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siding question: remove old or side over it? styrofoam backing good or bad?

siding question: remove old or side over it? styrofoam backing good or bad?

Old 07-05-14, 07:01 AM
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siding question: remove old or side over it? styrofoam backing good or bad?

I'm about to replace my wood siding with vinyl siding. Have a few questions:

1) Is it better to retain the old wood siding, and just put new siding on top of it? The extra later of old siding would improve R value, but I'm afraid it might also trap moisture more and lead to rot.

2) The new vinyl siding can be purchased with a Styrofoam backing to it. It's suppose to improve the R value of the vinyl siding. But, I'm afraid moisture of condense on the vinyl siding, and get trapped by the styrofoam...is that a valid concern?

If I don't opt for the styrofoam backing, I would have no insulation whatsoever.
Old 07-05-14, 07:27 AM
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Welcome to the forums. What type siding do you presently have? Lap, T1-11, etc? One problem with siding over siding is the protrusion you will experience at your windows and doors. Insulation backed siding is almost worthless except to those selling it. Why is it you don't have any insulation in your walls? If you have none, then remove all your existing siding and insulate the walls, covering the insulation with 7/16" OSB. Then you can apply your vinyl siding.
Old 07-05-14, 11:30 AM
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The main benefit of foam backed siding is to provide support to the siding to help keep it straight and ripple free. It does have an R value but the click joint of each strip of siding is purposefully loose to let the siding expand and contract without binding which also means it's not air tight. The labyrinth click seam does block much of the wind but some does get through so it's not as good as real insulation and house wrap.

Since you have no insulation now your walls are probably somewhere between 2 and 4 for R value. On an insulated home an extra 2 or 4 R value points of insulated siding would be a small percentage and possibly not worth the expense. In your case you would improve your insulation dramatically.

Chandler's suggestion is valid and more proper. It's also more expensive and time consuming. I'm not trying to bash or imply anything about the value of your home but the lower the value I would be more inclined to put the siding right over your existing. Windows can be boxed in with wood ripped down as needed then trimmed with aluminum trim stock so the extra thickness can be dealt with with minimal expense. If the house is nicer/more valuable then the extra expense of a more proper job is warranted.

If you decide to rip off your existing siding you will have truly opened a can of worms. The hard part will be deciding where to stop. When the walls are open do you upgrade electrical wiring? Put in those extra circuits and outlets you've wanted? Maybe move that door or window that's been bugging you?
Old 07-05-14, 05:12 PM
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I don't have a lot to add. But will comment anyway. We could probably be more specific if we knew what kind of siding is on the house currently.

IMO it is often (almost always) beneficial to remove the siding. It's easy to do, doesn't really cost much to tear off (if you DIY) and as Larry said it keeps things from getting built out too far... keeps you from needing to clad windows or build them out, etc... which adds up to a lot of labor AND materials.

The r-value of the siding is probably negligible. Wood is R 1.3 per inch, so if your siding is an average of lets say 1/2" thick, that's not much. Plus r-value is only accurate in a dead air space. If you have lap siding, I bet it's a little drafty, which negates your r-value. You want a dead air space / air barrier. When you tear old siding off you can apply a WRB like Tyvek. If you don't tear siding off, you still should apply a WRB (per code) behind vinyl siding. The insulation doesn't really qualify as a WRB as it doesn't protect what's underneath from water.

I'm afraid moisture
This is why, by code, there needs to be a WRB behind the vinyl siding. This is true whether you tear the siding off or not. In many cases there IS a WRB behind the old siding, but that ain't going to keep that old siding from rotting if it gets wet under a window or door or what have you. So that's why most ppl will put a new WRB over the old siding, whether that be Tyvek or maybe a layer of 4x8 sheets of insulation with the seams taped. (not insulated siding where the insulation is bonded to the vinyl siding)

I agree the "insulated siding" is not very effective at increasing the r-value. If you don't go Chandler's route and actually put insulation in from the exterior, you might consider removing the old siding, putting up sheets of ISO or XPS foam, taping the seams (as a WRB), and then putting up your vinyl siding, insulated or not.

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