Sign In to join the community | Help
Building Materials


attic insulation questions in Wisconsin - cape cod

We have a 1940's cape cod. The crawl space that runs the width of the house (about 40-50 feet) is hot, which we believe is the primary culprit for why our upstairs area is hot (venting issues aside).


The attic underside of the roof has insulation already, the rvalue I am not certain. From the pdfs I have reviewed from .gov energy sitse you should insulate your attic two ways:

a. L shape (floor and knee wall)

b. underside of roof 


We have no insulation on our attic floor or knee wall. What can we do to reduce heat BUT not increase moisture/humidity/stale error issues. The concern is if we insulate the floor or knee wall it would trap moisture or make problems worse.


Any thoughts? 

Not what you were looking for ? Try posting a question
Posted 2012-07-17T14:46:29+0000  by jerger jerger


jerger wrote:

...if the ceiling remains insulated... would it be ok to put the metal radiant barrier on the floor and knee wall to reflect heat or would that just make it worse?...

No.  You don't want metal there.


jerger wrote:
...just wondering what i could do low budget now keeping the roofing insulation in tact...

For now the low budget move would be to insulate the knee-wall with faced insulation.  The facing should contact the inside wall closest to the living space.  This will reduce the heat entering the attic living area.


Later you can work on ventilation and the crawl space floor when budget permits.


I hope this helps,





Best Answer

Posted 2012-07-17T17:53:01+0000  by Chris_HD_CHI




Your house is typical for its age. World War 2 era homes and before  had little or no insulation. It wasn't until the first energy crisis of the early 70's that insulation standards were seriously upgraded.


The crawl space is treated as any other attic space. It is cold/hot unconditioned air. To this extent, the inside of the knee wall and the floor  should be insulated with vapor barrier toward the heated area. With no insulation on the floor, I would be surprised that cold spots are not showing on the downstairs ceilings. Being cold surfaces, moisture tends to condense on it and household airborn dust sticks to it.


Ventilation would normally be under eave vents which allow air into the crawl space. Provision would normally be allowed to let air pass through into the upper attic, where it would exit through high mounted roof vents or a continuous ridge vent.


The crawl space could be converted to a conditioned air space by fastening insulation to the underside of the rafters, leaving a couple inches of space between the insulation and the underside of the roof. Air must be able to flow upward through this space into the upper attic, where again it would exit through roof vents. Obviously, if this is done, insulation would no longer be neccessary on the knee wall or floor, since this would now be heated/cooled space adjoining your conditioned living areas. This would be the more involved solution as you must prevent air infiltration. The average house loses more heat to air infiltration than to poor insulation.

Posted 2012-07-17T15:51:53+0000  by ordjen

thanks for the reply. 


what would be the best option without removing the insulation from the underside of the roof?  would it be best to put insulation on the floor first or knee wall? if im on a budget.


with a cape cod i haven't looked too much but i wonder what the rest of the space looks like between the upper floor and roof that is not in the crawl space. 


can you post a link from home depot store on what type of r19 or higher insulation to get with the vapor barrier? thanks! 

Posted 2012-07-17T15:58:08+0000  by jerger


Hello Jerger and thank you for posting your question here.


Jerger insulating Cape Cod homes can be very challenging.


Before I start posting suggestions can you help me get a better picture of the set up in your attic?


First let me ask do you have any soffit vents on your home?

Second for the secondary attic, what type of vents do you have gable or ridge?

What size of rafters do you have up there?

What type of insulation in the secondary attic and are there any baffle vents?


What type of heating/cooling do you use?







Posted 2012-07-17T16:03:33+0000  by George_HD_CHI

ordjen: maybe i read your post wrong.


so i have insulation already... between the roof rafters... would i add MORE insulation to the base of the rafter so there would be air between the two layers of insulation?


steeltoes: i'm not sure how to distinguish vents, any tips are appreciated. garble, ridge, baffle, soft etc are new terms to me. central air and gas furnace. 

Posted 2012-07-17T16:10:11+0000  by jerger



No problem Jerger :)


Ridge vent is a vent that is installed on a peak of the sloped roof and it typically runs its entire length.

Gable vent is a vent that is installed on side of the attic wall (gable roof).


Soffit or eave vents are vents that are installed on the portion of the roof that overhangs the walls.

Baffles are corrugated sheets that are stapled in between rafters to create a cavity for the air to flow.


Ant there is also a power fan which is basically an electric fan that is installed close to the peak of the roof…got one of those ?:)






Posted 2012-07-17T16:25:26+0000  by George_HD_CHI

I will take a look thanks! 

Posted 2012-07-17T16:31:10+0000  by jerger
i'm wondering if we have gable vents since there are the slotted open areas on the sides of the house. i do not think we have baffles.
Posted 2012-07-17T16:33:32+0000  by jerger


Yup those are gable vents is there an actual fan up there or is just the slots ?


On the insulation question;


I don’t think you can add more insulation in between rafters.

What ordjen was trying to explain….is that you need to have an air gap in between insulation and the roof decking so that hot air trapped in the crawlspace can travel towards the peek.


For the air to travel flow you would need an outlet on the lower and top portion of the roof which would be a soffit  and gable or a ridge vent.


Posted 2012-07-17T16:39:09+0000  by George_HD_CHI

Hey jerger.  Thanks for joining the Community!


Let me throw in a picture so you can see the venting we are talking about:







Posted 2012-07-17T16:46:17+0000  by Chris_HD_CHI
Not what you were looking for ? Try posting a question