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Bungalow, Knee Wall Insulation and Venting


theparamount's Avatar
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01-19-15, 03:21 PM   #1  
Bungalow, Knee Wall Insulation and Venting

I, as many others have scoured these forums for days reading everything I can regarding my new house and its stupid knee wall attics.

I have a 1947 built Bungalow which is a pain with its ice dams and its poorly controlled heating/cooling upstairs.

The house has two vents per side that are on the roof. They are not gable vents. They are directly on the roof. There are no soffit or soffit vents. I have attached a picture of the backside of the vent after I ripped some insulation down.

Currently there is insulation in the form of faced fiberglass batts on the rafters, knee wall and limited cellulose blown onto the floor of the attic space.

The first question is, without soffit vents and living in detroit (zone 5), is there any way to insulate the sloped rafter side, thereby putting the attic "inside the conditioned space" without creating an environment that is prone to mold/condensation?

If this is impossible, as I think it is, I am stuck with insulating the knee wall and the attic floor and air sealing under the knee wall to put the attic space "outside". In doing so, does the kneewall insulation go, from inside to out, sheetrock, unfaced R-19 batts, then rigid foam?

I plan on using blown in cellulose on the floor of the attic space.Name:  FullSizeRender-2.jpg
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01-19-15, 05:13 PM   #2  
Ice dams are a pain and the details to minimize them are well known, but not back in 1947. I'll give you a couple of links to get you warmed up. The really good news is that all of the steps from air sealing, air blocking, extra insulation, and proper ventilation all add up to reduced heating bills.

Two Ways to Insulate Attic Kneewalls - Fine Homebuilding Article

http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-attic-venting

I let you read some of those and then we can discuss your venting options. Is there an upper attic space with any venting?

Bud

 
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01-19-15, 06:22 PM   #3  
Yea, the upper attic has three of the same on the back side. They all look like this.[ATTACH=CONFIG]45204[/ATTACH]

I've read those articles! Thanks but still wondering about the knee walls insulation. Also since I don't have soffit vents should I put up a barrier right next to the roof so the blown insulation doesn't hit it?

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01-19-15, 08:07 PM   #4  
You do not want the new insulation to be directly against the bottom of the roof. Any warm air that leaks into that kneewall space will deposit its moisture on that cold surface. You end up with ice on the inside and icicles on the outside.

Your pictures show insulation up in the rafter cavities as well as down in the ceiling joists. Since you do not have traditional soffits for low venting you could go with just the insulation in the floor and the back of the kneewall. With venting that would make the kneewall space cold and reduce the ice dam problems. But your two roof vents may not be enough. You would also want to be sure there is a vent channel above the insulation in the sloped section going up to the high attic. Is there currently a gap above that insulation? And are those 2x6's (5.5")?

A problem you will face is being able to install sufficient insulation. A 2x6 cavity doesn't allow a lot of space for both insulation and a vent channel.

Bud

 
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01-19-15, 08:34 PM   #5  
Yes, they are 2x6's. As I'm looking more it may be easier to insulate that roof instead of the other way (the knee wall and floor), but is this possible with the vents I have and no soffit vents?

And in the sloped roof there is space. Could I put a baffle in the sloped portion and "connect" the upper attic to each knee wall attic and then dense pack the rest with cellulose?

I hate to make it an outside space as it could easily be used as storage.

 
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01-19-15, 08:55 PM   #6  
First, there are edge vents that could be installed under the last shingle, but not with it as cold as it is and probable should wait until you replace the roof. Without soffit venting you need some way to introduce cold air into the lower areas of the roof.

Just to give you an idea as to what you are facing, the slopes and that kneewall need about a foot of insulation. The floor below a bit more. Your current sloped ceiling that is sheetrocked on the inside has probably r-11 or r-13 installed. Then fill the vent space above the insulation with outside cold air and that r-value is cut in half.

I don't recommend it, but I've read many posters say the weatherization programs which are everywhere will just dense pack those cavities from bottom to the attic up top. Since dense packing is not an easy DIY installation, you might want to ask for a quote from a cellulose contractor and see what they say about that type of installation. Your local weatherization program might even refer you to the contractor they use. If the contractor has often used this approach, it is worth considering.

I could dig up some of that discussion if needed, was on one of the linked-in groups.

Bud

 
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01-20-15, 01:10 PM   #7  
That is what one person said they would do, dense pack the slopes, and I assume they would do that without any air flow through there. Now in terms of the knee walls, what should I place in there?

Is there any way to just spray foam the roof side and do an "unvented" attic?

 
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01-20-15, 01:51 PM   #8  
The trick to staying out of trouble with insulation directly against the bottom of the (cold) roof is zero air infiltration. If you were to spray foam you would use closed cell, but it still might need (to meet code) a fire barrier over it.

If you attached foil faced rigid foam board directly to the bottoms of the rafters they could dense pack above the rigid. Care must be taken to tape and seal all possible paths for air leaking into those cavities, moisture vapor will go right through dense cellulose. From kneewall to attic you may not have a good vapor barrier in place so applying a paint that has a vapor retarder rating would be advised. What to do with the existing fiberglass in there would be up to the experience of the installation company.

The advantages of the dense pack approach is it is easier and probably less expensive and it gives you a full rafter depth of insulation, approaching r-20.

The disadvantages are code compliance (some do not allow this approach) and potential moisture issues, but that is where a perfect air sealing job is of prime importance.

If this would cover all existing vents, then you would need to decide what to do with the small upper attic. I would of course advise something, either relocate a couple of the roof vents, add a couple gable vents, or install some ridge venting.

Bud

 
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01-20-15, 07:06 PM   #9  
I read about densepack cellulose in roof cavities on buildingscience.com. Find the information there. They don't seem to work out very well.

I had a similar situation as you with insulation. I wound up gutting and using closed cell spray foam under he roof. This eliminates the need for ventilation.

 
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01-20-15, 07:53 PM   #10  
What droo posted is what I have read as well. Here is a long link with a lot of negative about dense packing a cathedral ceiling:

http://www.buildingscience.com/docum...-cold-climates


Bud


Last edited by Shadeladie; 01-23-15 at 07:42 AM. Reason: Link removed per OP request
 
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01-21-15, 07:23 AM   #11  
Here is what I've been quoted for

Its a pdf (had to upload to 2 shared, too big for here)

A10-4a_Brochure.pdf download - 2shared

 
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01-21-15, 08:13 AM   #12  
I clicked, but it wants me to install something and my pc guy says never.
Don't know if there is anything here that can help:
http://www.doityourself.com/forum/li...rt-images.html

If not maybe one of the more pc intelligent volunteers will jump in.

Bud

 
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01-21-15, 02:04 PM   #13  
Sorry, it was a pdf download. Heres a picture of part of the PDF.

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01-21-15, 06:00 PM   #14  
Just made notes as I read, but if they have had good success with this and will guarantee no moisture problems it does provide a lot of insulation. My list is long and all may not apply, just there for information for you.

What will they do with the existing fiberglass insulation currently in the slopes between the kneewall attic and upper attic? From your picture it looks like they will just dense pack above the fiberglass and compress if out of the way.

Their SilverGlo rigid foam sounds like it is foil faced so needs to be foil taped to complete the moisture barrier. The sloped ceiling and the flat ceiling however do not have a good vapor barrier, assuming just the Kraft faced fiberglass, especially if it was stapled on the inside of the rafters as shown.

The top plate on those outside walls needs to be air sealed, not just covered with dense pack. From your pictures yours will be hard to access, but they must do so.

If they do this during cold weather you should ask for an infrared camera inspection to be sure all voids are filled. Unfortunately, the foil surfaces will be difficult to inspect with IR.

How about venting for the top attic space? Any ceiling lights in that flat ceiling?

Kneewalls are often used for passing plumbing vents from below up through the roof, those would need to be well sealed.

The top of the kneewall also needs to be air sealed and blocked just like they show the ceiling joists out by exterior walls. The top plate on a kneewall is never well fitted to the rafters and drywall due to that angle.

Curious what type of warranty they provide saying that their approach will not cause moisture damage?

Gable end walls should also be upgraded with better insulation and air sealing.

The existing roof vents pose a potential leak issue and cannot just be left in place or removed without repairing the shingles from above.

If your current shingles are old it would be nice to have them replaced before the dense pack is installed. Once the dense pack is in there you will not see small leaks for a long time allowing them to perhaps cause damage.

Bud

 
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