Helpful? 0

What is the best insulation for an unfinished work/craft room in the basement?

I have a basement workroom that I'd like to expand to a craft room for our kids, but it's currently uninsulated poured concrete and freezing in the winter. I was hoping to slap up something like a rigid board insulation, that could be left uncovered, but it seems even polyisocyanurate needs a gypsum board layer.

We live in VA, with pretty humid summers, though our landscaping has left our basement completely dry, except for one wall of a former crawl space that has shown some moisture damage on items stored there after a very wet year. (We need to address drainage there, so it's a separate issue, I believe, and is in a room adjacent to the area I'd like to insulate.)

Is there any one-step or minimum-step insulation I can put up to make a "roughly finished" room without creating stud bays or layering multiple materials? Or am I asking for the moon? I'll need to something, because there's currently no insulation between the unfinished workroom and the main level kitchen above.

BTW, I am a moderately skilled DIYer with limited time, but willing to do what it takes to get my home comfortable and efficient without compromising my family's health.

Eager for your advice,

Asked by Laura Braceland
Posted Sun, 03/16/2014 - 14:58


4 Answers

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Helpful? 1

You can install Thermax Fire rated foil faced polyiso without covering it with drywall, but it must have a class A fire rating. Most readily available foil faced insulation do not have that rating, so you might have to order it from a lumberyard. I just paid about $52 per sheet. You should also caulk your sill plate/foundation joint and the joint at the sill/rim joist with a urethane caulk to stop any air leaks. This is the most comom location for air leaks in most houses. Alternatively you could spray foam those areas but the spray foam should be painted with an intumescent paint which should be available at any good paint store.

Answered by Bob Irving
Posted Sun, 03/16/2014 - 16:59

Helpful? 0

Thanks! So I would attach the board directly to the cement wall with construction adhesive? And then caulk the edges?

Answered by Laura Braceland
Posted Sun, 03/16/2014 - 19:09

Helpful? 0

I suggest that you contact your local building department to make sure that exposed Thermax is accepted in your jurisdiction; code interpretations vary on this point.

Assuming that your local inspector accepts the plan, you can proceed as Bob suggests. For more information on attaching rigid foam to the interior of a basement wall, see How to Insulate a Basement Wall.

In that article, I wrote: "Rigid foam can be adhered to concrete with foam-compatible adhesive or can be attached with special fasteners like Hilti IDP fasteners or Rodenhouse Plasti-Grip PMF fasteners. (For more information on using Hilti IDP fasteners to attach rigid foam to a basement wall, see Marc Rosenbaum’s article, Basement Insulation — Part 2. For more information on Rodenhouse Plasti-Grip PMF fasteners, see New Green Building Products — June 2013.) To prevent interior air from reaching the cold concrete, make sure to seal the perimeter of each piece of rigid foam with adhesive, caulk, a high-quality European tape, or canned spray foam."

For more information on addressing rim joists, see Insulating Rim Joists.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 03/17/2014 - 04:15

Helpful? 0

Thank you both for all the specifics. I see that Home Depot here has Thermasheath-3, which comes up when I do a search for Dupont Thermax--do you know if that's a the HomeDepot version? It looks like Thermax is approved as a finish material by ICC, which is what my county code led me to, so I think I'm on the right track.

Our poured concrete has been very resistant to any drilling, so I will probably go with an adhesive. I have ECO-bond, which says it binds foam, so I hoped that would work for all types. If that isn't appropriate, I have a powder-actuated nailer, but I'm not sure that would work in a vertical application (I got it for fastening the floor plate down in stud walls). If so, it sounds like I would have to caulk those penetrations as well.

I really appreciate your help with this; without this step, I've got a 3-season workroom at best.


Answered by Laura Braceland
Posted Mon, 03/17/2014 - 08:48

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