard procedure, am I just being anal-retentive?
 
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Old 06-20-06, 05:20 PM
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josh,

I won't go as far as saying, "yes, you're being..." but I don't believe you have anything to worry about. When you apply the fanfold, nail ONLY to the high points of your current lap siding. I prefer to use roofing "cap nails" as they hold the fanfold nicely. If you nail only on the high points of the siding, and nail frequently, the foam will be tight enough to support the siding just fine. Remember that the siding is only "hung" on the roofing nails, which are left loose, so you want the siding to be able to move in and out just a little bit anyway so that it can expand and contract.

The only thing you might want to do if you are really concerned about the foam moving... you can rip some strips of 1/4" fanfold and use them as shims. If you have 10" lap siding, run a strip of fanfold (1 1/2" wide) horizontally across the siding at 5" (in the middle of the lap) so that when you put a straightedge from one lap to the next, the foam will be supported in the middle of that 10" span. (for example.)

I sometimes will do something like this when the horizontal seam of the fanfold falls between the laps of the old siding. I like to shim the old lap siding so that my fanfold seams come together nicely and lay perfectly flat. Maybe I'm anal too.

But since there are thousands of contractors slapping fanfold on houses like yours and putting the siding right over it, I'm sure you'll be fine if you do the same, provided you don't nail too tightly and suck the foam in too far as you put the siding up.
 
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Old 06-20-06, 05:51 PM
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Wow, thank you very much for your complete response. I have used cap nails and nailed at the proper spots, so it looks like I'm good. Thank you very much.
 
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