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brettu 09-14-2011 05:26 PM

1.5 Story Insulating Dilemma
So, I am brand new to the forum, and looking for an answer, I will do some searches, but am kind of looking for some quick responses if that is possible.
We decided to reinsulate our 1.5 story upper level on our Cape Cod style house. When we tore apart the walls we could see why we were losing so much heat in winter and not keeping cool in summer.
The Knee walls had like this old thin type of fiberglass with about an R4 value, and then behind the knee wall in the floor of the attic space was large wood shavings. On the angle ceiling there was the same insulation as the knee wall (so it wasn't vented) and the overhead attic had the same deal. The only venting that was happening was the small slots in the gable ends, on all three attics.
Now we have two choices, we have one contractor who wants to vent it right and insulate with R40 fiberglass, which is going to involve a lot of build out on the existing walls (especially the slant roof, which will have to come down 12"!!) Then there is the spray foam guy who wants to turn everything into an exterior wall - so to say, and spray the underside of the roof and all the exterior ends.
The first contractor says that we won't be happy with the spray foam as it won't quite come up to Code, (will only get up to R 30 ish) and the other guy says that the whold venting it right theory doesn't actually work in these old drafty homes with 1.5 story's.
The spray guy can also do my uninsulated basement as well for the same price as what the first contractor would only do my upper level for.
I am leaning toward spray foam???

msaeger 09-14-2011 08:17 PM

I am working on finishing my 1.5 story upper level I think these type of houses are a rarity because I don't see too much info on the internet about them.

I am using fiberglass because I know I can't afford to pay someone for spray foam :)

I think I am going to insulate the knee walls but haven't gotten that far so I could still change my mind. I just figured I could get more insulation in there that way and it would be harder to get in there to do the underside of the roof. Plus putting up vapor barrier would be tough but you wouldn't have to worry about that with spray foam.

Wouldn't building out the walls to handle R40 lose you a lot of room?

brettu 09-14-2011 09:41 PM

Yes it would, and that contractor was supposed to show up tonight after work between 5:30 and 6:00 and he never did, so that helps make my decision.
Currently everything is gutted up stairs, so there is no issue with getting in and doing the foam.
How are you going to do your slant ceiling? If you are going with fiberglass you now have to vent your slant ceiling and insulate, which loses you a lot of room too. I think, this is what I have gotten from my research.

msaeger 09-14-2011 10:34 PM

I have 2x8's on the slant. I am going to put in durovents then R21 on top of those because that's all that will fit. That's why I think insulating the knee walls might be better. I might be able to get more insulation in then. If I do the underside of the roof the most I can get is R21.

What R value is 7 inches of spray foam?

brettu 09-15-2011 07:23 AM

Now, I am no expert, I have just had a few contractors in telling me what they would do. So, research what I say here, It would be nice if someone else could chime in.
You need to insulate where cold meets hot. Now if your house is like mine, you have three attics per se, where you have unconditioned space, where you vent it to be the same temp as the outside. Two of those are behind the knee wall and one is above the ceiling. Now, in order to do the job properly, I believe you have to insulate the Knee walls, lik you are going to do, the floor of these "attics", the attic above the ceiling, and then the slant walls that sort of connects the knee wall to the upper ceiling attic. Am I making sense.??
You also have to vent everything properly, which means you need airflow between the three spaces. So yes, you need to vent the slant walls and insulate them, like you said, but then you also need to insulate the knee wall as well as the floor behind the knee wall.
Again, it would be really nice for someone to chime in here.

In my case, I think we are going to go with the spray foam, and just create everything into conditioned space. SO the underside of the roof gets sprayed, as does the gable ends of the house.
I believe spray foam gives you around 6.0 of R value per inch, so...

AGWhitehouse 09-15-2011 10:24 AM

If the budget alots and you need a roof soon, you could always add rigid polyisocyanurate panels (vented nailbase panels) to the exterior of the roof sheathing. (one example is:

Gary in WA 09-15-2011 11:11 AM

If you go SPF, be sure you know the product;

Check with your local AHJ, you may be required to cover with a thermal barrier or at least 2" of fiberglass insulation;

Also wind-block the insulation edge over the knee wall, under the knee wall, and the face on attic side with a housewrap, if using f.g.

Air seal first, if not using SPF;

Check on his work afterward:


Msradell 09-15-2011 10:44 PM

Is the foam he's proposing closed cell or open cell? Closed has a higher R value and doesn't require a vapor barrier. It's the preferred want to be using. I believe some of them go as high as R8 per inch. It's definitely the way to go no matter which one you use.

brettu 09-16-2011 10:26 AM

the foam is closed cell, 2#, I believe. Let's say if it is not done properly, after I check?? What then, do I have the right do ask them to fix it, I assume so...

Msradell 09-16-2011 10:55 AM


Originally Posted by brettu (Post 729409)
the foam is closed cell, 2#, I believe. Let's say if it is not done properly, after I check?? What then, do I have the right do ask them to fix it, I assume so...

Definitely, if there's a problem with the application they should have a problem fixing it. The actual application process is quite forgiving however so there shouldn't be any problems.

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