Why Put Fanfold Polystyrene Under Siding

And even though some manufacturers call it rigid foam insulation for the purpose of vinyl siding it basically has the same insulating value as a piece of plywood.

Why put fanfold polystyrene under siding.

Fan fold comes in foam sheets and is nailed directly to the sheathing. As many things in building science go you my dear reader have to learn something. Why insulation under the siding is important. I thought i should show why continuous foam under the exterior siding is so important.

Fan fold is typically sold in 1 4 inch by 4 foot by 50 foot sections and is installed horizontally across the existing siding to level out irregularities before re siding with vinyl. I get asked if this or that in the in the cavity works as well as foam under the siding. Installing foam insulation under vinyl siding is a wise choice for homeowners who are seeking to protect their homes against moisture infiltration as well as improve energy efficiency. Available with a durable film norandex 1 2 insulation can meet high performance requirements in.

Fanfold foam residing board is a thin perforated extruded polystyrene foam board faced on one side with a plastic film facer and combines proven xps foam technology with a unique design to enhance the application of new or replacement siding. Norandex 1 2 extruded polystyrene foam insulation is a specially formulated 1 2 extruded polystyrene board sealed between select facing materials and produced in continuous 24 by 4 fanfold sections. Dupont has said on their website and product flyers that if using both fanfold and housewrap and committed to both put the tyvek housewrap over the fanfold but they actually recommend assuming the insulation is totally closed cell with very low absorption rate putting the insulation directly under the siding overlying dupont drainwrap which is designed to provide a better drainage path between the two than regular housewrap. It also serves as an air barrier.

This creates a horizontal seam every 4 feet. While fan fold has minimal insulation value it does even out wall defects and cuts down on drafts. In reality rigid foam board which sometimes comes in fanfold usually only has an insulating factor of r 1 and does not add any appreciable insulation effect to your home. I have not seen any studies that show how well tape adheres to foam over the long haul.

In addition flat foam insulations can help level out inconsistencies in the wall for a more perfect siding appearance.