Housewrap vs Rigid Foam: Best Under New Siding in DFW

Start with the Siding Replacement Opportunity

If you are replacing siding on a DFW home built before 2000, you have a wall insulation problem. Most of those houses have uninsulated or under-insulated wall cavities. The Department of Energy says: If you replace the exterior siding on your home, consider adding insulation at the same time. This is your only chance to add continuous insulation without tearing drywall off inside. I am Neal. I run DFW Attic Insulation. I see homeowners spend thousands on siding and leave the walls bare behind it. That is a missed opportunity. The sheathing is exposed. The cavity is open. Adding rigid foam or housewrap now costs a fraction of doing it later. You are paying for labor either way. Choose the option that insulates.

The IECC 2021 sets R-38 as the minimum attic insulation for Climate Zone 3 (DFW area), with the International Residential Code (IRC) Section R806 requiring balanced ventilation at 1:300 ratio.

Housewrap Stops Air Leaks, Not Heat Transfer

Housewrap is a weather-resistant barrier. It stops liquid water from getting in and lets vapor escape. It is required by code under most siding types. But housewrap does not add continuous insulation. A typical housewrap (Tyvek or similar) has an R-value of about 0. Does it stop thermal bridging? No. Thermal bridging happens when heat moves through wall studs directly from inside to outside. In a DFW summer, that means your AC runs longer. Housewrap protects the sheathing from moisture damage. That is its job. Do not skip it. But do not think it insulates. If you install only housewrap under new siding, you get zero R-value improvement. Your walls stay as inefficient as they were before the siding replacement. Use housewrap as the code-required WRB, then add rigid foam on top for insulation.

Rigid Foam Stops Thermal Bridging and Adds R-Value

Rigid foam insulation (polyiso or XPS) installed over the sheathing provides continuous exterior insulation. The Building Science Corporation explains that continuous insulation eliminates thermal bridging through wood or metal studs. In DFW, that means your walls are not transferring 100-degree heat directly into your living room. A typical 2x4 wall with fiberglass batts has an effective R-value around R-11 or R-12 after thermal bridging. Adding 1 inch of rigid foam (R-5 to R-6) on the exterior bumps that to R-16 or R-17. Two inches gives R-10 continuous, pushing the wall assembly toward R-21. That is a meaningful difference for a home in Coppell or Plano. Rigid foam also adds a drainage plane for moisture. Install it over housewrap, then furring strips, then siding.

DFW Climate Demands Both Layers

DFW is in Climate Zone 3 according to Energy Star. Summer heat is brutal. Winter cold snaps happen. Humidity levels are high. A wall system that works in Minnesota will not work here. You need a drainable wall assembly. Housewrap provides the primary drainage plane. Rigid foam adds the insulation layer and a secondary drainage path. Without rigid foam, your sheathing temperature stays close to outdoor air temperature. That can cause condensation issues in winter when warm indoor air hits cold sheathing. With rigid foam, the sheathing stays warmer, reducing condensation risk. I see contractors argue about which one to use. The answer is both. Housewrap against the sheathing. Rigid foam over it. Furring strips for a vented air gap. Then siding. That assembly works for DFW weather.

When to Skip Rigid Foam (Rare, But Honest)

I tell people when not to buy something. Here is one case: If your wall cavity is already fully insulated with closed-cell spray foam (R-20 or higher), and your siding is in good shape, do not rip it off to add rigid foam. The payback is too long. Another case: If your home has historic siding that cannot be modified with added thickness at windows and doors, rigid foam may not fit. In that case, use housewrap only and focus on air sealing. But for 90% of DFW homes replacing siding, I recommend at least 1 inch of rigid foam. The DOE recommends R-5 to R-10 continuous exterior insulation for Zone 3. One inch gives you R-5 or R-6. Two inches gives R-10. Price the difference. It is usually under $1 per square foot for the foam. HomeAdvisor reports the national average attic insulation cost at $2,100 with most homeowners paying $1,700 to $2,500. Angi data shows DFW pricing runs $1 to $3 per square foot for blown-in installation.

Installation Order: Get This Right

Wrong order means moisture problems. Here is the correct sequence for siding replacement with insulation. First, remove old siding and inspect sheathing. Repair rot. Then install housewrap (Tyvek or equivalent) directly over the sheathing. Tape all seams with compatible tape. Next, install rigid foam insulation over the housewrap. Use cap screws or insulation fasteners. Then install furring strips vertically (or horizontally for lap siding). These create a 3/4-inch air gap behind the siding. That air gap allows drainage and drying. Finally, install siding over the furring strips. Do not compress the rigid foam by nailing siding directly through it. That pins the foam and reduces R-value. The furring strips are critical. This assembly gives you drainage, insulation, and a thermal break. It meets DFW building codes.

What This Costs and Saves

A typical 2,000-square-foot home in DFW has roughly 1,500 square feet of wall area. Adding 1 inch of rigid foam costs around $0.80 to $1.20 per square foot for materials. Add labor for installation: roughly $0.50 to $0.75 per square foot. Total: $2,000 to $3,000 for the insulation layer during siding replacement. Compared to the cost of siding itself ($8,000 to $15,000), that is a 15% to 20% increase for a permanent efficiency gain. The energy savings vary by home, but Energy Star estimates continuous insulation can reduce wall heat gain by 15% to 20%. In a DFW summer, that translates to $150 to $300 per year in cooling savings. Payback is 8 to 15 years. But you also get comfort: rooms that stay cooler in summer, warmer in winter, and less noise from outside. That is worth something.

Frequently Asked Questions

If you are replacing siding on a DFW home and want to insulate the walls at the same time, I can help. Call me at (469) 895-2695 to discuss housewrap, rigid foam, and the right assembly for your home. I will tell you what you need and what you do not. If you want a straight answer on your attic, call me at (469) 895-2695. I'll inspect it with a thermal camera, tell you exactly what you need, and give you a written quote. No upsell. No pressure.

P.S. Every attic is different. The numbers above are ballpark estimates based on DFW averages. Call us at (469) 895-2695 and we'll come take a look with a thermal camera, give you a written quote, and tell you honestly if you even need anything. No upsell. No pressure.