Blown in insulation depth

Question Icon
Posted by: from Lloydminster
7/3/2012 at 12:34:29 PM

My new house (well new to me) has blown in insulation. How deep should that isulation be to equal r-25 or r- 40.

Thanks for your advice!!

User Icon
Date/Time7/3/2012 at 2:17:39 PM

Loose cellulose, fiberglass (both blown and in batts), and rock wool (both blown and in batts) all possess an R-value of roughly R-2.5 to R-4 per inch.

Usually r-40 is 11"

User Icon
Gaby from Amg Renovation in Hearst
Date/Time7/3/2012 at 2:30:44 PM


Usually we go equal to the 2x6 like the other said its around R-25, if you need to go there later you really want to see your 2x6 to walk on, make sure you don't block your soffit vents when putting new insulation or you will have problems with season changing, oh ya make sure you also have a vapour barrier on the heating side of your selling,

Good luck.


Certified Contractor

Certified Inspector

User Icon
Date/Time7/3/2012 at 4:25:43 PM

If your home was built within the last 10 years, then it should be at R-40 (about 10-11 inches of cellulose fibre, more than 12 inches if it is blown fibreglass).

You could check with your builder to what level it was blown to or look for some identifying info near your electrical panel. 2012 Ontario Building Code is now R-50.

User Icon
Date/Time7/3/2012 at 6:57:07 PM

For R-40 an average is 12". BUT, keep in mind that the fluffy stuff does settle and the measurement may provide a false reading. Best to call you local building inspector (County or City can provide details) and see about codes. I also recently heard that the "new" norm os R 50 for attics in cooler climates.

Good luck,


User Icon
Date/Time7/4/2012 at 8:02:42 AM

This would depend on the type of material that is in your attic now. Blown and batt insulation have different r-values based on depth.

Reitzel Insulation


User Icon
Gaby from Amg Renovation in Hearst
Date/Time7/4/2012 at 8:07:13 AM

Ya brent is right 2x6 + your trust 2x4 =10 to 11 in. sorry for not explaining myself right but brent said it the right way, I wanted to answer your question (How deep should that insulation be to equal R25 or R40) for R25 its around 6 in, and R40 is around 10 in, of blown insulation, you have all kind of quality (Again Sorry for not explaining myself right)

User Icon
Date/Time7/11/2012 at 12:11:45 PM

R-25 is approx. 7 inches of blown insulation...R-40 is 12 inches of blown insulation. This is the building code minimum for attics in Ontario.

Paul Justice

Search the TrustedPros directory and discover the best contractors in your area.

Find your home service pro
Great renovations start with a great contractor.

Since 2004, TrustedPros has been helping homeowners find the right contractor for their home improvements and repairs.

Post Your Project

Within hours you'll be comparing offers from top-rated professionals. It's free to post and you're under no obligation to hire.

Trustedpros Inc. does not warrant the accuracy, completeness, safety, legality or usefulness of any Content, or Whether Content is Current and up-to-date, and TrustedPros Inc. Shall have no liability whatsoever with respect to your use or reliance upon any content or for content being removed or otherwise ceasing to be available. Please refer to the terms and conditions of use of this websites for more details.

Get Free Estimates

Post your project and compare offers from top-rated pros.