Fan Fold insulation


Old 05-01-11, 05:04 AM
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Join Date: May 2011
Location: usa
Posts: 2
Fan Fold insulation

I'm doing my vinyle siding installation myself. I'm currently in the process of tearing off all my wood clapboards. I bought 3/8 in fan fold insulation with the shiny insulation on one side. I was told by the person who I bought the insulation from to install the shiny side facing towards the siding. everything I've read about shiny insulation tells you to install the shiny side toward the heat source. Wouldn't that be towards the inside of the house? Which way should I install the shiny side, towads the house or away from the house? I live in the newengland area if that has any bearing. Also, is it neccessary to install a house wrap (i.e. tyvek) as well? If so, does it need to go on before the insulation or over the top of it? Thanks.
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Old 05-01-11, 06:52 AM
Join Date: Jan 2011
Location: USA
Posts: 4,185
Personaly I've never once seen a DIY siding job come out right. I'm on my third one in a year completly removing everything and redoing it. Seems like a simple enough job, but done wrong it buckles, seams open up, falls off, causes more water leaks then you had before.
Why are you removing the old wooden siding and not just going over it with fan fold to level it out?
You did build out all the window and door trim and wrap it with coil stock, install new vinyl soffit material and wrap the fashias with coil, removed any cable, or phone boxes, install split boxes around any outside faucets and install siding blocks, before starting the siding right?
If your going to all the trouble to remove the siding then you should be also up dating any old electric, adding any extra outlets, installing insulation, then installing OSB or CDX plywood, tyvek then the siding, not just foam insulation.
Old 05-01-11, 07:33 AM
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Join Date: May 2011
Location: usa
Posts: 2
I installed new windows all through out the house last year, with the j-channel built in to the windows and am also replacing the doors as well.. I'm removed all the siding because there was evidence of rotting and I figure there's more of a problem underneath as well and plan to fix that. If I had gone over the old siding it would have built it over the windows. I'm not removing the soffits as they are in good shape. I have all the split boxes, siding blocks, and once I get to the electrical boxes, and lights, I plan on having the electrical meter built out as well. I actually thought about running new wire as well since now is the time to do it, but I figure that may be a bigger job than what I'm expecting. I realize there's a lot of little things to watch out, but I figure if I take my time it should go ok. Regarding the TYVEK, it sounds like it is neccessary to have it on there. I was under the impression that fan fold (coupled with taping) provides not only insulation but is also a vapor barrier. Which side of insulation goes outside, the shiny or dull side? Thanks.
Old 05-01-11, 12:20 PM
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Fanfold's main purpose is to provide an underlayment for siding when the new vinyl siding is being applied over the top of an irregular surface, such as clapboard siding. If you have removed the siding, there is no need for fanfold.

Fanfold does have "some" r-value but it is not air-tight, so you will not achieve the advertised r-value. If air can move behind the fanfold then it's not really effective as an air-barrier, thus it's not providing the r-value you might think it would. Yes you can tape the seams but if the perimeter is unsealed it's not the best bang for your buck. How well the seam tape holds over time is also suspect. Fanfold also doesn't lay "perfectly" flat.

If you really want some r-value, you should apply 4x8 or 4x9 sheets of ISO or XPS foam, 1/2" would give you roughly r-3, and it will lay flatter than fanfold. If seams are taped, no tyvek is needed, since the foam would be your WRB (weather resistive barrier). Even then, adding that little amount of r-value may not be worth it.

The problem I see is that since your windows have nailing flanges and an integral nailing flange that is probably only 3/4" thick, you may have no room for added fanfold OR sheet insulation plus the siding to fit into your integral nailing flanges. But maybe you can provide more details on that.

If you have reflective fanfold, the shiny side generally goes toward the house in a heating climate, and toward the outside in climates where you run the A/C the majority of the year. I have read that reflective foil barriers only work properly when there is an airspace left next to the reflective surface. In reality, I'm not convinced the foil surface has any benefit at all.

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