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Carpenter 01-18-2009 10:14 PM

Room in Attic Delimea
First I would like to say hello and that this is my first post on these forums.

(Not sure if this is the right Forum)

I would like some advise on a room in attic insulation problem. I have a 1 1/2 story home with an unfinished attic built in 1956. Seeing as it tax time and this is our first home we qualify for a $7500 tax credit, which I will be using to finish off. The only thing is, is I am running into problems already and I haven't even started. First thing is first I need to come up with a creative way to vent the attic and I think I have that one figured out. I donít believe that I am going to be able to run a continuous soffit vent so I am going to use the 3 or 4" round popins.

Now if I install those I should be alright for venting low, but I am not sure if a gable vent is going to be enough air flow to keep the space Comfterable.

So this is where i run into the problem. I only have 2x4 roof joists, now its now problem on the lower part of the roof but about half way to the top I am not sure that this is going to be enough space to insulate without causing a moisture issue. So my question is what do I do, just run the insulation, vapor barrier and the rock over it or should I fur down the joists to make enough room to get some air flow?

jaros bros. 01-19-2009 06:46 AM

In Minnesota, 2x4 rafters will not allow enough depth for adequate insulation. You should really have about R-50. Something tells me this room was probably never intended to be finished off. I am surprised that the rafters are only 2x4s as well. I would tend to think that the snow loads in Minnesota would require something larger, unless this room is by itself and the roof spans are incredibly short.
You probably are going to need to sister some new rafters in and then use spray foam. This is will turn your roof into what's called a "hot roof," eliminating the need for ventilation. This is acceptable to do now under current codes.
Trying to insulate with fiberglass in your situation and 2x4, with or without ventilation is going to rot your roof out because you don't have adequate depth for insulation. Your sheathing will fall below the dew point and cause condensation to buildup and then you'll have moisture problems galore.
Sister new rafters, 2x8s to get the needed Rx50 and then hire a spray foam contractor to install the spray foam to create your hot roof.

Josh Jaros (Jaros Bros. Construction)

Carpenter 01-19-2009 10:18 PM

Thanks for the input, I understand the whole needing more space for insulation but I am wondering about the whole "hot roof". See the Attic is 2x4 rafters 16" OC but only 4' of so of the whole rafter lenght is posing a problem. I guess I could get some pictures of what I am talking about and post them up here.

At the 1st Floor wall top plates where the rafters are sitting, about 5 feet in from both sides its just attic space, then knee walls that extend up to the roof joists and there is about a 4' Collar tie on each set of rafters about 2' or so from the top.

So I guess my question is could Spray foam the 4' section that is posing the problem and just fiberglass the rest like I was planing on doing? Or am I better off furring down and losing head room?

whyme 02-18-2009 06:28 PM

damn that sucks man, i hear what your saing thou

GNiessen 03-31-2009 01:53 PM

Look for the highest R-value per inch. That way you lose the least head room. But to get R-40, you will need more the 3 1/2". And once you are spraying the upper 4', you are probably better off doing it all, rather then trying to figure how to vent half way up the roof. But it can be done.

GBR 04-02-2009 03:44 PM

Hello back, carpenter. Welcome! Here's one: Welcome To Home Energy Magazine Online Be safe, GBR

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