Askjake Insulation


Insulating with vaulted ceilings

I have a cabin that has no roof insulation as the roof is vaulted, or floor insulation. It has no overhang in front or back from the roof so there is no sofit vents. I want to insulate the roof and put boards on ther bottom of the 2 x 6 roofing so it has that nice vaulted look still.

I just dont know how to do it without any lower vents to allow air to travel up to maybe a roof line vent. I have a front and back porch on it with metal roofs tied into the house right above the sofit area. 

- John




I don’t know what part of the country you live in so I’m not certain as to what R value you require in your ceilings. In the Kansas City area we require a R value of 38 in the ceilings. I would suggest you put vent plugs on the facia board, behind the gutter, between each joist space.  

On the ceiling in each joist space, place the corrugated baffles to allow for air movement from the vent plugs up to the ridge. At the ridge, install a continuous ridge vent on the roof, then maximize the insulation you can put in your joist cavity. This should allow for proper ventilation and minimize the chances of moisture building up in the cavities.  

The best way to add insulation in these cases is to have a product like icynene  installed. This product maximizes the R value and does not require any type of ventilation. It’s more expensive in the short run, but will probably save you in the long term. 

Good luck in your project and let me know how it turns out. 


Re-insulating a botched 4 season room

Im reinsulating between 2×8 floor joists of a 4 season room that wasnt done properly. 

It is almost at grade level, no access to underside of joists. Am putting full 1 x 1 strips on each side of joist flush with bottomm of joists. Then I am putting 1/2 inch wolmanized lumber down on top of these rails with screws. Then I want to put r19 kraft faced insulation, faced side up to floor. 

Am I doing this in the right way and do I need to be concerned about trapping any moisture? Ventilation needed? I will be adding a cold air return, another hot air vent too for a total of 2. The other existing vent was not run back to main plenum. Also adding a gas pipe for a gas fireplace. 

Thank you, 


Jakes answer:


The way you are installing the insulation sounds like it will work.  

All crawl spaces must be ventilated to help control moisture.  The crawl space should have some sort of covering over the soil as well, like a 6 mil plastic sheeting.  I know this could be hard to do if there is no access.  You might be able to do it when you are installing the wood to hold the insulation in place. This will help contain the moisture and minimize the amount of moisture that can rise from the moisture in the soil.  

Is there anyway you can add some ventilation, at least one on each corner?  If you can accomplish these two items, you should be in pretty good shape.

Insulating the floor

Valerie asks:

Hey Jake,

I am adding on a new 3-seasons porch. I will add a gas line for a fireplace as well and since the furnace room is so close, may run ductwork out there in the future. 

The 11×20 porch will have a gable roof tied into the house w/single hung windows and 2 doors all around. It is being built over 1/2 existing concrete patio and 1/2 lawn. There will be about 18 for joists underneath. 

I live in ND with extreme temps and last year tons of snow melt. To prevent moisture/mold will plastic with rocks over the grassed area suffice? How do you seal the perimeter from snow melt/rain? Green treated lumber dug into the ground a bit? I have a contractor but he wasnt going to put any plastic down and said it would be fine. The inspector suggested it. What would be the best way to insulate the floor? I was thinking plywood under the joists, seal all with that expanding foam sealer and foamboard insulation? Thanks in advance for your expertise. I truly appreciate it. Valerie

Jakes answer:


You might want to consider using treated joists.  At 18” and less the code requires it.  By using treated lumber you minimize the chances of rot and insect problems. 

Definitely put a 6 mil or thicker plastic over the soil and patio, with a minimum of 2” of gravel.  This will help to reduce moister from permeating the floor system.

You should use some sort of treated lumber to seal around the perimeter of the room.  The code does require that these crawl spaces be ventilated year round.  For the size of room you are constructing, you will need 2 vents at least 1 square foot each.

The 2006 International Residential Code calls for an R-30 floor insulation.  Anytime you use batt insulation you should also provide for ventilation.  This reduces the chances of mold forming. 

I hope you are using a professional designer to take into account these issues.  In the long run, you will have a very comfortable room to enjoy those North Dakota winters in. 

Vapor barriers

Question from Mark : 

Im in the process of remodeling a mud room and want to know if I should vapor barrier the ceiling after put insulation up. We plan to have the room heated during the winter months. 

Jakes answer : 

Mark, Vapor barriers go towards the warm side of the insulation, so you would want to install the vapor barrier first. If you are using kraft faced batts, the kraft paper will act as your vapor barrier. Otherwise, you should install a plastic vapor barrier.

Old insulation in the basement ceiling

Question. Hi Jake, I recently purchased an older home with a stone unfinished basement. The previous owner insulated the ground floor with what appears to be an unfaced wool type blanket material but with nothing covering it, just exposed blanket. It’s old, quite an eyesore, and gives the impression of tiny bits floating down. The only function of the basement is laundry, but I would like to add a workbench and a small gym. Can I simply cover up the insulation with vinyl or a similar material? I don’t want to install a drop ceiling. Thanks, noma.

Jake’s Answer: Noma, I don’t see any problem with covering up this insulation with just about any type of material. I would make sure that you don’t make it completely air tight so moisture won’t form. If you wanted to do it yourself, you could probably find some sort of fabric and staple it to the joists. Make sure what ever you use that you keep it away from any hot light bulbs etc. If you are keeping the basement heated and cooled the insulation is not really needed for thermal purposes. If you like it for sound insulation then it might be a good idea to keep it. Good luck

Re-insulating a camp

Question: i bought an unfinished camp where R38-backed insulation was used in the walls. 2×6 should i replace it with R19 before installing pine interior? thanks

Jake’s answer: Yes, that would be a good idea. The R-38 would not compress into the 2 x 6 cavity to allow you to install any type of material over it. I don’t know where this camp is located, but it is rare to have R-38 called out for the walls. Good luck

Insulating the ceiling of a 4 seasons room

Question: I am having my back porch enclosed to make it a 4 season room. It is a cement pad and the house roof extends to cover the porch area. The room will have its own heat/cool unit. Although the house ceilings are insulated there is no insulation above the porch and I can not easily reach it from the attic (too low). The current porch ceiling is just 1/2 plywood. I was thinking of adding furring strips & tong & groove pine wood. Should I try to insulate the ceiling and what would you recommend. Thanks.

Jake’s answer. Yes, by all means figure out a way to insulate the ceiling. In our part of the country, we would use a minimum of R-38 with a vapor barrier. If this is a do-it-yourself project, remove the plywood and install batt insulation. Or if there is other access, rent a blow in machine and do it that way. If the attic is not currently vented, install some roof vents, probably around 2 would suffice. This room may be difficult to heat due to the uninsulated slab. There’s not much you can do about that. You might consider some electric floor heat so the floor will be nice and toasty this next winter.

Exposed Rafters

I’m having a building built to turn into a vacation retreat. It is a barn design with a hip roof. I’m considering leaving the exposed rafters on the second floor as part of the interior decoration. Any suggestions on how to insulate and leave the rafters with some of it exposed The room will be the master bedroom. Thanks RED


If you are having the building built I would suggest you consider adding an insulation board above the exposed roof sheeting. This is usually a foam board of some type that has insulation qualities based on the thickness of the board. Ceilings should have a minimum of a R-30 insulation, but the higher the better. Expanded polysyrene board will provide an R-Value of 3.8 per inch while an extruded polystyrene board will give you R-Value of 4.8 per inch. To achieve an R-Value of 30 or higher, you might consider traditional batt insulation covered with wood or drywall and add some fake beams/rafters. Don’t forget to properly vent your insulation to avoid damaging condensation. Gook luck.

Moisture barrier

I am turning a barn (carriage house) into a guest house. But I very concerned about moisture/leaks. The barn currently has only 5 lap siding over the 24o.c. studs.

Without removing the siding, how can I create an effective moisture barrier and add insulation before I put up the

gyp board?

Thanks for any help you can offer.



The product I would recommend is called icynene insulation. We have used it in situations such as vaulted ceilings. It does not require any type of vapor barrier since it is air tight and it provides for maximum R value. You can do a google search for more information on it. It is a spray on type that requires professional installation.

Montana house

Assuming that you have a R-19 insulation in your 2 x 6 walls, most of the studies that I have seen, would indicate that it would not be worth it to re insulate your walls. I would check your doors and windows along with your ceiling insulation to get the most bang for your buck. Most of your heat loss occurs in your ceiling and attic.

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