Radiant heat under a wood floor gives you warm, even comfort without radiators or vents in the way. But without insulation below the system, a lot of that heat slips straight down into the crawl space or basement instead of rising into your rooms. Adding a reflective barrier under the floor fixes that. This guide covers two simple ways to do it, so you can pick the one that fits your joists.
Products to use: SmartSHIELD in the thickness that suits your space, SmartSHIELD 10MM, SmartSHIELD 5MM, SmartSHIELD 1/4 Inch, or SmartSHIELD 20MM.
Tools and Materials
- SmartSHIELD (see the two methods below for guidance on fit)
- Staple gun and staples
- Reflective foil tape
- Utility knife and a straightedge
- Tape measure
Before You Start
- Measure your joist spacing first. It decides which method and roll size you'll use.
- Work in dry conditions and clear any debris or old insulation from between the joists.
- Have a helper for the under-joist method. It keeps long runs flat and straight.
Choose Your Method for Radiant Heating Under A Wood Floor Insulation
There are two ways to install SmartSHIELD under a wood floor. Both reflect heat upward, so pick based on your joist setup and how much taping you want to do.
Method A: Attach Under the Joists
Best for a fast, continuous layer across the whole floor.
Step 1: Roll SmartSHIELD across the underside of the floor joists.
Step 2: Staple it up into the bottom edge of the joists, keeping it flat.
Step 3: Tape the seams with reflective foil tape to seal the layer.
Method B: Staple Between the Joists
Best when joist spacing makes an under-joist run awkward.
Step 1: Cut SmartSHIELD to fit the gap between your joists.
Step 2: Staple it by the tab 4 to 6 inches below the floorboard, leaving an air gap above it.
Step 3: Tape the seams with reflective foil tape.
Quick Tips
- The air gap is what makes a radiant barrier work. In Method B, keep that 4 to 6 inch space above the material.
- Keep the barrier flat and relaxed, not stretched tight, so it doesn't tear at the staples.
- SmartSHIELD acts as a thermal break, radiant barrier, and vapor barrier all in one, so it also helps with moisture and drafts, not just heat.
Frequently Asked Questions
Which method should I choose?
Method A gives you a fast, continuous layer across the whole floor. Method B works better when your joist spacing makes an under-joist run tricky. Both reflect heat back up.
What thickness of SmartSHIELD do I need?
It depends on your joist depth and how much space you're working with. If you're unsure, call our team and we'll help you match the right thickness to your floor.
Will it work under any flooring?
SmartSHIELD works under most flooring materials, so you can pair it with wood, tile, and more.
Need Help Choosing?
Not sure which SmartSHIELD thickness fits your joists? Explore SmartSHIELD at Insulation MarketPlace, or call our team at (786) 202-0704 and we'll help you match the right roll to your project. Every order ships free in 2 to 4 days.
