Why Put Fanfold Polystyrene Under Siding

I thought i should show why continuous foam under the exterior siding is so important.

Why put fanfold polystyrene under siding.

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. The house has wrap under the siding. 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. This creates a horizontal seam every 4 feet.

However another important consideration is what to put under your siding. I am having the siding removed from our house and 2 foam board but under the siding. This is the same stuff your disposable coffee cup and is made out of and it s used to protect fragile items in their packaging. It provides an r value of 4 per inch of thickness and is the cheapest type of foam board insulation.

This generally means choosing between tyvek homewrap made by dupont since it is the most popular brand and exterior fanfold insulation. 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. 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. It also serves as an air barrier.

As many things in building science go you my dear reader have to learn something. The house was build in the 19970 s 2 4 walls and pink insulation between the studs. Eps is used under roofing over foundation walls and beneath siding. I get asked if this or that in the in the cavity works as well as foam under the siding.

By glenn hooper june 2 2015. The windows are being removed and moved out the 2 to line up with the foam board. 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. Will this cause any condensation issues.

Why insulation under the siding is 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 have not seen any studies that show how well tape adheres to foam over the long haul.