# Rigid Foam Insulation in the basement



## Cath (Feb 3, 2008)

Craig is looking for feedback on how to apply rigid foam insulation in the basement. 

If I understand correctly, if we were finishing the basement now, there would need to be a one inch air space between the framing and the wall. However, if we were simply to put the insulation up and apply it directly to the walls, could we frame it and put up additional insulation in between the studs when we finish the basement later? 

Thanks, 
~Cath


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## precaud (Feb 3, 2008)

Where are you located? And what R value are you planning on installing?


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## Cath (Feb 3, 2008)

We are in Massachusetts.  The 1' foam is R 5; 1.5' is R 7.5 and 2' is R 11.  I did a little research and apparently most jurisdictions require a non-combustible cover which would add more insulating value.  

Craig mentioned something about foil faced foam --which would probably have a greater R value-- but I couldn't find anything at Home Depot's website.  

~Cath


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## precaud (Feb 3, 2008)

My project this winter is doing what you're about to do. I'm about 2/3 done. My research convinced me the foilface offers no benefit in this situation. I am using this stuff: 
http://www.dow.com/styrofoam/na/res-us/products/styrofoam/tongue_groove.htm

I believe Home Depot sells Owens Corning products, their equivalent is called Foamular. It's good stuff. Which thickness are you going with? From what I read, the 'sweet spot' of cost/benefit for interior walls is in the R6 to R9 zone.

Here are the instructions I followed:
http://www.dow.com/styrofoam/na/pro-us/literature/installations/interior_basement_drywall.htm

If you're insulating over concrete walls, a hammer drill is an essential tool for this job...


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## ansehnlich1 (Feb 3, 2008)

In our home we used foil faced batting, using a hammer drill and insulation fasteners. If I ever wish to finish off any part of the basement I'll just stud it out an inch or so from the insulation.


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## EWILT (Feb 6, 2008)

Does it hurt to just attach 4x8 sheets of 1 inch directly to the wall with glue?

Eric


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## d.n.f. (Feb 7, 2008)

EWILT said:
			
		

> Does it hurt to just attach 4x8 sheets of 1 inch directly to the wall with glue?
> 
> Eric



Just make sure you use the right glue (PL200???).  You can't leave the sheets unfaced though as it is an extreme fire hazard and they burn and poison quickly.


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## buszuw (Mar 13, 2008)

EWILT said:
			
		

> Does it hurt to just attach 4x8 sheets of 1 inch directly to the wall with glue?
> 
> Eric



Nope - doesn't hurt at all.  It is one of the easiest ways to make a dry but uninsulated basement a bit more bearable for the winters.  I did this (actually used 1/2 inch sheets) in a rental home's basement... and what a difference it made too!  The basement previously had only half-wall covering of fiberglass insulation and I didn't want to be breathing the fibers in while working and exercising in the basement.  Plus the fiberglass only covered half the walls which was quite bizarre and very ineffective.  The temperature absolutely leveled out once I completed the project.  Was it beautiful?... No.  It was functional and affordable.  If I had purchased the home like I originally planned to I would have constructed studs and put up drywall to complete the job, as it turned out I moved out a few years later.  I took down the foam before leaving and the landlord never said anything about the glue marks on the foundation walls left behind.


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## Molson (Mar 13, 2008)

Don't leave an air gap between the concrete wall and insulation. Yes you can insulate the wall before installing studding or strapping, or stud then insulate. Leaving an air gap will not provide the thermal break.  I too am doing it this summer and will be using steel studs, rocksol, and concrete board around the stove, and generic batts and wood everywhere else.


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## diyer (Mar 30, 2008)

I agree with not leaving an air gap.  If you do, you may have the cold air from the top of the wall dropping while the 50F air underneath it rises.  These convection currents will start condensing moisture at the top of the wall.  

If you can stop air movement, it would be better.

diyer in NH, USA


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## loggie (Apr 1, 2008)

In commecial applications they use Z channel which holds the foam to the wall with one side and the other is shot to the concrete I think it comes in different thicknesses. the drywall is then screwed to it for the finnish,I will do my basement this way


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## spot (Apr 5, 2008)

There are three ways to insulate a basement:

Rigid insulation with furring strips applied directly to the wall.
This method gives you the most open floor space ... however there is little room to run wiring or pipes. (it is possible though)
This method is best used on straight, plumb foundation walls.

Standard 2x4 wall with batts.
This method is simpler to build for most DIY-ers, gives you plenty of room for wiring and pipes ... but eats up alot of floor space.
This method is better for crooked, bowed, rough foundation walls.

Hybrid method of rigid insulation (no furring) glued directly to the wall, then a 2x4 wall with batts built directly in front of that.
This is the method you are considering ... it is the most work and eats up the most floor space (because you are doing _both_ above methods) however it gives you the most insulation R-value.

As always: make sure you correct water infiltration or foundation settling problems first.

Instructions on building all three methods can be found online, in magazines such as "Family Handyman", and in DIY books at your local Lowes, HD, or Menards.

Good luck and have fun!!


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## ennis (Apr 9, 2008)

check this site for best advice: http://www.eere.energy.gov/buildings/building_america/pdfs/db/35017.pdf


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## begreen (Apr 10, 2008)

Good link pretender, thanks for the posting.


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## Gooserider (Apr 14, 2008)

Agreed, the Building Science link is excellent, sounds like the fiberglass bat type walls are not though...

Interesting, but will be a real pain for us given that we have a mostly finished basement that came with the house, so upgrades require demo, and added costs...

We have batt walls covered w/ wood paneling in the house right now, and the basement is COLD...  However there is also nothing insulating the floor or rim-joist area.  The good part is that the basement is dry, at least as long as the sump pumps keep running.

Gooserider


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## ennis (Apr 14, 2008)

Here is another site that will jolt your senses:http://www.insulation4less.com/tech_foil.asp. This adds a new dimension to all these projects. Always keep in mind that basement walls must be able to breath. Heat out in the winter and heat in the summer. 
Gooserider: I would recommend removing one sheet paneling to make sure that there is no mold issues.
Home depot has been selling 2"x4'x8' sheets of Owens Corning (Pink) extruded foamboard (fmbd)for $19. R value is 10
 One method I use is trim one 2x4x8 treated to 3 1/4, nail to floor with Ramset nailer. ( this will come even when drawall is attached. Nails must be suitable for treated lumber. Trim one non treated 2x4x8 to 2 inch. Using Titebond adhesive (29) ounce that's suitable for foamboard, apply to wall and treated pc that been nailed to the floor. Now nail 2" trimed pc (with appropraite nails as you are nailing to treated lumber) to the floor attached pc .  The space at the joist and the rim plate a nailer will be added to extend no more than 2 inches from concrete wall. Cut and fit and remove so that all cavities are filled with foam sealer, ( especiallly if it's block wall) then nail to joists. Cut another pc treated to 2 inches, drill 3/4 hole  about 1 inch deep. Lay one sheet horizontal on floor nailers butting into corner, mark wall. Remove and add Titebond to wall at outer perimeter so as to make a good seal.. Place sheet against wall using small removable nailers to hold foamboard at btm. Apply Titebond to top area of fmbd. Using Ramset nailer in predrilled 3/4 hole to secure treated pc to wall. Now cut and fit 2nd sheet to top half of wall. Remove and add generous amts of Titebond to wall at the perimeter and inside that area. Foil tape the center seam. Make sure that outer edges are sealed tight and especially where it abuts the other concrete wall. 
At each end and 24 inch centers  vertical furring strips 3/4 x 3 are attached to nailers. This will hold fmbd and also be used for drywall sheets. Cavity can be used for wiring. Additional R can be had by adding 1/2 inch Tuff-R(R-3) with foil side facing in, to the top half only. Use Titebond or other appropriate sealer .
With radiant heat issues other modifications can be implemented . Pretender


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## Gooserider (Apr 14, 2008)

Won't argue the point, but I've seen LOTS of discussion of foil insulation here and on other websites - bottom line conclusion was that except for certain very limited special circumstances, the only thing it insulates well is the seller's wallet - by increasing the number of FRN's contained therein...  Only place I can think of where I'd even consider using it is if I were to put in a solar or wood burning hydronic setup, and wanted a single layer around a storage tank, as part of a much thicker sandwich of insulation.

Gooserider


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## WILDSOURDOUGH (Apr 17, 2008)

Gooserider-
"basement is COLD… However there is also nothing insulating the floor or rim-joist" 
If I were you I would make it a priority to insulate those rim joists this year- you will be pleasently
suprised what a difference that will make. Without insulation there- you only have the rim boards and 
siding between you and that frigid air outside, and that cold air just goes to your floors... brrrr.


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## ennis (Apr 17, 2008)

Wildsourdough: Rim joist insulation  suggestion is excellent. If basement wall is concrete block make sure to seal any cavity at the rim plate and where the rim plates
 meet. Redoing mine at the hight of the cold winter found insulation at the outer area frozen at joint of sill plates. Moisture was coming through the joint and freezing. Sealed and later taped and that corrected the problem.

Pretender


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