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Should I Add Additional
 Insulation To My Walls?

Should I Insulate
 The Wall Plates?

Blowing Insulation Over 
Recessed Lights

Ventilated Attic 
Access Covers

Insulating An Attic 
With No Access Hole

Adding Additional Attic 
Insulation Over Fiberglass Batts

Skylight Covers To
 Reduce Air Infiltration

Do I need a vapor barrier?

Insulating Over Knob and
Tube Wiring

Vapor Barriers On
Basement Concrete Walls

Insulating The Ridge Of
Cathedral Ceilings

Adding Insulation 
Over Vermiculite

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How To Insulate A Metal Joist Floor

Debbie O. wrote:

I have an addition on my home that is built over a vented crawlspace. I would like to insulate the floors. I have read your directions on how to do this, but my floor joist are metal I beams. What method would your recommend to keep the batts of insulation in? I cannot nail anything to the joists and I believe tape would come loose with the cold. Please advise.

Thank you

This is one I've never encountered before but I have a couple of ideas.

You could try using lightning rods. These are wire fasteners that are flexible and attach themselves between the joints giving support to the insulation above using spring tension. They come in many sizes but the most common would be 16" or 24" and they are available in home improvement stores.

Using one hand to hold the fiberglass batt up you would want use the other hand to install the lightning rod by bending it just a little and placing it against both floor joists. HERE'S THE CATCH: I've never tried this with metal joists and can't attest to how well it will hold in place. But with wood joists it works like a champ and it makes the job fast and easy.Another option would be to wire in the insulation. This would require drilling screws into the metal joists and attaching wire in a criss-cross pattern under the fiberglass batts. As you can see it's a little more time consuming.

My final suggestion is to have foam insulation installed. It will adhere to the floor and metal joists and there would be no need to support it.

Like I said I've never insulated floors with metal joists so these are just suggestions.

Good luck with your project!

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Related Tips and Advice:

How To Insulate A New Unfinished Floor
How To Insulate A Floor Framed With Beams
How Much Floor Insulation Do I Need?