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-   -   Roofing insulation help (http://www.diychatroom.com/f9/roofing-insulation-help-175329/)

chrisk1500 03-23-2013 05:06 PM

Roofing insulation help
 
Hey Guys,

I live in an old farm house in central Saskatchewan. The house is from the 40's. It is a 1.5 story house with a finished attic (bathroom and two bedrooms up there).

This has been a very hard winter up here - lots of snow and cold temps. A big ice dam formed on the south facing roof (the width of the roof, about 5 feet tall and 1 foot thick).

This ice dam led to condensation litteraly running down the inside south walls of the house.

There is currently NO venting from the roof - no soffit and no gable vents.

Inside the attic crawlspace cavity (between the knee wall and the roof) is plumbing for the upstairs bathroom and the chimney runs straght up through.

There is insulation in the floor joists in the crawlspace AND insulation in between the rafters with vapor barrier on the warm side of the roof.

This is quite obviously a bad situation as an ice dam formed and caused water damage inside the house.

The shingles need to be replaced anyways, so I was thinking of doing the following:

1. Take out all of the insulation and vapor barrier in the crawlspace

2. Remove all of the old shingles down to the decking (which is 1x3 boards)

3. Use some type of insulation product on top of the roof - the whole roof except for the top two feet or so towards the peak

5. Put roof vents across the peak to allow airflow

6. Shingle on top of the insulation


I am *assuming* that by doing it this way, the crawlspace will be considered a 'warm' space with the insulation on top of the roof decking. This will allow me to remove the old soaked insulation that is currently inside that space.

On the right track???

Thanks!

joecaption 03-23-2013 05:25 PM

Nope.
Need to air seal any place wiring, plumbing ceiling lights or fans are, add soffit vents, a ridge vent, if you have old ballon framing the top and bottoms of those walls need to be sealed up, and the proper amount of insulation added to the kneewalls and ceiling.

chrisk1500 03-23-2013 07:48 PM

Thanks


I need to keep the crawl space behind the knee wall 'conditioned'. The plumbing for the upstairs bathroom is in there and the chimney for the furnace keeps it warm in there anyways.

So how will air flow work in that case? There are no soffit vents and I need to keep that space warm.

joecaption 03-23-2013 07:59 PM

You need to go back and add your location to your profile.
Really helps when asking questions like this.
If you live in an area where it freezes then plumbing should never should have been run in an outside wall or through an attic space, one way to have an unwanted sprinkler system.

chrisk1500 03-23-2013 08:11 PM

Thanks

I said in my opening line that I am in Saskatchewan - but I will definately add that to my profile.

The plumbing is run up from the kitchen on the main floor and runs alongside the knee wall of the east bedroom and into the east wall of the south facing bathroom.

I am sure that I could build a wall around the pipes and then cut a vent in the interior of the knee wall through to the backside of the knee wall where the pipes are. This would allow interior heat to keep the plumbing warm.

I didn't design the house - just need to keep it alive.

Thanks again for the responses.

jagans 03-23-2013 09:44 PM

No.

Tear off the roof.

Install 30 lb felt over the existing deck.

Install 2 x 2 PT vertical sleepers over felt over old deck and re-sheathe over sleepers. Install new roof system with eaves and ridge ventilation. Insulate under the old deck between rafters with VR inside then drywall.

Roof deck now cold. Plumbing warm, Problem solved! :thumbsup:

Next!

Gary in WA 03-23-2013 10:55 PM

Fig.9: http://www.buildingscience.com/docum...on?full_view=1

http://www.buildingscience.com/docum...n-roof-venting

Many choices, and qualities for each; http://www.buildingscience.com/docum...study-analysis

Gary

chrisk1500 03-23-2013 11:08 PM

Thanks!

Option #3 on page 4 was exactly what I was describing with insulating on top of the roof deck.

Is there a reason why that wouldn't work for me?

Would a person using that technique install roof vents anywhere?

I really appreciate the insight - the advice from everyone isn't falling on deaf ears - I just want all options...

chrisk1500 03-23-2013 11:15 PM

I guess what I am asking is if a SIP roof would work on top of my old decking.

jagans 03-24-2013 04:39 AM

What is an SIP roof? This is funny. Ive been in this business a long time and I never hear of one. :eek:

jagans 03-24-2013 05:01 AM

Quote:

Originally Posted by Gary in WA (Post 1144331)

Hi Gary, I just went to the first link that was posted, and I am still laughing at the illustration they have on the very first page. Apparently the guy that drew that has never been in an attic, or on a roof. I have stated several times that the best way to take care of the pinch condition at the undereaves is to install glass faced rigid isocyanurate foam between the ceiling joists/ lower chord for about 4 feet in, then install fiberglass bat or blown in insulation in the center. What that person shows is ludicrous and would be almost impossible to execute. I see that a lot

Gary in WA 03-24-2013 09:21 PM

Chris, that option 3 is a "closed roof" system, no vents, unless you mean bath exhaust which I would run through the gable end to stay away from soffit intakes or snow load on roof in your location.

jagans, that link was directed to Fig. 9, not the others- the soffit vent is in the wrong area for optimal air-flow/moisture intake. As many new homes are now being built with a "raised heel" to eliminate the high cost of SPF, XPS, PIC, and EPS, I'm glad to see you are pushing it at the walls, as I did that for the first two years on this forum, but the link/picture is now removed- outdated. I used this one as well;

"The first step should be to seal any air leaks in the ceiling. Use a can of foam to seal any wire penetrations, cracks or spaces that connect the attic to the living space below. The second step should be to provide adequate levels of insulation. Since space is restricted at the roofs edge, use an insulation material that has a high R-value per inch of thickness. Polyisocyanurate foam board, like Thermax, has an R-value of 7 per inch. So cut the insulation into strips and stack layers of these strips between the rafters directly over the outside wall. Cut the strips of material so they fit snugly against the roof- and ceiling-framing members. Be sure they extend into the attic 2-feet. Leave enough room (1 1/2”)above the stack of foam blocks to allow the passage of air for soffit-to-ridge venting. Seal the strips of foam board to the framing members with spray foam from the can to make the connection air tight." From; http://bct.eco.umass.edu/publication...o-save-energy/ Keep up with that, it is important!
Page 18, in the last link mentions SPF at reduced headroom also.

Gary

joecaption 03-24-2013 09:48 PM

Check the price of SIP's and the added work of having to redo all the roof edge trim and you may change your mind about it.


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