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kokanee123 09-17-2009 09:26 PM

Insulating a finished attic properly?
We have a potential problem in our new attic storage area, and I'd love some advice on how to avoid a problem developing. Roofers? Any solid advice?

Our carpenter put in a pull down ladder and a floor in our attic, then (uninsulated) knee walls, and an insulated, vapor barriered ceiling, cutting out gaps in the plywood ceiling for the existing roof vents.

The studs are 2x6 so he put in R12 insulation (designed for 2x4 construction) and a vapor barrier before putting on the ceiling plywood. With any luck this preseved an air channel for air flow.

On speaking to our roofing company after the fact, they described a system of styrofoam venting channels that perserve a 2" airspace between insulation and the roof deck, so that condensation shouldn't be a problem.

I'm hoping that if we have the ceiling, insulation and vapor barrier removed, then put in the styrofoam venting channels he described, that we should have no issues with condensation, but on reading an earlier thread (2007?) in this chatroom, I'm not reassured that it will make a difference.

Can anyone give me details on how the styrofoam channels work, and if there is any way to make sure that the insulated attic room doesn't turn into the worst mistake we could have made in the house?


Scuba_Dave 09-17-2009 09:31 PM

R12 is made for 3.5" insulation, 2x6 = 5.5"
So you already have a 2" air space
Is there a ridge event?
Soffit vents?
Air spaces mean nothing without venting

But that is VERY low insulation for any space to be heated or kept cool
Attics get very hot, R38 is usually a min
Walls usually get R13

Ceiling plywood? Why not sheetrock?

kokanee123 09-17-2009 09:47 PM

The carpenter didn't think he'd be able to haul up the drywall through the little attic hatch (you know - the pull-down ladder type) so he used paper-faced plywood instead since he could cut it in 2'x8' lengths and pulled it up there.

There are attic vents in 3 places at the top of the room near the ridgeline, so that's good.

I'm just hoping that the insulation he used (there was some of the pink fibreglass up there already and I have no idea what R value it has) was all that thickness.

And being a total novice and having the roofing company threaten to invalidate the warrantee has me wondering if we need to take the whole ceiling / insulation down and redo it so we can guarantee we won't have a moisture issue in future.

As for it being enough insulation to keep the attic storage cool enough, I'm hoping that it will be enough... its not like we plan to spend much time up there, and as long as its dry, our things should be ok up there... hopefully!

The roof has soffit vents all around.

Scuba_Dave 09-17-2009 09:52 PM

If the roofing company doesn't believe you then find another roofing company

Gary in WA 09-17-2009 11:44 PM

then (uninsulated) knee walls,--------- The moisture in the air coming in the attic will mildew the storage items, without a v.b. on the knee walls.

cutting out gaps in the plywood ceiling for the existing roof vents. --------- He is letting the moisture out through the vents, or so is his idea. The vents are to exhaust the air channel that comes in each rafter bay by way of the soffit continuous venting. Flowing up the bays and out the continuous ridge vent, or out individual turtle-back vents rated for your individual roof. 150th of your sq. ft. of attic space, divide 1/2 of intake (soffit) vents and 1/2 of exhaust ridge vents.

described a system of styrofoam venting channels that perserve a 2" airspace ------- you will be fine with the thinner insulation as this gives you a 2" air space.

There are attic vents in 3 places at the top of the room near the ridgeline, ---------- this may not be enough. 1. How many vents? 2. How many square feet is the room? 3. Is there a triangle of attic above the sloped ceiling, and how wide (from slope to slope)?
4. Are the vents in the sloped ceiling area that he closed off from the other bays?

Some reading for you:,M1
Be safe, Gary

Scuba_Dave 09-18-2009 07:21 AM

Why are the knee walls uninsulated?
Is this are just for storage?

mics_54 09-18-2009 10:55 AM

Is this new construction or a retrofit or remod?

#1) This isn't a "roofer" problem.

#2) you are creating a "hot roof" where the"attic space" isn't to be vented (2" space for airflow between the cieling and roof sheath"), yet you say there are vents in 3 places cut through the ceiling. This sounds like you are venting the attic space rather than the rafter bays where it should be.

I'm not sure but I think you called the rafters "2x6 studs".

Also your "carpenter" built "pony walls" someplace that were not insulated?? ...AND your floor was placed on the existing ceiling joists. Is there insulation under the plywood floor??? Were the joists designed to support a floor and storage?

kokanee123 09-18-2009 11:29 AM

6 Attachment(s)
Hi Scuba dave and others - thank you so much for your advice and information. Here are some photos of the project, and a few answrs to your questions.

The builder didn't think the knee walls needed to be insulated. Now I'm thinking the whole project needs to be re-done.

Yes - the room is solely for storage. So, its maybe 150-200 square feet of space. The knee walls are unisulated (builder's decision)

I just had a walk around and discovered there are no soffit vents in the front part of the house which is the portion of the attic we finished for storage. the eaves are however open to the rest of the attic space, where there are soffit vents the whole house around.

To properly have built this I'm guessing that:

1. venting channels should have been installed
2. insulation should have been placed in the knee walls and ceiling
3. Vapor barrier over top of insulation (by the way - does vapor barrier touch insulation or not? how does that all work?)
4. There may have been no need to cut out the holes for the vents, since its the air outside the room that needs to be vented away...???
5. We probably should install soffit vents around the olderr part of the roof.

Having sleepless nights at the moment. Grrr.

Thank you so much for your help

mics_54 09-18-2009 11:46 AM

after seeing your pictures...

the attic space with hip roof is not designed for a hot roof as there is no way to vent many of the rafter spaces economically to a common ridge vent.

The attic storage should have been designed and treated as an unconditioned space.

Installing eave vents is pointless if there is no place to vent the flow TO.

sorry...your project gets a :no:

Scuba_Dave 09-18-2009 12:23 PM

4. Yup, venting the attic space is not what you want to achieve
So your roofer is right (pics make all the difference)
They could put a ridge vent in which would solve part of the problem

Proper way would have been to put a flat ceiling in just below the roof vents
That would allow all rafter spaces to vent outside
If he used screws you could take the top plywood down & make a flat roof

1. Venting channels are not needed since you went with lower insulation that will not fill the rafter space

2. Yes, I would have insulated the knee walls
BUT - if he ran insulation all the way down the rafter space down to the floor beyond the knee wall then not entirely needed

3. Vapor barrier - if brown faced (kraft) insulation was used then that is your vapor barrier (retarder)

5. yes - if an entire side does not have soffit vents then they should be installed

At least this was caught before you re-roofed
Everything can be fixed & made right

AaronB 09-18-2009 08:00 PM

Hip vents solves the roof ventilation problem. Any real roofer will kow what I'm talking about.

kokanee123 09-18-2009 08:20 PM

Thank you all, Aaron, scuba dave, mics 54 and gbr in wa.

We are going to take down the ceiling, insulation, vapor barrier etc., but your information helped us look into an issue that we hadn't considered before, and never would have found out about until it was too late - - that was the soffit venting. Evidently our soffit vents in the newer part of the house may have been covered up with insulation (or even faked - I'm not sure - have to go crawl around to find out!), (so that would explain why its always been so hot in the house....), and without any on the front, we would have had trouble brewing anyway.

Thanks hugely. We'll go get it all remedied. At least it wasn't a grossly expensive mistake, and it may have saved us further grief in the long run.

Thanks Sooooooooooo much for all your input!!!


Leftyho 09-18-2009 09:21 PM


The vents for the storage space are a great idea. You can block them off for the winter months. The rest of the year the heat will be vented outside. This will keep your house cooler in the summertime.

You do not need the styrofoam panels.

A ridge vent can be installed.

How is taking all this out giving you soffit vents???

Taking the room out will solve nothing.

kokanee123 09-18-2009 09:48 PM

Evidently (got the owner of a roofinf company to come and assess it all this afternoon), since there are lots of static vents throughout the roof, a ridge vent wouldn't do much good, but the soffit vents (or lack thereof) we hadn't noticed until the attic venting issue came up, and without them, there is hardly any air flowing through the attic at all, room or no room. We are not removing the storage room - rather just the ceiling that is blocking air circulation.

Thanks for the input.

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