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Reuben Saltzman

My Beef With One-And-One-Half Story Houses

ReubensBeef I’ve lived in a one-and-one-half story house in Minneapolis for the last six years, and I feel like I’ve earned the right to complain about them.  My main beef with them is insulation and ventilation; they’re a pain in the butt and they’re expensive to get right.

There are two primary ways to insulate a one-and-one-half story house: traditionally, or with a hot roof.

Hot Roof

Hot roofs are actually pretty simple.  A hot roof will have foam insulation sprayed against the roof decking, and won’t have any ventilation.  If a closed-cell foam is used, it will act as a perfect vapor barrier, and will prevent any air leakage.  Simple.  I’m a big fan of this method, and I even did it at my own house.


The problem with spray foam is that it’s hideously expensive, and the installers need to have access to the roof boards; that means the attic space needs to be gutted before the work can happen.  If you’re doing a big remodel, great… otherwise, it’s just not practical.  Another way to get access is to tear the roof off, but that’s not too practical either.


The traditional way to insulate and ventilate a one-and-one-half story home is to insulate right up against the first floor ceiling, the knee walls, the vaulted roof sections, and again at the second floor ceiling.  The diagram below illustrates this nicely.

Insulation Outline

The cold spaces shown above are all supposed to be ventilated.  The ventilation will help to keep these spaces cool during the winter, which helps to reduce the potential for ice dams at the exterior and condensation in the attic.  The illustration below shows one way to do this.

Ventilation Diagram

In this illustration, soffit vents are installed at the eaves, baffles are installed between the lower and upper attic spaces, and gable end vents are installed.  There are other ways to achieve a similar venting strategy, such as using a continuous ridge vent at the top section instead of gable end vents, but the main idea remains the same.

The problem with traditional insulation is that it’s very difficult to retrofit an existing installation.  Some homes have access to all three of the attic spaces, while others don’t have access to any of the attic areas – and there is never access to the vaulted roof sections between these attic spaces.  To get at these areas, it often involves gutting the upper level.  Sure, more insulation can easily be added at the knee wall attic areas, but that’s just a fraction of the total heat loss that’s occurring here.

With traditional insulation, attic bypasses also need to be sealed… and these houses have a ton of them.  Perhaps the largest bypass is the one that occurs right below the knee wall, which is illustrated below.  This area needs to be sealed off to prevent warm air from leaking in to the unheated attic areas.

Attic Bypass under knee wall

What this all boils down to: if you’re buying a one-and-one-half story home that hasn’t been properly insulated and ventilated, just get used to it.  If you want to fix it, you’ll probably have to gut your upper level, frame out the rafters to make room for more insulation and re-insulate, or tear off the roof and do the same.  If you don’t do this, you’ll get ice dams.  That’s almost a guarantee.  If that’s the case, read my blog post on preventing ice dams from the exterior:

Oh, and another thing… these homes will often have just one supply and one return register from the furnace at the upper level; combine that with poor insulation, and you have a cool space in the winter and a hot space in the summer.

Reuben Saltzman, Structure Tech Home Inspections – Email – Home Inspector Twin Cities

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Note: The diagrams in this blog entry came from  I marked up the diagrams to help illustrate my points.

No responses to “My Beef With One-And-One-Half Story Houses”

  1. Reuben Collins
    May 11, 2010, 8:53 am

    Oh jeez. Don’t even get me started. Hot roof is totally the way to go. There are even more complicating factors you haven’t mentioned:

    1. in a lot of these homes, the roof rafters are 2×4’s, which means that on the sloping portions of the roof, you’re trying to fit insulation and ventilation within a mere 4″. You’re either not gonna have much insulation or you’ll have poor ventilation. I’ve heard of some people tacking 2×2’s to the bottom of the rafters just to give them 2″ extra space.

    2. In a lot of these homes, the eave end of the 2×4 roof rafters terminate right on top of the 2×4 double top plate on the walls. If there are eaves/soffits, it’s a totally separate structure and air space. This means that there’s no passageway for air to get from the soffits to the space between the rafters. In some homes, some sort of flared eave system was created, which allows for a passageway. But flared eaves just create more problems – especially for ice dams.

    In my house, I have pretty much given up on the idea of proper ventilation. I’d rather have insulation and I’m just gonna take my chances with condensation, I guess….

    Also, this is just a personal opinion, but I think knee walls are dumb and waste valuable space in these small 1.5 story homes. I’m seriously considering removing mine – or at least cutting some holes through them to access that space. I’m still trying to figure out the structural status of the knee walls, but I’ll probably be breaking into them sometime this summer.

  2. Reuben Saltzman
    May 11, 2010, 5:22 pm

    Reuben – I completely agree.

    On point number 1 – if I hadn’t done a hot roof on my house, I definitely would have added 2×2 on to my rafters for more space. No question about it.

    On number 2 – you’re exactly right. It’s very difficult to get the ventilation correct.

    Good luck with the knee walls – be sure to post photos.

  3. Graham Allan
    October 31, 2010, 10:21 am

    Seeing the same problem, having tried to both insulate and ventilate, I see there’s no way to pass any ventilation from the eaves, and it’s impossible to prevent ice dams etc.

    Do you have any opinion about retrofitting a cold roof on top of the existing one – there’s a good explanation at

    Seems like this wouldn’t be so hard to do, at the same time as replacing the shingles.

  4. Reuben Saltzman
    October 31, 2010, 1:39 pm

    Graham – I think that retrofitting a cold roof on top of an existing one would be an excellent plan.

    I actually just read an article this morning from the March 2010 edition of JLC titled “An Ice Dam Analyzed” , where the solution was to do exactly what you’re asking about.

    I’ve never inspected a house that has had this done, much less had the opportunity to evaluate how well this system works, but it certainly makes sense.

  5. tami
    October 1, 2011, 7:55 am

    i’m about to undergo having open-cell foam applied to my attic which has a furnace in it to create a hot roof. any comments on using open celled icynene instead of closed cell?

  6. Reuben Saltzman
    October 1, 2011, 8:00 pm

    Hi Tami – I would definitely go with closed cell foam. It has about twice the insulating value, it won’t allow moisture in, and it costs about the same as Icynene, which is an expensive brand name for open cell foam. You can read more about the differences here – . The guy who wrote that article, Kevin Klein, is a very knowledgeable insulation contractor who I’ve recommended dozens of times.

  7. Graham Allan
    October 8, 2011, 6:00 pm

    Well, almost exactly a year after my previous comment, I’m about 90% of the way through retrofitting a cold roof atop my existing one, using the Dan Perkins article as a guide. It’s been a lot of work, and I have yet to install the metal before the snow arrives, but it will be interesting to see what difference it makes this winter.

    As an aside, your point about recessed lights (elsewhere) was spot on. We *tried* to insulate adequately above these on the upstairs when they were installed several years ago, but I pulled some “sample” sheathing of the top of the roof to inspect, and could see the tops of the cans poking through the fiberglass. Took enough boards off the roof during the project to stuff a couple layers of R-30 on top of them from above, which should take care of it…

  8. Tim
    October 28, 2011, 10:05 pm

    I am this exact situation right now… we live in a 1.5 story in minneapolis and are renovating the upstairs. We have gutted the entire space and have access to all of the rafters. We contracted a spray foam company to do a hot roof however after talking with him and the sheetrockers they decided they did not want to mess around with doing the space behind the knee walls. Apparently if foam is used behind the knee walls it also needs to be sheetrocked for fire code reasons. I was initially okay with not foaming behind the knee walls because it cut the cost by more than a third. However now that I’ve been investigating how to ventilate and insulate the upstairs i think it might be nearly impossible to do it sufficiently. There is not enough space at the eaves to add any soffits any therefore it is pointless to add any exhaust vents. Is this correct? What has your experience been with your hot roof? Are the temperatures manageable in the upstairs? Do you have any problems with ice dams?

  9. Reuben Saltzman
    October 29, 2011, 4:47 am

    @Graham – thanks for sharing your experience. I’m interested to hear how the rest goes.
    @Tim – I strongly recommend you foam behind the knee-walls. Part of the benefit to doing a hot roof in a 1.5 story home is that you completely eliminate all of the attic bypasses. It’s not big deal to add drywall in the knee-wall spaces; you don’t need to make it look pretty. I think you can actually even get away with 3/8″ drywall in those spaces.

    Yes, you’re correct with your theory on vents, mostly. If you didn’t do a hot roof you could at least add gable end vents to knee-wall attic spaces, but this is a far less desirable option than making the entire space warm.

    I was very glad I did the hot roof, and I would certainly do it again. If I could do it again, I would have made my 2×4 rafters a little thicker by adding 2x2s, in order to have two more inches of foam insulation. I also would have added 1″ foam sheets of insulation all over the interior when done, to help eliminate thermal bridging. The wood rafters are a poor insulator; when frost showed up on my roof on cold mornings, I could see exactly where every rafter was when standing outside, because they created warm ‘streaks’ where frost wouldn’t appear. That really bugged me.

    Nevertheless, the hot roof was great. The upper level was instantly much cooler in the summer, and stayed very comfortable in the winter – I was able to turn off all of the heat registers going to the upper level in the winter, because the walls were so warm. It was great.

    I still had some small ice dams, but nothing like what I had before re-doing the roof. I’m pretty sure that I could have completely eliminated the ice dams had I done what I described above. Good luck.

  10. Steve Rasmusson
    January 10, 2012, 11:10 am

    We have an old story and a half farmhouse – balloon framed with plastered ceilings, 2×4 rafters and woefully inadequate insulation. I have been considering Dan Perkin’s idea for insulating, but am concerned about trapping moisture at the point of the old roof boards. My greatest concern is for the sloping roof/ceiling section with the rafters. Have you heard of any way (short of removing all the plaster and lath) of controlling the moisture penetration from inside the house into the rafters and roof boards. This issue might be moot, since the damage may already be doen after 120 years…

  11. Reuben Saltzman
    January 10, 2012, 8:20 pm

    Two ways – one would be with a straight hot roof, and the other looks like this –

    – Reuben

  12. Matt
    November 30, 2012, 4:42 pm

    I ran across your site due to an energy audit today that reveals a lot of air leakage in my upper half story in St. Paul. It has 1 foot fiber board tiles on the slants and upper ceiling. The blower test revealed 2400 cubic feet of air movement and the auditor said a lot of air was coming from the seams between the fiber board tiles. This leads me to believe that whatever insulation exists is just sitting on the tiles and there isn’t much in the way of air sealing. If I decide to pull down the tiles but leave the kneewalls up, can I do a hot roof for just those portions and just add more insulation to the kneewall and floor behind the kneewall, or is a hot roof all or nothing?


  13. Reuben Saltzman
    November 30, 2012, 8:32 pm

    Matt – here’s an example of what you’re proposing, right? This would make it better, no question. You would still have a bunch of air leaking underneath the floor though. I’ve never read any studies on ‘half-hot-roofs’, so I really don’t know how well this would work. If it were me, I’d do the whole thing.

  14. Steve Rasmusson
    December 4, 2012, 12:42 pm

    We are in the process of doing a cold roof on our farmhouse. We have stripped the roof to the old boards, added 1/4 inch fanfold insulation covered by permafelt, since I figured there might be a few rainstorms before I got the rest of the work done. We then added 2″ of closed cell insulation (R-10) and laid 2×4’s over the top of the existing rafters, fastening them in with Spax screws. Then we put purlins every 2 feet up the roof, and vented both the eaves and the soffits above the closed cell. I can now fill the voids between the plaster and the old roof with blown-in insulation and have about an r-30. We completed the north facing side of the house this fall and it is already warmer upstairs.

  15. james
    December 20, 2012, 4:51 pm

    curious from outside on the direct roof planks – older homes, particleboard – newer homes couldn,t you put exterior blue foam direct to the roof place one by fours on top then treat the roofing finish like you would a metal roof this would allow air movement up the roof line while keeping the inside warm air where it needs to be ??

  16. Reuben Saltzman
    December 21, 2012, 4:53 am

    James – sure. Even better yet, get a product that does this for you, such as Thermacal.

  17. Adam
    January 29, 2013, 10:53 am

    Last summer we had a energy audit done in our one-and-one-half story home. This is where the nightmare begins.

    In the half story slant walls there was some 1940’s newspaper insulation, the knee wall had some cellulose insulation on the floor and newspaper on the roof boards, no soffit venting. There a 2 upper and lower square roof vents.

    The suggestion was to dense pack the slant walls with cellulose and place a vapor barrior on the kneew wall. I was againts the idea of denspacking the slant walls. I figured we had some air flow throught the news paper and preventing condensation. After be reassured from the energy audit and insulation company; I had the slant walls denspacked.

    Now there is condensation in the knee wall. The insulation company came back out and told me the “wood was drying and this was the moisture I was seeing.” It has going worse as this winter progresses. They also informed me that I did not need soffit venting in the knee wall and it would not help with the condensation. The company is full of it. They did build a nice tight access to the knee wall.

    Last weekend I did the nearly impossible job of adding one soffit baffel. I also decieded to tear out to truss space of the slant wall above to see what was going on there. I found water and ice in the knee wall just where it hits the slant wall. There is also lots of water at the top of the knee wall where it meets the ceiling. They dense packed the cleing space with cellouse also.

    I think something should be done to try and stop insulation companies from this practice. I fear there are more home owners in my situation.

    I am so scared of mold growth now. Do you have an idea to to remedy this without tearing out all the dry wall and foam insulating this area?

    I am near house broke at this point. I rebuilt the kneewall/slant walls and unvented low slop roof in the houses addtion this last year because of condensation. Of course I was a first time home owner of 4 years ago. The condensations issues where never discloused and it took me 2 1/2 years to figure out what was going on.

    Ruben – Thanks for all the great free information and the blog. I’m guessing you have helped many.

  18. Reuben Saltzman
    January 29, 2013, 11:49 am

    Hi Adam,

    Thanks for sharing your story. I’ve seen variations of your situation happen occur over and over again. I don’t have any simple solutions to recommend. One insulation company I’ve found that does an excellent job of looking at the entire picture is Cocoon. The owner of that company will be doing a guest post on this site next week.

    If you’re located in the Twin Cities, you might want to hire that company to come out to give you recommendations.

  19. Hugo VanPelt
    March 10, 2013, 8:42 pm

    I have a problem with the drywall joint in the livingroom ceiling where the kneewall from the roof sits on top of it. one section In drywlled paralell to the ceiling joist and it doesnt crack. The other section where I installed the drywall perpendicular to the ceiling joists I have both joints paralell to nthe kneewak=ll above it cracked

  20. Debbie
    May 7, 2013, 6:54 am

    hi, I own a 1 1/2 story house and have a question… when walking thru the little door in the knee wall to access the storage space… the inside wall has vapour barrier on it as well as the outside wall/roof. Is there supposed to be this vapour barrier/plastic on all sides??

  21. Reuben Saltzman
    May 7, 2013, 8:48 am

    Hi Debbie, there should only be a vapor barrier on the ‘warm-in-winter’ side of the insulation.

  22. Teresa Theesfeld
    September 29, 2013, 9:13 am

    My house was built in 1890 and is a story and a half until I gutted the back half and raised the roof eliminating the attic. I insulated with closed cell insulation. The middle and front of the house were left untouched. I don’t have central air and would like to install a Tamarack whole house fan in the second floor hallway. I only have a crawl space for an attic in this portion of the house and am wondering what you think of this method of cooling a house in the Minnesota Summer.

  23. Reuben Saltzman
    September 29, 2013, 1:07 pm

    Hi Teresa,

    I’m sure that would help to cool your house down, especially at night, but just remember that’s it’s no substitute for central air. Most people that have those types of fans love them.

  24. Teresa Theesfeld
    September 29, 2013, 8:32 pm

    By the way, my house was a story and a half until I gutted the back half of the 2nd floor, raising the knee walls to 8 feet and vaulting the ceiling. I insulated with closed cell insulation and love it. I installed a white pebble-coated steel roof and Halcyon window shades to reduce the amount of heat coming in through the windows in the summer and am very happy with the results. I only wish I could have afforded to eliminate the knee walls in the entire 2nd floor. I agree, they are an absolute waste of space.

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